Q1: What is a homogeneous mixture? Give two examples.
Ans: A homogeneous mixture has a uniform composition throughout. Examples include vinegar (acetic acid in water) and aerated drinks like soda (carbon dioxide in water).
Q2: What is a heterogeneous mixture? Give one example.
Ans: A heterogeneous mixture is one that is not uniform in composition – its components are not evenly distributed. A stirred mixture of sand and water is an example.
Q3: What is the difference between a solute and a solvent?
Ans: A solute is the substance that gets dissolved in a solution, while a solvent is the substance that dissolves the solute. For example, in a sugar solution, sugar is the solute and water is the solvent.
Q4: Define concentration of a solution.
Ans: The amount of solute dissolved in a given amount of solvent or solution is termed as the concentration of the solution. The right proportion of solute and solvent is always essential when preparing a solution.
Q5: Write the formula for mass by mass percentage concentration.
Ans: Mass by mass percentage tells us how many grams of solute are present in 100 grams of the total solution.
Q6: Write the formula for mass by volume percentage concentration.
Ans: Mass by volume percentage tells us how many grams of solute are present in 100 millilitres of the solution.
Q7: Write the formula for volume by volume percentage concentration.
Ans: Volume by volume percentage is used when two miscible liquids are mixed. It tells us how many millilitres of solute are present in 100 millilitres of the solution.
Q8: What is a saturated solution?
Ans: A solution that cannot dissolve any more solute at a given temperature is called a saturated solution. The solubility of a solid solute generally increases with temperature.
Q9: What is crystallization?
Ans: Crystallization is the process of forming crystals from a saturated solution. It is used to separate and purify solids, based on the differences in the solubility of a substance at different temperatures.
Q10: What is distillation and when is it used?
Ans: Distillation is the process of separating a homogeneous mixture of two miscible liquids by heating until the liquid with the lower boiling point vaporises, then cooling the vapour back into a liquid. It is used when the liquids differ in boiling point by at least about 25 °C.
Q11: What is paper chromatography and on what principle does it work?
Ans: Paper chromatography is a method of separating the components of a mixture using differences in the interactions of the components with the solvent and the paper. The liquid carries substances up the paper, separating them based on how fast they move.
Q12: What are immiscible liquids? How are they separated?
Ans: Liquids that do not mix with each other and form separate layers are called immiscible liquids. They are separated using a separating funnel, which allows the denser liquid to drain out from the bottom first.
Q13: What is sublimation and what is deposition?
Ans: Sublimation is the transition of a solid directly into a vapour below its melting point without passing through the liquid state. The reverse process, where vapour cools and changes back into a solid without becoming a liquid, is called deposition.
Q14: What is an alloy? Give two examples.
Ans: A homogeneous mixture of two or more metals, or a metal and a non-metal, is called an alloy. Examples include brass (approximately 80% copper and 20% zinc) and bronze (approximately 80% copper and 20% tin).
Q15: What is a suspension? Give two examples.
Ans: A suspension is a heterogeneous mixture in which solid particles do not dissolve but remain suspended throughout the medium. Sawdust suspended in water and tea leaves in water are examples of suspensions.
Q16: What is centrifugation and where is it used?
Ans: Centrifugation is the process of spinning a mixture in a tube at high speed so that the heavier particles move outwards and settle at the bottom while the lighter liquid remains at the top. It is widely used to separate components of blood, such as red blood cells and plasma.
Q17: What is coagulation? Give one everyday example.
Ans: Coagulation is the process of adding a substance called a coagulant to make smaller suspended particles clump together and settle down. The formation of cheese (paneer) from milk using lemon juice or vinegar as a coagulant is a common everyday example.
Q18: What is a colloid? How is it different from a solution and a suspension in terms of particle size?
Ans: A colloid is a mixture that is neither a true solution nor a true suspension. The particle size in a solution is less than 1 nm, in a colloid it is 1-1000 nm, while particles in a suspension are more than 1000 nm in diameter.
Q19: What is the Tyndall effect?
Ans: The scattering of light by particles in a colloid or suspension is known as the Tyndall effect. It is named after scientist John Tyndall, who first studied the scattering of light by particles. Scattering does not occur when light passes through a transparent solution.
Q20: What is fractional distillation and where is it applied?
Ans: Fractional distillation is the process of separating components of a mixture that have relatively small differences (less than 25 °C) in their boiling points. It is applied in petroleum refineries to separate crude oil into useful products such as petrol, kerosene, diesel, and others.