1. (a) True.
2. (b) True.

1. (a) Separating funnel
2. (b) Heterogeneous mixture; separated by centrifugation.

1. When we try to melt brass, it does not have a sharp melting point. This shows that it is not a compound.
2. It is a homogeneous mixture of copper and zinc and is called an alloy.

1. Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from water.
2. The processes involved in the purification of water in the waterworks system are: sedimentation, loading, filtration, and chlorination.

1. Water from the reservoir is passed into a sedimentation tank and allowed to remain there for a few hours, so solids settle down.
2. The water is then passed into a loading tank to sediment the suspended impurities.
3. The next stage is a filtration tank which contains layers of gravel and sand.
4. The final step is chlorination — done to rid the water of bacteria by adding bleaching powder.
5. The chlorinated water is then sent to homes.

1. Mass of glucose (solute) = 5 g. Volume of solution = 100 mL.

1. = (5/100) × 100 = 5% m/v.

1. Evaporation: Water will evaporate leaving behind sodium chloride.

1. Yes, the solubility of a substance changes with temperature. Solubility generally increases with an increase in temperature, and decreases on decreasing the temperature.
2. Example: You can dissolve more sugar in hot water than in cold water.

1. Mass of salt (solute) = 10 g. Mass of water (solvent) = 90 g. Total mass of solution = 10 + 90 = 100 g.

1. = (10/100) × 100 = 10% m/m.

1. The freezing point of water (solid state) is 0°C (or 273 K). In many cases, the freezing point has to be lowered, which is generally achieved by mixing some common salt or other salt with ice.
2. This is known as a freezing mixture. In ice, sodium chloride acts as an impurity, and it is a fact that impurities always lower the freezing point temperature of a liquid.

1. Zinc oxide = (4/100) × 300 = 12 g.

1. In a colloidal solution, the particle size is larger, i.e. of the order 1 nm to 100 nm, such that these particles scatter the light rays as they fall on them.
2. Because of scattering, the path of the light as well as the particles become visible.
3. But in a true solution, the particle size is so small (less than 1 nm) that these particles are not able to scatter light. Therefore, a true solution does not show any Tyndall effect.

1. Solute: A solute is that component of a solution (usually present in lesser amount) which is added to the solvent. E.g. Common salt in a salt solution.
2. Solvent: A solvent is that component of a solution (usually present in larger amount) to which the solute is added or which dissolves the solute. E.g. Water in a salt solution.
3. Solution: A solution is a homogeneous mixture composed of two constituents — a solute and a solvent — mixed uniformly without undergoing any chemical change.

1. Mass of given saturated solution = 25 g. Mass of salt in the solution = 5 g. So, mass of water in the solution = 25 − 5 = 20 g.
2. Now, 20 g of water has dissolved 5 g of salt. So 1000 g of water has dissolved = (20×1000)/5 = 250 g of salt.
3. As solubility of the salt is its mass present in 100 g (100 mL) of water: 100 g of water has salt = (5/20) × 100 = 25 g.

1. A solution, such as salt water, has particles too small to scatter light, so it does not exhibit the Tyndall effect — a light beam's path remains invisible.
2. A suspension, like muddy water, has large particles that settle over time and effectively scatter light, clearly showing the Tyndall effect.
3. A colloid, like milk, has intermediate-sized particles that do not settle and also effectively scatter light, thus exhibiting the Tyndall effect.

1. Yes, the size of crystals changes with the rate of evaporation.
2. Fast evaporation forms small crystals. Slow evaporation forms large crystals.
3. Slow evaporation allows particles more time to arrange properly, forming bigger crystals, while fast evaporation leads to quick, irregular formation of smaller crystals.

1. Sample 'B' will not freeze at 0°C because it may contain impurities.
2. At 1 atm, the boiling point of pure water is 100°C and the freezing point of pure water is 0°C. Since B boils higher than 100°C, it is likely impure.

1. Acetone can be separated from the mixture of salt solution and water by distillation.
2. There is a considerable difference in the boiling point of acetone (56°C) and water (100°C).
3. So, when the solution is heated, acetone will evaporate before water does, and it can be collected after condensation.

1. They do not come closer because of the presence of either positive or negative charge on them.
2. Due to mutual repulsion, these particles remain scattered in a colloidal solution.

1. Emulsions are classified as oil-in-water or water-in-oil.
2. This classification indicates which liquid forms the dispersed phase and which forms the continuous dispersion medium.
3. For example, oil-in-water emulsions have oil droplets dispersed in water, while water-in-oil emulsions have water droplets dispersed in oil. This distinction describes the structural arrangement of the components within the emulsion.

1. Clouds are a colloid.
2. They consist of tiny water droplets or ice crystals dispersed in air. The particles are small enough to remain suspended and do not settle down.
3. They can scatter light (show the Tyndall effect). Hence, clouds are a colloidal mixture (aerosol).

1. (i) The concentration of a solution is expressed by: mass by mass percentage, volume by volume percentage, and mass by volume percentage of a solution.
2. (ii) Chromatography is a technique used to separate those solutes of a mixture that are soluble in the same solvent. It works on the principle of adsorption, and is used to separate coloured components (dyes) in black ink.
3. (iii) Centrifugation: We put the milk in a closed container in a big centrifuge machine and spin it at very high speed. The centrifugal forces separate the mixture into cream (lighter, floats on top) and skimmed milk (at the bottom), then the cream can be separated.

OR

1. A mixture of two or more miscible liquids, for which the difference in boiling points is less than 25 K, can be separated by the process called Fractional Distillation.

1. (i) Crystallization is a process used to separate and purify solids from a solution by forming crystals. It occurs when a saturated solution is cooled, causing the dissolved substance to come out in a pure solid form.
2. (ii) Crystals form when a solution is cooled because the solubility of the solute decreases. As a result, the excess solute can no longer remain dissolved and separates out in the form of solid crystals.
3. (iii) The principle of crystallization is based on the change in solubility with temperature. Most solids dissolve more at higher temperatures and less at lower temperatures. When a hot saturated solution is cooled, excess solute crystallises out as pure solid particles.

OR

1. A natural example of crystallization is the formation of snowflakes or salt crystals. In laboratories, crystallization is used to purify substances and separate solids from mixtures where components are dissolved in the same solvent.

1. (i) Since blood is a colloid, the Tyndall effect is observed when a beam of light is passed through it, because the dispersed particles of a colloid are large enough to deflect light.
2. (ii) The phenomenon by which colloidal particles scatter light is called the Tyndall effect. If light is passed through a colloid, it is scattered by the larger colloidal particles, and the beam becomes visible.
3. (iii) Colloidal solutions are mixtures in which the substances are regularly suspended in a fluid. A colloid is a very tiny and small material that is spread out uniformly all through another substance.

OR

1. Example: Fog. Liquid (water drops) acts as the dispersed phase, and gas (air) as the dispersion medium.

1. (i) Distillation is a method used to separate components of a mixture of miscible liquids by heating and cooling. It involves vaporising the liquid with a lower boiling point and then condensing it back into liquid form.
2. (ii) Distillation works on the principle that different liquids have different boiling points. The liquid with the lower boiling point vapourises first, allowing it to be separated through condensation.
3. (iii) In distillation, the mixture is heated until the component with lower boiling point vapourises. The vapour passes through a condenser where it cools and turns into liquid. This liquid is collected separately while the remaining component stays in the flask.

OR

1. One practical application of distillation is the purification of liquids, such as separating acetone from water or extracting natural fragrances for perfumes using traditional methods in places like Kannauj.

1. (i) Dispersion medium is a continuous medium in which the dispersed phase is distributed throughout. Dispersed phase is the phase composed of particles distributed through another phase.
2. (ii) Homogeneous mixtures generally have a uniform composition throughout, and the whole mixture is in the same phase. Heterogeneous mixtures have composition which may vary from point to point, and substances can be of two phases with layers that may separate.
3. (iii) An emulsion is a mixture of two or more liquids that are usually immiscible, but under specific transforming processes will adopt a macroscopic homogeneous aspect and a microscopic heterogeneous one.

OR

1. An example of a solid sol is a coloured gemstone.

(i) Steps to obtain pure copper sulphate

• Dissolve copper sulphate in water.
• Add a few drops of dil. H₂SO₄ to get a clear solution.
• Heat the solution in a China dish till crystallisation point is reached.
• Cool this saturated solution.
• Crystals of pure copper sulphate are formed. Impurities remain behind in the solution.
• Separate these crystals from the solution by filtration and dry them.

(ii) Application

1. The method is crystallisation. It is used for the purification of common salt from water.

(iii) Why better than evaporation

1. Soluble impurities can be removed by this technique, which is not removed by evaporation.

Apparatus for paper chromatography — jar, chromatography paper strip, sample dot, and solvent, showing blue and black spot separation

1. Name of the process: Paper chromatography.
2. Principle: Different components of a mixture move with different speeds in a solvent, so they separate at different heights. Here blue ink and black ink rise with the help of solvent at different speeds to form two spots at different heights.

(ii) Physical and chemical changes

1. Burning of magnesium in the air: Chemical change
2. Tarnishing of silver spoon: Chemical change
3. Sublimation of iodine: Physical change
4. Electrolysis of water: Chemical change

1. (i) ORS must be prepared using a fixed proportion of salt, sugar, and water. The correct balance of these components is essential because even a small change in proportion can make the solution ineffective or harmful instead of beneficial.
2. (ii) If too little pesticide is used, it will not effectively control pests on crops. As a result, pests may survive and multiply, leading to greater crop damage and reduced agricultural yield, affecting overall productivity.
3. (iii) If too much pesticide is used, it can harm the crops and soil. Excess chemicals may damage plant tissues, reduce soil fertility, and also cause environmental pollution, affecting surrounding organisms and ecological balance.

1. By using a magnet: Moving a magnet over the mixture will result in iron filings getting stuck to the magnet. Thus, iron will be separated from the mixture.
2. Sublimation: The remaining mixture is heated in a china dish. Ammonium chloride is a sublimating substance and will evaporate without passing through the liquid phase. The crust of ammonium chloride can be collected by placing an inverted funnel on top of the china dish.
3. Sedimentation, decantation, and filtration: The remaining mixture is dissolved in water and allowed to settle. Sand, being insoluble in water, settles at the bottom. The liquid is decanted into another beaker and then filtered to remove any traces of sand.
4. Evaporation: The liquid is now a solution of salt in water. This is heated in a beaker so that the water evaporates. Once all the water evaporates, salt remains in the beaker.

1. (i) The fundamental principle behind crystallisation is the difference in solubility of a substance at different temperatures. A substance is more soluble at higher temperatures and less soluble at lower temperatures, which allows it to separate in solid form when conditions change.
2. (ii) For purification, the impure solid is first dissolved in a suitable solvent at high temperature to form a saturated solution. On cooling, the pure substance crystallises out because its solubility decreases, while the minor soluble impurity remains dissolved in the mother liquor, allowing separation.
3. (iii) A natural example of this principle is the formation of snow or ice crystals. When water vapour cools in the atmosphere, its solubility as a gas decreases and it changes directly into solid ice crystals, forming snowflakes or frost structures.

(i) Factors affecting solubility

1. Temperature: For most solid-in-liquid and liquid-in-liquid solutions, solubility increases with temperature. For gas-in-water solutions, solubility decreases with increase in temperature.
2. Pressure: Applicable to gas-in-liquid solutions. An increase in pressure increases the solubility of a gas (e.g. aerated drinks contain CO₂ under pressure).
3. Mechanical Stirring: Increases solubility — e.g. sugar dissolves faster on stirring with a spoon.
4. Size of Solute Particles: Smaller particle size gives greater solubility — e.g. it is easier to dissolve powdered sugar than granules of sugar.

(ii) Compounds vs Mixtures

1. Compounds are pure substances made up of two or more elements combined chemically, in a fixed ratio, with fixed properties different from their constituents, separable only by chemical methods.
2. Mixtures are impure substances made by physically mixing substances, in varying ratios, with properties same as their constituents, and no new substance is formed.

1. (i) Precise proportions are necessary in solutions like ORS because they are designed for a specific physiological function. The correct ratio of salt, sugar, and water ensures effective rehydration. If these amounts are varied freely, the balance is disturbed and the solution may become ineffective or even harmful to the body.
2. (ii) Mass by mass percentage is used when both solute and solution are measured in terms of mass. It is suitable for solid-solid mixtures or solid dissolved in liquid when weighing is convenient. Mass by volume percentage is used when a solid is dissolved in a liquid and measuring the volume of solution is easier, such as in medicines or lab solutions.
3. (iii) Solubility differences with temperature affect usage of substances in practice. For solids, solubility generally increases with temperature, helping in processes like crystallisation and faster dissolution. For gases, solubility decreases with temperature, so cold conditions are used to retain gases like CO₂ in soft drinks and oxygen in water for aquatic life.

1. (i) A homogeneous mixture is a mixture where the components are uniformly distributed throughout, and individual components are not visibly distinguishable.
2. (ii) A solute is the substance that gets dissolved in a solution, while a solvent is the substance that dissolves the solute. For example, in saltwater, salt is the solute and water is the solvent.
3. (iii) A saturated solution is one where the maximum amount of solute has been dissolved in a given amount of solvent at a specific temperature. Beyond this point, no more solute can dissolve, and any additional solute would typically remain undissolved or precipitate out.

1. (i) Mitti ka Ittar is prepared by collecting the natural earthy fragrance released from wet soil after the first rain. This scented soil is then heated in a traditional setup so that the vapours containing the fragrance are captured and condensed, producing a natural perfume that carries the smell of rain-soaked earth.
2. (ii) The Deg-Bhapka method is used for the distillation of Mitti ka Ittar. In this traditional process, the fragrant vapours are collected in a receiver and cooled so that the essence is separated and stored as perfume.
3. (iii) Kannauj is famous as the "perfume capital of India." It has a long-standing tradition of producing natural perfumes using age-old distillation techniques, known for its skilled artisans and heritage-based fragrance industry passed down through generations.

(i)

1. Mass of solution = 36 + 100 = 136 g.
2. = (36/136) × 100 = 26.4% (by mass).

(ii)

1. Given: Mass of solution (M) = 200 g, Concentration = 25%.
2. Mass by mass % = (Mass of solute / Mass of solution) × 100 ⇒ 25 = (m/200) × 100 ⇒ m = (25×200)/100 = 50 g.
3. Mass of solute (glucose) = 50 g. Mass of solvent (water) = 200 − 50 = 150 g.