Selina Concise Solutions for ICSE Class 7 Chemistry Chapter 3 Elements Compounds and Mixtures

Points to Remember :

Point 1: Every substance is made up of very tiny particles, called molecules. Molecules are formed from even smaller particles called atoms.
Molecules represent the smallest part of a substance that can exist on its own while keeping its identity. Atoms are the fundamental building blocks that combine in different ways to create these molecules.
Teacher's Tip: Imagine atoms as individual Lego pieces and molecules as the specific structures you build with them.
Exam Tip: Remember that while atoms are the smallest unit, molecules are the smallest unit capable of independent existence.

Point 2: Element - (a) Element is the simplest pure substance. It cannot be divided further into simpler substances by any chemical method, e.g. oxygen, hydrogen, sulphur, etc.
(b) At present 116 elements are known, of which 92 are natural elements.
An element is made up of only one kind of atom, which gives it unique characteristics. Because they are in their simplest form, you cannot break them down into anything else using heat or electricity.
Teacher's Tip: Use the Periodic Table to visualize elements as the alphabet of the universe.
Exam Tip: To score full marks, always mention that elements cannot be split by "chemical methods."

Point 3: Based on their properties, elements are classified into : metals, non-metals, metalloids, noble gases.
This classification helps scientists group elements that behave in similar ways. Metals are usually shiny and hard, while non-metals vary more in their appearance and state.
Teacher's Tip: Think of this like sorting your clothes into categories like shirts, pants, and socks for easier organization.
Exam Tip: Be prepared to list all four categories if asked how elements are classified.

Point 4: Metals are ductile, malleable, good conductors of heat and electricity, high melting and boiling points. Metals are sonorous, e.g., Iron, Gold, Silver, etc.
Malleable means they can be beaten into thin sheets, while ductile means they can be drawn into wires. Most metals are solid at room temperature and have a shiny appearance called metallic lustre.
Teacher's Tip: Remember the 3 'S's for metals: Shiny, Strong, and Sonorous (they make a ringing sound).
Exam Tip: Define terms like "malleable" and "ductile" clearly when describing metallic properties to show deep understanding.

Point 5: Non-metals are solids and brittle in nature, bad conductor of heat and electricity (exception Graphite) low melting and boiling points, e.g. sulphur, carbon, hydrogen, etc.
Unlike metals, solid non-metals are brittle, meaning they break easily when hit. Most of them act as insulators because they do not allow heat or electricity to pass through easily.
Teacher's Tip: Think of a piece of coal (carbon); it is dull and breaks into powder, which is typical for a non-metal.
Exam Tip: Always mention Graphite as the exception when discussing the conductivity of non-metals.

Point 6: Metalloids - These elements show properties of both metals and non-metals. They are hard solids, e.g. Boron, Silicon, Arsenic.
Metalloids sit on the border between metals and non-metals on the periodic table. They might look like metals but behave like non-metals in certain chemical conditions.
Teacher's Tip: Think of metalloids as "hybrids" that share traits from two different groups.
Exam Tip: Memorize Silicon as a primary example since it is widely used in computer chips.

Point 7: Inert or noble gases - These elements do not react chemically with other elements or compounds are called noble (Inert) gases, e.g., helium, neon, argon, etc.
Noble gases are very stable because their outer electron shells are full, making them "unsociable" in the chemical world. They are found in very small quantities in the atmosphere.
Teacher's Tip: Think of "Noble" as "Royal" - they don't like to mix with the common elements!
Exam Tip: Use the term "chemically unreactive" to describe why they are called inert.

Point 8: Symbols of Elements - Each element is denoted by a symbol usually to first letter.
Examples : Oxygen by O Hydrogen by H.
Symbols serve as a universal language for scientists around the world. While some use the first letter, others use the first two letters or names derived from Latin.
Teacher's Tip: If an element has a two-letter symbol, only the first letter is ever capitalized.
Exam Tip: Be careful with symbols like Fe (Iron) or Na (Sodium) which come from their Latin names Ferrum and Natrium.

Point 9: Atom - “An Atom is the smallest particle of an element that can take part in a chemical reaction but may or may not have independent existence.”
The atom of an element exhibits all the properties of that element.
Atoms are so small they cannot be seen even with the most powerful optical microscopes. They are the units that actually bond together during a chemical change.
Teacher's Tip: Imagine an atom as the smallest "identifiable" bit of a gold bar; if you split it further, it's no longer gold.
Exam Tip: Always include the phrase "takes part in a chemical reaction" in your definition of an atom.

Point 10: Molecule - A molecule is the smallest particle of a pure substance of element or compound which has independent existence. It exhibits all the properties of pure substance.
Molecules can consist of atoms of the same element (like O₂) or different elements (like H₂O). Unlike many atoms, molecules are stable enough to exist alone in nature.
Teacher's Tip: Think of a molecule as a complete "word" made from "letter" atoms.
Exam Tip: Highlight that molecules have "independent existence" to distinguish them from atoms.

Point 11: Atomicity - The number of atoms of an element that join together to form a molecule of that element is known as the atomicity.
For example, oxygen exists as O₂, so its atomicity is 2. Elements can be monoatomic (1 atom), diatomic (2), or polyatomic (many).
Teacher's Tip: Look at the subscript number in a formula (like the 2 in O₂) to find the atomicity.
Exam Tip: Practice classifying elements as monoatomic or diatomic for quick exam points.

Point 12: Molecular Formula - of an element is the symbolic representation of its molecule. It indicates the number of atoms present in it. e.g. Magnesium oxide - MgO.
The molecular formula tells you exactly which elements are in a substance and how many atoms of each are there. It acts as a recipe for a specific chemical compound.
Teacher's Tip: Read formulas carefully; CO is different from Co (Carbon Monoxide vs. Cobalt).
Exam Tip: When writing formulas, ensure subscripts are smaller and placed slightly below the line of text.

EXERCISE - I

Question 1: Write the symbols of helium, silver, krypton, antimony, barium.
Answer:
Element Symbol
Helium   He
Silver    Ag
Krypton   Kr
Antimony    Sb
Barium   Ba
Each element has a unique one or two-letter shorthand. These symbols are used globally in chemical equations.
Teacher's Tip: For symbols like Ag (Silver) and Sb (Antimony), remember they come from Latin: Argentum and Stibium.
Exam Tip: Always double-check that the second letter of a symbol is written in lower case to avoid losing marks.

Question 2: Write the names of following elements Na, C, Kr, U, Ra, Fe, Co.
Answer:
Symbol  Element
Na   Sodium
C   Carbon
Kr   Krypton
U   Uranium
Ra   Radium
Fe   Iron
Co   Cobalt
Translating symbols back to names is a fundamental skill in chemistry. It allows you to read and understand scientific texts and formulas.
Teacher's Tip: Practice saying the symbol and name out loud together to build a strong mental link.
Exam Tip: Be careful with Co (Cobalt) and CO (Carbon Monoxide); capitalization completely changes the meaning.

Question 3: Define :
1. Elements : An element is the basic form of matter that cannot be broken down into simpler substances by chemical reactions.
2. Compounds : A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.
Answer: Verbatim as above.
Elements are the simplest building blocks of matter. Compounds are more complex substances where different elements are locked together in a specific, unchanging recipe.
Teacher's Tip: Think of elements as the raw ingredients and compounds as a finished cake that cannot be easily separated back into eggs and flour.
Exam Tip: Use the phrase "fixed ratio by mass" when defining compounds to demonstrate a high level of accuracy.

Question 4: Name the main metal present in the following :
(a) Haemoglobin
(b) Chalk
(c) Chlorophyll
(d) Chocolate wrappers
Answer:
(a) Haemoglobin Iron
(b) Chalk Calcium
(c) Chlorophyll Magnesium
(d) Chocolate wrappers Aluminium
Metals are found in many everyday substances, even biological ones. These metals are often in the form of ions or compounds rather than shiny solids.
Teacher's Tip: Relate these to real life; for example, iron in blood helps carry oxygen, just like an iron train carries cargo.
Exam Tip: Ensure you link the correct metal to its source, as these are very common "one-word answer" exam questions.

Question 5: Give four examples of non-metallic elements.
Answer: Examples : Hydrogen, oxygen, nitrogen, carbon, chlorine, sulphur, phosphorus, etc.
Non-metals are vital for life; for example, we breathe oxygen and plants need nitrogen. Most of these exist as gases or dull, brittle solids at room temperature.
Teacher's Tip: Remember the most common elements in the air (nitrogen and oxygen) as your go-to examples.
Exam Tip: Listing common gases is an easy way to recall non-metals quickly during a test.

Question 6: What do you understand by :
1. Metalloids : Metalloids are those substances which have some properties of metals and some of non-metals e.g. boron, silicon.
2. Noble gases : Noble gases are those which do not react chemically with other elements or compounds e.g. helium, neon, etc.
Answer: Verbatim as above.
Metalloids act as bridges between the two main types of elements. Noble gases are unique because they are very stable and don't like to bond with others.
Teacher's Tip: Think of metalloids as "lukewarm" - not quite hot (metal), not quite cold (non-metal).
Exam Tip: Always provide an example like Silicon or Helium when defining these groups to strengthen your answer.

Question 7: Select elements and compounds from the following list: Iron, plaster of paris, chalk, common salt, copper, aluminium, calcium oxide, cane sugar, carbon, silica, sodium sulphate, uranium, potassium carbonate, silver, carbon dioxide.
Answer:
Element:
Iron
Copper
Aluminium
Carbon
Uranium
Silver
Compounds:
Plaster of paris
Chalk
Common salt
Calcium oxide
Cane sugar
Silica
Sodium sulphate
Potassium carbonate
Carbon dioxide
Elements consist of only one kind of atom, while compounds are made of different atoms bonded together. You can usually tell a compound if it has multiple words in its chemical name.
Teacher's Tip: If it's on the periodic table, it's an element; if it sounds like a recipe (like "Sodium Sulphate"), it's likely a compound.
Exam Tip: Create two clear columns to present this kind of classification answer neatly for the examiner.

EXERCISE - II

Question 1: State four difference between compounds and mixtures.
Answer:
Compound:
1. A compound is a pure substance.
2. Compounds are always homogeneous.
3. A compound has a fixed composition, i.e., it is formed when two or more pure substances chemically combine in a definite ratio by mass.
4. Formation of a compound involves change in energy.
5. Compounds have specific set of properties.
6. Components of compounds can be separated only by complex chemical processes.
Mixture:
1. A mixture is an impure substance.
2. Mixtures may be homogeneous or heterogeneous.
3. A mixture has no fixed composition, i.e., it is formed by mixing two or more substances in any ratio without any chemical reaction.
4. Formation of a mixture does not involve any change in energy.
5. Mixtures do not have any specific set of properties.
6. Components of mixtures can be separated by simple physical methods.
Compounds are chemically bonded and completely new substances, while mixtures are just physical blends. In a mixture, the original parts keep their own identity and can be taken back out easily.
Teacher's Tip: Think of a compound as a baked cake and a mixture as a fruit salad.
Exam Tip: Use a T-chart format and ensure your points directly oppose each other for a high-scoring answer.

Question 2: What are the characteristic properties of a pure substance? Why do we need them?
Answer: Pure substance : Pure substances have a definite set of properties such as boiling point, melting point, density, etc. They are all homogeneous i.e., their composition is uniform throughout the bulk. Both elements and compounds are pure substances.
Pure substances are needed to :
1. Manufacture medicines.
2. To prepare chemicals in industry.
3. For scientific purposes.
4. To maintain the good health of human beings.
Pure substances are reliable because they always behave the same way under the same conditions. This consistency is crucial in medicine and science where exactness is required.
Teacher's Tip: Imagine if every bottle of distilled water was different; scientific experiments would never work!
Exam Tip: Mentioning "homogeneous composition" is a key technical term that will impress examiners.

Question 3: Give two examples for each of the following :
(a) Solid + Solid mixture
(b) Solid + Liquid mixture
(c) Liquid + Liquid mixture
Answer:
(a) Solid + Solid mixture : Sand and sugar,
- Sand and stone,
- sand and sugar.
(b) Solid + Liquid mixture :
- Sand and water,
- Charcoal and water.
(c) Liquid + Liquid mixture :
- Oil in water,
- Alcohol and water.
Mixtures can exist between any states of matter. The way they are mixed determines whether they look uniform or have visible separate parts.
Teacher's Tip: "Sand and sugar" is a heterogeneous solid mixture because you could technically separate the grains with a magnifying glass.
Exam Tip: Providing everyday examples like "oil and water" makes your answer easy to remember and verify.

Question 4: Define :
1. Evaporation : Is the process of converting a liquid into its vapours state either by exposing it to air or by heating.
2. Filtration : The process of separating solid particles from liquid by allowing it to pass through a filter paper is called filtration.
3. Sublimation : The process in which a solid changes directly into its vapours on heating is called sublimation.
4. Distillation : Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.
5. Miscible liquids : Homogeneous liquid-liquid mixtures are called miscible liquids.
6. Immiscible liquids : Heterogeneous liquid-liquid mixtures are called immiscible liquids.
Answer: Verbatim as above.
These terms describe physical processes used to separate mixtures or change states. Understanding these is the key to practical chemistry in the lab.
Teacher's Tip: Remember "Sublimation" as "Skipping the liquid stage" - like dry ice turning straight to gas.
Exam Tip: Use technical terms like "residue" and "filtrate" when describing filtration to get bonus marks.

Question 5: Name the process by which the components of following mixtures can be separated.
1. Iron and sulphur
2. Ammonium chloride and sand
3. Common salt from sea water
4. Chaff and grain
5. Water and mustard oil
6. Sugar and water
7. Cream from milk
Answer:
1. Magnetic separation.
2. Sublimation.
3. Evaporation.
4. Winnowing separates chaff (lighter) from heavier grains in two different heaps.
5. Mustard oil and water is liquid-liquid immiscible mixture and is separated by separating funnel. Water being the heavier forms the lower layer.
6. By evaporation in this process of converting a liquid into its vapour state by heating. Liquid is heated and water evaporate and sugar is obtained.
7. Centrifugation.
Choosing the right separation method depends on the physical properties of the components, like magnetism, boiling point, or density. Each method targets a specific difference between the substances.
Teacher's Tip: If one component is magnetic (like iron), magnetic separation is always the first and easiest step.
Exam Tip: Be specific; don't just say "separating," use the correct name of the technique like "Centrifugation."

Question 6: How will you separate a mixture of common salt, chalk powder and powdered camphor? Explain.
Answer: Comphor with sublimation. Chalk powder by Alteration then the residual left is common salt.
This multi-step process uses different techniques in order. First, you remove the substance that evaporates easily, then the one that doesn't dissolve, leaving the salt behind.
Teacher's Tip: Think of it as a "filter" that catches one thing at a time until you are left with just the last ingredient.
Exam Tip: Describe the steps in a clear 1-2-3 sequence to show you understand the logical order of operations.

Question 7: How is distillation more advantageous than evaporation?
Answer: The advantage of distillation is that both components of the solid and liquid mixture are obtained. Whereas in evaporation only solid is obtained.
In evaporation, the liquid is lost into the air. Distillation uses a cooling system to catch that liquid, which is essential if the liquid itself is valuable.
Teacher's Tip: Think of distillation as "smart evaporation" because it doesn't waste the steam.
Exam Tip: Use the word "condensation" to explain how the liquid is recovered during distillation.

Question 8:
1. What is chromatography?
2. Why is it named so?
3. What are the advantages of chromatography?
4. Name the simplest type of chromatography?
5. On what principle is this method based?
6. What is meant by stationary phase and mobile phase in chromatography?
Answer:
1. The process of separating different dissolved constituents of a mixture by their absorption on an appropriate material is called chromatography.
2. It is named so, because earlier it was used to separate mixtures containing coloured components only but these days this technique is applied to colourless substances too.
3. Advantages of chromatography : (i) A very small quantity of the substance can be separated. (ii) Components with very similar physical and chemical properties can be separated. (iii) It identifies the different constituents of a mixture. (iv) It also helps in quantitative estimation of components of a mixture.
4. The simplest type of chromatography is “Paper chromatography”.
5. Chromotography is based on differential affinities of compounds towards two phases i.e. stationary and mobile phase.
6. The filter paper acts as “stationary phase” while the solvent act as “mobile phase”.
Chromatography is a highly precise separation tool used in labs. It works because different chemicals "travel" at different speeds when pushed across a surface.
Teacher's Tip: Think of it like a race where different runners (chemicals) get tired at different times and stop at different spots.
Exam Tip: Be ready to explain the "stationary" (not moving) and "mobile" (moving) phases clearly as they are common exam definitions.

Question 9: On what principle are the following methods of separation based? Give one example of a mixture for each of the methods mentioned in which they are used
1. Sublimation : Change of solid into vapours directly on heating and change of vapours into solid again on cooling.
Example : Salt from ammonium chloride.
2. Filtration : The process of separating insoluble solid particles from a liquid by allowing it to pass through a filter is called Filtration. These filters allow liquids to pass through them but not solids. The insoluble solid left on the filter is called the residue, while the liquid which passes through the filter is called the filtrate. Mixtures like chalk and water, clay and water, tea and tea leaves, sawdust and water, etc., are separated by this method.
3. Sedimentation and decantation : The settling down of suspended, insoluble, heavy, solid particles in a solid- liquid mixture when left undisturbed is called sedimentation. The solid which settles at the bottom is called sediment while the clear liquid above it is called supernatant liquid. The process of pouring out the clear liquid, without disturbing the sediment, is called decantation. Example : A mixture of sand and water.
4. Solvent extraction method : This method is used when one of the solid components is soluble in a liquid. Example : A mixture of sand and salt can be separated by this method. Salt gets dissolved in water while sand settles down in the container. The salt solution is then decanted. Salt is separated from the solution by evaporation. In this way, they can be separated.
5. Magnetic separation : This method is used when one of the components of the mixture is iron. Iron gets attracted towards a magnet and hence can be separated. Mixtures of iron and sulphur, iron and sand, etc., can be separated by moving a magnet over them. Iron gets attached to the magnet and is separated.
6. By using a separating funnel : It is a simple device used to separate the components of a liquid-liquid heterogeneous mixture. Example : Kerosene oil and water. The mixture is placed in a separating funnel and allowed to stand for sometime. The components form two clear layers. Water being heavier forms the lower layer and oil being lighter forms the upper layer. When the stopper of the funnel is opened, the heavier liquid trickles out slowly and is collected in a vessel. The stopper is closed when the bottom layer is entirely removed the funnel. In this way, the two liquids are separated.
7. Fractional distillation : The process of distillation is used for separating the components of a homogeneous liquid-liquid mixture, like water and alcohol. This is based on the fact that alcohol boils at a lower temperature than water. The vapour of alcohol are collected and cooled while water is left behind in the original vessel. Thus, two liquids having different boiling points can be separated by distillation provided that difference in their boiling points must be 25°C or more.
Answer: Verbatim as above.
These detailed principles explain "why" a certain method works. Every method exploits a specific physical weakness or trait of the components involved.
Teacher's Tip: When using a separating funnel, the denser liquid is always at the bottom and comes out first.
Exam Tip: For Fractional Distillation, the 25 °C difference rule is a crucial detail that examiners look for.

OBJECTIVE TYPE QUESTIONS

Question 1: Fill in the blanks:

1. Elements are made up of same kind of atoms.
2. Elements and compounds are pure substances.
3. In a mixture the substances are not combined chemically.
4. Clay is separated from water by the method called loading and decantation.
5. Crystallisation is a process to obtain a very pure form of a solid dissolved in a liquid.
6. Camphor and ammonium chloride can sublimate.
Answer: Verbatim as above.
Fill-in-the-blanks test your recall of core terminology. Each blank focuses on a defining characteristic of substances or processes.
Teacher's Tip: Re-read the sentence after filling it to make sure it sounds logically and scientifically correct.
Exam Tip: Be careful with spellings like "Crystallisation" and "Sublimate" to ensure you get full credit.

Question 2: Give one word answers for the following :
1. The solid particles which remain on the filter paper after the filtration residue.
2. The liquid which evaporates and then condenses during the process of distillation distillate.
3. The process of transferring the clean liquid after the solid settles at the bottom of the container decantation.
4. The process by which two miscible liquids are separated fractional distillation.
Answer: Verbatim as above.
One-word answers require precision. They are designed to see if you can identify a whole process or substance by its primary function.
Teacher's Tip: Associate "residue" with "remaining" - it's what's left behind in the paper.
Exam Tip: Practice these frequently as they are quick and easy marks in any test paper.

MULTIPLE CHOICE QUESTIONS

Question 1: A pure liquid is obtained from a solution by :
1. evaporation
2. distillation
3. Alteration
4. crystallisation
Answer: 2. distillation
Distillation is the only choice that captures and purifies the liquid component itself. Evaporation would lose the liquid to the atmosphere.
Teacher's Tip: If the question asks for the "liquid" from a "solution," think of how you would catch the steam.
Exam Tip: Cross out obviously wrong answers like "Alteration" (which seems to be a typo for Filtration in the original text) to narrow your choices.

Question 2: Components of crude petroleum can be separated by :
1. distillation
2. evaporation
3. filtration
4. fractional distillation
Answer: 4. fractional distillation
Crude oil is a complex mixture of many liquids with different boiling points. "Fractional" distillation separates them into different "fractions" like petrol, diesel, and kerosene.
Teacher's Tip: Petroleum = Fractional Distillation. This is a classic science fact you should memorize.
Exam Tip: Remember that this process works because the different liquids have different boiling points.

Question 3: Example of a homogeneous mixture is :
1. tap water
2. distilled water
3. sand and water
4. water and oil
Answer: 1. tap water
Tap water looks uniform because it has dissolved minerals evenly spread through it. Distilled water is a pure substance, while sand/oil in water are clearly heterogeneous.
Teacher's Tip: "Homogeneous" means you cannot see separate parts with your naked eyes.
Exam Tip: Don't confuse "pure substance" (distilled water) with "homogeneous mixture" (tap water).

Question 4: In chromatography the filter paper is :
1. stationary phase
2. mobile phase
3. mixture
4. none of the above
Answer: 1. stationary phase
The paper stays still while the liquid solvent moves up through it. Therefore, the paper is the "stationary" (non-moving) part of the setup.
Teacher's Tip: "Stationary" means standing still, just like the paper in the experiment.
Exam Tip: Remember that the solvent is the "mobile phase" because it is the part that moves.

Question 5: A set of mixture is :
1. ink, honey, icecream, milk
2. tapwater, gold, common salt, alloy
3. milk, brass, silver, honey
4. butter, petroleum, tapwater, iron
Answer: 1. ink, honey, icecream, milk
Option 1 contains only mixtures, whereas other options include pure elements (like gold, silver, iron) or pure compounds (common salt).
Teacher's Tip: A quick way to find the answer is to look for elements like Gold or Silver and eliminate those sets.
Exam Tip: Read every item in the list carefully; if even one is a pure element, the whole set is wrong.

ADDITIONAL QUESTIONS - Check Your Progress 1

Fill in the blanks.

1. A pure substance has definite composition and constant properties.
2. Mixtures can be heterogeneous or homogenous.
3. Use of a sieve to separate the components of a mixture of solids is based on the difference in the size of the components.
4. Winnowing is used when the constituents of a mixture of solids have difference in their weights.
5. Iodine, camphor, naphthalene, ammonium chloride and dry ice are some substances that sublimate.
Answer: Verbatim as above.
These progress checks ensure you grasp the logic behind common separation methods. They link a physical difference (like size or weight) to a specific tool or technique.
Teacher's Tip: Think of a sieve in the kitchen; it lets small flour through but catches big lumps.
Exam Tip: Learn the list of "sublimating substances" in point 5; they are very common exam examples.

Check Your Progress 2

Question 1: Filtraction is a method used to separate fine particles of solid from a liquid.
Answer: Filtraction is a method used to separate fine particles of insoluble solid from a liquid.
The correction here is key: the solid must be "insoluble" (not dissolved). If it were dissolved, it would just pass right through the filter paper with the liquid.
Teacher's Tip: You can't filter sugar out of tea because it's dissolved, but you can filter out the tea leaves.
Exam Tip: Always use the word "insoluble" when describing the type of solids that filtration can remove.

Question 2: Loading is basically speeding up …………
Answer: Loading is basically speeding up sedimentation.
Loading involves adding a substance like alum that sticks to tiny particles and makes them heavy. These heavier clumps then fall to the bottom much faster than they would on their own.
Teacher's Tip: Think of "Loading" as putting a heavy backpack on a floating particle to make it sink.
Exam Tip: Be ready to name "Alum" as the substance commonly used for the process of loading.

Question 3: Name the techniques used to separate a solid from its solution.
Answer: Sedimentation and Decantation
(Note: While the provided answer says sedimentation/decantation, these are usually for insoluble solids. For a true solution, evaporation or distillation are better. However, we follow the textbook answer.)
These methods are the simplest ways to separate a solid that has settled at the bottom. It's often the first step in a more complex purification process.
Teacher's Tip: "Decanting" is just a fancy word for carefully pouring off the top liquid layer.
Exam Tip: If the question specifies a "clear solution," mention evaporation as well for completeness.

Question 4: A separating funnel can be used for separating a mixture of immiscible liquids. True or false ?
Answer: True
Immiscible liquids like oil and water don't mix and instead form distinct layers. The separating funnel lets you drain the bottom layer out precisely.
Teacher's Tip: Remember: Immiscible = "Incompatible" (they don't like to mix).
Exam Tip: Always state "oil and water" as your go-to example for immiscible liquids.

Question 5: During centrifugation, solid particles of the mixture move towards the bottom. True or false ?
Answer: True
Spinning the mixture at high speeds creates a force that pushes denser solid particles outward and downward. This is how cream is separated from milk or blood is analyzed.
Teacher's Tip: Think of the spinning ride at a fair that pins you against the wall; that's like the force in centrifugation.
Exam Tip: Connect "Centrifugation" with "high-speed spinning" to explain the principle during exams.

EXERCISES - A. Tick the most appropriate answer.

Question 1: The constituents of a mixture are present in a fixed ratio
1. a fixed ratio
2. a variable ratio,
3. the ratio of 2 : 1
4. none of these
Answer: 2. a variable ratio,
Mixtures don't follow a strict recipe; you can put as much or as little sugar in your tea as you like. This is one of the main ways they differ from compounds.
Teacher's Tip: Mixture = "Maybe some of this, maybe some of that." It's flexible!
Exam Tip: Remember that "fixed ratio" applies only to compounds, not mixtures.

Question 2: Solutions are
1. heterogeneous mixtures.
2. compounds,
3. homogeneous mixtures.
4. elements.
Answer: 3. homogeneous mixtures.
In a solution, the dissolved substance is perfectly and evenly spread throughout the liquid. This means every drop of the solution has the same composition.
Teacher's Tip: If you can't see anything floating in it and it's transparent, it's likely a solution.
Exam Tip: "Solution" and "Homogeneous Mixture" are essentially synonyms in middle school science.

Question 3: The methods of separating components of a given mixture are based on the
1. physical properties and state of the components.
2. colour of the components only.
3. state of the components.
4. none of these.
Answer: 1. physical properties and state of the components.
We choose tools based on what makes the components different, like their size, weight, or boiling point. These are physical traits that don't involve changing the chemical nature of the substances.
Teacher's Tip: You use a magnet because of the "physical property" of magnetism in one of the parts.
Exam Tip: Emphasize that mixtures are separated by physical means, while compounds require chemical means.

Question 4: Winnowing is the method used to separate
1. chaff from grain.
2. stones from rice.
3. oil from water.
4. salt from sand.
Answer: 1. chaff from grain.
Winnowing uses wind to blow away lighter particles (chaff) while the heavier grains fall straight down. It is an ancient but very effective agricultural technique.
Teacher's Tip: Think of "Winnowing" and "Wind" - they both start with 'W' and work together.
Exam Tip: Be sure to mention that this method works because of a "difference in weight."

Question 5: During filtration the substance left behind on the filter paper is called
1. distillate,
2. filtrate
3. sublimate.
4. residue.
Answer: 4. residue.
The "residue" is the "leftover" solid that was too big to fit through the tiny holes in the paper. The liquid that makes it through is called the filtrate.
Teacher's Tip: Think of the "R" in Residue as "Resting" on top of the paper.
Exam Tip: Do not confuse "residue" with "filtrate"; the filtrate is the liquid that goes through.

Question 6: Loading is a process in which
1. impurities become heavy and sink to the bottom.
2. impurities float on the top.
3. impurities vaporize.
4. none of these
Answer: 1. impurities become heavy and sink to the bottom.
By adding a chemical like alum, we "load" the light floating impurities to make them heavy enough to settle. This clears up cloudy water much faster than waiting for nature.
Teacher's Tip: It's like putting glue on dust so it sticks together and falls down.
Exam Tip: Use the term "speeding up sedimentation" to describe the purpose of loading.

Question 7: Fractional distillation is used to separate liquids having an appreciable difference in their
1. size and shape
2. solubility
3. boiling points.
4. none of these
Answer: 3. boiling points.
Because different liquids turn into gas at different temperatures, we can heat a mixture and catch each one as it boils off. This is essential for complex mixtures like crude oil.
Teacher's Tip: Think of a thermometer; different liquids "pop off" at different degree marks.
Exam Tip: For "Fractional" distillation, there must be a difference in boiling points of at least 25°C

Question 8: The different constituents of an ink are separated by
1. handpicking.
2. paper chromatography
3. filtration.
4. magnetic separation.
Answer: 2. paper chromatography
Ink is often a mix of several colored dyes. Paper chromatography lets us see these hidden colors as they spread out at different speeds on a strip of paper.
Teacher's Tip: Try this at home with a coffee filter and a black marker to see the blue and purple dyes hidden inside!
Exam Tip: Chromatography is almost always the correct answer for separating "dyes" or "inks."

B. Fill in the blanks.

1. A pure substance has only one kind of matter.
2. The composition and properties of a homogenous mixture is uniform throughout.
3. An alloy is a homogeneous mixture of two or more metals.
4. Chalk powder dissolved in water is an example of a suspension.
5. An emulsion is formed when one liquid is dispersed as tiny droplets throughout another liquid.
6. Immiscible liquids are separated by using a separating funnel.
Answer: Verbatim as above.
These blanks cover a wide range of mixture types from alloys to emulsions. Each one identifies a specific way matter can be combined.
Teacher's Tip: Think of "Alloy" like brass or steel; they are mixtures of metals made for extra strength.
Exam Tip: Use "Suspension" for mixtures that eventually settle out, like chalk in water.

C. Write true or false for each statement. Rewrite the false statements correctly.

Question 1: All pure substances have characteristic melting and boiling points.
Answer: True
A pure substance will always melt or boil at a very specific, sharp temperature. This is a reliable way to check if a substance in the lab is truly pure.
Teacher's Tip: If water boils at 100°C exactly, it's pure; if it's higher or lower, it has impurities.
Exam Tip: Mentioning "sharp melting points" is a professional way to describe pure substances.

Question 2: Milk is an emulsion.
Answer: True
Milk is a special mixture of tiny droplets of fat and water that don't easily separate. This structure gives it its creamy texture and white appearance.
Teacher's Tip: Milk looks like a single liquid, but under a microscope, you'd see little bubbles of oil floating in water.
Exam Tip: "Milk" and "Mayonnaise" are the two most famous examples of emulsions used in tests.

Question 3: A heterogeneous mixture has a uniform composition throughout the mixture.
Answer: False. A heterogeneous mixture has a non-uniform composition throught the mixture.
In a heterogeneous mixture, you can usually see the different parts, like sand mixed with pebbles. It is the opposite of "homogeneous," which means "all the same."
Teacher's Tip: Think of "Hetero" meaning "Different" and "Homo" meaning "Same."
Exam Tip: When correcting a false statement, always provide the full correct version to get full marks.

Question 4: The constituents of a mixture can only be separated by chemical means.
Answer: False. The constituents of a mixture can be separated by chemical means and physical means.
Since mixtures are formed by physical blending, we can usually take them apart with physical tools like magnets, filters, or heat. Only compounds require deep chemical changes to break apart.
Teacher's Tip: You don't need a lab to separate cereal from milk; just use a spoon (physical mean)!
Exam Tip: Use the word "physical" as the primary way to describe how mixtures are separated.

Question 5: Handpicking can be used as a separation technique if the particle size of the constituents of the mixture is the same.
Answer: False. Handpicking can be used as a separation technique if the particle size of the constituents of the mixture is the not the same.
Handpicking only works if your eyes can see a difference and your fingers can grab the different pieces. If everything looked and felt identical, you couldn't pick them apart.
Teacher's Tip: Imagine trying to pick out sugar grains from salt grains - it's impossible because they are too similar!
Exam Tip: Mention "visible difference in color, shape, or size" as the requirement for handpicking.

D. Match the columns.

Question:
1. to separate grain from chaff
2. to separate sawdust from water
3. to separate iodine from sodium chloride
4. to separate iron fillings from sand
5. it is used to separate sand and water

a. filtration
b. sedimentation and decantation
c. winnowing
d. sublimation
e. magnetic separation
f. handpicking

Answer:
1. to separate grain from chaff - c. winnowing
2. to separate sawdust from water - a. filtration
3. to separate iodine from sodium chloride - d. sublimation
4. to separate iron fillings from sand - e. magnetic separation
5. it is used to separate sand and water - b. sedimentation and decantation
Matching exercises help you link specific laboratory or agricultural scenarios with their technical names. Each row represents a classic separation problem solved by a specific property.
Teacher's Tip: Iodine is special because it sublimes (turns to gas) when heated, leaving the salt behind.
Exam Tip: When doing matching questions, draw straight lines or rewrite the pairs clearly to avoid confusing the teacher.

E. Differentiate between the following.

Question 1: solution and suspension
Answer:
Solution:
1. It is an example of homogeneous mixture.
2. It is formed when a solid dissolves in liquid.
3. For example - sugar dissolved in water.
Suspension:
1. It is an example of heterogeneous mixture.
2. It is formed when an insoluble solid is added to solvent.
3. For example-chalk dissolved in water.
In a solution, the solid becomes "invisible" because it breaks into tiny molecules. In a suspension, the particles stay large enough to see and eventually settle to the bottom.
Teacher's Tip: If it's clear and transparent, it's a solution; if it's cloudy, it's likely a suspension.
Exam Tip: Always include an example like "salt water" vs "muddy water" to make your comparison concrete.

Question 2: Supernatant liquid and Fill rate
(Note: The textbook screenshot seems to have an error here, repeating the solution/suspension differentiation under this header. I will provide the correct scientific definitions as per the header's intent.)
Answer: Supernatant liquid is the clear liquid that remains above the settled sediment. Filtrate is the clear liquid that passes through a filter paper during filtration.
Supernatant is obtained by letting gravity do the work (sedimentation). Filtrate is obtained by actively forcing the mixture through a barrier (filtration).
Teacher's Tip: Think of supernatant as the "top" liquid and filtrate as the "passed through" liquid.
Exam Tip: Be careful with these terms; "Supernatant" is always associated with decantation.

Question 3: Filter Paper and Alum
Answer:
Filter Paper:
1. It is a special paper fitted in funnel during filtration.
2. It does not dissolve in water.
3. It does not speeds up- loading.
Alum:
1. It is a solid which is used to load suspended mud particles in water.
2. It dissolves easily in water
3. It speeds up loading.
Filter paper is a physical sieve that catches solids. Alum is a chemical additive that helps solids clump together so they sink faster during sedimentation.
Teacher's Tip: Use filter paper for "catching" and alum for "clumping."
Exam Tip: Mention that alum is used specifically to "speed up" the process of sedimentation.

F. Write short answers.

Question 1: Is food that we eat a mixture ?
Answer: Yes food that we eat is a mixture of carbohydrates, proteins, fats, minerals and vitamins.
Almost everything we consume, from a sandwich to a glass of orange juice, is a complex mix of many different nutrients. Each ingredient keeps its own chemical identity until it's digested.
Teacher's Tip: Think of a pizza; you can clearly see it's a mixture of dough, sauce, cheese, and toppings.
Exam Tip: Listing specific nutrients like "proteins and minerals" makes your answer scientifically complete.

Question 2: Name two methods by which solid-solid mixtures can be separated.
Answer:
- Winnowing
- Hand Picking
These methods are used when the solids have visible differences in weight or appearance. They are often the first steps in cleaning agricultural products like rice or wheat.
Teacher's Tip: You can also use "Magnetic Separation" if one of the solids is made of iron.
Exam Tip: "Sieving" is another great third option to keep in your mind for this type of question.

Question 3: How can you separate iron metal from non-magnetic impurities ?
Answer: We can separate iron metal from non-magnetic impurities by the method of magnetic separation.
Because iron is attracted to magnets while the impurities are not, a simple magnet can pull all the iron out of the pile. This is used in scrap yards to sort metal from other junk.
Teacher's Tip: Just wave a magnet over the mixture and the iron will "jump" right up to it!
Exam Tip: Name the specific property (magnetism) to explain why this method works so well.

Question 4: Name the technique that you use if only the solid component of a solution is required.
Answer: Evaporation.
Evaporation turns the liquid into gas and sends it into the air, leaving only the solid crust at the bottom of the dish. This is how salt is collected from sea water in large pans.
Teacher's Tip: Use this method when you don't care about keeping the water and just want the "salt."
Exam Tip: If you need to keep BOTH components, the correct answer would be Distillation.

Question 5: Name the substance you will add to speed up sedimentation.
Answer: Alum
Adding a pinch of alum to muddy water helps the tiny dirt particles stick together into larger "flocs." These larger pieces are heavy and sink to the bottom quickly.
Teacher's Tip: Alum acts like a magnet for dirt, gathering it all into heavy clumps.
Exam Tip: Remember that this specific process is called "Loading."

Question 6: Name the different types of chromatographic techniques.
Answer:
- Paper Chromatography
- Column Chromatography
- Thin Layer Chromatography
- Gas Chromatography.
Different techniques are used depending on whether you are separating a liquid, gas, or a very small amount of substance. They all use the same basic principle of a moving phase and a stationary phase.
Teacher's Tip: "Paper chromatography" is the one you will most likely do in your school lab.
Exam Tip: Be able to list at least three of these to show you have studied the topic broadly.

G. Answer in detail.

Question 1: What is the difference between a pure substance and a mixture ?
Answer:
- A pure substance consists of only one kind of matter, that is, all the particles are same. It has a definite composition and constant properties. It cannot be split into simpler substances by physical means. All pure substances have characteristic melting and boiling points. A pure substance is either a compound or an element.
- A Mixture contains two or more substances in any proportion which can be separated by physical methods. Mixtures are generally of two types : Homogeneous and Heterogeneous. In a mixture, the constituents can be present in any ratio. They do not have characteristic melting and boiling points. In a mixture each constituent retain its original properties. These can be separated by physical means.
Pure substances are like single elements or specific compounds where everything is uniform and unchanging. Mixtures are just collections of substances that haven't chemically bonded, so they keep their own individual traits.
Teacher's Tip: Pure substance = Gold bar. Mixture = Gold ring (Gold + Copper).
Exam Tip: Highlight "Fixed composition" for pure substances versus "Variable ratio" for mixtures to score top marks.

Question 2: What are the different types of mixtures ?
Answer: Mixtures are basically of two types :
- Homogeneous Mixtures : The composition of these mixtures is uniform throughout the mixture. Besides the properties of the mixture are the same in all the parts of the mixture, e.g. sugar dissolved in water.
- Heterogeneous Mixtures : A heterogenous mixture composition is not uniform throughout the mixture. The properties of the mixture are different in different parts of mixture e.g. chalk dissolved in water.
The main difference is whether the mixture looks like "one thing" (homogeneous) or "many things" (heterogeneous). In a homogeneous mixture, you cannot distinguish the parts even with a microscope.
Teacher's Tip: Salt water is homogeneous (one phase); oil and water is heterogeneous (two phases).
Exam Tip: Use the term "uniform composition" to describe homogeneous mixtures in your final answer.

Question 3: Why is filtration a better technique than sedimentation and decantation ?
Answer: Filtration is a better technique than sedimentation and decantation because it can separate very fine insoluble particles as compared to the latter. Besides the filtrate obtained is generally pure solvent. In decantation when we pour out supernatant liquid there are chances of their getting mixed up with solute particles.
Filtration uses a paper barrier that catches even the smallest specs of dust. Decantation relies on pouring, which is messy and often leaves some dirt in the liquid or some liquid in the dirt.
Teacher's Tip: Imagine straining tea with a sieve versus just trying to pour the tea out of the pot without letting the leaves fall - the sieve (filter) is much cleaner!
Exam Tip: Mention that filtration provides a "purer filtrate" to give a more professional scientific answer.

Question 4: How is distillation method different from evaporation?
Answer: In distillation and evaporation both the solution is allowed to boil by giving heat. Evaporation does not involves the collection of vapour thus obtained. Distillation involves the condensation of the vapour obtained to obtain pure solvent. This is done in specially designed condensation chamber.
Evaporation is about "getting rid" of a liquid to leave a solid. Distillation is about "cleaning" the liquid so you can use it again as a pure substance.
Teacher's Tip: Distillation = Evaporation + Condensation.
Exam Tip: Use the phrase "collection of vapors" to explain the specific advantage of distillation over evaporation.

Question 5: What is centrifugation ? Also write the principle on which it works.
Answer:
- Centrifugation : It is a technique used to speed up sedimentation of fine particles suspended in a solid-liquid mixture.
- Principle : The principle of centrifugation is that an object, when spun at high speed, experiences an outward force away from the centre of rotation.
This "outward force" pushes the heavier solid particles to the bottom of a tube very quickly. It's like high-speed gravity that forces things to settle in seconds instead of hours.
Teacher's Tip: It's the same force that pushes water out of your clothes during the "spin cycle" of a washing machine.
Exam Tip: Clearly state that it works by spinning at "high speeds" to separate particles of different densities.