Maharashtra Board Class 8 Science Chapter 6 Composition of Matter Solutions

Std 8 Science Chapter 6 Composition Of Matter Question Answer Maharashtra Board

Class 8 Science Chapter 6 Composition Of Matter Question Answer Maharashtra Board

1. Choose the appropriate option and rewrite the following statements:

Question a. The intermolecular force is ........ in the particles of solid.
(a) minimum
(b) moderate
(c) maximum
(d) indefinite
Answer: (c) maximum
In simple words: In solids, the particles are very close to each other, resulting in the strongest intermolecular forces.

🎯 Exam Tip: Remember the order of intermolecular force strength: solids > liquids > gases. This helps explain their physical properties.

Question b. Solids retain their volume even when external pressure is applied. This property is called ........
(a) plasticity
(b) incompressibility
(c) fluidity
(d) elasticity
Answer: (b) incompressibility
In simple words: Incompressibility means a substance's volume doesn't change much under pressure, a key characteristic of solids due to their tightly packed particles.

🎯 Exam Tip: Distinguish between incompressibility (resistance to volume change) and rigidity (resistance to shape change) for solids.

Question c. Matter is classified into the types mixture, compound and element, by applying the criterion ........
(a) states of matter
(b) phases of matters
(c) chemical composition of matter
(d) all of these
Answer: (c) chemical composition of matter
In simple words: Elements, compounds, and mixtures are categories based on how different atoms or molecules are chemically arranged or combined.

🎯 Exam Tip: The classification by chemical composition is distinct from physical states (solid, liquid, gas).

Question d. Matter that contain two or more constituent substances is called ..........
(a) mixture
(b) compound
(c) element
(d) metalloid
Answer: (a) mixture
In simple words: A mixture is formed when two or more substances are combined physically but not chemically, retaining their individual properties.

🎯 Exam Tip: Remember that in a mixture, the components can be separated by physical means and their proportions are not fixed.

Question e. Milk is an example of type of matter called ..........
(a) solution
(b) homogeneous mixture
(c) heterogeneous mixture
(d) suspension
Answer: (c) heterogeneous mixture
In simple words: Milk, though appearing uniform, contains tiny fat globules and protein particles dispersed in water, making it a heterogeneous mixture (specifically, a colloid).

🎯 Exam Tip: Colloids are a type of heterogeneous mixture where particles are larger than in solutions but too small to settle out easily.

Question f. Water, mercury and bromine are similar to each other, because the three are ........
(a) liquids
(b) compounds
(c) nonmetals
(d) elements
Answer: (a) liquids
In simple words: Despite their different chemical nature, water, mercury, and bromine all exist in the liquid state at room temperature.

🎯 Exam Tip: When comparing substances, consider both their physical states and chemical classifications.

Question g. Valency of carbon is 4 and that of oxygen is 2. From this, we understand that there are ........ chemical bond/bonds between the carbon atom and one oxygen atom in the compound- carbon dioxide.
(a) 1
(b) 2
Answer: (b) 2
In simple words: In carbon dioxide (\(CO_2\)), carbon forms two double bonds, one with each oxygen atom, meaning there are two bonds between one carbon and one oxygen.

🎯 Exam Tip: Valency determines the number of bonds an atom can form; a valency of 4 for carbon and 2 for oxygen explains the double bond in \(CO_2\).

2. Identify the odd term out and explain.

Question a. Gold, silver, copper, brass.
Answer: Brass. (Others are elements.)
In simple words: Gold, silver, and copper are pure elements, while brass is an alloy, which is a mixture of metals.

🎯 Exam Tip: Knowing the definition of elements (pure substances) versus mixtures (combinations of substances) is key for such classifications.

Question b. Hydrogen, hydrogen peroxide, carbon dioxide, water vapour.
Answer: Hydrogen. (Others are compounds.)
In simple words: Hydrogen is a single element, whereas hydrogen peroxide, carbon dioxide, and water are all compounds made of two or more elements chemically bonded together.

🎯 Exam Tip: Elements cannot be broken down further by chemical means, unlike compounds.

Question c. Milk, lemon juice, carbon, steel.
Answer: Carbon. (Others are mixtures.)
In simple words: Carbon is an element, while milk, lemon juice, and steel are all mixtures of different substances.

🎯 Exam Tip: Differentiate between pure substances (elements, compounds) and mixtures (homogeneous, heterogeneous).

Question d. Water, mercury, bromine, petrol.
Answer: Petrol. (Others are inorganic compounds.)
In simple words: Water, mercury, and bromine are inorganic substances (or elements), whereas petrol is a complex organic mixture of hydrocarbons.

🎯 Exam Tip: Recognize common inorganic substances and the general organic nature of fuels like petrol.

Question e. Sugar, salt, baking soda, blue vitriol.
Answer: Sugar. (Others are inorganic compounds.)
In simple words: Sugar is an organic compound, while salt (sodium chloride), baking soda (sodium bicarbonate), and blue vitriol (copper sulfate) are inorganic compounds.

🎯 Exam Tip: Organic compounds primarily contain carbon and hydrogen, often with oxygen, while inorganic compounds typically lack C-H bonds.

Question f. Hydrogen, sodium, potassium, carbon.
Answer: Carbon. (Others are monovalent elements)
In simple words: Hydrogen, sodium, and potassium typically have a valency of 1, meaning they form one chemical bond, whereas carbon typically has a valency of 4.

🎯 Exam Tip: Understanding valency is crucial for predicting how elements combine to form compounds.

3. Answer the following question.

Question a. Plants synthesize glucose in sunlight with the help of chlorophyll from carbon dioxide and water and give away oxygen. Identify the four compounds in this process and name their types.
Answer: Photosynthesis:
\[6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2\]
Carbon dioxide Water Chlorophyll Glucose Oxygen
Carbon dioxide, water, glucose, and Chlorophyll are compounds.
Types: Organic compounds: Glucose
Inorganic compounds: Carbon dioxide and water
Complex compounds: Chlorophyll.
In simple words: Photosynthesis uses inorganic compounds (\(CO_2\), \(H_2O\)) with a complex compound (chlorophyll) to produce an organic compound (glucose) and oxygen.

🎯 Exam Tip: For processes like photosynthesis, be able to identify reactants, products, and catalysts, and classify them by type (organic, inorganic, complex).

Question b. In one sample of brass, the following ingredients were found: copper (70%) and zinc (30%). Identify the solvent, solute and solution from these.
Answer: Brass is an alloy, it contains 70% copper and 30% zinc. The largest proportion is solvent, i.e. copper. The smaller proportion is solute, i.e. zinc. The solution is Brass.
In simple words: In the brass alloy, copper is the main component (solvent), zinc is the dissolved component (solute), and brass itself is the final solid solution.

🎯 Exam Tip: In solutions, the component present in the largest amount is generally considered the solvent, and others are solutes, even in solid-solid solutions like alloys.

Question c. Seawater tastes salty due to the dissolved salt. The salinity (the proportion of salts in water) of some water bodies Lonar lake - 7.9%, Pacific Ocean 3.5%, Mediterranean sea - 3.8%, 5 Dead sea 33.7%. Explain two characteristics of mixtures from the above information.
Answer:
1. The constituents of a mixture (the proportion of salts in water) do not combine chemically.
2. Their constituents are present in any proportion by weight.
3. The constituent of a mixture can be separated by a physical process.
In simple words: Seawater's varying salinity shows that mixture components don't react chemically, can be in different proportions, and can be separated physically.

🎯 Exam Tip: Key characteristics of mixtures are variable composition, retention of component properties, and physical separability.

4. Give two examples each.

Question a. Liquid element.
Answer: Mercury (\(Hg\)), Bromine (\(Br_2\))
In simple words: Mercury and bromine are unique elements that exist as liquids at standard room temperature.

🎯 Exam Tip: Be able to recall specific examples of elements in different physical states.

Question b. Gaseous element.
Answer: Hydrogen (\(H_2\)), Oxygen (\(O_2\)).
In simple words: Hydrogen and oxygen are common elements that exist as gases under normal conditions.

🎯 Exam Tip: Common gaseous elements include hydrogen, oxygen, nitrogen, and all noble gases.

Question c. Solid element.
Answer: Iron (\(Fe\)), Copper (\(Cu\)), Silver (\(Ag\)).
In simple words: Iron, copper, and silver are typical examples of elements found in a solid state at room temperature.

🎯 Exam Tip: Most metals are solid elements at room temperature.

Question d. Homogeneous mixture.
Answer: Sea water, blue vitriol dissolved in water.
In simple words: Homogeneous mixtures like seawater or a sugar solution appear uniform throughout, with no visible separate phases.

🎯 Exam Tip: A key feature of a homogeneous mixture is its uniform composition and appearance.

Question e. Colloid.
Answer: Milk, blood.
In simple words: Milk and blood are examples of colloids, where tiny particles are evenly dispersed in a medium but are too small to settle.

🎯 Exam Tip: Colloids exhibit the Tyndall effect (scattering of light) and are considered heterogeneous at a microscopic level.

Question f. Organic compound.
Answer: Glucose, urea.
In simple words: Glucose and urea are typical organic compounds, which are characterized by the presence of carbon and hydrogen atoms.

🎯 Exam Tip: Organic compounds are often derived from living organisms and typically contain carbon-hydrogen bonds.

Question g. Complex compound.
Answer: Chlorophyll, Haemoglobin.
In simple words: Chlorophyll and haemoglobin are complex compounds with large, intricate structures, often containing a metal atom at their core.

🎯 Exam Tip: Complex compounds play crucial roles in biological systems, facilitating processes like photosynthesis and oxygen transport.

Question h. Inorganic compound.
Answer: Soda, rust, limestone.
In simple words: Soda (sodium carbonate), rust (iron oxide), and limestone (calcium carbonate) are examples of inorganic compounds, which generally do not contain carbon-hydrogen bonds.

🎯 Exam Tip: Most minerals and salts found in nature are inorganic compounds.

Question i. Metalloid.
Answer: Silicon, arsenic.
In simple words: Silicon and arsenic are metalloids, which means they exhibit properties intermediate between those of metals and non-metals.

🎯 Exam Tip: Metalloids are important in electronics due to their semiconducting properties.

Question j. Element with valency 1.
Answer: Sodium (\(Na\)), potassium (\(K\)), chlorine (\(CI\)).
In simple words: Sodium, potassium, and chlorine are elements that typically gain or lose one electron to achieve a stable electron configuration, hence having a valency of 1.

🎯 Exam Tip: Group 1 metals (alkali metals) and Group 17 non-metals (halogens) commonly exhibit a valency of 1.

Question I. Element with valency 2.
Answer: Magnesium (\(Mg\)), Calcium (\(Ca\)).
In simple words: Magnesium and calcium are elements with a valency of 2, indicating they tend to form two chemical bonds.

🎯 Exam Tip: Group 2 metals (alkaline earth metals) commonly have a valency of 2.

5. Write the names and symbols of the constituent elements and identify their valencies from their molecular formulae given below:
\(KCl\), \(HBr\), \(MgBr_2\). \(K_2O\), \(NaH\), \(CaCl_2\), \(CCl_4\), \(HI\), \(H_2S\), \(Na_2S\), \(FeS\), \(BaCl_2\).

Question a. Write the names and symbols of the constituent elements and identify their valencies from their molecular formulae given below:
\(KCl\), \(HBr\), \(MgBr_2\), \(K_2O\), \(NaH\), \(CaCl_2\), \(CCl_4\), \(HI\), \(H_2S\), \(Na_2S\), \(FeS\), \(BaCl_2\).
Answer:

Molecular formula	Constituent element/Name symbol	Valency
1. \(KCl\)	Potassium (\(K\)) Chlorine (\(Cl\))	1 1
2. \(HBr\)	Hydrogen (\(H\)) Bromine (\(Br\))	1 1
3. \(MgBr_2\)	Magnesium (\(Mg\)) Bromine (\(Br\))	2 1
4. \(K_2O\)	Potassium (\(K\)) Oxygen (\(O\))	1 2
5. \(NaH\)	Sodium (\(Na\)) Hydrogen (\(H\))	1 1
6. \(CaCl_2\)	Calcium (\(Ca\)) Chlorine (\(Cl\))	2 1
7. \(CCl_4\)	Carbon (\(C\)) Chlorine (\(Cl\))	4 1
8. \(HI\)	Hydrogen (\(H\)) Iodine (\(I\))	1 1
9. \(H_2S\)	Hydrogen (\(H\)) Sulphur (\(S\))	1 2
10. \(Na_2S\)	Sodium (\(Na\)) Sulphur (\(S\))	1 2
11. \(FeS\)	Iron (\(Fe\)) Sulphur (\(S\))	2 2
12. \(BaCl_2\)	Barium (\(Ba\)) Chlorine (\(Cl\))	2 1

In simple words: This table systematically breaks down molecular formulas to identify individual elements and their bonding capacity (valency), which is essential for understanding chemical structure.

🎯 Exam Tip: Practicing the identification of constituent elements and their valencies from molecular formulas reinforces fundamental chemical principles.

6. Chemical composition of some matter is given in the following table. Identify the main type of matter from them.

Question a. Chemical composition of some matter is given in the following table. Identify the main type of matter from them.

Name of matter	Chemical composition	Main type of matter
Sea water	\(H_2O\) + \(NaCl\) + \(MgCl_2\)+...
Distilled water	\(H_2O\)
Hydrogen gas filled in a ballon	\(H_2\)
The gas in LPG cylinder	\(C_4H_{10}\) + \(C_3H_8\)
Baking soda	\(NaHCO_3\)
Pure gold	\(Au\)
The gas in oxygen cylinder	\(O_2\)
Bronze	\(Cu\) + \(Sn\)
Diamond	\(C\)
Heated white powder of blue vitriol	\(CuSO_4\)
Lime stone	\(CaCO_3\)
Dilute hydrochloric acid	\(HCl\) + \(H_2O\)

Answer:

Name of matter	Chemical composition	Main type of matter
Sea water	\(H_2O\) + \(NaCl\) + \(MgCl_2\) +...	Mixture
Distilled water	\(H_2O\)	Compound
Hydrogen gas filled in a balloon	\(H_2\)	Element
The gas in LPG cylinder	\(C_4H_{10}\) + \(C_3H_8\)	Mixture
Baking soda	\(NaHCO_3\)	Compound
Pure gold	\(Au\)	Element
The gas in oxygen cylinder	\(O_2\)	Element
Bronze	\(Cu\) + \(Sn\)	Mixture
Diamond	\(C\)	Element
Heated white powder of blue vitriol	\(CuSO_4\)	Compound
Limestone	\(CaCO_3\)	Compound
Dilute hydrochloric acid	\(HCl\) + \(H_2O\)	Mixture

In simple words: Matter can be broadly categorized into elements (pure substances like gold), compounds (chemically combined substances like water), and mixtures (physically combined substances like sea water or alloys).

🎯 Exam Tip: Practice classifying common substances into elements, compounds, and mixtures, as this is a fundamental skill in chemistry.

7. Write scientific reason.

Question a. Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish fire.
Answer:
1. Water is a compound of hydrogen and oxygen.
2. In a compound, the constituents do not retain their individual properties. Hence, hydrogen is combustible and oxygen helps combustion, but water is neither combustible nor supports combustion, it helps to extinguish fire.
In simple words: Water's properties are entirely different from its constituent elements, hydrogen (flammable) and oxygen (combustion supporter), because they are chemically bonded to form a new substance.

🎯 Exam Tip: A defining characteristic of compounds is that their properties are distinct from the properties of their constituent elements.

Question b. The constituent substances of a colloid cannot be separated by oridinary filtration.
Answer:
1. A colloidal solution is heterogeneous.
2. The diameters of colloidal particles are of the order of \(10^{-5}\) m.
3. The particles of a colloid can easily pass through a filter paper as the pore size of a filter paper is big. Hence, the constituents of a colloidal cannot be separated by filtration.
In simple words: Colloidal particles are too small to be trapped by standard filter paper, allowing them to pass through during ordinary filtration.

🎯 Exam Tip: The small size of colloidal particles, larger than solution particles but smaller than suspension particles, explains why they can't be filtered normally and exhibit the Tyndall effect.

Question c. Lemon sherbat has sweet, sour and salty taste and it can be poured in a glass.
Answer:
1. Lemon sherbat is a mixture. It is made up of lemon juice, sugar, salt and water.
2. Formation of lemon sherbat does not involve any chemical reaction.
3. The constituents of sherbat retain their individual properties. Hence, lemon sherbat is sweet, sour and salty to taste and it can be poured in a glass.
In simple words: Lemon sherbat is a mixture because its components (lemon juice, sugar, salt, water) are physically combined, allowing each to retain its original taste and the mixture to behave like a liquid.

🎯 Exam Tip: The retention of individual properties by components is a key indicator that a substance is a mixture, not a compound.

Question d. A solid matter has the properties of definite shape and volume.
Answer:
1. The forces among the constituent particles (atom/molecules) are called intermolecular forces.
2. In solids these forces are strong enough to keep the particles together in fixed positions, as a result solids have a definite shape and volume.
In simple words: Solids possess a definite shape and volume because the strong intermolecular forces lock their particles into fixed positions.

🎯 Exam Tip: The strength of intermolecular forces is directly responsible for the characteristic shape and volume of solids.

8. Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method.

Question a. C (Valency 4) & Cl (Valency 1)
Answer:
Step 1: Write the symbols of the constituent elements.
C Cl
Step 2: Write the valency below the respective elements.
C Cl
4 1
Step 3: Cross multiply the valencies.
(Imagine C receiving the valency of Cl (1) and Cl receiving the valency of C (4))
The molecular formula: \(CCl_4\)
In simple words: Carbon, with a valency of 4, combines with four chlorine atoms, each with a valency of 1, to form the molecular formula \(CCl_4\).

🎯 Exam Tip: The cross-multiplication method is a straightforward way to derive molecular formulas by balancing the valencies of combining elements.

Question b. N (Valency 3) & H (Valency 1)
Answer:
Step 1: Write the symbols of the constituent elements.
N H
Step 2: Write the valency below the respective elements.
N H
3 1
Step 3: Cross multiply the valencies.
(Imagine N receiving the valency of H (1) and H receiving the valency of N (3))
The molecular formula: \(NH_3\)
In simple words: Nitrogen, with a valency of 3, combines with three hydrogen atoms, each with a valency of 1, to form the molecular formula \(NH_3\).

🎯 Exam Tip: The derived formula should represent the simplest whole-number ratio of atoms, reflecting the valencies.

Question c. C (Valency 4) & O (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.
C O
Step 2: Write the valency below the respective elements.
C O
4 2
Step 3: Cross multiply the valencies.
(Imagine C receiving the valency of O (2) and O receiving the valency of C (4))
The formula: \(C_2O_4\)
The number of constituent atoms in the final molecular formula should be the smallest possible whole number. Divide the formula \(C_2O_4\) by suitable number.
Final molecular formula obtained by dividing by '2'.
Molecular formula: \(CO_2\)
In simple words: Carbon and oxygen initially combine as \(C_2O_4\) based on their valencies, but this simplifies to \(CO_2\) as the smallest whole-number ratio of atoms.

🎯 Exam Tip: Always reduce the subscripts in a molecular formula to their simplest whole-number ratio after cross-multiplication.

Question d. Ca (Valency 2) & O (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.
Ca O
Step 2: Write the valency below the respective elements.
Ca O
2 2
Step 3: Cross multiply the valencies.
(Imagine Ca receiving the valency of O (2) and O receiving the valency of Ca (2))
The formula: \(Ca_2O_2\)
Divide the formula by suitable number '2'.
The molecular formula: \(CaO\).
In simple words: Calcium and oxygen both have a valency of 2, so they combine in a 1:1 ratio, simplifying the initial \(Ca_2O_2\) to \(CaO\).

🎯 Exam Tip: When valencies are the same, they cancel out, resulting in a 1:1 ratio in the final molecular formula (after simplification).

Project:

Question a. Collect the wrappers of ready-made foodstuff. Use the information given and prepare a chart of foodstuff and the ingredients in it. Procure the ingredients available. Discuss with friends and teacher, test the procured ingredients with combustion test under the supervision of your teacher. Thereby identify the ingredients as organic or inorganic.
In simple words: This project involves identifying ingredients in processed foods, noting their composition, and performing a combustion test to classify them as organic or inorganic.

🎯 Exam Tip: Understanding ingredient classification (organic/inorganic) and practical testing provides valuable insights into food chemistry.

Class 8 Science Chapter 6 Composition Of Matter Additional Important Questions And Answers

Rewrite the sentences after filling the blanks:

Question 1. ........... have no definite shape, but have a definite volume.
Answer: Liquids have no definite shape, but have a definite volume.
In simple words: Liquids take the shape of their container but maintain a constant volume.

🎯 Exam Tip: Recall that liquids have definite volume but indefinite shape, a property intermediate between solids and gases.

Question 2. ........... have neither a definite shape nor a definite volume.
Answer: Gases have neither a definite shape nor a definite volume.
In simple words: Gases expand to fill any container, lacking both a fixed shape and a fixed volume.

🎯 Exam Tip: Gases are characterized by indefinite shape and volume due to very weak intermolecular forces.

Question 3. The properties of a ........... are different than those of the constitute elements.
Answer: The properties of a compound are different than those of the constitute elements.
In simple words: When elements chemically combine to form a compound, the resulting compound has new properties, distinct from its original elements.

🎯 Exam Tip: This property helps distinguish compounds from mixtures, where components retain their original properties.

Question 4. The part of matter having uniform composition is called ...........
Answer: The part of matter having uniform composition is called phase.
In simple words: A phase is any region within a system that has uniform physical and chemical properties.

🎯 Exam Tip: Understanding phases is crucial for classifying matter and distinguishing between homogeneous and heterogeneous systems.

Question 5. The heterogeneous mixture of a liquid and a solid is called a ...........
Answer: The heterogeneous mixture of a liquid and a solid is called a suspension.
In simple words: A suspension is a mixture where solid particles are dispersed in a liquid but are large enough to eventually settle out.

🎯 Exam Tip: Suspensions are characterized by visible particles that settle over time and can be separated by filtration.

Question 6. A colloid is a ...........
Answer: A colloid is a heterogeneous mixture.
In simple words: Colloids are mixtures where tiny particles are evenly spread throughout a medium, making them appear homogeneous but actually being heterogeneous.

🎯 Exam Tip: Colloids represent an intermediate state between solutions and suspensions, showing properties of both.

Question 7. Bronze contains atoms of the elements ........... and ...........
Answer: Bronze contains atoms of the elements copper and tin.
In simple words: Bronze is an alloy primarily made by mixing copper and tin.

🎯 Exam Tip: Remember common alloys and their constituent metals, as they are practical examples of solid solutions.

 

Question 8. When all the components of a mixture form one phase, it is called ............ .
Answer: When all the components of a mixture form one phase, it is called homogeneous mixture.
In simple words: A homogeneous mixture is one where all parts of the mixture are uniformly spread out and appear as a single substance.

🎯 Exam Tip: Understanding the term 'homogeneous' is key to defining mixtures that appear uniform throughout.

 

Question 9. ............ is a mixture of water, lactose, fats and proteins.
Answer: Milk is a mixture of water, lactose, fats and proteins.
In simple words: Milk is a blend of different substances like water, sugar (lactose), fats, and proteins, making it a mixture.

🎯 Exam Tip: Recognizing common everyday substances as mixtures helps apply concepts to real-world examples.

 

Question 10. The intermolecular force is ............ in the gaseous state.
Answer: The intermolecular force is very weak in the gaseous state.
In simple words: Gas particles have very weak forces between them, allowing them to move freely and occupy any available space.

🎯 Exam Tip: The strength of intermolecular forces directly impacts the state of matter, with gases having the weakest forces.

Choose the appropriate option and rewrite the following statements:

 

Question 1. When a liquid is poured from one container to another, its shape may change, but its volume ............ .
(a) increases
(b) decreases
(c) remains the same
(d) none of them
Answer: (c) remains the same
In simple words: Liquids adapt their shape to the container, but the total amount of liquid, or its volume, stays constant.

🎯 Exam Tip: A key characteristic of liquids is their fixed volume but indefinite shape, distinguishing them from solids and gases.

 

Question 2. The property by which some solids maintain their shape even when subjected to external forces is called ............ .
(a) elasticity
(b) fluidity
(c) rigidity
(d) plasticity
Answer: (c) rigidity
In simple words: Rigidity is the ability of a solid to resist changes to its shape when external pressure is applied.

🎯 Exam Tip: Differentiate between rigidity (resistance to deformation), elasticity (ability to return to original shape), and plasticity (permanent deformation) for solids.

 

Question 3. ............ is a complex compound.
(a) Glucose
(b) Blue vitriol
(c) Chlorophyll
(d) Soda
Answer: (c) Chlorophyll
In simple words: Chlorophyll is a large, intricate molecule containing a metal atom (magnesium) at its core, making it a complex compound.

🎯 Exam Tip: Complex compounds often have large molecular structures and may contain metal ions, like chlorophyll or hemoglobin.

 

Question 4. ............ is a homogeneous mixture.
(a) Sand + water
(b) Flour + water
(c) Salt + water
(d) Oil + water
Answer: (c) Salt + water
In simple words: When salt dissolves in water, it forms a uniform solution where the salt is evenly distributed, appearing as a single phase.

🎯 Exam Tip: A homogeneous mixture has a uniform composition and properties throughout, unlike heterogeneous mixtures where components are visibly separate.

State whether the following statements are True or False:

 

Question 1. Liquids do not have a definite shape
Answer: True.
In simple words: Liquids take the shape of their container because their particles can move past each other.

🎯 Exam Tip: Remember that liquids have a definite volume but an indefinite shape, adapting to the vessel they are in.

 

Question 2. Gases have a definite shape and volume.
Answer: False. (Gases do not have shape and volume.)
In simple words: Gases spread out to fill their entire container, meaning they have neither a fixed shape nor a fixed volume.

🎯 Exam Tip: Gases are characterized by indefinite shape and indefinite volume, due to very weak intermolecular forces.

 

Question 3. The crystals of blue vitriol form a single phase.
Answer: True.
In simple words: Blue vitriol crystals are a pure substance, meaning they have a uniform composition throughout, forming one single phase.

🎯 Exam Tip: A single phase refers to a physically distinct and homogeneous part of a system, like a pure crystalline solid.

 

Question 4. Water is a mixture.
Answer: False. (Water is a compound)
In simple words: Water is a compound because it is made of hydrogen and oxygen chemically combined in a fixed ratio, not just mixed.

🎯 Exam Tip: Differentiate between compounds (chemically bonded elements) and mixtures (physically combined substances without chemical bonds).

 

Question 5. Milk is a colloid.
Answer: True.
In simple words: Milk is a colloid because it contains tiny particles of fat and protein dispersed throughout water, which don't settle out.

🎯 Exam Tip: Colloids are heterogeneous mixtures where particles are larger than in a solution but small enough not to settle, often scattering light (Tyndall effect).

 

Question 6. A suspension does not scatters light.
Answer: True.
In simple words: This statement is actually False. Suspensions *do* scatter light because their particles are large enough to be seen and block light.

🎯 Exam Tip: Suspensions have large particles that settle over time and scatter light, making the light path visible, unlike true solutions.

 

Question 7. Copper sulphate is a mixture.
Answer: False. (Copper sulphate is a compound.)
In simple words: Copper sulphate is a compound because copper, sulfur, and oxygen atoms are chemically bonded together in a specific ratio.

🎯 Exam Tip: Substances with fixed chemical formulas like CuSO₄ are compounds, not mixtures.

 

Question 8. An atom forms as many chemical bonds with other atom as its valency.
Answer: True.
In simple words: An atom's valency indicates its capacity to form chemical bonds, so it typically forms that many bonds.

🎯 Exam Tip: Valency is a fundamental concept in chemistry, representing the combining power of an element and dictating the number of bonds it can form.

 

Question 9. The strength of intermolecular forces is weak in the liquid state.
Answer: False. (The strength of intermolecular forces is moderate in the liquid state.)
In simple words: Intermolecular forces in liquids are strong enough to keep particles close but weak enough for them to slide past each other, making them moderate.

🎯 Exam Tip: The order of intermolecular force strength is strongest in solids, moderate in liquids, and weakest in gases.

 

Question 10. All the gases present together constitute a single phase.
Answer: True.
In simple words: Different gases mix completely and evenly, forming a uniform system that appears as one phase.

🎯 Exam Tip: Gas mixtures are always homogeneous, forming a single phase because gas particles are far apart and move freely.

Match the column:

 

Question 1.

Column I	Column II
1. Potassium dichromate	a. Complex compound
2. Cyanocobalamine	b. Element
3. Air	c. Compound
4. Silver	d. Mixture

Answer:

Column I	Column II
1. Potassium dichromate	c. Compound
2. Cyanocobalamine	a. Complex compound
3. Air	d. Mixture
4. Silver	b. Element

In simple words: Potassium dichromate is a compound, Cyanocobalamine is a complex compound, Air is a mixture of gases, and Silver is a pure element.

🎯 Exam Tip: Classifying substances as elements, compounds, or mixtures based on their composition is a fundamental skill in chemistry.

 

Question 2.

Column 1	Column II
1. Milk	a. Alloy
2. Lemonade	b. Colloid
3. Sand and water	c. Solution
4. Brass	d. Suspension

Answer:

Column 1	Column II
1. Milk	b. Colloid
2. Lemonade	c. Solution
3. Sand and water	d. Suspension
4. Brass	a. Alloy

In simple words: Milk is a colloid, lemonade is a solution, sand and water form a suspension, and brass is a solid alloy mixture.

🎯 Exam Tip: Understanding the types of mixtures (solutions, colloids, suspensions, alloys) and their characteristics is essential for classification.

 

Question 3.

Column I	Column II
1. Sea water	a. Solid in solid
2. Vinegar	b. Solid in liquid
3. Air	c. Liquid in liquid
4. Bronze	d. Gas in liquid
5. Chlorinated water	e. Gas in gas

Answer:

Column I	Column II
1. Sea water	b. Solid in liquid
2. Vinegar	c. Liquid in liquid
3. Air	e. Gas in gas
4. Bronze	a. Solid in solid
5. Chlorinated water	d. Gas in liquid

In simple words: Sea water has salt (solid) in water (liquid), vinegar is acetic acid (liquid) in water (liquid), air is gases mixed with gases, bronze is metals (solids) mixed with metals (solids), and chlorinated water is chlorine gas in water (liquid).

🎯 Exam Tip: Knowing the state of matter of the solute and solvent helps correctly identify the type of solution or mixture.

Answer the following questions in one sentence:

 

Question 1. Why does a solid have definite volume ?
Answer: In solids intermolecular forces are strong enough to keep the particles together in fixed positions, as a result solids have definite volume.
In simple words: Solids have strong forces between their particles, holding them in fixed positions, which gives them a constant volume.

🎯 Exam Tip: The strength of intermolecular forces dictates whether a substance has a definite volume and shape.

 

Question 2. Why does a liquid have indefinite shape?
Answer: In a liquid intermolecular forces are not strong enough to keep the particles together in fixed positions, as a result liquid has indefinite shape.
In simple words: Liquid particles can slide past each other because their intermolecular forces aren't strong enough to lock them into fixed positions, allowing liquids to take the shape of their container.

🎯 Exam Tip: Liquids flow and take the shape of their container because their particles have more freedom of movement than solids, but are still close enough to maintain a definite volume.

 

Question 3. Why does a gas have indefinite volume and shape?
Answer: In a gas intermolecular forces are very weak and the distance between the particles is very large, as a result gas has indefinite volume and shape.
In simple words: Gas particles are far apart and have almost no attractive forces, so they spread out completely to fill any container and don't have a fixed shape or volume.

🎯 Exam Tip: The weak intermolecular forces and large inter-particle distances in gases are responsible for their indefinite shape and volume, allowing them to expand freely.

 

Question 4. What can you say about the distance between the neighbouring particles of solid?
Answer: The particles of solid are very close to each other and the distance between them is minimum.
In simple words: In solids, particles are packed tightly together, so the space between them is very small.

🎯 Exam Tip: The close packing of particles in solids is due to strong intermolecular forces, which also explains their fixed shape and volume.

 

Question 5. What can you say about the distance between the constituent particles of gas?
Answer: The intermolecular force is very weak in gases. The distance between the particles of gas is very large. They move freely and occupy all the available space.
In simple words: Gas particles are far apart with weak forces, moving freely to fill all available space.

🎯 Exam Tip: Gases are characterized by large inter-particle distances and highly energetic, random motion of particles.

 

Question 6. State whether the mixture of oil in water is a homogeneous or heterogeneous mixture.
Answer: The mixture of oil in water is a heterogeneous mixture.
In simple words: Oil and water don't mix uniformly; they separate into distinct layers, making it a heterogeneous mixture.

🎯 Exam Tip: Heterogeneous mixtures have visibly distinct components or phases, whereas homogeneous mixtures appear uniform.

 

Question 7. State whether seawater is a homogeneous or heterogeneous mixture.
Answer: Seawater is a homogeneous mixture.
In simple words: Seawater appears uniform because the salts and other substances are thoroughly dissolved and evenly distributed in the water.

🎯 Exam Tip: Solutions like seawater are always homogeneous because the solute particles are uniformly dispersed at a molecular level.

 

Question 8. Give two examples of liquid in liquid.
Answer: Examples of liquid in liquid:
Vinegar, dilute sulphuric acid.
In simple words: Vinegar (acetic acid in water) and dilute sulfuric acid (sulfuric acid in water) are examples where one liquid is dissolved in another liquid.

🎯 Exam Tip: Liquid-in-liquid solutions are common, especially when two liquids are miscible (can mix together).

 

Question 9. Give two examples of gas in gas.
Answer: Examples of gas in gas: Air, cooking gas.
In simple words: Air (a mixture of nitrogen, oxygen, etc.) and cooking gas (a blend of propane and butane) are examples of different gases mixed together.

🎯 Exam Tip: All mixtures of gases are homogeneous and are considered gas-in-gas solutions due to the free movement and weak interactions of gas particles.

 

Question 10. Give two examples of solid in solid.
Answer: Examples of solid in solid: Brass, stainless steel.
In simple words: Brass (copper and zinc) and stainless steel (iron, chromium, nickel) are alloys, which are solid mixtures of different metals.

🎯 Exam Tip: Alloys are common examples of solid-in-solid solutions, where metals are melted and mixed to form a new solid with enhanced properties.

 

Question 11. Give two examples of gas in liquid.
Answer: Examples of gas in liquid: Chlorinated water, hydrochloric acid.
In simple words: Chlorinated water has chlorine gas dissolved in it, and hydrochloric acid is hydrogen chloride gas dissolved in water.

🎯 Exam Tip: Carbonated drinks are another common example of gas-in-liquid solutions (carbon dioxide in water).

 

Question 12. Give molecular formulae of 1. potassium chloride, 2. sodium sulphide.
Answer:1. Molecular formula of potassium chloride: KCl
2. Molecular formula of sodium sulphide: Na₂S.
In simple words: The chemical formula for potassium chloride is KCl and for sodium sulfide is Na₂S.

🎯 Exam Tip: Correctly writing molecular formulas requires knowing the valencies of the constituent elements and balancing charges.

 

Question 13. State the molecular formula and number of hydrogen atoms in methane.
Answer: Molecular formula of methane: CH₄
The number of hydrogen atoms in methane is 4.
In simple words: Methane's formula is CH₄, meaning it has one carbon and four hydrogen atoms.

🎯 Exam Tip: A molecular formula explicitly shows the types and number of atoms in a single molecule of a compound.

 

Question 14. Identify the valency of chlorine in
(i) KCl and (ii) CaCl₂.
Answer:i. The valency of chlorine in KCl is 1.
ii. The valency of chlorine in CaCl₂ is 1.
In simple words: In both potassium chloride and calcium chloride, chlorine atoms have a valency of 1, meaning they can form one bond.

🎯 Exam Tip: Valency can often be determined by the number of hydrogen atoms an element combines with, or by the charges in ionic compounds.

Answer the following questions:

 

Question 1. State two principal ways of classifying matter.
Answer: Two principal ways of classifying matter are:
1. On the basis of physical state as a solid, liquid or gas.
2. On the basis of chemical constitution as an element, compound or mixture.
In simple words: Matter can be grouped by whether it's a solid, liquid, or gas, or by its chemical makeup as an element, compound, or mixture.

🎯 Exam Tip: These two classification systems (physical states and chemical composition) are fundamental to understanding the properties of matter.

 

Question 2. What are the different states of matter?
Answer: The different states of matter are solid, liquid and gas.
In simple words: Matter typically exists in three main forms: solid, liquid, and gas.

🎯 Exam Tip: The states of matter are distinguished by their definite shape, definite volume, and the arrangement/movement of their constituent particles.

 

Question 3. Define solid.
Answer: A substance which has a definite shape and volume is called a solid.
In simple words: A solid is a substance that keeps its own shape and volume.

🎯 Exam Tip: The fixed shape and volume of solids are due to strong intermolecular forces holding particles in rigid positions.

 

Question 4. State any three characteristics of solids.
Answer:1. Solids have a definite shape and volume.
2. Most of the solids are rigid while some are plastic and some elastic.
3. Solids have practically negligible compressibility, i.e., their volume is not very much changed by external forces.
In simple words: Solids maintain their shape and volume, are often rigid, and are very difficult to compress.

🎯 Exam Tip: Focus on rigidity, definite shape/volume, and low compressibility as key distinguishing features of solids.

 

Question 5. What is meant by rigidity of solids?
Answer: The property by which solids maintain their shapes when subjected to external forces is called rigidity.
In simple words: Rigidity is a solid's ability to resist bending or changing shape when pushed or pulled.

🎯 Exam Tip: Rigidity is directly related to the strong intermolecular forces that hold particles in fixed positions in a solid lattice.

 

Question 6. What is meant by elasticity of solids?
Answer: Some solids undergo a change in their shapes and volume when subjected to external forces and regain their original shapes and volume on removal of the forces. This property of solids is called elasticity.
In simple words: Elasticity is when a solid temporarily changes its shape or size under pressure but then springs back to its original form once the pressure is removed.

🎯 Exam Tip: Elasticity is crucial for materials like rubber bands or springs, where temporary deformation is desired and reversible.

 

Question 7. What is meant by plasticity?
Answer: Some solids are deformed by external forces and do not regain their original shapes on removal of the forces. This property of solids is called plasticity.
In simple words: Plasticity is the property where a solid permanently changes its shape when a force is applied and doesn't return to its original form.

🎯 Exam Tip: Distinguish plasticity from elasticity; plastic deformation is permanent, while elastic deformation is temporary.

 

Question 8. Solids have a high density and negligible compressibility. Explain.
Answer:1. The forces among the constituent particles (atoms/molecules) are called intermolecular forces.
2. In solids these forces are strong enough to keep the particles together in fixed positions, as a result solids have a high density and negligible compressibility.
In simple words: Solids are dense and hard to compress because their strong intermolecular forces pack particles closely together in fixed positions.

🎯 Exam Tip: The close packing and strong forces in solids lead to their characteristic high density and resistance to compression.

 

Question 9. Define liquid.
Answer: A substance which does not have a definite shape, but has a definite volume is called a liquid.
In simple words: A liquid is a substance that has a fixed volume but takes the shape of its container.

🎯 Exam Tip: Remember that liquids are unique in having a definite volume but an indefinite shape, a balance between solids and gases.

 

Question 10. State any three characteristics of liquids.
Answer:1. Liquids have a definite volume.
2. Liquids do not have a definite shape. They take the shape of the container in which they are stored.
3. When they spill on a plane surface, they spread and flow in the surrounding areas, i.e., they have fluidity.
4. They have very small compressibility.
In simple words: Liquids have a constant volume, no fixed shape (they adapt to containers), can flow, and are difficult to compress.

🎯 Exam Tip: Focus on definite volume, indefinite shape, fluidity, and low compressibility to characterize liquids.

 

Question 11. What is meant by fluidity?
Answer: Liquids flow easily and change their shapes in response to external forces. This property of liquids is called fluidity. It is exhibited by gases also.
In simple words: Fluidity is the ability of a substance to flow and change its shape easily, a property seen in both liquids and gases.

🎯 Exam Tip: Fluidity is a common property of both liquids and gases, distinguishing them from solids, which resist flow.

 

Question 12. Liquids have fluidity and they do not have a definite shape. Explain.
Answer:1. The forces among the constituent particles (atoms/molecules) are called intermolecular forces.
2. In liquids, the intermolecular forces are strong enough to keep the particles within the bulk in aggregation, but not strong enough to keep them in fixed positions. As a result, they flow easily and change shapes according to that of container.
In simple words: Liquids flow and lack a definite shape because their intermolecular forces are strong enough to keep particles together but too weak to hold them in rigid positions, allowing them to slide past each other.

🎯 Exam Tip: The intermediate strength of intermolecular forces in liquids explains both their definite volume (particles stay together) and indefinite shape (particles can move).

 

Question 13. Define gas.
Answer: A substance which has neither a definite shape nor a definite volume is called a gas.
In simple words: A gas is a substance that completely fills any container it's in, having no fixed shape or volume.

🎯 Exam Tip: Gases are characterized by indefinite shape and volume due to extremely weak intermolecular forces and large inter-particle distances.

 

Question 14. State any three characteristics of gases.
Answer:1. Gases have neither a definite shape nor a definite volume.
2. They spread in all directions.
3. They can be compressed or expanded easily.
4. In gases intermolecular forces are very weak.
In simple words: Gases have no fixed shape or volume, they expand to fill space, are easily compressible, and have very weak forces between particles.

🎯 Exam Tip: Emphasize the indefinite shape/volume, compressibility, and weak intermolecular forces when describing gases.

 

Question 15. Gases have neither a definite shape nor a definite volume. Explain.
Answer:1. The forces among the constituent particles (atoms/molecules) are called intermolecular forces.
2. In gases the intermolecular forces are extremely weak. As a result, the molecules of a gas move freely and a gas occupies all the available space.
In simple words: Gases lack a fixed shape or volume because the forces between their particles are extremely weak, allowing them to move independently and spread out to fill any container.

🎯 Exam Tip: The kinetic molecular theory explains that gas particles have high kinetic energy and minimal attraction, leading to their characteristic properties.

 

Question 16. Why are gases more compressible, than liquids?
Answer: In liquids the distances between the neighbouring molecules are less than those in the gases. The intermolecular forces are extremely weak in gases, but not so weak in liquids. Hence, gases are more compressible than liquids.
In simple words: Gases are more compressible than liquids because gas particles have much larger empty spaces between them and weaker intermolecular forces, allowing them to be pushed closer together more easily.

🎯 Exam Tip: Compressibility is inversely related to the space between particles; more empty space means easier compression.

 

Question 17. What is an element? Give two examples.
Answer: A type of matter composed of only one kind of substances where each smallest indivisible part of it has the same properties is called an element. It cannot be subdivided into simpler substances by any physical or chemical means.
Examples: Oxygen, nitrogen, silver.
In simple words: An element is a pure substance made of only one type of atom that cannot be broken down into simpler substances. For example, oxygen and silver.

🎯 Exam Tip: Elements are the basic building blocks of all matter and are found on the periodic table.

 

Question 18. Write any two characteristics of an element.
Answer:1. All the atoms/molecules of an element are alike.
2. Atoms/molecules of different elements are different.
3. An element cannot be decomposed into simple substances by any chemical reaction or simple physical process.
In simple words: All atoms of an element are identical, and elements cannot be broken down into simpler substances by ordinary chemical or physical methods.

🎯 Exam Tip: The uniformity of atoms and indivisibility by simple means are fundamental defining characteristics of elements.

 

Question 19. What is a compound? Give two examples.
Answer: A substance produced by a chemical reaction of two or more elements combined in a fixed proportion is called a compound.
Examples: Water, common salt, sugar.
In simple words: A compound is a substance formed when two or more elements chemically combine in a set ratio. Examples include water and common salt.

🎯 Exam Tip: Compounds have properties distinct from their constituent elements and can only be separated by chemical reactions.

 

Question 20. Write any two characteristics of a compound.
Answer:1. The proportion of constituent elements in a compound is constant.
2. The properties of a compound is different than those of the constituent elements.
In simple words: Compounds have a fixed ratio of elements, and their properties are entirely different from the individual elements they are made of.

🎯 Exam Tip: Fixed composition and new properties are the hallmarks of compounds, differentiating them from mixtures.

 

Question 21. What is a mixture? Give two examples.
Answer: When two or more elements or compounds which do not react chemically with each other are mixed in any proportion, a mixture is formed.
Examples: Air, steel, milk.
In simple words: A mixture is formed when two or more substances are combined physically without a chemical reaction and in any proportion. Air and milk are examples.

🎯 Exam Tip: Key aspects of mixtures are no chemical reaction, variable proportions, and retaining individual properties of components.

 

Question 22. Write any two characteristics of a mixture.
Answer:1. The constituent molecules of mixture are different from each other and notoined by chemical bonds.
2. The proportion of constituent substances are retained in the mixture.
3. The constituents of a mixture can be separated by a physical process.
In simple words: In a mixture, components are not chemically bonded, their individual properties are kept, and they can be separated by physical methods.

🎯 Exam Tip: Contrast these characteristics with those of compounds to clearly understand the difference between the two.

 

Question 23. Classify the following into elements, compounds and mixtures:
Sugar, sodium, nitrogen, sodium carbonate, air, sulphuric acid, mercury, stainless steel, cement, potassium dichromate.
Answer:- Elements: Sodium, nitrogen, mercury.
- Compounds: Sugar, sodium carbonate, sulphuric acid, potassium dichromate.
- Mixtures: Air, stainless steel, cement.
In simple words: Sodium, nitrogen, and mercury are elements; sugar, sodium carbonate, sulfuric acid, and potassium dichromate are compounds; air, stainless steel, and cement are mixtures.

🎯 Exam Tip: Practice classifying substances by remembering the definitions: elements are pure atoms, compounds are fixed chemical combinations, and mixtures are physical blends.

 

Question 24. Write the composition of the following materials by means of chemical formulae and classify them accordingly.

Name of the material	Chemical formula/composition	Type of matter
Water
Carbon
Oxygen
Air
Aluminium
Brass
Carbon dioxide

Answer:

Name of the material	Chemical formulae/composition	Type of matter
Water	H₂O	Compound
Carbon	C	Element
Oxygen	O₂	Element
Air	O₂ + N₂ + CO₂ + other gases	Mixture
Aluminium	Al	Element
Brass	Cu + Zn	Mixture
Carbon dioxide	CO₂	Compound

In simple words: This table lists materials, their chemical compositions (formulas), and classifies them as elements, compounds, or mixtures based on their fundamental nature.

🎯 Exam Tip: Practice identifying the chemical formula and type of matter for common substances to reinforce classification skills.

 

Question 25. What is meant by an organic compound? Give two examples.
Answer: The compound which when heated strongly gives black coloured carbon residue is called an organic compound or carbon compound.
Examples: Carbohydrates, proteins, hydrocarbons (petrol, cooking gas).
In simple words: Organic compounds are substances that typically contain carbon and hydrogen, and often leave a black carbon residue when strongly heated. Carbohydrates and petrol are examples.

🎯 Exam Tip: Organic compounds are usually derived from living organisms and contain carbon in complex structures.

 

Question 26. What is meant by an inorganic compound? Give two examples.
Answer: Compounds which when heated strongly decomposes to give a residue behind are called inorganic compounds.
Examples: Common salt, rust, blue vitriol, limestone.
In simple words: Inorganic compounds are generally non-carbon-based substances that leave a residue other than black carbon when strongly heated. Common salt and rust are typical examples.

🎯 Exam Tip: Inorganic compounds usually originate from non-living sources and typically do not contain carbon-hydrogen bonds, or they contain them in simple forms like CO₂.

 

Question 27. What is meant by complex compounds? Give two examples.
Answer: The molecules of compounds which have a complex structure formed by many atoms and in the centre of this structure metal atoms are also included are called complex compounds.
Examples: Haemoglobin, chlorophyll.
In simple words: Complex compounds are molecules with many atoms, including metal atoms at their center, forming intricate structures. Haemoglobin and chlorophyll are prime examples.

🎯 Exam Tip: Focus on the structural complexity and the presence of central metal atoms when identifying complex compounds.

 

Question 28. Classify the following compounds into organic compounds, inorganic compounds and complex compounds.
Petrol, common salt, haemoglobin, blue vitriol, cyanocobalamine, cooking gas.
Answer:

• Organic compounds: Petrol, cooking gas
• Inorganic compounds: Common salt, blue vitriol.
• Complex compounds: Cyano cobalamine, haemoglobin.

In simple words: Compounds are categorized based on their chemical structure and composition; organic compounds typically contain carbon, inorganic compounds are non-carbon based, and complex compounds have intricate structures often involving metal atoms.

🎯 Exam Tip: Remember key examples for each category to quickly classify compounds in exams.

 

Question 29. What is a phase?
Answer: The part of matter with uniform composition is called a phase.
In simple words: A phase is any region of a substance or mixture that has a uniform chemical composition and physical properties.

🎯 Exam Tip: Understand that a phase implies uniformity throughout that specific region of matter.

 

Question 29. What is a homogeneous mixture? Give two examples.
Answer: When all the components of a mixture form one phase, it is called homogeneous mixture.
Example: Solution of blue vitriol in water, solution of sugar in water.
In simple words: A homogeneous mixture has its components uniformly distributed, appearing as a single phase throughout, like sugar dissolved in water.

🎯 Exam Tip: For a homogeneous mixture, remember that the components are indistinguishable and form a single phase.

 

Question 30. What is heterogeneous mixture? Give two examples.
Answer: When the components of a mixture are distributed into two or more phases, it is called a heterogeneous mixture.
Examples: Oil and water, sand and water.
In simple words: A heterogeneous mixture has components that are not uniformly distributed and can be easily distinguished, forming two or more distinct phases.

🎯 Exam Tip: Identify heterogeneous mixtures by looking for distinct, non-uniform parts or layers.

 

Question 31. Define solution or What is meant by a solution? Give two examples.
Answer: A homogeneous mixture of two or more substances is called a solution.
Examples: Seawater, sugar, syrup.
In simple words: A solution is a special type of homogeneous mixture where one substance dissolves completely into another, creating a uniform blend.

🎯 Exam Tip: Emphasize "homogeneous mixture" as the core definition for a solution.

 

Question 32. What is meant by a solvent?
OR
Define solvent. Give two examples.
Answer: The component which is present in largest proportion in a solution is called a solvent.
Examples:
1. In sea water, water is the solvent.
2. In tincture iodine, alcohol is the solvent.
In simple words: A solvent is the substance in a solution that is present in the largest amount and dissolves other substances.

🎯 Exam Tip: The solvent is always the 'larger' component in a solution, responsible for dissolving the other parts.

 

Question 33. What is meant by a solute?
OR
Define solute. Give two examples.
Answer: The component of a solution which is present in smaller proportion than the solvent is called a solute.
Examples:
1. In sea water, salt is a solute.
2. When a small of amount of sugar is dissolved in water, sugar is the solute in the solution.
In simple words: A solute is the substance in a solution that is present in a smaller amount and gets dissolved by the solvent.

🎯 Exam Tip: The solute is the 'smaller' component that gets dissolved in a solution.

 

Question 34. Define suspension.
OR
What is meant by a suspension?
Answer: A heterogeneous mixture of a liquid and a solid is called a suspension. The diameter of the solid particles in a suspension is larger than \(10^{-4}\) m.
In simple words: A suspension is a cloudy, heterogeneous mixture where solid particles are spread throughout a liquid but are large enough to eventually settle out.

🎯 Exam Tip: Key characteristics of a suspension are large particle size and its heterogeneous nature, often leading to settling.

 

Question 35. Define colloid.
Answer: A heterogeneous mixture in which the particles cannot be seen with a naked eye is called a colloid. The diameter of colloidal particles is around \(10^{-5}\) m.
In simple words: A colloid is a mixture where tiny particles are dispersed evenly throughout another substance, appearing homogeneous to the eye but being heterogeneous at a microscopic level.

🎯 Exam Tip: Colloids are characterized by intermediate particle sizes that don't settle but are still heterogeneous.

 

Question 36. State the characteristics of a solution.
Answer:
1. A solution is clear and transparent, it passes through a filter paper.
2. The particles are not visible to the naked eye.
3. A light can easily pass through it without scattering.
4. A solution is homogeneous mixture.
In simple words: Solutions are transparent, uniform mixtures where particles are too small to be seen or filtered, and light passes straight through without scattering.

🎯 Exam Tip: Remember that solutions are truly homogeneous, meaning uniform at a molecular level.

 

Question 37. State the characteristics of a suspension.
Answer:
1. In suspension, the solute particles do not dissolve but remain suspended in it. The liquid and solid components of suspension are separated by filtration.
2. The particles are visible to the naked eye.
3. The particles in suspension are of very small size and scatter a beam of light passing through it.
4. It is heterogeneous in nature.
In simple words: Suspensions are heterogeneous, with visible particles that don't dissolve, can be filtered out, and scatter light, often settling over time.

🎯 Exam Tip: Highlight the visibility of particles and the ability to separate by filtration as key features of suspensions.

 

Question 38. State the characteristics of a colloid.
Answer:
1. In a colloid, the particles are spread uniformly throughout the solution.
2. The size of the particles is less than that of the particles in a suspension.
3. The particles are not visible to the naked eye.
4. The particles scatter a beam of light.
5. A colloidal solution appears to be homogeneous, but actually it is heterogeneous.
In simple words: Colloids have uniformly dispersed particles that are invisible to the naked eye, scatter light (Tyndall effect), and appear homogeneous but are microscopically heterogeneous.

🎯 Exam Tip: The scattering of light (Tyndall effect) is a defining characteristic of colloids, distinguishing them from true solutions.

 

Question 39. Give two examples of each of the following:
1. Phase
2. Homogeneous matter
3. Heterogeneous matter
4. Homogeneous mixture
5. Heterogeneous mixture
6. Solution
7. Suspension
8. Colloid.
Answer:
1. Phase: (i) Solid: Sodium chloride, blue vitriol, sand, (ii) Liquid: Water, alcohol, (iii) Gas: Chlorine, ammonia.
2. Homogeneous matter: Blue vitriol (solid), a solution of blue vitriol in water (a solid in a liquid), chlorinated water (a gas in a liquid).
3. Heterogeneous matter: Sand and water, sand and alcohol, blue vitriol and sand.
4. Homogeneous mixture: A solution of sodium chloride in water, air, a mixture of water and alcohol.
5. Heterogeneous mixture: A mixture of sand and blue vitriol, sodium chloride and iron filings, oil and water.
6. Solution: Seawater, a solution of sugar in water, a solution of blue vitriol in water.
7. Suspension: A mixture of sand and water, sand and alcohol, muddy water, limestone in water.
8. Colloid: Milk, milk of magnesia, blood, printing ink.
In simple words: This list provides various examples to illustrate different states and types of matter based on their uniformity and composition, from pure substances to complex mixtures.

🎯 Exam Tip: Familiarize yourself with these examples to clearly distinguish between phases, homogeneous/heterogeneous matter, and different types of mixtures.

 

Question 40. State the different types of solutions. Give one example.
Answer: The different types of solutions:
• Liquid in liquid. Examples: Vinegar, dilute sulphuric acid.
• Gas in gas. Example: Air.
• Solid in solid. Examples: Brass, stainless steel, bronze.
• Gas in liquid. Examples: Chlorinated water.
In simple words: Solutions can exist in various forms, combining different states of matter like liquid in liquid, gas in gas, solid in solid, or gas in liquid, each with distinct examples.

🎯 Exam Tip: Remember that solutions are not just liquid-liquid; they can involve any combination of states, such as alloys (solid-solid) or air (gas-gas).

 

Question 41. Classify the following into homogeneous solution and heterogeneous solution?
Soda water, potassium permanganate solution, milk, alcohol in water, ink solution, wheat flour in water.
Answer:
• Homogeneous solution: Soda water, potassium permanganate solution, alcohol in water.
• Heterogeneous solution: Milk, ink solution, wheat flour in water.
In simple words: Homogeneous solutions are uniform throughout, while heterogeneous solutions have visible or microscopically distinct parts.

🎯 Exam Tip: The key to classification is whether the mixture appears uniform at all levels of observation.

 

Question 42. Classify the following into solution, suspension and colloids:
Milk, sand in water, lemonade, smoke, oxygen in water.
Answer:
• Solution: Lemonade, oxygen in water.
• Suspension: Sand in water.
• Colloids: Milk, smoke.
In simple words: Mixtures are categorized into solutions (uniform, clear), suspensions (particles settle, visible), and colloids (particles dispersed, scatter light, appear uniform but are not).

🎯 Exam Tip: Distinguish between solutions, suspensions, and colloids based on particle size, visibility, and whether they settle or scatter light.

 

Question 43. What is meant by molecular formula?
Answer: The number of atom of each of the constituent elements present in one molecule of a compound is called molecular formula.
In simple words: A molecular formula shows the exact count of each type of atom in a single molecule of a compound.

🎯 Exam Tip: Remember that a molecular formula provides precise quantitative information about the atoms in a molecule.

 

Question 44. What is meant by valency of an element?
Answer: The capacity of an element to combine with another element is known as valency.
In simple words: Valency is an element's combining power, indicating how many bonds it can form with other elements.

🎯 Exam Tip: Valency is crucial for understanding how atoms bond and form compounds.

 

Question 45. Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method.
Answer:
Question a. H (Valency 1) and O (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.
H O
Step 2: Write the valency below the respective elements.
H O
1 2
Step 3: Cross multiply the valencies.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र वैलेंसी के क्रॉस-गुणा विधि को दर्शाता है। इसमें हाइड्रोजन (H) की वैलेंसी 1 और ऑक्सीजन (O) की वैलेंसी 2 को उनके प्रतीकों के नीचे लिखा गया है। फिर इन वैलेंसी को क्रॉस-मल्टीप्लाई करके अणु सूत्र प्राप्त किया जाता है।
. The molecular formula: H\(_{2}\)O.
In simple words: To find the molecular formula for hydrogen and oxygen, write their symbols, then their valencies (H:1, O:2), and cross-multiply the valencies to get H\(_{2}\)O.

🎯 Exam Tip: The cross-multiplication method is a straightforward way to determine molecular formulas using valencies.

 

Question b. Fe (Valency 2) and S (Valency 2)
Answer:
Step 1: Write the symbols of the constituent elements.
Fe S
Step 2: Write the valency below the respective elements.
Fe S
2 2
Step 3: Cross multiply the valencies.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र वैलेंसी के क्रॉस-गुणा विधि को दर्शाता है। इसमें आयरन (Fe) की वैलेंसी 2 और सल्फर (S) की वैलेंसी 2 को उनके प्रतीकों के नीचे लिखा गया है। फिर इन वैलेंसी को क्रॉस-मल्टीप्लाई करके अणु सूत्र प्राप्त किया जाता है, और क्योंकि वैलेंसी समान हैं, वे सरल हो जाती हैं।
The molecular formula: FeS
In simple words: For iron (valency 2) and sulfur (valency 2), write their symbols, their valencies, and then cross-multiply; since both valencies are 2, they simplify to give the formula FeS.

🎯 Exam Tip: Always simplify the subscripts in the molecular formula to their lowest whole-number ratio.

 

Question c. The valencies of the atom H, O and N are 1, 2 and 3 respectively. The molecular formulae of these gaseous elements are H\(_{2}\), O\(_{2}\) and N\(_{2}\) respectively. How many chemical bonds are there in each of these molecules?
Answer: Chemical bond in H\(_{2}\) is one
Single chemical bond
H-H
Chemical bond in O\(_{2}\) are two
Double chemical bond
O=O
Chemical bond in N\(_{2}\) are three
Triple chemical bond
N \(\equiv\) N
In simple words: Based on their valencies (H:1, O:2, N:3), hydrogen forms a single bond (H-H), oxygen forms a double bond (O=O), and nitrogen forms a triple bond (N\(\equiv\)N) in their diatomic molecules.

🎯 Exam Tip: The number of bonds an atom forms in a simple molecule directly corresponds to its valency.

 

Question 1. Hydrogen is an element.
Answer:
1. Hydrogen has only one kind of atoms.
2. Hydrogen cannot be further divided into new substances by any physical or chemical means. Therefore, hydrogen is an element.
In simple words: Hydrogen is an element because it consists of only one type of atom and cannot be broken down into simpler substances by ordinary physical or chemical methods.

🎯 Exam Tip: The key characteristics of an element are uniformity of atoms and indivisibility by simple means.

 

Question 2. Water is a compound.
Answer:
1. The composition of water is same throughout i.e., the elements hydrogen and oxygen whose atoms are combined in the ratio by weight is always 1 : 8.
2. The properties of water are totally different from those of its constituents, i.e. hydrogen and oxygen. Hence, water is a compound.
In simple words: Water is a compound because it is formed from hydrogen and oxygen in a fixed ratio, and its properties are distinct from those of its constituent elements.

🎯 Exam Tip: Remember that compounds have a fixed composition and properties entirely different from their elements.

 

Question 3. Air is a mixture.
Answer:
1. Air contains nitrogen, oxygen and other gases.
2. These gases retain their original properties. They do not combine with each other. Hence, air is a mixture.
In simple words: Air is a mixture because it's composed of several gases that maintain their individual properties and aren't chemically bonded.

🎯 Exam Tip: The retention of individual properties by components is a definitive sign of a mixture.

 

Question 4. A potassium permanganate solution in water is a homogeneous mixture, while a mixture of oil and water is a heterogeneous mixture.
Answer:
1. In a potassium permanganate solution in water the constituents, i.e. potassium permanganate and water are uniformly mixed throughout.
2. The properties and composition of a homogeneous mixture are the same throughout the mixture. Hence, potassium permanganate solution is a homogeneous mixture.
3. In a mixture of oil and water, the constituents are not uniformly mixed throughout the mixture.
4. The properties and composition of a heterogeneous mixture are not the same throughout the mixture. Hence, a mixture of oil and water is a heterogeneous mixture.
In simple words: Potassium permanganate in water forms a uniform, homogeneous mixture, while oil and water create distinct layers, making it a non-uniform, heterogeneous mixture.

🎯 Exam Tip: Distinguish between homogeneous and heterogeneous mixtures by observing the uniformity of composition and properties throughout.

 

Question 5. Milk is a colloid.
Answer:
1. In milk, the particles are spread uniformly throughout and due to very small size of the particles, milk appears to be homogeneous.
2. But milk is a colloid solution and it is a heterogeneous mixture. Here, milk is liquid particles of proteins and fats having a diameter around \(10^{-5}\) m dispersed in the aqueous medium. Hence, a milk is a colloid.
In simple words: Milk is a colloid because it appears homogeneous but contains tiny dispersed particles (fats, proteins) that are larger than those in a solution, making it microscopically heterogeneous.

🎯 Exam Tip: Remember that colloids can appear homogeneous but are fundamentally heterogeneous due to their dispersed particle size.

 

Question 1. Solids
Answer:

Solids	Liquids
1. Solids have a definite shape.	1. Liquids have no definite shape.
2. They have very low compressibility.	2. They have moderate compressibility.
3. In solids, the intermolecular forces are very strong. E.g. iron, stone, salt.	3. In liquids, the intermolecular forces are moderately strong. E.g., water, alcohol, mercury.

In simple words: Solids have a fixed shape, are hard to compress, and have strong intermolecular forces, while liquids lack a fixed shape, are moderately compressible, and have weaker intermolecular forces.

🎯 Exam Tip: Focus on the differences in shape, compressibility, and intermolecular forces to distinguish between solids and liquids.

 

Question 2. Liquids and Gases:
Answer:

Liquids	Gases
1. Liquids have a definite volume.	1. Gases do not have a definite volume.
2. They have moderate compressibility.	2. They have high compressibility.
3. In liquids, the intermolecular forces are moderately strong. E.g. water, alcohol, mercury.	3. In gases, the intermolecular forces are very weak. E.g. oxygen, air.

In simple words: Liquids have a definite volume but no fixed shape, are moderately compressible, and have moderate intermolecular forces, whereas gases have neither definite shape nor volume, are highly compressible, and have very weak intermolecular forces.

🎯 Exam Tip: Key distinctions lie in volume, compressibility, and the strength of intermolecular forces.

 

Question 3. Solids and Gases:
Answer:

Solids	Gases
1. Solids have a definite shape and volume.	1. Gases have neither a definite shape nor a definite volume.
2. They have incompressibility.	2. They have high compressibility
3. In solids, the intermolecular forces are very strong. E.g. iron, stone.	3. In gases, the intermolecular forces are very weak. E.g. hydrogen, oxygen.

In simple words: Solids have fixed shape and volume, are incompressible, and have strong intermolecular forces, while gases lack fixed shape and volume, are highly compressible, and have very weak intermolecular forces.

🎯 Exam Tip: Focus on rigidity, fixed volume/shape, and compressibility as primary differentiators.

 

Question 4. Element and Compound:
Answer:

Element	Compound
1. An element consists of only one kind of substance.	1. A compound is formed from two or more elements.
2. An element cannot be further divided into simpler substances by any physical or chemical means. E.g. iron, copper, oxygen.	2. A compound can be further divided into simple substances by chemical means. E.g. common salt, sugar, water.

In simple words: Elements are pure substances made of one type of atom and cannot be broken down, while compounds are formed by two or more elements chemically combined and can be broken down by chemical means.

🎯 Exam Tip: The key difference is whether the substance can be chemically broken down into simpler elements.

 

Question 5. Compound and mixture:
Answer:

Compound	Mixture
1. A compound is made of two or more elements chemically combined in a fixed proportion.	1. A mixture is obtained by just mixing two or more substances in any proportion.
2. A compound can be further subdivided into simpler substances by chemical means only.	2. A mixture can be further subdivided into simpler substances by simple physical processes.
3. The properties of a compound are entirely different from the properties of its constituents. E.g. common salt, sugar, water.	3. The constituents of a mixture retain their original properties. E.g. air, seawater.

In simple words: Compounds involve chemical bonding with fixed proportions and new properties, while mixtures are physical blends with variable proportions where components retain their original properties.

🎯 Exam Tip: Focus on chemical bonding, fixed/variable proportions, and property changes to differentiate compounds from mixtures.

 

Question 6. Colloids and Suspension:
Answer:

Colloidals	Suspension
1. The particles in a colloidal solution can pass through a filter paper.	1. The particles in a suspension cannot pass through a filter paper.
2. The colloidal particles cannot be seen with a naked eye.	2. The suspended particles can be seen with a naked eye.
3. The diameter of solid particles is around \(10^{-5}\) m	3. The diameter of the solid particles is larger than \(10^{-4}\) m.

In simple words: Colloids have tiny particles that pass through filters and are invisible to the naked eye, while suspensions have larger, visible particles that cannot pass through filters.

🎯 Exam Tip: Particle size and filterability are the main criteria for distinguishing colloids from suspensions.

 

Activity 1:
Apparatus: Plastic jar, balloon, thread
Material: Mustard seeds
Take some mustard seeds in a transparent plastic jar. Thread a long thread at the centre of a big balloon by means of a needle and tie it tight. Stretch this rubber diaphragm and fix it on the mouth of the jar by means or a rubber band. Pull the diaphragm up and down with the help of the thread first slowly, then with moderate force and then vigorously. Record your observation in the following table.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र "मूवमेंट ऑफ मस्टर्ड सीड्स" गतिविधि को दर्शाता है। इसमें एक पारदर्शी प्लास्टिक जार में सरसों के बीज भरे हैं, जिसके मुंह पर एक बड़ा गुब्बारा डायाफ्राम के रूप में कसा हुआ है। गुब्बारे के केंद्र से एक धागा जुड़ा हुआ है, जिसे ऊपर-नीचे खींचकर सरसों के बीजों की गति का अवलोकन किया जाता है।

Question 1.

Mode of pulling the diaphragm up and down	Movement of the mustard seeds
Slow	Vibration in the same place
with moderate force	.......
vigorous	.......

Answer:

Mode of pulling the diaphragm up and down	Movement of the mustard seeds
Slow	Vibration in the same place
with moderate force	The extent of vibration increases.
vigorous	They will move upwards so much that they will strike the bottom of the jar fall on the diaphragm and again move upwards.

In simple words: Pulling the diaphragm slowly causes seeds to vibrate in place, moderate force increases vibration, and vigorous pulling makes seeds jump and strike the jar bottom, illustrating particle movement with varying energy.

🎯 Exam Tip: This activity demonstrates how external force influences the kinetic energy and movement of particles, relating to states of matter.

 

Activity 2:
Apparatus: Hammer, sand paper
Material: Iron nail, copper wire, aluminium wire, coal.
Take the following objects: iron nail/sheet, copper wire, aluminium wire, a piece of coal. Rub each object on a fresh surface of sandpaper and observe. Hammer each object with force. (Take care not to hurt yourself.) Record your observations in the following table.
The objects in the activity are made of the elements iron (Fe), copper (Cu), aluminium (Al) and carbon (C); respectively. Fill the following table on the basis of the observations obtained on doing the above two tests on each of the objects.
Question 1.

Object	Is the surface shining? yes/no	Does the shape flatten/break into small pieces on hammering?
Iron nail
Copper wire
Aluminium wire
Coal piece
	Elements having a shiny surface
	Elements that flatten on hammering
	Elements with a dull surface
	Elements that break on hammering

Answer:

Object	Is the surface shining? yes/no	Does the shape flatten/break into small pieces on hammering?
Iron nail	Yes	The shape flattens on hammering
Copper wire	Yes	The shape flattens on hammering
Aluminium wire	Yes	The shape flattens on hammering
Coal piece	No	It breaks into small pieces on hammering
	Elements having a shiny surface	Copper
	Elements that flatten on hammering	Iron, Copper, Aluminium
	Elements with a dull surface	Iron
	Elements that break on hammering	Carbon

In simple words: This activity classifies materials based on their luster (shiny/dull) and malleability (flattening/breaking upon hammering), demonstrating properties of metals (shiny, malleable) and non-metals (dull, brittle).

🎯 Exam Tip: This activity highlights the fundamental physical properties used to distinguish between metals and non-metals.

 

Activity 3:
Apparatus: Evaporating dish, tripod stand, burner, etc.
Chemicals: Camphor, washing soda, blue vitriol, sugar, glucose, urea.
Keep the evaporating dish on the tripod stand. Take some camphor in the evaporating dish. Heat the camphor in the dish strongly with the help of a burner. Find out what remains behind in the evaporating dish. Repeat the above procedure using limestone, washing soda, blue vitriol, sugar, glucose and urea instead of camphor. Record your observation in the following table. (Do this activity carefully under the supervision of your teacher, as some of the powders may catch fire.)

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक वाष्पीकरण गतिविधि को दर्शाता है, जहाँ एक चीनी मिट्टी के कटोरे (evaporating dish) में एक पदार्थ को एक ट्राइपॉड स्टैंड पर रखकर बर्नर की लौ से गर्म किया जा रहा है। इसका उद्देश्य यह देखना है कि गर्म करने के बाद कोई अवशेष बचता है या नहीं, जो पदार्थों के रासायनिक गुणों की पहचान में सहायक होता है।

Activity 4: (Textbook page 43)

Question 1.Beaker Number: 1, Materials taken: Sand and water, What change seen on stirring: Sand at the bottom water above the sand, Number of phases in the mixture: Two phases, Types of mixture: Heterogeneous.
Beaker Number: 2, Materials taken: Blue vitriol and water, What change seen on stirring: Blue coloured solution, Number of phases in the mixture: Single phase, Types of mixture: Homogeneous.
Beaker Number: 3, Materials taken: Blue vitriol and sand and water, What change seen on stirring: Blue coloured solution Sand settles down at the bottom, Number of phases in the mixture: Two phases, Types of mixture: Heterogeneous.
Answer:

Beaker Number	Materials taken	What change seen on stirring	Number of phases in the mixture	Types of mixture
1	sand + water	Sand at the bottom water above the sand	Two phases	Heterogeneous
2	Blue vitriol+ water	Blue coloured solution	Single phase	Homogeneous
3	Blue vitriol + sand + water	Blue coloured solution Sand settles down at the bottom	Two phases	Heterogeneous

In simple words: This table categorizes different mixtures (sand + water, blue vitriol + water, blue vitriol + sand + water) based on their appearance after stirring, number of phases, and type (homogeneous or heterogeneous). It demonstrates how different substances interact when mixed with water.

🎯 Exam Tip: Understanding the concepts of homogeneous and heterogeneous mixtures and their characteristics is crucial for scoring well. Pay attention to how the number of phases determines the type of mixture.

 

Question 2.In the above activity after stirring a homogeneous mixture is formed in only one beaker? Which is that?
Answer:The homogeneous mixture is formed in the second beaker. It is a solution of blue vitriol.In simple words: Only the mixture of blue vitriol and water formed a homogeneous mixture, which is a solution where substances are uniformly mixed.

🎯 Exam Tip: Identify examples of solutions and understand why they are considered homogeneous. This is a common concept in mixture classification.

Activity 5: (Textbook page 44)

Question 1.

Beaker	Components of the mixture	Separate aqueous phase seen/not seen	Transparent/ opaque	Components are separated/ not separated by filtration
1	Common salt + water	Separate aqueous phase not seen	Transparent	Components are not separated by filtration
2	Saw dust + water	Separate aqueous phase seen	Aqueous phase transparent	Components are separated by filtration
3	Milk + water	Separate aqueous phase not seen	Opaque	Components are not separated by filtration

Answer:

Beaker	Components of the mixture	Separate aqueous phase seen/not seen	Transparent/ opaque	Components are separated/ not separated by filtration
1	Common salt + water	Separate aqueous phase not seen	Transparent	Components are not separated by filtration
2	Saw dust + water	Separate aqueous phase seen	Aqueous phase transparent	Components are separated by filtration
3	Milk + water	Separate aqueous phase not seen	Opaque	Components are not separated by filtration

In simple words: This table compares common salt in water (solution), sawdust in water (suspension), and milk in water (colloid) based on visual separation, transparency, and separability by filtration. It highlights the distinct properties of solutions, suspensions, and colloids.

🎯 Exam Tip: Memorize the characteristics distinguishing solutions, suspensions, and colloids, especially how they appear and whether their components can be separated by filtration. This is a fundamental concept.

Activity 6: (Textbook page 44)

Question 1.

Action	Colour of matter	Effect of horseshoe magnet
Iron filings and sulphur were mixed in the dish
Iron filings and sulphur in the dish were heated together

Answer:

Action	Colour of matter	Effect of horseshoe magnet
Iron filings and sulphur were mixed in the dish	Black & yellow	The magnet attracts iron filings from the mixture. (Thus iron filings and sulphur powder can be separated by a physical process.)
Iron filings and sulphur in the dish were heated together	Black	A compound iron sulphide (FeS) is formed. A magnet has no effect on iron sulphide.

In simple words: This activity shows the difference between a mixture and a compound. When iron and sulfur are mixed, iron retains its magnetic properties. When heated, they form a new compound (iron sulfide) with different properties, including no attraction to a magnet.

🎯 Exam Tip: This experiment clearly illustrates the key distinction between a physical mixture and a chemical compound. Focus on how properties change (or don't change) after mixing vs. chemical reaction.

Complete The Following:

 

Question 1.Complete the table:

Sr. No.	Name of the compound	molecular formula	Constituent elements	Number of atoms of constituent elements
1.	Water	H₂O	H O	2 1
2.	Hydrogen chloride	HCl
3.	Methane	CH₄
4.	Magnesium chloride	MgCl₂

Answer:Molecular formulae of some compounds are given in the following table. Use these to fill in the gaps in the table.

Sr. No.	Name of the compound	Molecular formula	Constituent elements	Number of atoms of constituent elements
1.	Water	H₂O	H O	2 1
2.	Hydrogen chloride	HCl	H Cl	1 1
3.	Methane	CH₄	C H	1 4
4.	Magnesium chloride	MgCl₂	Mg Cl	1 2

In simple words: This table breaks down common chemical compounds by their molecular formula, the elements they contain, and the number of atoms of each element. It helps in understanding the basic composition of compounds.

🎯 Exam Tip: Practice identifying constituent elements and their quantities from molecular formulas. This skill is essential for stoichiometry and understanding chemical reactions.

 

Question 2.Complete the table:

Sr. No.	Molecular formula of a compound	Constituent Elements H X	Valency of 'H'	Number of bonds formed by 'X' with 'H'	Valency 'X'
1	HCl	H Cl	1	1	1
2	H₂O	H O	1	2	2
3	H₂S
4	NH₃
5	HBr
6	HI
7	NaH
8	CH₄

Answer:Molecular formulae of various compounds formed by hydrogen with other elements are given in the following table. From that, deduce the valencies of the concerned elements.

Sr. No.	Molecular formula of a compound	Constituent Elements H X	Valency of 'H'	Number of bonds formed by 'X' with 'H'	Valency 'X'
1	HCl	H Cl	1	1	1
2	H₂O	H O	1	2	2
3	H₂S	H S	1	2	2
4	NH₃	H N	1	3	3
5	HBr	H Br	1	1	1
6	HI	H I	1	1	1
7	NaH	H Na	1	1	1
8	CH₄	H C	1	4	4

In simple words: This table demonstrates how to determine the valency of various elements (X) by analyzing their molecular formulas when combined with hydrogen (H), given that hydrogen has a valency of 1. The number of bonds formed by X with H directly indicates the valency of X.

🎯 Exam Tip: Valency is a key concept for writing chemical formulas. Remember that valency indicates the combining capacity of an element, often determined by the number of bonds it forms.

 

Question 3.Complete the table:

Element	Valency	Molecular formula of the corresponding compound
C	4
H	1
N	3
H	1
Fe	2
S	2
C	4
O	2

Answer:

Element	Valency	Molecular formula of the corresponding compound
C	4	CH₄
H	1
N	3	NH₃
H	1
Fe	2	FeS
S	2
C	4	CO₂
O	2

In simple words: This table asks to fill in the molecular formulas of compounds formed from the given elements, using their valencies. This exercise reinforces the concept of valency and its role in chemical bonding to create stable compounds.

🎯 Exam Tip: When forming molecular formulas, ensure that the total valencies of combining atoms balance. Use the criss-cross method of valencies as a quick way to derive correct formulas.