Selina Concise Solutions for ICSE Class 9 Chemistry Chapter 3 Elements Compounds And Mixtures

Exercise 3(A)

Solution 1:
An element is a pure substance composed of only one kind of atom. Example: C, H, O, Na, Ca, N etc.
Characteristics of an element:
1. An element is made up of only one kind of atoms.
2. An element is pure and homogeneous substance.
3. An element has fixed melting and boiling points.
4. An atom is the smallest particle of an element which takes part in a chemical reaction.
5. An element may chemically react with another elements or compounds.
6. An element can occur in solid, liquid or gaseous state.
7. The molecules are made up of one or more atoms of the same or different elements.

An element is the simplest form of matter that cannot be broken down further by chemical means. Every element has its own unique set of properties that distinguish it from others.

Teacher's Tip: Think of elements as the "alphabet" of the universe; just as letters make words, elements make everything around us.

Exam Tip: When listing characteristics, always mention that elements are "homogeneous," meaning they look the same throughout.

Solution 2:
The Elements are mainly classified into- Metals, Non-metals, Metalloids and Noble gases.
Elements Classification:
Metals - Examples: Iron, Copper, Sodium, Calcium etc.
Non-metals - Examples:
Solid: Carbon, Silicon, Phosphorous etc.
Liquid: Bromine
Gas: Hydrogen, Chlorine etc.
Metalloids - Examples: Boron, Germanium, Silicon, Arsenic, Antimony, Bismuth etc.
Noble gases - Examples: Helium, Argon, Neon, Krypton, Xenon, Radon.

Elements are grouped into these four categories based on their physical appearance and how they react with other chemicals. Metals are usually shiny and hard, while non-metals vary greatly in state and appearance.

Teacher's Tip: Use the acronym "M-N-M-N" (Metals, Non-metals, Metalloids, Noble gases) to remember the four main groups.

Exam Tip: Remember that "Metalloids" have properties of both metals and non-metals, which makes them very useful in electronics.

Solution 3:
Two elements which show exception to the properties of:
Metals :-
1. Mercury (Hg) is liquid at room temperature.
2. Tungsten (W) is a poor conductor of electricity.
Non-metals:-
1. Iodine is lustrous.
2. Carbon is ductile.

Most metals are solid and shiny, but Mercury is the only metal that stays liquid at room temperature. Similarly, while most non-metals are dull, Iodine is naturally shiny (lustrous).

Teacher's Tip: Think of "Silver Liquid" for Mercury and "Purple Shine" for Iodine to remember these exceptions.

Exam Tip: Exceptions are very common questions in exams, so memorize Mercury and Iodine specifically.

Solution 4:
(a) Molecule: A molecule is the smallest particle of a pure substance (element or compound), and it has all the properties of that substance. It is composed of atoms. It is capable of existing in a free state. Example: O₂, H₂, Cl₂ are molecules.
(b) Atomicity: Atomicity is the number of atoms present in a molecule of an element.
(c) Compound: A compound is a pure substance composed of two or more elements combined chemically in a fixed proportion by mass. The properties of compounds are different from the properties of their constituent elements. Example: H₂O, CO₂ etc.

Molecules are the tiny units that make up substances, while atomicity simply tells us "how many" atoms are in that unit. A compound is like a cake where the ingredients (elements) change completely once they are baked (chemically combined).

Teacher's Tip: Molecule starts with 'M' for "Massive" (larger than an atom), and Atomicity is just a "Count" of atoms.

Exam Tip: For the definition of a compound, never forget the phrase "fixed proportion by mass."

Solution 5:
(a) A diatomic element: Nitrogen (N₂)
(b) A tetratomic element: Phosphorus (P)
(c) Monoatomic element: Helium (He)
(d) Lustrous non-metal: Iodine
(e) Liquid non-metal: Bromine (Br₂)
(f) A gas filled in electric bulbs: Argon (Ar)
(g) A liquid metal: Mercury (Hg)
(h) A non metal conductor of electricity: Graphite
(i) A metal non malleable and non ductile: Zinc (Zn)
(j) A lustrous non metal: Graphite

This list shows specific examples of elements with unique characteristics, such as Graphite being a non-metal that can conduct electricity. These special cases are very important in real-world technology and chemistry.

Teacher's Tip: Remember that "Mono" means one, "Di" means two, and "Tetra" means four.

Exam Tip: Make sure to include the chemical symbols like (Hg) or (N₂) next to the names for better marks.

Solution 6:
(i) Sodium chloride is obtained when sodium chemically combines with chlorine in ratio of 23:35.5 by weight.
(ii) When molten sodium chloride is subjected to electrolysis, the ratio by weight of sodium and chlorine liberated at electrodes is 2:3.

Sodium chloride (table salt) always forms using the same specific "recipe" of weight. Even when we use electricity to break it apart, the components appear in a predictable ratio.

Teacher's Tip: Think of chemical ratios like a specific recipe for your favorite cookies that must always be the same.

Exam Tip: Be careful with numbers in ratios; 23:35.5 is the standard mass ratio for salt (NaCl).

Solution 7:
Type: Element, Substances: Chlorine, Sulphur. Reason: They cannot be split up into any simpler substance.
Type: Compound, Substances: Carbon dioxide. Reason: It can be produced by chemical analysis of two or more simpler substances with different properties.
Type: Mixture, Substances: Honey, milk, sea water, gun powder, apple juice, brine, syrup and bronze. Reason: These are produced by mere mixing of two or more substances in any proportions by weight.

This classification depends on whether a substance is pure or made of many different things mixed together. Elements are the basic pieces, compounds are chemically bonded pieces, and mixtures are just physically mixed.

Teacher's Tip: If you can separate it by hand or a filter without a chemical reaction, it is a mixture!

Exam Tip: In the reason for "Mixture," always mention that they can be in "any proportion" to distinguish them from compounds.

Solution 8:
(a) This is because molecules have all the properties of that substance and is capable of existing in a free state, molecules are composed of atoms.
(b)
Element Comparison:
1. It is a pure substance which cannot be converted into simpler substances by any physical or chemical means.
2. It is made up of only one kind of atoms.
3. The molecules are made up of one or more atoms.
Compound Comparison:
1. It is a pure substance made up of two or more elements combined chemically in a fixed ratio.
2. It is made up of two or more different kinds of atoms.
3. The molecules are made up of two or more atoms.

Elements are made of identical atoms, whereas compounds are made when different atoms join together permanently. Molecules are the smallest independent units for both, holding the identity of the substance.

Teacher's Tip: Atoms are like lone students, and molecules are like students holding hands to form a group.

Exam Tip: Use a table format for comparison questions as it is easier for the examiner to read and grade.

Solution 9:
It is true that the elements can form different compounds. Example: Hydrogen and oxygen combine to give two different compounds, water (H₂O) and hydrogen peroxide (H₂O₂) under different conditions.

 Even with the same "ingredients," you can make different "dishes" by changing the amounts or the environment. Water is safe to drink, but hydrogen peroxide is used for cleaning wounds, showing how properties change with ratios.

Teacher's Tip: Remember H₂O for life and H₂O₂ for medicine to show how one extra oxygen atom changes everything.

Exam Tip: Providing a chemical example like H₂O and H₂O₂ is the best way to prove this statement.

Solution 10:
Characteristics of a compound:
1. A compound is made up of one or more atoms of the same or different elements.
2. It has a homogeneous composition.
3. In a compound the elements are present in a fixed ratio by mass.
4. The properties of a compound are different from those of its Constituent elements.

Compounds are unique because they act as a single substance even though they are made of different parts. The most important fact is that they don't look or act like the elements they were made from.

Teacher's Tip: Think of a compound like a "chemical marriage" where two elements join to become one new unit.

Exam Tip: Mentioning "homogeneous composition" is vital because it means every part of the compound is exactly the same.

Solution 11:
The properties of compounds are different from the properties of their constituent elements. Example: H₂O, FeS, C₁₂H₂₂O₁₁
1. H₂O: Water is a liquid, while constituent elements, Hydrogen and Oxygen are gases.
2. FeS: Iron sulphide is a black substance, not attracted by a magnet and insoluble in carbon disulphide. While constituent elements, Iron is grey colored, attracted by a magnet. Sulphur is a yellow colored, soluble in carbon disulphide.
3. C₁₂H₂₂O₁₁: Sugar is a crystalline solid, sweet to taste and soluble in water. But, its constituent elements, Carbon, is black insoluble solid. Hydrogen and Oxygen are invisible and odorless gases.

This shows how chemistry works like magic, transforming gases into liquids or magnetic metals into non-magnetic black solids. Once elements join to form a compound, their old personalities disappear completely.

Teacher's Tip: Use the "Sugar" example; it's made of black carbon (coal) and gases, but it tastes sweet and looks white!

Exam Tip: Be very specific about properties like "color" and "magnetism" when giving examples of change.

Solution 12:
A compound is a pure substance composed of two or more elements combined chemically in fixed proportions by mass. The properties of a compound are different from the properties of their constituent elements.
1. H₂O: Water is a liquid, while constituent elements, Hydrogen and Oxygen are gases.
2. FeS: Iron sulphide is a black substance, not attracted by a magnet and insoluble in carbon disulphide. While constituent elements, Iron is grey colored, attracted by a magnet. Sulphur is a yellow colored, soluble in carbon disulphide.
3. C₁₂H₂₂O₁₁: Sugar is a crystalline solid, sweet to taste and soluble in water. But, its constituent elements, Carbon, is black insoluble solid. Hydrogen and Oxygen are invisible and odorless gases.

This repeated definition emphasizes that compounds are chemically combined in a specific way that creates entirely new substances. For example, iron is magnetic, but when mixed with sulfur to make iron sulfide, it loses its magnetic power.

Teacher's Tip: Always remember that "chemical combination" means a permanent change has happened.

Exam Tip: Use the Iron Sulphide (FeS) example often as it clearly shows changes in color, magnetism, and solubility.

Solution 13:
A mixture cannot be represented by a chemical formula because constituents present in a mixture are in any ratio and they are not chemically united.

Since mixtures don't have a strict recipe, you can't write a single formula for them like you do for water (H₂O). A bowl of fruit salad is still just fruit mixed together, not a new chemical.

Teacher's Tip: If you can add "a little more of this" without ruining it, it's a mixture, not a compound!

Exam Tip: Explain that the lack of "chemical union" is why there is no fixed formula for mixtures.

Solution 14:
(a) Air
(b) Concrete
(c) Milk

These are common everyday examples of mixtures where different substances are found together. Air is a mixture of gases, concrete is a mixture of solids, and milk is a complex liquid mixture.

Teacher's Tip: Look around your room; almost everything you see (like a wooden table or a plastic toy) is actually a mixture.

Exam Tip: Air is the most important mixture to remember as it contains N₂, O₂, CO₂, and other gases.

Solution 15:
Elements: Mercury
Compounds: Sugar, Distilled water, Alcohol, Nitre, Washing soda, Rust, Marble
Mixtures: Air, Milk, Wax, Sea water, Paint, Brass, Bread, Soap, Tap water

This table helps you sort materials into the three big categories of matter based on their purity. Mercury is an element because it is made of only one type of atom, while salt water is a mixture because you can vary the saltiness.

Teacher's Tip: Distilled water is a compound (H₂O), but Tap water is a mixture because it has minerals and gases dissolved in it!

Exam Tip: Pay close attention to "Brass" and "Steel"; they are mixtures of metals called alloys.

Solution 16:
On adding sulphuric acid to water we will get a Homogeneous Mixture (true solution).
This mixture will have different densities and boiling points depending upon the amounts of acid and water. The properties of acid and water will remain same even after mixing.

Mixing acid and water creates a solution where the components stay as they are but are evenly spread out. Unlike a compound, the individual properties of the acid and water don't disappear.

Teacher's Tip: Always add acid to water, not water to acid, for safety in the lab!

Exam Tip: A "Homogeneous Mixture" means the solution looks perfectly uniform throughout, like clear saltwater.

Solution 17:
Iron and sulphur when mixed, forms a mixture. It can be identified as follows:
- A grayish yellow mixture will be produced.
- All the individual properties of iron and sulphur will be shown separately in a mixture. Iron particles will be attracted by magnet. Sulphur will dissolve in carbon disulphide.
Iron and sulphur when heated forms a compound. It can be identified as follows:
- A grey dark solid will be produced.
- The compound formed is homogeneous.
- It is neither attracted by a magnet nor it is soluble in carbon disulphide.

This experiment shows the difference between just mixing things and reacting them with heat. Heat provides the energy needed to turn a simple mixture into a completely new compound.

Teacher's Tip: Use a magnet to tell them apart; if the iron jumps to the magnet, it's still just a mixture.

Exam Tip: Heat is the "trigger" that usually changes a mixture of elements into a compound.

Solution 18:
Mixture vs Compound Comparison:
1. Mixture: It is obtained by the physical combination of either elements, or compounds, or both. Compound: It is obtained by the chemical combination of more than one element.
2. Mixture: The composition of elements present in a mixture is not fixed. Compound: The composition of elements present in a compound is fixed.
3. Mixture: It shows the properties of all its constituent elements. Compound: The properties of a compound are different from those of its elements.
4. Mixture: Its constituents can be separated using physical methods. Compound: Its constituents can be separated by using only chemical and electrochemical methods.
5. Mixture: The mixtures can be homogeneous or heterogeneous. Compound: A compound is always homogeneous in nature.

This chart is the master guide for understanding how matter is put together. The key difference is that mixtures can be pulled apart easily, while compounds are glued together by chemical bonds.

Teacher's Tip: Remember "Physical for Mixture" and "Chemical for Compound."

Exam Tip: This is a very common 5-mark question; memorize at least four points of difference clearly.

Solution 19:
1. Types of mixture: Two solids. Example: Bronze (Zn, Cu, Sn). Nature: Homogeneous
2. Types of mixture: A solid in liquid. Example: Sugar in water, Salt in water. Nature: Homogeneous. Example: Iodine in alcohol. Nature: Homogeneous. Example: Sugar in oil. Nature: Heterogeneous.
3. Types of mixture: Liquids. Example: Oil in water, Kerosene in water. Nature: Heterogeneous. Example: Acetone + water. Nature: Homogeneous.
4. Types of mixture: Liquid and gas. Example: Moisture in air. Nature: Homogeneous.

Mixtures can happen between any states of matter—solid, liquid, or gas. Whether they are "homogeneous" or "heterogeneous" depends on how well the ingredients mix together.

Teacher's Tip: "Homo" means same (uniform), and "Hetero" means different (layers or bits visible).

Exam Tip: Bronze is an important "solid-solid" homogeneous mixture to remember for your examples.

Solution 20:
Homogeneous mixtures Comparison:
1. A mixture is said to be homogeneous if its constituents are uniformly distributed and are not physically distinct.
2. They have the same composition and properties throughout their mass.
3. For example: sugar solution, salt in water etc.
Heterogeneous mixture Comparison:
1. A mixture is said to be heterogeneous if its constituents are not uniformly distributed and are physically distinct.
2. They have the different composition and properties in different parts of their mass.
3. For example: Mixture of sand in water, Mixture of oil in water.

In a homogeneous mixture, everything looks perfectly blended like a soft drink. In a heterogeneous mixture, you can see the different parts, like sand sitting at the bottom of a glass of water.

Teacher's Tip: Think of clear apple juice (homogeneous) versus chicken soup (heterogeneous).

Exam Tip: Use the term "physically distinct" to describe the layers seen in heterogeneous mixtures.

Solution 21:
(a)
1. The properties of ammonia are different from those of its components i.e nitrogen and hydrogen.
2. When ammonia is formed from nitrogen and hydrogen, energy is given out.
3. In ammonia, N and H are present in fixed ratio of 14 : 3 by mass.
(b) Air is considered as mixture not a compound because:
1. The composition of air is different at different places and different altitudes.
2. The constituents of air can be easily separated by physical means.
3. The properties of air vary according to the properties of oxygen and nitrogen.
(c) Tap water does not have a fixed melting point. It may have various dissolved as well as undissolved impurities. Also it does not have a fixed composition.

These explanations show why some things are compounds (like ammonia) while others are mixtures (like air and tap water). Compounds are strict and fixed, while mixtures are flexible and depend on their environment.

Teacher's Tip: Air is a mixture because you can breathe the oxygen in it directly; in a compound, elements are "locked away."

Exam Tip: "Energy change" (like heat given out) is a big sign that a compound has been formed.

Solution 22:
A pure substance is a homogeneous material with a definite, invariable chemical composition, and definite, invariable physical and chemical properties.
Sugar is a pure substance as all sample of sugar consists of same chemical composition. i.e. carbon, hydrogen and oxygen, C₁₂H₂₂O₁₁.

A pure substance is something that is the same no matter where you get it from. Because every sugar crystal in the world has the exact same chemical formula, it is considered pure.

Teacher's Tip: Pure doesn't just mean "clean"; in science, it means "only one type of chemical."

Exam Tip: Remember that pure substances include both elements and compounds.

Solution 23:
If dilute hydrochloric acid is added to the compound formed of iron and sulphur, Hydrogen sulphide gas is produced. (With a rotten egg smell).

This is a classic chemistry test to check if you have a compound or just a mixture. The "rotten egg" smell is a very famous way to identify the presence of sulfur in a compound form.

Teacher's Tip: If you smell rotten eggs in a lab, you are likely smelling Hydrogen Sulphide (H₂S) gas!

Exam Tip: Always associate the "rotten egg smell" with the reaction between Iron Sulphide and an acid.

Solution 24:
Comparison between True Solution and Suspension:
True solution:
- A homogeneous solution in which the size of the particle is about 10^-10 m.
- Particles are invisible.
- Appears transparent.
- Do not show Tyndall Effect.
- Particles diffuse readily.
- Can pass through a filter paper and semi-permeable membrane.
Suspension:
- A heterogeneous mixture in which very fine particles, about 10^-7 m, of a solid are dispersed in any medium like a liquid or a gas.
- Particles can be seen by naked eye or by simple microscope.
- Appears opaque.
- Tyndall Effect may be shown to some extent.
- Particles do not diffuse.
- Cannot pass through a filter paper nor a semi-permeable membrane.

True solutions are perfectly clear because the particles are so small they disappear into the liquid. Suspensions are cloudy because the particles are large enough to be seen and eventually sink to the bottom.

Teacher's Tip: Think of saltwater (True Solution) vs. muddy water (Suspension).

Exam Tip: Memorize the particle sizes (10^-10 m vs 10^-7 m) as they are key technical details.

Solution 25:
When a mixture of powdered iron and sulphur is heated in a test tube, the powder starts melting and a pungent smell of a gas is given out. A dark grey solid is produced and this is called iron sulphide.

Heating changes the physical state and triggers a chemical reaction between the iron and sulfur. The result is a brand new substance that no longer looks like the original powders.

Teacher's Tip: The dark grey solid (FeS) is a classic example of a chemical change caused by heat.

Exam Tip: Mention the "pungent smell" and "dark grey color" to describe the result of this reaction accurately.

Solution 26:
Solute: A substance which gets dissolved in a solvent is called as solute.
Solvent: A substance in which solute gets dissolved in it is called as solvent.
Solution: A homogeneous mixture of two or more substances which are chemically non reacting, whose composition can be varied within certain limits is called a solution.
Solution = Solute + Solvent

This simple formula helps you understand how mixtures like lemonade are made. The sugar is the solute, the water is the solvent, and the lemonade is the final solution.

Teacher's Tip: Solvent is usually the larger amount (like water), and Solute is the smaller amount (like salt).

Exam Tip: Remember the equation: {Solution} = {Solute} + {Solvent}.

Solution 27:
A homogeneous solution in which the size of the particle is about 10^-10 m is called a true solution.
Properties of true solution:
1. It is a homogeneous mixture.
2. The solute particles are very small, about 10^-10 m.
3. It is clear and transparent.
4. It does not scatter light.
5. The components cannot be separated by filtration or by any physical means.
6. The solute particles in a solution do not settle down.
7. The particles are invisible.
8. The particles diffuse rapidly.

True solutions are so well-mixed that the solute particles become part of the liquid's structure. This is why you can't see them or filter them out even with the best equipment.

Teacher's Tip: If light can pass through it without a "path" being visible, it's a true solution.

Exam Tip: "Does not scatter light" is a fancy way of saying it doesn't show the Tyndall effect.

Solution 28:
Properties of suspension are:
1. Suspension is a heterogeneous mixture.
2. The solute particles in a suspension have a size of greater than ^-7 m.
3. It is opaque in nature.
4. The particles are visible to naked eye or under a simple microscope.
5. The particles do not pass even through ordinary filter paper.
6. The particles of a suspension do not diffuse.
7. The particles in a suspension settle down on standing.
8. It scatters light to some extent.

Suspensions are temporary mixtures where heavy particles are "hanging" in a liquid. If you let a suspension sit still, the particles will slowly fall to the bottom due to gravity.

Teacher's Tip: Think of "Suspension" as "Suspended"—the particles are just floating there for a while.

Exam Tip: Remember that suspensions can be separated by simple "filtration" using paper.

Solution 29:
A homogeneous looking heterogeneous mixture in which particles having a size between 10^-10 m and 1^-7 m dispersed in a continuous medium is called as colloid.
Colloid Systems examples:
1. Solid (Disp. medium) + Gas (Disp. phase) = Solid foam. Example: Pumice stone.
2. Liquid + Gas = Foam. Example: Shaving cream.
3. Liquid + Liquid = Emulsion. Example: Milk.
4. Solid + Liquid = Gel. Example: Jelly.
5. Gas + Liquid = Aerosol of liquids. Example: Fog.
6. Solid + Solid = Solid sol. Example: Gems.
7. Liquid + Solid = Sol. Example: Starch solution.
8. Gas + Solid = Aerosol of solids. Example: Smoke.

Colloids are "trick" mixtures that look smooth but are actually made of different phases. They sit right in the middle between a true solution and a suspension in terms of particle size.

Teacher's Tip: Milk is the most famous colloid—it looks like one thing but contains tiny droplets of fat!

Exam Tip: Learn the terms "Dispersion Medium" and "Dispersed Phase" for labeling colloid tables.

Solution 30:
The movement of colloidal particles towards a particular electrode under the influence of an electric field is called electrophoresis. It is shown by only those solutions, the particles of which carry a charge. Thus this phenomenon can be used to find the nature of charge carried by colloidal particles. For example, if particles move towards cathode, they are positive; if they move towards anode, they are negative.

Electrophoresis is like a "tug-of-war" using electricity to see which way tiny particles want to go. This process is very useful in science labs to identify and separate different biological parts like DNA.

Teacher's Tip: Opposites attract! Positive particles always run toward the negative electrode (Cathode).

Exam Tip: Remember that "Electrophoresis" is the specific test for identifying the charge on colloids.

Solution 31:
Comparison Table:
1. Particle size: True Solution (< 10^-10m), Suspension (> 10^-7m), Colloids (10^-10 to 10^-7m).
2. Filtrability:
- True Solution: Pass easily through ordinary filter paper as well as animal membranes.
- Suspension: Do not pass even through ordinary filter paper.
- Colloids: Pass easily through ordinary paper but not through animal membranes.
3. Visibility of particles: True Solution (Invisible), Suspension (Visible to naked eye), Colloids (Visible under Ultra microscope).

This comparison helps you distinguish the three main types of mixtures by looking at particle size and behavior. While you can't see colloid particles with your eyes, they are still larger than the particles in a true solution.

Teacher's Tip: Use the "Filter Test"—if it goes through paper but not a tight membrane, it's a colloid.

Exam Tip: Particle size ranges are the most common objective-type questions for this chapter.

Solution 32:
A suspension is a heterogeneous mixture in which very fine particles, about 10^-7 m, of a solid are dispersed in any medium like a liquid or a gas.
Dispersed substance:
1. Cannot pass through a filter paper nor a semi-permeable membrane.
2. It is visible to the naked eye.
3. They settle down after sometime.
Examples: Chalk in water, Sand in water, Coagulated matter.

Suspensions are the most "obvious" mixtures because you can usually see the particles floating around. Because they are heavy, gravity eventually pulls them down to the bottom of the container.

Teacher's Tip: If you see "Shake well before use" on a medicine bottle, it's probably a suspension!

Exam Tip: "Settling down" is a characteristic property unique to suspensions in this group.

Solution 33:
Tyndall effect can be defined as, the scattering of beam of light by colloidal particles present in a colloidal solution. Tyndall effect can be observed when a fine beam of light passes through a small hole in the dark room. This happens due to the scattering of light by the particles of dust or smoke present in the air.

The Tyndall effect is why you can see a "path of light" in a dusty room or through fog. Tiny particles bounce the light around, making the beam visible to our eyes.

Teacher's Tip: Think of car headlights in the fog—that's the Tyndall effect in action!

Exam Tip: Be sure to use the word "scattering" when defining the Tyndall effect for full marks.

Solution 34:
The effect is called as the Tyndall effect. Tyndall effect is shown by colloidal solution.
Properties of colloidal solution:
1. The particles of colloidal solution do not settle under gravity. They can be made to settle down by centrifugation.
2. It is a heterogeneous mixture.

Colloids are stable mixtures because the particles are small enough that gravity doesn't easily pull them down. However, you can force them to separate using a high-speed spinning machine called a centrifuge.

Teacher's Tip: Gravity can't win against colloids, but the Tyndall effect always reveals their secret particles!

Exam Tip: Mentioning "Centrifugation" shows you know how to separate stable colloids.

Solution 35:
(a) Liquid in water - e.g. Alcohol solution, ammonia solution.
(b) Non-aqueous solution - e.g. solution of iodine in alcohol- This is called Tincture iodine.
(c) Solid in non-aqueous solvent - e.g. solution of stearic acid in ethanol.

Solutions aren't just things dissolved in water; they can use other liquids like alcohol too. These "non-aqueous" solutions are very important in making medicines and cleaning supplies.

Teacher's Tip: "Aqueous" means water-based, and "Non-aqueous" means anything else!

Exam Tip: "Tincture of Iodine" is a common example asked for non-aqueous solutions.

Solution 36:
Common names of colloids:
1. Solid -gas is Solid foam
2. Solid -Liquid is Gel
3. Liquid - Solid is Sol

These names help scientists quickly identify the physical state of a colloid's components. For example, a "Gel" is a specific structure where liquid is trapped inside a solid network.

Teacher's Tip: Hair gel is a perfect example of a "Gel"—it's a liquid that acts like a solid!

Exam Tip: Don't confuse "Sol" (Liquid + Solid) with "Solid foam" (Solid + Gas).

Solution 37:
1. Solution: The solute is not present in any fixed proportion but its composition is uniform.
Mixture: The composition is not uniform. The component may be present in any proportion.
Compound: The constituents of a compound are combined in a definite proportion.
2. Solution: The solute can be recovered by evaporating the solvent, i.e. by physical means.
Mixture: The components can be separated by ordinary physical means.
Compound: The components can be separated by chemical means only.

This comparison shows how the "tightness" of the bond changes how we can separate substances. Physical methods work for solutions and mixtures, but only chemical reactions can break apart a compound.

Teacher's Tip: If heat alone (boiling) separates it, it's a solution or mixture!

Exam Tip: Use "definite proportion" as the defining keyword for compounds.

Solution 38:
The distributed substance in the solution is called as dispersed phase.
The medium in which distributed substance is dispersed is referred to as dispersion medium.

In the world of colloids, the "dispersed phase" is the stuff being spread out, and the "dispersion medium" is the background substance. It's very similar to the solute and solvent in a regular solution.

Teacher's Tip: Think of chocolate chips (dispersed phase) in cookie dough (dispersion medium).

Exam Tip: Always identify which is which when describing a colloid example.

Solution 39:
Blood - colloidal solution
Sugar solution - true solution
Salt solution - true solution
Starch solution - colloidal solution
Ink - colloidal solution

This list classifies common liquids into true solutions or colloids based on how their particles behave. Even though blood and ink look like single liquids, they are actually colloids containing tiny solid particles.

Teacher's Tip: True solutions are always clear/transparent; if it's "cloudy" or opaque, it's likely a colloid.

Exam Tip: "Blood" is a very frequent exam question for classifying colloids.

Solution 40:
Starch solution, milk, soap solution, blue vitriol will scatter light as these are colloidal solutions.

Scattering light is a unique power of colloidal solutions because their particles are just the right size to bump into light waves. This "scattering" is exactly what the Tyndall effect describes.

Teacher's Tip: Shine a laser through these liquids, and you will see a glowing line inside the liquid.

Exam Tip: Use the term "scatter light" to explain why these specific liquids look different under a beam.

Exercise 3(B)

Solution 1:
The methods used to separate solid-liquid mixture are:
1. Evaporation
2. Distillation
3. Filtration
4. Sedimentation and decantation
5. Centrifugation /churning
6. Chromatography

There are many ways to separate solids from liquids depending on if the solid is dissolved or just floating. Choosing the right method depends on things like particle size and boiling point.

Teacher's Tip: Think of "Filtering" for sand and "Boiling" for salt to remember the basics.

Exam Tip: If the solid is "dissolved," you must use evaporation or distillation, not filtration.

Solution 2:
(a) Sand and water are separated by Filtration. Since sand is insoluble in water and forms Heterogeneous mixture. Water dissolves sodium chloride. The solution is than filtered with the help of a filter paper. Sand gets collected as a residue on the filter paper. And the dissolved sodium chloride in water can later be evaporated.
(b) Salt from an aqueous salt solution - Salt can be separated from aqueous salt solution by the process of evaporation. For this the aqueous salt solution (i.e. salt in water) is taken in a beaker and heated over flame. The liquid i.e. water will get evaporated leaving behind salt.
(c) Pure water from salt water - Pure water can be separated from salt water by the process of distillation. Distillation is the process of converting a liquid into vapour by heating and the subsequent condensation of the vapour back into a liquid. Water evaporates and recondenses in pure form and it is collected in a receiver. The salt residue remains in the distillation flask.
(d) Tea leaves from prepared tea - Tea leaves can be separated from prepared tea by the process of filtration. For this purpose a sieve or mesh made of steel or nylon is taken through which prepared tea is passed, thereby leading to retaining of tea leaves on the mesh.
(e) Cream from milk - Cream can be separated from milk by the process of centrifugation. The mixture is taken in centrifuge tubes and placed in holders. The holders are then rotated rapidly. After sometime, the rotation is stopped and the centrifuge tubes are taken out. It is observed that separation of mixture takes place on the bases of density. i.e. the more denser components settles at the bottom and the other becomes the supernatant which can be separated. In case of mixture of cream and milk. Cream comes in the upper layer and is recovered from milk.
(f) Sugar from sugar solution - It is separated by crystallisation. Heat the solution to obtain a saturated solution. Filter the solution while hot and allowed to cool. Crystals of sugar will be formed which are collected.
(g) Dye from black ink - Dye from black ink is separated by the process of chromatography. In this the constituents of a mixture are separated by their absorption over an appropriate absorbing material.

This detailed list explains how we use science to clean and sort everyday items. Whether it's making tea or separating cream, we use physical differences like weight, size, and boiling points to get what we need.

Teacher's Tip: Distillation is like "Evaporation plus a cool-down" to keep both parts of the mixture.

Exam Tip: Use the term "Residue" for what stays in the filter and "Filtrate" for what goes through.

Solution 3:
(a) Carbon tetrachloride and water form immiscible mixture and can be separated by Separating Funnel. Since, they are immiscible liquids and forms two distinct layers. Carbon tetrachloride is heavier liquid with the density of 1.59 g/cm³. Water is lighter with the density of 1g/cm³. Thus, the denser liquid carbon tetra chloride forms a lower level in the funnel which can be separated out first. The remaining water can be collected in the separate beaker.
(b) Lead chloride and silver chloride can be separated by solvent extraction. For this the given mixture is dissolved in water. Silver chloride dissolves in water but lead chloride does not dissolve. The solution is filtered through a filter medium, lead chloride will be retained on the filter medium and the filtrate containing water and silver chloride is collected. Then the filtrate is evaporated to get silver chloride.

Immiscible liquids like oil and water don't mix, making them easy to separate using their weight (density). In solvent extraction, we use a "helper liquid" (solvent) that only picks up one of the solids, leaving the other behind.

Teacher's Tip: A separating funnel is like a bottle with a tap at the bottom—open it to let the heavy layer out!

Exam Tip: Explain "Immiscible" as "liquids that do not mix with each other" for full marks.

Solution 4:
The method of separation depends on both the type of mixture and the physical properties of its constituents. These are :
(i) The physical state of the constituents.
(ii) The differences in the physical properties of the constituents such as :
(a) boiling point, (b) melting point, (c) density, (d) magnetic properties, (e) ability to sublime, (f) volatility, (g) solubility in various solvents .

Scientists pick a separation tool based on what makes the components "different." For example, if one thing is magnetic and the other isn't, a magnet is the obvious tool to use.

Teacher's Tip: Separation is like "sorting laundry"—you sort by color, size, or material!

Exam Tip: Listing "boiling point" and "solubility" is essential as they are the most common properties used for separation.

Solution 5:
It is the process of dissolving one of the components in a particular liquid when one of the components is soluble in water or in some other solvents and the other component is not. For example, a mixture of iron filings and sulphur is separated by using carbon disulphide as solvent. A mixture of sodium chloride and chalk can also be separated by using water as the solvent for sodium chloride.

Solvent extraction is like using a magnet, but instead of magnetism, we use "dissolvability." We pick a liquid that "likes" one substance but "hates" the other to pull them apart.

Teacher's Tip: Water is the most common solvent, but special chemicals like carbon disulphide are used for things like sulphur.

Exam Tip: Be sure to name the specific solvent (like water or carbon disulphide) when describing this method.

Solution 6:
(a) Mercury, silver
(c) Magnesium, sodium carbonate (NO₂O₃)
(b) Calcium, lead
(d) Sodium

These are identifications of various elements and compounds found in chemical exercises. Knowing the names and formulas of these substances is the first step in chemistry.

Teacher's Tip: Sodium (Na) is a very reactive metal that must be stored in oil!

Exam Tip: Always capitalize the first letter of a chemical symbol (Na, Mg) but keep the second letter lowercase.

Solution 7:
(a) Sublimation: Sublimation is the change of state of matter from solid to gaseous state without passing through the liquid state. For example, To separate the mixture of ammonium chloride and sodium chloride, sublimation is used. On heating ammonium chloride will change into vapour which will condense into a solid in the neck of the inverted funnel which can be scrapped off. Sodium chloride remains in the evaporating dish.
(b)
Evaporation Comparison:
1. Evaporation is change of state matter from solid state to gaseous state.
2. Evaporation takes place below its boiling point by supply of heat.
Sublimation Comparison:
1. Sublimation is the change of state of matter from solid state to gaseous state.
2. Sublimation takes place below its melting point by supply of heat.

Sublimation is a "shortcut" where a solid turns straight into a gas, skipping the melting phase. This is perfect for separating special solids like ammonium chloride that have this unique property.

Teacher's Tip: Dry ice and mothballs (naphthalene) are famous everyday things that sublime.

Exam Tip: For sublimation, mention the "inverted funnel" setup as it is a key part of the experiment.

Solution 8:
(a) Distillation is the process of converting a liquid into vapour (by heating) and the subsequent condensation of the vapour back into a liquid.
(b) Fractional distillation is a process which involves distillation and collection of fractions or different liquids boiling at different temperatures.
(c) Centrifugation is the method of separating solids from a liquid, where the mixture is homogeneous.

These techniques use temperature and motion to divide mixtures into their purest parts. Fractional distillation is especially important for separating complex mixtures like crude oil into petrol and diesel.

Teacher's Tip: Distillation = Boiling + Cooling.

Exam Tip: Use "Centrifugation" specifically for mixtures like blood or cream where particles are too small for filters.

Solution 9:
(a) Two miscible liquids can be separated by 1. Distillation or by 2. Fractional Distillation depending on difference in their boiling points.
(b) Yes, mixture of chloroform (B. P. 61° C) and carbon-tetrachloride (B. P. 77° C) can be separated by Fractional Distillation as difference in their B. P. is less than 30° C. Chloroform has a lower boiling point 61° C, so, it distils out first. It is collected in a receiver, leaving behind carbon tetrachloride (having boiling point 77° C). Modification: A fractionating G-Column is fitted over distilling flask.

Miscible liquids are those that mix perfectly, like water and alcohol. We separate them by heating them up; the one that boils first (lower boiling point) leaves the mixture and is caught in another container.

Teacher's Tip: It's like a race—the liquid with the lower boiling point "wins" and comes out of the tube first!

Exam Tip: Mention the "Fractionating Column" as the special tool that makes this separation possible for liquids with close boiling points.

Solution 10:
(a) Dissolve the mixture of carbon and sulphur in carbon disulphide. Sulphur gets dissolve in carbon disulphide. The undissolved solid (carbon) is removed by filtration. The filtrate is evaporated to dryness in order to recover the soluble solid i.e. sulphur powder.
(b) (i) Separation of potassium chloride: Prepare the suspension of mixture in water. The potassium chloride dissolves, but neither carbon nor sulphur, Filter the suspension and collect clear filtrate of potassium chloride in a separate beaker. Evaporate the clear filtrate on low heat. The water evaporates leaving behind white potassium chloride.
(ii) Separation of sulphur: Dissolve the residue in carbon disulphide. Sulphur dissolves in carbon disulphide leaving behind carbon. Filter the suspension and collect clear filtrate. Evaporate the filtrate in shade. The carbon disulphide evaporates leaving behind sulphur.
(iii) Removal and purification of carbon: Wash the residue of carbon on filter paper with carbon disulphide, so as to remove any sulphur. Dry the residue in shade. Carbon disulphide evaporates leaving behind carbon.

This complex separation uses two different liquids (water and carbon disulphide) to pull out specific ingredients one by one. By carefully choosing what to dissolve first, we can separate a three-part mixture into three pure substances.

Teacher's Tip: Always follow the "Solubility Rule": dissolves first, then filter, then evaporate.

Exam Tip: For "Carbon," remember it never dissolves in water or carbon disulphide; it is always the "residue" in these tests.

Solution 11:
(a) Chromatography
(b) Sedimentation
(c) Evaporation
(d) Fractional distillation

These are the best tools for different separation jobs in the lab. Chromatography is great for colors, while evaporation is the simplest way to get salt back from water.

Teacher's Tip: Sedimentation is just "letting things settle" at the bottom of a glass.

Exam Tip: Be ready to match these methods to specific mixture examples in your test.

Solution 12:
By Sublimation method. Ammonium chloride and potassium chloride are placed in an evaporating dish and covered with an inverted funnel. On heating ammonium chloride will change into vapour which will condense into a solid in the neck of the inverted funnel which can be scrapped off. Sodium chloride remains in the evaporating dish.

This is a standard lab procedure to separate salts where one of them can turn into a gas. By catching the gas in the funnel's neck, we keep the two salts completely separate.

Teacher's Tip: "Ammonium chloride" is the most common school example for a substance that sublimes.

Exam Tip: Explain that the solid in the funnel neck is called the "Sublimate."

Solution 13:
When caustic soda is added to an aqueous solution of copper sulphate, a blue precipitate of Cu(OH)₂ , is obtained. Cu(OH)₂ will be separated from mixture by filtration.

A chemical reaction creates a solid "precipitate" from two clear liquids. Once this solid appears, we can easily catch it using a filter paper just like we filter sand from water.

Teacher's Tip: A precipitate is just a fancy science word for "solid that appears out of nowhere" in a liquid.

Exam Tip: Note the color "Blue" as it is the signature color of copper compounds.

Solution 14:
Three commercial materials obtained from fractional distillation of petroleum are as follows:
1. Natural gases
2. Kerosene oil
3. Lubricating oil
Use of Natural gases: 1. It is used as fuel.
Use of Kerosene oil: 1. It is used as fuel in homes. 2. It is used for lighting the lamps on roads and home.
Use of lubricating oil: 1. It is used to lubricate different parts of machines and vehicles. 2. It is used to prepare black polish etc.

Crude oil is a giant mixture, and we separate it to get useful products for our daily lives. From the gas we cook with to the oil that keeps car engines smooth, it all comes from this separation process.

Teacher's Tip: Petroleum is often called "Black Gold" because it has so many useful mixtures inside it!

Exam Tip: Be ready to list at least two uses for each petroleum product mentioned.

Solution 15:
(a) By Sublimation: Heat the impure iodine in a china dish over a low flame. When violet fumes of iodine starts coming out. Place a cold inverted funnel over the china dish. The violet fumes condense on the cooler sides of funnel to form tiny crystals of pure iodine.
(b) By Magnetic Separation: Roll a strong horse shoe magnet on the mixture. The iron filings cling to the magnet, leaving behind c

These methods exploit very specific "powers" of elements, like iodine's ability to sublime or iron's magnetism. Using a magnet is the fastest way to pull metals out of a non-metal pile without using any chemicals.

Teacher's Tip: "Violet fumes" are the signature of Iodine being heated.

Exam Tip: For magnetic separation, specify that "Iron is attracted to the magnet" while the rest is left behind.

Solution 16:
(a) Alcohol from a mixture of alcohol and water can be separated through fractional distillation. Alcohol liberates first because it has a lower boiling point than water.
(b) The components which are soluble in water but their solubilities are different. For example, (i) Sodium nitrate and sodium chloride. (ii) Potassium chlorate and potassium chloride.

Separation isn't always about what dissolves; sometimes it's about "how much" dissolves at a certain temperature. By heating and cooling a mixture of salts, we can make one salt "crash out" as crystals while the other stays dissolved.

Teacher's Tip: This method is called "Fractional Crystallization"—it's like magic with temperature!

Exam Tip: Explain that "difference in solubility" is the reason we can separate these specific salts.

Solution 17:
(a) Nitre and common salt: Take a beaker and prepare a saturated solution of the mixture in boiling water. On cooling, nitre will crystallize out while common salt will remain in solution. The process is repeated two or three times to separate the components completely.
(b) Ammonia and hydrogen: The mixture of gases is bubbled through a Woulfe's bottle containing the solvent i.e. water in which Ammonia dissolves. The insoluble gas component i.e. hydrogen passes out through the delivery tube and is collected in gas jar. The soluble gas component is obtained from its aqueous solution by boiling the solution.
(c) Powdered Chalk and Sugar: Dissolve given mixture in water. Sugar dissolves but chalk does not as it is insoluble chalk. Filter the mixture. Chalk is residue and is dried in the folds of filter paper. Filtrate is crystallized to get crystals of sugar.
(d) Sand, table salt: Dissolve mixture in water. Salt dissolves but sand do not. Filter the solution to collect sand on filter paper. Then the filtrate is evaporated to get salt.
Iron filings and naphthalene: By magnetic separation. Iron fillings get cling to the magnet and are separated. Remaining will be naphthalene.

These step-by-step guides show you exactly how to handle different types of mixtures in a lab. The main trick is always identifying which substance dissolves in water and which one doesn't.

Teacher's Tip: For Nitre and Salt, remember that "Cooling" is the secret step that makes Nitre turn into crystals.

Exam Tip: Always describe the "filtration" step after dissolving, as it is the bridge to getting the pure substances back.

Solution 18:
(a) Ingredients of gun-powder are - (nitre, sulphur and charcoal): Dissolve mixture in water. Nitre dissolves but not sulphur and charcoal. Filter the mixture and collect the clear filtrate of nitre. Heat filtrate to crystallisation point. On cooling crystals of nitre separate out. Filter the crystals and dry them. Dissolve the sulphur and charcoal in Carbon disulphide. Sulphur dissolves but charcoal does not. Filter the solution. Allow the filtrate to evaporate in shade. Carbon disulphide evaporates leaving behind sulphur. Charcoal is dried on filter paper.
(b) Sulphur, Sand and common salt: Dissolve mixture in water. Common salt dissolves but sulphur and sand are insoluble in water. Filter the solution. sulphur and sand will get collected on the filter paper. Evaporate the solution to get common salt Collect the residue (Sand and Sulphur powder) and dissolve it in carbon disulphide, CS₂. Sulphur dissolves in carbon disulphide but sand is insoluble in carbon disulphide. Filter the solution and evaporate it to get sulphur. Sand is dried on filter paper.
(c) Carbon dioxide and Carbon Monoxide: When mixture is passed through a long tube having a number of porous partitions, Carbon monoxide will diffuse more rapidly as compared to Carbon dioxide. Thus if there is sufficient partitions, in the end, Carbon dioxide comes out.
(d) Water and Sugar: Take a beaker half filled with water and dissolve as much sugar as you can in it, with constant stirring. Now heat the solution and go on adding sugar till it stops dissolving. Filter solution while it is hot. Allow the solution to cool. The crystals of pure sugar settle down at the bottom of the beaker.
(e) Sand and Iodine: The mixture is placed in a china dish and an inverted dry funnel is placed over it, with its stem closed with cotton wool. It is then gently heated at a low flame. Iodine sublimes on the cooler side of funnel in the form of fine powder crystals. The residue left behind in the china dish is sand.

Gun-powder is a famous historical mixture that shows how three very different solids can be carefully pulled apart. By using water first and then a special chemical (CS₂), we can isolate every single ingredient perfectly.

Teacher's Tip: Remember: Nitre likes Water, Sulphur likes CS₂, and Charcoal likes Nothing!

Exam Tip: In the Iodine separation, don't forget to mention "closing the funnel stem with cotton wool" to trap the vapors.

Solution 19:
Remove Iron using a Magnetic Separation: Dissolve mixture in water. Sodium Chloride dissolves but not sulphur and charcoal. Filter the solution and allow the filtrate to evaporate to get Sodium Chloride. Now dissolve Sulphur and Charcoal in carbon disulphide solution, CS₂. Sulphur dissolves but not charcoal. Filter the solution. Allow the solution to evaporate to get sulphur. Dry, charcoal in folds of filter papers.

This is a multi-step "rescue mission" for chemicals where you pull out the easiest thing first (Iron with a magnet). Then you move from water to CS₂ to sort out the remaining solids based on what they like to dissolve in.

Teacher's Tip: Start with the magnet; it's the only physical way to remove iron without adding liquids.

Exam Tip: List the order of separation clearly: Magnet → Water → CS₂.

Solution 20:
(a) solid-solid mixture: 1. Magnetic separation: Example- Iron + Sulphur 2. Solvent extraction: Example- Carbon + Sulphur 3. Sublimation: Example- NH₄Cl + NaCl
(b) Solid-liquid mixture: 1. Evaporation: Example- Salt water solution 2. Distillation: Example- Impure water 3. Filtration: Example- Chalk + Water
(c) liquid-liquid mixture: 1. Separating funnel: Example- Water + Carbon tetra chloride 2. Fractional distillation: Example- Benzene + Toluene 3. Distillation: Example- Acetone + Water

This summary lists the "best tools for the job" for every possible combination of matter. Whether you have two solids or two liquids, there is a specific physical property (like weight or boiling point) that lets you separate them.

Teacher's Tip: Use a separating funnel for liquids that form layers, and distillation for liquids that blend together.

Exam Tip: Provide one specific example for each method to ensure you get full marks for the category.

Solution 21:
The mixture is separated by exploiting the following facts in the order given below:
1. Saw dust by gravity
2. Ammonium chloride is soluble in water.
3. Iodine sublime on heating
4. Sand is insoluble in water

Separating a complex mixture is like solving a puzzle where you remove one piece at a time. By knowing which substance floats, which dissolves, and which sublimes, you can easily sort them into separate piles.

Teacher's Tip: Always look for the substance that "floats" (like saw dust) to remove it first by just skimming it off.

Exam Tip: State the "Property" (like solubility or sublimation) alongside the "Action" taken.

Solution 22:
(a) Dissolve given mixture in hot water lead chloride dissolves but not lead sulphate. Filter the mixture. Residue is lead sulphate. Dry it in the folds of filter paper.
(b) Dissolve given mixture in water, Na₂CO₃, dissolves but not ZnCO₃. Filter it ZnCO₃ is residue and is dried in the folds of filter paper.
(c) Separation of given mixture can be done by fractional distillation. Boiling point of Benzene is 80° C and is less as compared with toluene having boiling point 111° C. So, Benzene distills over first.
(d) PbCl₂ from a mixture of PbCl₂ and AgCl. Dissolve given mixture in water. AgCl dissolves, but not PbCl₂. Filter the solution. Evaporate the filtrate to get PbCl₂.

These examples show that even similar-looking chemicals have tiny differences in how they react to hot water or heat. We use these "secret" differences to pull them apart cleanly in the laboratory.

Teacher's Tip: Hot water is a special solvent that can dissolve some things that cold water cannot!

Exam Tip: Mention the specific boiling points (80° C and 111° C) when explaining the benzene-toluene separation.

Solution 23:
(a) Solid to gaseous state.
(b) Iodine

Sublimation is the scientific term for a solid changing directly into a gas without becoming a liquid. Iodine is the most famous element that does this, turning into beautiful purple vapors when heated.

Teacher's Tip: Think of "Dry Ice"—it's a solid that turns into smoke-like gas without making a puddle!

Exam Tip: Use the term "Sublime" as the verb to describe this action.

Solution 24:
Dissolve given mixture in dilute nitric acid. Copper oxide dissolves, but not charcoal. Filter the mixture, residue is charcoal. Dry it in the folds of filter paper. Now heat the filtrate to get copper oxide.

This separation uses an acid as a special "picky" solvent that only likes the copper oxide. Once the charcoal is filtered out, we just have to remove the liquid to get the copper back.

Teacher's Tip: Acids are powerful solvents used in labs to dissolve metals and oxides.

Exam Tip: Always describe "charcoal" as the "residue" in this experiment since it never dissolves.

Solution 25:
To separate nitrogen from the air:
1. Air is passed through filters or an electronic precipitator to remove dust. (ii) Then air is repeatedly compressed by increasing the pressure.
2. Air is then cooled by decreasing the temperature.
3. Now air becomes liquefied.
4. Liquid air containing carbon dioxide, oxygen, nitrogen and inert gases is subjected to fractional evaporation.
5. Carbon dioxide separates out as solid ice at -78° C.
6. Liquid containing has a lower boiling point of -196° C, so it distills out first. Oxygen with boiling point -183° C is left behind.

Getting pure nitrogen from the air is a high-tech process of turning air into a cold liquid first. Because each gas in the air has a different "cold" boiling point, they come out one by one as we slowly let the liquid warm up.

Teacher's Tip: Liquid Nitrogen is incredibly cold—at -196° C, it can freeze a flower instantly!

Exam Tip: Memorize the order: Dust removal → Liquefaction → Fractional Distillation.

Solution 26:
The two main components (oxygen and nitrogen) are separated from the air as follows:
1. Air is passed through filters or an electronic precipitator to remove dust.
2. Then air is repeatedly compressed by increasing the pressure.
3. Air is then cooled by decreasing the temperature.
4. Now air becomes liquefied.
5. Liquid air containing carbon dioxide, oxygen, nitrogen and inert gases is subjected to fractional evaporation.
6. Carbon dioxide separates out as solid ice at -78° C.

This process allows us to capture oxygen for hospitals and nitrogen for industry from the very air we breathe. It relies on the fact that carbon dioxide turns into a solid (dry ice) much faster than oxygen or nitrogen.

Teacher's Tip: Think of this like "reversing the atmosphere"—taking a gas and making it so cold it becomes a liquid soup.

Exam Tip: Mention that CO₂ is removed as "solid ice" during the early cooling stage.

Solution 27:
(a) Chromatography: The process of separation of different dissolved constituents or mixture by absorbing them over an appropriate adsorbent material is called chromatography.
(b) The principle on which this technique is based is the difference in the adsorption different substances on the surface of a solid medium.
(c) Chromatograms are the distinct coloured rings or zones which are formed due to separation of mixture containing coloured substances by the process of chromatography.
(d) Advantages of chromatography: 1. It can be carried out by very small amount of material. 2. The substances under investigation do not get washed in chromatographic separation.

Chromatography is a beautiful way to see what colors are hidden inside ink or food dyes. It works because different chemicals "travel" at different speeds across a piece of paper or special material.

Teacher's Tip: You can do chromatography at home using a coffee filter and a black marker!

Exam Tip: Use the word "Adsorption" (with a 'd') to describe how substances stick to the paper.

Solution 28:
(a) Centrifugation is used in diagnostic laboratories for testing blood/urine samples. It is also used for separation of cream from milk and butter from curd in dairies.
(b) Chromatography is used for purification of number of industrial products.

These methods are vital for modern medicine and food production. Centrifugation spins things so fast that the heavy parts (like blood cells) are forced to the bottom, separating them from the liquid.

Teacher's Tip: A washing machine on the "spin cycle" is actually a big centrifuge for your clothes!

Exam Tip: "Testing blood/urine" is the most important use to mention for Centrifugation.

Solution 29:
The methods employed to separate two liquids are: 1. Distillation and fractional distillation 2. By using separating funnel.

To separate two liquids, we first check if they mix. If they don't mix (like oil and water), we use a funnel; if they do mix (like water and alcohol), we use heat to boil them apart.

Teacher's Tip: Funnel for "layered" liquids, Heat for "blended" liquids.

Exam Tip: Use the term "Miscible" for liquids that mix and "Immiscible" for those that do not.

Solution 30:
The apparatus used to separate oil and water is separating funnel. In this the two immiscible liquids are separated on the basis of their density differences. Thus, the heavier liquid will settle at bottom and the lighter one will form upper layer.

Oil and water are classic enemies that never mix, forming two clear layers. The separating funnel lets us tap off the bottom water layer perfectly, leaving the oil safe and sound in the container.

Teacher's Tip: Density is just a science word for "how heavy something is for its size."

Exam Tip: Always mention that "water is heavier (denser) than oil" to explain why it settles at the bottom.

Solution 31:
(a) Magnetic separation
(b) Solvent extraction
(c) Fractional crystallization
(d) Chromatography
(e) Boiling
(f) Separating funnel
(g) Distillation
(h) Evaporation
(i) Solvent extraction

This list identifies the correct separation method for various laboratory challenges. Each choice is based on a specific physical property of the ingredients, such as magnetism or boiling point.

Teacher's Tip: Choosing the right method is the "Secret Sauce" of being a good chemist.

Exam Tip: Practice identifying which method belongs to which mixture to save time during the exam.

Solution 32:
Take a rectangular sheet of filter paper approximately 10 cm × 8cm. Mark a horizontal line on the sheet about 2 cm from the lower edge and mark a cross (x) near the middle of the line. Prepare a mixture by mixing red and blue inks nearly-in equal proportions. With the help of dropper put about 2 to 3 drops of ink mixture on the cross (x) marked on the line. Allow it to dry. Fix the paper to a cork in a tall jar so that its lower end rests at the bottom of the jar. Pour a mixture of water and alcohol into the jar. (1 : 1) so that about a 2 cm of filter paper dips in water-alcohol mixture. Leave it for about one hour. Solvent rises slowly by capillary action and reaches the cross marked on line and then goes on rising higher. Two coloured lines are seen at different heights. When the difference in heights is appreciable, remove the paper from jar and let it dry. In this way we can separate coloured constituents present in a mixture of ink.

This experiment proves that ink is actually a mixture of many different colored dyes hidden together. As the liquid crawls up the paper, it carries each color to a different "parking spot," letting us see them separately.

Teacher's Tip: "Capillary action" is the same way plants pull water up from their roots to their leaves!

Exam Tip: Be sure to mention that the paper must "dip" into the liquid but the "ink spot" must stay above it.

Solution 33:
(a) sublimation
(b) filtration
(c) immiscible, separating funnel
(d) sublimation
(e) methylated spirit

These one-word answers summarize the most effective ways to solve common chemical separation problems. Methylated spirit is a common laboratory solvent used to dissolve specific types of organic materials.

Teacher's Tip: "Sublimation" is your go-to answer for Iodine or Ammonium Chloride.

Exam Tip: Use "Immiscible" whenever you are talking about using a separating funnel for two liquids.