Selina Concise Solutions for ICSE Class 8 Chemistry Chapter 3 Elements Compounds and Mixtures

Points to Remember:
Every substance is made up of very tiny particles, called molecules. Molecules are formed from even smaller particles called atoms.

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.

Based on their properties, elements are classified into: metals, non-metals, metalloids, noble gases.
Metals are ductile, malleable, good conductors of heat and electricity, high melting and boiling points. Metals are sonorous, e.g., Iron, Gold, Silver, etc.
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.

Metalloids- These elements show properties of both metals and non-metals. They are hard solids, e.g. Boron, Silicon, Arsenic.

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.

Symbols of Elements- Each element is denoted by a symbol usually to first letter.
Examples: Oxygen by O, Hydrogen by H.

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.

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.

Atomicity- The number of atoms of an element that join together to form a molecule of that element is known as the atomicity.
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.

Exercise 3(A)

Question 1: Define: (a) Elements (b) Compounds
Answer:
(a) Elements: Element is a substance which cannot be broken further into simpler substances and has a definite set of properties. Elements are made up of only one kind of atoms.
(b) Compounds: Compounds are pure substances composed of two or more elements in definite proportion by mass and has properties, entirely different from those of its constituents elements.
Compound, are made up of different types of atoms combined chemically.
Elements are the basic building blocks of matter that contain only one type of atom. Compounds are formed when different elements join together in a fixed ratio to create something new.
Teacher's Tip: Think of elements as single LEGO bricks and compounds as a model built from different bricks.
Exam Tip: Mention that compounds cannot be separated into their elements by physical methods like filtration.

Question 2: Give two examples for each of the following: (a) Metals (b) Non-metals (c) Metalloids (d) Inert gases
Answer:
(a) Metals: Iron, silver, gold.
(b) Non-metals: Carbon, sulphur, oxygen.
(c) Metalloids: Antimony, silicon, boron.
(d) Inert gases: Helium, argon, neon.
These categories help scientists organize all known elements based on how they behave and react. Each group has special physical traits, like how metals are shiny and non-metals are usually dull.
Teacher's Tip: Use the mnemonic "He-Ne-Ar" to quickly remember the names of the first three noble gases.
Exam Tip: Always memorize at least three examples for each category to ensure you have a backup during tests.

Question 3: Differentiate between: (a) Pure and impure substances (b) Homogenous and heterogenous substances
Answer:
(a) Pure substances -
1. Pure substances have definite composition and definite physical and chemical properties.
2. They are all homogeneous i.e. their composition is uniform throughout the bulk.
3. Examples: Elements and compounds.
Impure substances -
1. Impure substances are made up of two or more pure substances mixed together in any proportion.
2. They may be homogeneous or hetergeneous i.e. their composition is not uniform throughout the bulk.
3. They are all mixtures.
Examples: air, sea water, petroleum, a solution of sugar in water are all impure substances.
(b) Homogeneous mixture - is a mixture where the components that make up the mixture are uniformly distributed throughout the mixture.
Example - air, sugar water, rain water.
Heterogeneous mixture - is a mixture, where the components of the mixture are not uniform or have localized regios with different properties.
Example-Cereal in milk, vegetable soup.
Pure substances consist of only one type of particle, whereas impure substances are blends of different particles. Homogeneous mixtures look the same all over, but heterogeneous mixtures have parts you can clearly distinguish.
Teacher's Tip: If you can see the different parts of a mixture, it is definitely heterogeneous.
Exam Tip: Use a table to present differences between substance types for better clarity and full marks.

Question 4: Write the chemical name of the following and also give their molecular formulae: (a) Baking soda (b) Vinegar (c) Marble (d) Sand
Answer:
(a) Sodium bicarbonate (Baking soda) - NaHCO₃
(b) Acetic acid (Vinegar) - CH₃COOH
(c) Calcium carbonate (Marble) -CaCO₃}
(d) Silicon dioxide (Sand) - SiO₂
These chemical names and formulas tell us exactly which atoms are bonded together to form these common materials. Understanding these symbols is the first step in learning how chemical reactions occur in our daily lives.
Teacher's Tip: Remember that "Soda" often contains Sodium (Na), so look for that symbol in its formula.
Exam Tip: Practice writing the numbers as small subscripts in LaTeX ({}) to show the correct count of atoms.

Question 5: Name: (a) a soft metal (b) a metal which is brittle (c) a non-metal which is lustrous (d) a liquid metal (e) a metal which is a poor conductor of electricity. (f) a non-metal which is a good conductor of electricity. (g) a liquid non-metal (h) the hardest naturally occurring substance (i) an inert gas
Answer:
(a) Gold
(b) Zinc
(c) Iodine
(d) Mercury
(e) Tungsten
(f) Graphite
(g) Bromine
(h) Diamond
(i) Neon, helium
These substances are unique because they have properties that are different from the "standard" rules of metals and non-metals. For example, while most non-metals are dull, Iodine stands out because it has a metallic shine.
Teacher's Tip: Mercury is the only metal that is liquid at room temperature, making it very special!
Exam Tip: Questions about "exceptions" like Graphite (a non-metal conductor) are very frequent in exams.

Question 6: How is sodium chloride different from its constituent elements ?
Answer:
The properties of sodium chloride are completely different from those of sodium and chlorine. Sodium is a soft, highly reactive metal. Chlorine is a poisonous non-metallic gas while sodium chloride is a very useful non poisonous compound which is added to our food to get minerals and also to add taste to it.
When elements react to form a compound, they lose their original characteristics and gain entirely new ones. This transformation is why a dangerous metal and a toxic gas can turn into safe table salt.
Teacher's Tip: Think of a compound as a new "recipe" where the individual ingredients disappear into the final dish.
Exam Tip: Use the term "chemical combination" to explain why the properties of a compound differ from its elements.

Question 7: Why is iron sulphide a compound ?
Answer:
Iron sulphide is a compound which can be broken into the elements iron and sulphur they both have different properties. The properties of compound are entirely different from there of its constituents elements.
Iron sulphide is formed by a chemical reaction that bonds iron and sulfur atoms together in a fixed ratio. Unlike a mixture, you cannot pull the iron out with a simple magnet once it has become iron sulphide.
Teacher's Tip: If you cannot separate the parts with a magnet or by hand, you are likely looking at a compound.
Exam Tip: Always mention that the components of a compound are combined in a "fixed proportion by mass."

Exercise 3(B)

Question 1: Classify the following substances into compounds and mixtures:
Carbon dioxide, air, water, milk, common, salt, blood, fruit juice, iron sulphide.
Answer:
Carbon dioxide - (Compound)
air - (Mixture)
water - (Compound)
milk - (Mixture)
common salt - (Compound)
blood - (Mixture)
fruit juice - (Mixture)
iron sulphide - (Compound)
Compounds have a fixed chemical formula and set properties, while mixtures are combinations of substances with varying ratios. This classification helps us understand which items need chemical versus physical methods for separation.
Teacher's Tip: If you can write a short scientific formula like H₂O or CO₂ for it, it is a compound.
Exam Tip: Group your answer into two clear columns titled "Compounds" and "Mixtures" for clarity.

Question 2: Give one example for each of the following types of mixtures (a) solid-solid homogenous mixture (b) solid-liquid heterogenous mixture (c) misicible liquids (d) liquid-gas homogenous mixture
Answer:
(a) Solid-solid homogenous mixture - Alloys of metals e.g. brass, bronze stainless steel etc.
(b) Solid-liquid heterogenous mixture - Sand and water, mud and water, sugar and oil.
(c) Misicible liquids - water and ethanol.
(d) Liquid-gas homogenous mixture - Air
Mixtures can be formed by combining different states of matter in many ways. Homogeneous mixtures look the same throughout, while heterogeneous ones have clearly visible separate parts.
Teacher's Tip: All metal alloys are examples of solid-solid homogeneous mixtures.
Exam Tip: "Air" is a common example of a homogeneous mixture of various gases.

Question 3: Suggest a suitable technique to separate the constituents of the following mixtures. Also give the reason for selecting the particular method. (a) Salt from sea water (b) Ammonium chloride from sand (c) Chalk powder from water (d) Iron from sulphur (e) Water and alcohol (f) Sodium chloride and potassium nitrate (g) Calcium carbonate and sodium chloride
Answer:
(a) The technique used to separate the salt from seawater is Evaporation. Reason - Because this method is used to separate the components of the homogeneous solid-liquid mixture. In this method, sea water is collected in a shallow bed and allowed to evaporate in the sun. When all the water is evaporated, salt is left behind. By this method, we only get solid and liquid is evaporated in its vapour form.
(b) Technique used to separate Ammonium chloride from sand is sublimation. Because this method is used for solid mixtures in which one of the components can sublime on heating. In this method, Ammonium chloride changes into vapours on heating and salt is left behind.
(c) Technique used to separate chalk powder from water is filtration. Reason - Because this process is used to separate the components of a heterogeneous solid-liquid mixture in which solids are lights and insoluble in liquids. Substances used as filters are sand filter paper at C. These filters allows the liquid to pass through them, but not solids.
(d) Technique to separate iron from sulpher is magnetic separation. Because, this method is used when one of the component of mixture is Iron. Iron gets attracted towards the magnet and hence get separated.
(e) Technique used to separate water and Alcohol is Fractional Distillation. Because in this method, the vapours of water is left behind in the original vessel as the alcohol boils at lower temperature than water. Thus these two liquids can be separated.
(f) Technique used is Fractional-crystallisation. Because: This method is used when solubility of solid components of mixture and different in the same solvent. Here, sodium chloride and potassium nitrate. Both are soluble in water but solubility of potassium nitrate is more.
(g) Technique used is Solvent Extraction Method: Because, by this method, salts get dissolve in water while calcium carbonate being insoluble in water settles down in the container. And hence get separated about.
Separation techniques rely on the differences in the physical properties of the components, like boiling point or magnetism. Choosing the right method ensures that the materials are recovered efficiently without changing them chemically.
Teacher's Tip: Use the "magnet test" first if you suspect any iron or steel is present in a dry mixture.
Exam Tip: For each part, provide the name of the technique followed by a one-sentence reason for choosing it.

Question 4: (a) Define mixture. (b) Why is it necessary to separate the constituents of a mixture. (c) State four differences between compounds and mixtures.
Answer:
(a) "Mixtures can be defined as. a kind of matter which is formed by mixing two or more pure substances (elements and compounds) in any proportion, such that they do not undergo any chemical change and retain their individual properties. Therefore they are impure substances.
(b) Because: The mixtures contain unwanted substances which may be harmful and may degrade the properties of mixtures. So we, need to separated them and extract useful substances. This is necessary because (i) It removes unwanted and harmful substances (ii) to obtain pure and useful substances them. Example: Sea water is rich in common salt which is an important ingredient of our food to add taste and nutrients. But sea water, cannot be directly used to get the salt. Hence, it is necessary to separate both.
(c) Compound
1. A compound is formed from its constituent elements as a result of chemical reaction.
2. A compound is always homogeneous in nature.
3. In a compound the elements are present in a fixed ratio by weight.
4. The components of a compound can't be separated by physical methods but can be separated by chemical methods only.
5. The properties of a compound are different from those of its elements.
6. The formation of a compound from its elements is accompanied by energy changes.
Mixture
1. A mixture is obtained form its (elements, compounds) components as a result of physical change.
2. The mixtures can be homogeneous or heterogeneous.
3. In a mixture the components can be present in any ratio.
4. The components of a mixture can be separated by physical methods only.
5. The properties of a mixture lie between those of-its components.
6. The formation of a mixture from its constituents is not accompanied by energy changes.
Mixtures are physically combined substances that can be easily pulled apart using their physical traits. We separate mixtures to clean our resources, such as removing salt from water or purifying air.
Teacher's Tip: Remember that a mixture's properties are just a "sum" of what's inside it, but a compound is totally new.
Exam Tip: When stating differences, present them in a side-by-side numbered list for a clean look.

Question 5: (a) What is chromatography ? For which type of mixture is it used ? (b) What are the advantages of chromatography.
Answer:
(a) This is one of the latest techniques to separate the coloured components of a mixture when all the components are very similar in their properties. Example: Components of ink are separated by this method. Ink is a mixture of different dyes, which are separated by chromatography because some of the dyes are less soluble and some are more soluble in a solvent.
(b)
1. A very small quantity of the substance can be separated.
2. Components with very similar physical and chemical properties can be separated.
3. It identifies the different constitutes of a mixture.
4. It also helps in quantitive estimation of components of a mixture.
Chromatography works by letting components of a mixture travel across a surface at different speeds based on their solubility. It is an extremely precise method used often in labs to study dyes, chemicals, and even medicine.
Teacher's Tip: Think of chromatography as a "race" where different colors finish at different times.
Exam Tip: Mention that it is used specifically for "coloured components" to get the marks for its application.

Question 6: Choose the most appropriate answer from the options given below:

(a) a mixture of sand and ammonium chloride can be separated by
1. filtration
2. distillation
3. sublimation
4. crystallisation
Answer: 3. sublimation

(b) A pair of metalloids are
1. Na and Mg
2. B and Si
3. C and P
4. He and Ar
Answer: 2. B and Si

(c) Which of the following property is not shown by compounds?
1. They are heterogeneous.
2. They are homogeneous.
3. They have definite molecular formulae.
4. They have fixed melting and boiling points.
Answer: 1. They are heterogeneous.

(d) A solvent of Iodine is
1. Water
2. Kerosene oil
3. Alcohol
4. Petrol
Answer: 3. Alcohol

(e) Which of the gas is highly soluble in water ?
1. Ammonia
2. Nitrogen
3. Carbon monoxide
4. Oxygen
Answer: 1. Ammonia

These multiple-choice questions cover the essential characteristics of matter and how we manipulate it. Knowing the specific solvents and separation behaviors of different chemicals is key to success in chemistry lab work.
Teacher's Tip: "B and Si" stand for Boron and Silicon, two very common metalloids.
Exam Tip: Read every option carefully before ticking, as some distractors can look very similar to the right answer.

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.
These blanks highlight the core definitions and processes we use to categorize and clean materials. For example, winnowing relies on the wind to blow away lighter pieces while heavier ones fall straight down.
Teacher's Tip: "Sublimate" means the solid turns straight into gas without ever melting into a liquid.
Exam Tip: Pay close attention to the specific physical property (like size or weight) being used in each separation method.

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.
Filtration works by using a barrier with tiny holes that let the liquid through but catch the solid particles. This is exactly how a coffee filter or a water purifier works at home.
Teacher's Tip: If a solid dissolves (like salt), filtration won't work—it only works for "insoluble" solids.
Exam Tip: Use the term "residue" for the solid left on the paper and "filtrate" for the liquid that passes through.

Question 2: Loading is basically speeding up ........
Answer Loading is basically speeding up sedimentation.
During loading, a chemical like alum is added to water to make tiny dirt particles clump together. These clumps become heavy and sink to the bottom much faster than they would on their own.
Teacher's Tip: Think of alum as a "glue" that gathers up the dust in water.
Exam Tip: Mention "Alum" as the primary substance used for loading in water purification.

Question 3: Name the techniques used to separate a solid from its solution.
Answer: Sedimentation and Decantation
These methods allow heavy solids to settle at the bottom of a liquid so that the clear liquid can be poured off. It is a simple, non-chemical way to clean water that contains sand or mud.
Teacher's Tip: Let the glass sit perfectly still for the best results in sedimentation.
Exam Tip: Don't confuse decantation with filtration; decantation doesn't use a filter paper.

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 do not mix and form separate layers. The separating funnel lets us drain the bottom layer out through a tap while keeping the top layer in the funnel.
Teacher's Tip: "Immiscible" is just a fancy word for liquids that won't stay mixed together.
Exam Tip: Use oil and water as your standard example when describing the use of a separating funnel.

Question 5: During centrifugation, solid particles of the mixture move towards the bottom. True or false ?
Answer: True
Centrifugation uses rapid spinning to create an outward force that pushes heavy particles to the far end of a tube. This method is much faster than waiting for gravity to do the same job.
Teacher's Tip: This is the same principle that pulls your clothes against the side of the washing machine drum during the spin cycle.
Exam Tip: Remember that centrifugation is a form of "forced sedimentation."

EXERCISES

Tick the most appropriate answer.

Question 1: The constituents of a mixture are present in
1. a fixed ratio
2. a variable ratio,
3. the ratio of 2: 1
4. none of these
Answer: 2. a variable ratio,
Unlike a compound, you can add more or less of any ingredient in a mixture without changing its identity. For example, a bowl of cereal is still cereal whether you have a lot of milk or just a little.
Teacher's Tip: "Variable" means it can change!
Exam Tip: Use "variable ratio" as a key point when writing the differences between mixtures and compounds.

Question 2: Solutions are
1. heterogeneous mixtures.
2. compounds
3. homogeneous mixtures.
4. elements.
Answer: 3. homogeneous mixtures.
In a solution, the solute is dissolved so perfectly that the mixture looks the same from top to bottom. Salt water is a classic example where you cannot see the individual salt particles anymore.
Teacher's Tip: If you can see through it clearly, it is likely a homogeneous solution.
Exam Tip: Remember that solutions consist of a "solute" dissolved in a "solvent."

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.
To separate a mixture, we look for something that is different between the parts, like size, weight, or boiling point. If both parts were identical in every way, we wouldn't be able to separate them at all.
Teacher's Tip: Think of separation as finding the "odd one out" property.
Exam Tip: Mention "differences in physical properties" as the general principle for separation techniques.

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.
This ancient farming technique uses the wind to carry away the light, outer shells of seeds while the heavy grain falls straight down. It is a perfect example of separating components based on their weight.
Teacher's Tip: Imagine dropping a mix of feathers and marbles; the wind would blow the feathers away!
Exam Tip: Identify the "wind" as the agent that makes winnowing possible.

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 solid waste or material that was too large to pass through the tiny pores of the filter. The liquid that successfully passes through the paper is given a different name entirely.
Teacher's Tip: Residue is what "resides" or stays on top of the paper.
Exam Tip: Be very careful not to mix up "residue" and "filtrate" in your labels.

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 alum, we force light dirt particles to stick together and gain mass. Once they are heavy enough, gravity pulls them down to the bottom of the container, leaving the top liquid clearer.
Teacher's Tip: Loading is like adding a heavy weight to a floating balloon so it sinks.
Exam Tip: This process is essentially "accelerated sedimentation."

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.
In this method, the mixture is heated, and the liquid with the lower boiling point turns into vapor first. This vapor is then collected and cooled back into a liquid in a separate container.
Teacher's Tip: Different liquids "boil off" at different temperatures, just like different runners finish a race at different times.
Exam Tip: Specify that it is used for "miscible" liquids that have different boiling points.

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 made of several different colored dyes that are mixed together. Chromatography lets us see each individual color by letting them travel up a piece of absorbent paper at different rates.
Teacher's Tip: If you put a dot of black ink on a napkin and dip the edge in water, you can see this happen at home!
Exam Tip: Associate "ink" or "dye" immediately with "chromatography."

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.
These blanks introduce the specialized names for different types of mixtures we encounter every day. For example, milk is an emulsion, while steel is an alloy used in construction.
Teacher's Tip: "Uniform" means it looks exactly the same everywhere inside the container.
Exam Tip: Learn the spelling of "immiscible" and "emulsion" as they are common technical terms.

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
Every pure element and compound will always boil or melt at the exact same temperature under normal conditions. This acts like a "fingerprint" that scientists use to identify unknown substances.
Teacher's Tip: If water boils at 100°C, you know it's likely pure water!
Exam Tip: Use this fact to explain why we can separate mixtures using boiling points.

Question 2: Milk is an emulsion.
Answer: True
An emulsion is a special kind of mixture where tiny drops of fat are floating in water. Even though it looks like one liquid, it is actually two that don't fully dissolve into each other.
Teacher's Tip: Mayonnaise and milk are the most common emulsions in your kitchen.
Exam Tip: Define an emulsion as "liquid-in-liquid" mixture for full marks.

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 find different concentrations of components in different parts. For instance, in a bowl of trail mix, one handful might have more nuts than the next.
Teacher's Tip: "Hetero" means different, which is why the composition is non-uniform.
Exam Tip: When a statement is false, you must rewrite the correct version to get credit.

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.
Most mixtures can be taken apart using simple physical methods like boiling, filtering, or using a magnet. Chemical means are usually reserved for breaking down compounds into elements.
Teacher's Tip: Mixtures are held together physically, so they can be pulled apart physically.
Exam Tip: List examples like "filtration" and "evaporation" as physical means of separation.

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 works best when you can clearly see and grab different items, like picking stones out of a bag of lentils. If all particles look identical in size and color, you cannot pick them apart by hand.
Teacher's Tip: Your eyes and fingers are the "tools" for handpicking, so the parts must be visible and distinct.
Exam Tip: Mention that handpicking also requires the quantity of the mixture to be small.

D. Match the columns.
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

These matches show the perfect tool for every separation job in the chemistry lab. By matching the physical property (like magnetism or weight) to the method, we ensure the components stay intact.
Teacher's Tip: Remember that Iodine always "sublimes" (turns straight to gas) when heated.
Exam Tip: Draw neat, straight lines or clearly write the numbers and letters to avoid confusion during grading.

E. Differentiate between the following.
1. solution and suspension
2. Supernatant liquid and Fill rate
3. Filter Paper and Alum
Answer:
1. Solution and Suspension
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.
2. Supernatant liquid and Filtrate
Supernatant liquid
1. It is obtained during sedimentation.
2. It is used to separate mixture of liquid and insoluble solid heavier than liquid.
3. No filter paper is used.
Filtrate
1. It is obtained during filtration.
2. It is used to separate fine particles of insoluble solids from liquids.
3. filter paper is used.
3. Filter Paper and Alum
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 watei.
2. It dissolves easily in water.
3. It speeds up loading
These differences explain how we choose the right tools for purifying liquids. A solution is clear and transparent, while a suspension is cloudy and will eventually settle at the bottom.
Teacher's Tip: If you can see through it, it's a solution; if it's cloudy, it's likely a suspension.
Exam Tip: Present your differentiations in side-by-side columns to make comparisons easier for the examiner.

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.
Even though it might look like one thing, every meal is actually a complex blend of different organic compounds our body needs. These parts remain separate chemicals until our body digests them.
Teacher's Tip: Almost everything we eat or drink is some kind of mixture!
Exam Tip: Mention at least three nutrients (like proteins, fats, and vitamins) to prove food is a mixture.

Question 2: Name two methods by which solid-solid mixtures can be separated.
Answer:
(i) Winnowing (ii) Hand Picking
These methods are great for large particles where we can use wind or our own hands to pull things apart. They are the most basic physical ways to clean up dry materials like grains.
Teacher's Tip: Winnowing is for different weights, while handpicking is for different looks.
Exam Tip: Use (i) and (ii) numbering to keep your list organized.

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.
Since iron is strongly attracted to magnets, we can hover a magnet over the mixture to pull the iron out easily. The non-magnetic dirt or sand will stay exactly where it is.
Teacher's Tip: Magnetic separation only works for iron, nickel, and cobalt metals.
Exam Tip: Always mention that magnetism is the physical property being used here.

Question 4: Name the technique that you use if only the solid component of a solution is required.
Answer:
Evaporation.
In this process, we heat the solution until all the liquid turns into vapor and disappears into the air. This leaves the dry solid particles behind at the bottom of the dish.
Teacher's Tip: This is how we get salt from the big "salt pans" near the ocean.
Exam Tip: Remember that in evaporation, the liquid part is "lost" to the atmosphere.

Question 5: Name the substance you will add to speed up sedimentation.
Answer:
Alum
Alum acts as a coagulant, meaning it makes tiny, light dirt particles stick together and get heavy. Once they are heavy, they sink to the bottom much faster, cleaning the water above.
Teacher's Tip: Alum is the most common chemical used in local water tanks to clean muddy water.
Exam Tip: Name the process "Loading" alongside the substance "Alum."

Question 6: Name the different types of chromatographic techniques.
Answer:
1. Paper Chromatography
2. Column Chromatography
3. Thin Layer Chromatography
4. Gas Chromatography.
Scientists use these different types depending on whether the mixture is a liquid or a gas and how much of it they need to study. Paper chromatography is the one most students perform in school labs.
Teacher's Tip: Think of these as different "versions" of the same color-separating race.
Exam Tip: Memorize the names exactly as they are technical scientific terms.

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 meAll 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 have a fixed "recipe" and stay the same every time you see them. Mixtures are like a bag of marbles where you can change the number of red and blue ones whenever you like.
Teacher's Tip: If you can write one chemical symbol for it, it's pure; if not, it's likely a mixture.
Exam Tip: Use the boiling/melting point point as a key differentiator between pure substances and mixtures.

Question 2: What are the different types of mixtures ?
Answer:
Mixtures are basically of two types: (i) Homogeneous (ii) Heterogeneous
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.
In homogeneous mixtures, everything is so well mixed that it looks like a single substance. In heterogeneous mixtures, you can often see different layers or pieces floating around.
Teacher's Tip: "Homo" means same, and "Hetero" means different.
Exam Tip: Give an everyday example (like lemonade vs. sand-water) to illustrate each type.

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 with microscopic holes that act as a strict security guard, stopping even the smallest bits of dirt. Decantation is much more "risky" because you might accidentally spill some sediment while pouring the water.
Teacher's Tip: Filtration is "perfect" while decantation is just "good enough."
Exam Tip: Mention "fine insoluble particles" to explain why filtration is more precise.

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 used when we only want the solid at the end and don't care about the liquid. Distillation is the "complete" package because it lets us save both the solid and the clean liquid.
Teacher's Tip: Distillation is basically Evaporation + Condensation.
Exam Tip: Emphasize that distillation allows for the "collection of the solvent" for full credit.

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.
Think of a centrifuge as a high-speed carousel for chemicals that forces the heavy bits to the bottom in seconds. It is widely used in hospitals to separate blood cells from the liquid plasma.
Teacher's Tip: This is the same force that pulls you toward the door of a car when it takes a sharp turn.
Exam Tip: Use the term "outward force" to correctly describe the scientific principle behind it.