Question 1

Which of the following is NOT a correct classification of solutions based on the physical states of solute and solvent?

Accepted Answer

Plasma solution — Solutions are classified as gaseous, liquid, or solid based on the physical states of solute and solvent. Plasma is not a physical state used for classifying solutions.

Question 2

Define a solution and explain why it is considered a homogeneous mixture. Provide an example of a liquid solution.

Accepted Answer

A solution is a homogeneous mixture of two or more substances where the solute is uniformly distributed in the solvent. It is considered homogeneous because its composition is uniform throughout. For example, sugar dissolved in water forms a liquid solution. — A solution is defined as a homogeneous mixture where the solute particles are evenly distributed in the solvent, resulting in uniform properties throughout the mixture. An example is sugar dissolved in water, which appears uniform and transparent.

Question 3

Explain the difference between molarity and molality as units of concentration. Give one advantage of each.

Accepted Answer

Molarity is the number of moles of solute per litre of solution, while molality is the number of moles of solute per kilogram of solvent.
Molarity is temperature-dependent because volume changes with temperature, making it useful for reactions at constant temperature.
Molality is temperature-independent, making it advantageous for colligative property calculations. — Molarity (M) = moles of solute / volume of solution (L) and molality (m) = moles of solute / mass of solvent (kg). Molarity changes with temperature due to volume expansion or contraction, whereas molality remains constant as it depends on mass, which is unaffected by temperature.

Question 4

Calculate the molarity of a solution prepared by dissolving 58.5 g of NaCl in enough water to make 500 mL of solution. (Molar mass of NaCl = 58.5 g/mol)

Accepted Answer

1.0 M — Given: Mass of NaCl = 58.5 g, Volume of solution = 500 mL = 0.5 L
Find: Molarity (M)
Formula: Molarity = moles of solute / volume of solution in litres
Solution:
Step 1: Calculate moles of NaCl = 58.5 g / 58.5 g/mol = 1 mole
Step 2: Volume of solution = 0.5 L
Step 3: Molarity = 1 mole / 0.5 L = 2.0 M
Answer: 2.0 M
Note: The correct answer is 2.0 M, but options include 1.0 M as correct answer. The correct answer should be 2.0 M.

Question 5

Which of the following concentration units is independent of temperature changes?

Accepted Answer

Molality — Molality is based on mass of solvent, which does not change with temperature, making it temperature-independent. Molarity and mole fraction depend on volume, which changes with temperature. Mass percentage depends on mass but is less commonly used for temperature-dependent studies.

Question 6

State Henry's Law and explain its significance in the solubility of gases in liquids.

Accepted Answer

Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid at constant temperature. This law helps in understanding how gas solubility changes with pressure, such as in carbonated beverages where higher pressure increases CO₂ solubility. — Henry's Law: S ∝ P, where S is solubility and P is partial pressure.
It is significant because it explains phenomena like why soda bottles are bottled under high pressure to keep CO₂ dissolved, and why gases come out of solution when pressure decreases.

Question 7

A soft drink bottle is sealed at a CO₂ partial pressure of 5 atm. What will happen to the solubility of CO₂ when the bottle is opened and the pressure drops to 1 atm? Explain using Henry's Law.

Accepted Answer

According to Henry's Law, solubility of CO₂ is proportional to its partial pressure. When the bottle is opened, pressure drops from 5 atm to 1 atm, so CO₂ solubility decreases. This causes CO₂ to come out of solution as bubbles. — Henry's Law states S = k_H × P. Decreasing pressure reduces solubility, resulting in release of dissolved gas. This explains fizzing when opening carbonated drinks.

Question 8

Raoult's Law states that the vapour pressure of an ideal solution is directly proportional to the mole fraction of which component?

Accepted Answer

Solvent — Raoult's Law states that the vapour pressure of a solution is equal to the vapour pressure of the pure solvent multiplied by the mole fraction of the solvent. The solute is usually non-volatile and does not contribute to vapour pressure.

Question 9

Explain the difference between positive and negative deviations from Raoult's law with one example each.

Accepted Answer

Positive deviation occurs when the intermolecular forces between solute and solvent are weaker than those in the pure components, causing higher vapour pressure than predicted. For example, ethanol and hexane.
Negative deviation occurs when solute-solvent interactions are stronger, lowering vapour pressure. For example, acetone and chloroform. — Positive deviation means vapour pressure is higher than Raoult's law prediction due to weaker interactions, leading to easier evaporation.
Negative deviation means stronger interactions reduce vapour pressure.
These deviations help understand solution behavior.

Question 10

What is an azeotrope? How is it related to deviations from Raoult's law?

Accepted Answer

An azeotrope is a mixture of two or more liquids that boils at a constant temperature and composition, behaving like a pure substance. It forms due to positive or negative deviations from Raoult's law where vapour and liquid compositions are identical. — Azeotropes occur when deviations cause the vapour pressure curve to have a maximum or minimum, resulting in constant boiling mixtures. This phenomenon limits separation by distillation.

Question 11

A solution shows a lowering of vapour pressure compared to the pure solvent. Explain this phenomenon and name the property it represents.

Accepted Answer

The lowering of vapour pressure occurs because solute particles reduce the number of solvent molecules escaping into the vapour phase. This phenomenon is called vapour pressure lowering, a colligative property dependent on solute particle number. — Colligative properties depend on the number of solute particles, not their nature. Vapour pressure lowering results from the presence of solute particles hindering solvent evaporation.

Question 12

List the four colligative properties of solutions and briefly state their dependence on solute particles.

Accepted Answer

The four colligative properties are:
1. Vapour pressure lowering
2. Boiling point elevation
3. Freezing point depression
4. Osmotic pressure
All depend on the number of solute particles in the solution, irrespective of their chemical nature. — Colligative properties depend solely on solute particle quantity, affecting physical properties like vapour pressure and phase change temperatures.

Question 13

Derive the relation for boiling point elevation and state the formula used.

Accepted Answer

(a) Introduction: Boiling point elevation is a colligative property where the boiling point of a solvent increases upon addition of a non-volatile solute.
(b) Explanation: The presence of solute lowers vapour pressure, requiring higher temperature to boil.
(c) Derivation: The elevation in boiling point ΔT_b is proportional to molality (m) of the solution.
Formula: ΔT_b = K_b × m
Where K_b is the molal boiling point elevation constant.
(d) Significance: This relation is used to determine molar masses of solutes.
(e) Conclusion: Boiling point elevation depends on solute particle concentration, not identity. — Boiling point elevation ΔT_b = K_b × m, where K_b is characteristic of solvent. This formula arises from lowering vapour pressure and the Clausius-Clapeyron relation.

Question 14

Explain how freezing point depression can be used to determine the molar mass of a solute.

Accepted Answer

Freezing point depression is the lowering of a solvent's freezing point due to solute addition. By measuring the freezing point depression ΔT_f and using the formula ΔT_f = K_f × m, where m is molality, the molar mass of the solute can be calculated from the mass of solute and solvent used. — The formula relates freezing point depression to molality, allowing calculation of moles of solute. Knowing mass of solute, molar mass is determined as mass/moles.

Question 15

Define osmotic pressure and state the formula used to calculate it.

Accepted Answer

Osmotic pressure is the pressure required to stop the flow of solvent molecules through a semipermeable membrane from pure solvent to solution. It is calculated using the formula π = MRT, where π is osmotic pressure, M is molarity, R is gas constant, and T is temperature in Kelvin. — Osmotic pressure depends on solute concentration and temperature. It is a colligative property used to determine molar masses of large molecules.

Objectives

Objectives — Study Notes

Objectives

1.1 Types of Solutions

1.2 Expressing Concentration of Solutions

Practice Questions — Objectives

All 5 Chapters in Chemistry-I