Solutions: Important Questions

Very Short Answer Questions (1 Mark)

Ques. The volume occupied by a single gas in a mixture at the same temperature and pressure is referred to as the single-gas volume.

1. Absolute volume
2. Partial volume
3. Total volume of a gas mixture
4. None of the mentioned

Ans. b

Explanation: At the same temperature and pressure, the volume occupied by a single gas alone in a combination is a portion of a volume.

Ques. Atmospheric pollution is generally measured in the units of

1. mass percentage
2. volume percentage
3. volume fraction
4. ppm

Ans. d

Explanation: Since the amount of pollutants present in the atmosphere is very minor, atmospheric pollution is measured in parts per million (ppm).

Ques. The law which indicates the relationship between solubility of a gas in liquid and pressure is

1. Raoult’s law
2. Henry’s law
3. Lowering of vapour pressure
4. Van’t Hoff law

Ans: a

Explanation: Henry's Law is the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

Ques. What is an example of camphor in N₂ gas?

1. Solid in gas solution
2. Gas in gas solution
3. Solid in liquid solution
4. Liquid in gas solution

Ans: a

Explanation: Solid in gaseous solution is an example of camphor in N₂ gas. Gaseous solution refers to a solution in which the solvent is gaseous. Other gaseous solutions include air (O₂ + N₂), iodine vapours in air, humidity in air, etc.

Ques. What happens when a solute crystal is added to a supersaturated solution?

1. It becomes a colloidal solution
2. The solute dissolves in the solution
3. The solution desaturates
4. The solute precipitates out of the solution

Ans: d

Explanation: Solute particles leave the solution and form a crystalline precipitate when a solute crystal is added to a supersaturated solution. Seeding refers to the addition of the solute crystal.

Ques. Which of the following options is not a viable option?

1. Brass
2. Bronze
3. Hydrated salts
4. Aerated drinks

Ans: d

Explanation: A solid solution is a one- or more-solute solid-state solution in a solvent. Solid solutions include brass, bronze, and hydrated salts. Liquid solutions include aerated beverages.

Ques. What is a Solvent?

Ans. The component that dissolves the other component is called the solvent.

Ques. What is Solute?

Ans. The component(s) that is/are dissolved in the solvent is/are called solute(s).

Ques. Define “Concentration of a Solution”.

Ans. The amount of solute in a given solution is called the concentration of a solution.

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Short Answer Questions (2 Marks)

Ques. What is a Mixture?

Ans. Mixtures are substances that are made up of two or more types of material. Air, soil, water, etc. are different examples of mixtures. Based on the nature of the components and their distribution, mixtures are classified as homogeneous and heterogeneous mixtures.

Ques. What is Osmotic Pressure?

Ans. Osmotic pressure can be defined as the minimum pressure that must be applied to a solution to halt the flow of solvent molecules through a semipermeable membrane (osmosis)

Ques: Define an ideal solution and write one of its characteristics. 

Ans: An ideal solution is a combination of substances in which the molecules of other species are different, unlike the ideal gas, the molecules in the ideal solution use forces on one another. Ideal solutions obey Raoult’s law over the entire range of concentration. Examples: n-hexane and n-heptane.

Characteristics-

Enthalpy of mixing (Δ_mixH) of the pure components to form the solution is zero. Volume of mixing (Δ_mixV) is also equal to zero.

Ques. Define the following terms: (i) Ideal solution (ii) Azeotrope 

Ans:

1. Ideal Solution - An ideal solution is a combination of substances in which the molecules of other species are different, unlike the ideal gas, the molecules in the ideal solution use forces on one another. Ideal solutions obey Raoult’s law over the entire range of concentration. 
2. Azeotrope - A mixture of two or more liquids that displays the same level of concentration in the liquid and vapour phase is known as Azeotrope. 

Ques: Differentiate between molarity and molality of a solution. 

Ans: Molarity: Molarity (M) can be defined as the number of moles of solute dissolved in one litre of solution.

Molality: Molality (m) can be defined as the number of moles of the solute per thousand grams of solvent.

If MB is the molar mass of solute, d is the density of solution then the relation between the molarity (M) of a solution and its molality (m) can be given as 

m=1000×d−M×MB1000×M

Ques. What is Raoult’s Law formula?

Ans. Raoult's is a chemical law that refers to a solution’s vapour temperature based on the mole fraction of a solution that is applied. Raoult’s law is expressed by formula, Resolution = Χsolvent x Psolvent.

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Long Answer Questions (3 Marks)

Ques. List the Properties of Solution.

Ans. 1. Different properties of solutions are:

2. It is a homogeneous mixture.
3. Its particles are too tiny and have a diameter less than 1 nm.
4. Particles don’t scatter a beam of light passing through it and hence the path of the light is not visible.
5. Solutes are inseparable from the mixture and do not sediment.

Ques. What is the Van’t Hoff Factor?

Ans. The Van’t Hoff factor offers insight on the effect of solutes on the colligative properties of solutions. It is denoted by the symbol ‘i’. The Van’t Hoff factor can be defined as the ratio of the concentration of particles formed when a substance is dissolved to the concentration of the substance by mass.

Ques. What is Boiling Point Elevation?

Ans. Boiling point elevation refers to the increase in the boiling point of a solvent upon the addition of a solute. When a non-volatile solute is added to a solvent, the resulting solution has a higher boiling point than that of the pure solvent. For example, the boiling point of a solution of sodium chloride and water is greater than that of pure water.

Ques. Give a few examples of Solutions.

Ans.

1. Air is a homogeneous mixture of gases (both the solvent and the solute are gases).
2. Sugar syrup is a solution where sugar is dissolved in water using heat ( water is the solvent and sugar is the solute).
3. Tincture of iodine, a mixture of iodine in alcohol (Iodine is the solute whereas alcohol is the solvent).

Ques. Define Association & Dissociation.

Ans. Association is the joining of two or more particles to form one entity. For example, association of two particles is the dimerization of carboxylic acids when dissolved in benzene.

Dissociation refers to the splitting of a molecule into multiple ionic entities. For example, sodium chloride (NaCl) dissociates into Na⁺ and Cl^– ions when dissolved in water.

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Very Long Answer Questions (5 Marks)

Ques. One mole of table salt is dissolved in one litre of water. At a temperature of 27ºC, what would be the osmotic temperature of this solution?

Ans. The molar concentration of table salt (sodium chloride) in the solution = 1mol/1 litre = 1M

Since salt (NaCl) dissociates into two ions, the value of the van’t Hoff factor here is 2. Converting 27ºC to the Kelvin scale, the required temperature becomes 300K.

Therefore, the osmotic pressure of the solution is:

π = (2) * (1 mol.L^-1) * (0.0821 atm.L. mol^-1.K^-1) (300 K)

π = 49.26 atm.

The osmotic pressure of the 1M salt solution is 49.26 atmospheres at a temperature of 27ºC.

Ques. Why Does Boiling Point Elevation Occur?

Ans. The boiling point of a liquid is the temperature at which its vapour pressure is equal to the pressure of its surrounding environment. Non-volatile substances do not readily undergo evaporation and have very low vapour pressures (assumed to be zero). When a non-volatile solute is added to a solvent, the vapour pressure of the resulting solution is lower than that of the pure solvent.

Therefore, a greater amount of heat must be supplied to the solution for it to boil. This increase in the boiling point of the solution is the boiling point elevation. An increase in the concentration of added solute is accompanied by a further decrease in the vapour pressure of the solution and further elevation in the boiling point of the solution.

Ques. The osmotic pressure of a potassium chloride solution (at 300K) is 50 atmospheres. What is the molar concentration of potassium chloride in this solution?

Ans. Rearranging the osmotic pressure equation, the following equation can be obtained:

π = iCRT ; C = π/(iRT)

Here, the value of i is 2 (since KCl dissociates into two ions).

Therefore, the molarity of KCl is:

C = (50 atm)/(2)*(0.0821 atm.L.mol^-1.K^-1)*(300K)

C = 50/49.26 M = 1.015 M

Therefore, the molar concentration of potassium chloride in the solution is 1.015 M.

Ques. Calculate the boiling point of a 3.5% solution (by weight) of sodium chloride in water.

Ans. 1 kg of the given solution contains 0.035kg of NaCl and 0.965kg of H₂O. Since the molar mass of NaCl is 58.5, the number of moles of NaCl in 1 kg of the solution is:

(35g)/(58.5g.mol^-1) = 0.598 moles

The molality of NaCl in 1kg of the solution:

m = (0.598mol)/(0.965 kg) = 0.619 molal

The boiling point elevation constant of water is 0.512ºC.kg/molal. Since NaCl dissociates into 2 ions, the Van’t Hoff factor for this compound is 2. Therefore, the boiling point elevation (ΔT_b) can be calculated as:

ΔT_b = 2*(0.52oC/molal)*(0.619 molal) = 0.643ºC

Boiling point of the solution = boiling point of pure solvent + boiling point elevation

= 100ºC + 0.643ºC = 100.643ºC

Therefore, the boiling point of the 3.5% NaCl solution is 100.643ºC.

Ques. An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?

Ans: Given that,

P_s= 1.004 bar

W₂=2g

Mass of solution = 100g

W₁=100−2 = 98g

M₁=18 gmol⁻¹

We know that VP of pure water, P⁰= 1atm =1.013 bar

By Raoult’s law;

1.013−1.004/1.013 = 2×18/ M₂×98

Thus, the molar mass of the solute, M₂=41.35 gmol⁻¹.

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