Question 1

A solution is prepared by dissolving 68 g of sucrose (C₁₂H₂₂O₁₁) in sufficient water to make 500 mL of solution. Calculate the molarity. (Molar mass of sucrose = 342 g/mol)

Accepted Answer

Molarity = (moles of solute) / (volume in L) = (68/342) / 0.5 = 0.4 M.

Question 2

A solution contains 36 g of glucose (C₆H₁₂O₆) dissolved in 1000 g of water. Calculate the molality of the solution. (Molar mass of glucose = 180 g/mol)

Accepted Answer

Molality = (moles of solute) / (mass of solvent in kg) = (36/180) / 1 = 0.2 m.

Question 3

Which of the following is a colligative property of solutions?

Accepted Answer

Boiling point elevation depends only on the number of solute particles, not their identity, making it a colligative property.

Question 4

A 2.0 M solution of NaCl is prepared. What is the mass of NaCl required to prepare 500 mL of this solution? (Molar mass of NaCl = 58.5 g/mol)

Accepted Answer

Mass = Molarity × Volume (L) × Molar mass = 2.0 × 0.5 × 58.5 = 58.5 g.

Question 5

What is the mole fraction of solute in a solution containing 46 g of ethanol (C₂H₅OH) dissolved in 72 g of water? (Molar mass: ethanol = 46 g/mol, water = 18 g/mol)

Accepted Answer

Moles of ethanol = 46/46 = 1; moles of water = 72/18 = 4; mole fraction = 1/(1+4) = 0.2, or approximately 0.25.

Question 6

A solution is prepared by dissolving 5.85 g of NaCl in 1 L of water. If the density of the solution is 1.005 g/mL, what is the molarity of the solution? (Molar mass of NaCl = 58.5 g/mol)

Accepted Answer

Molarity = moles/volume in L = (5.85/58.5)/1 = 0.1 M.

Question 7

Which of the following is NOT a colligative property of solutions?

Accepted Answer

Color depends on the nature of solute molecules, not on the number of solute particles, so it is not a colligative property.

Question 8

If the osmotic pressure of a solution at 27°C is 4.92 atm, what is the molarity of the solution? (R = 0.082 L·atm·mol⁻¹·K⁻¹)

Accepted Answer

Using π = MRT, M = π/(RT) = 4.92/(0.082 × 300) = 0.2 M.

Question 9

A solution contains 36 g of glucose (C₆H₁₂O₆) dissolved in 1000 g of water. What is the molality of this solution? (Molar mass of glucose = 180 g/mol)

Accepted Answer

Molality = moles of solute/kg of solvent = (36/180)/1 = 0.2 m.

Question 10

The freezing point of a 0.5 m aqueous solution of a non-electrolyte is lowered by approximately:

Accepted Answer

ΔTf = Kf × m = 1.86 × 0.5 = 0.93°C (Kf for water = 1.86 K·kg·mol⁻¹).

Question 11

Which term describes the pressure required to prevent the flow of solvent into a solution across a semipermeable membrane?

Accepted Answer

Osmotic pressure is the minimum pressure needed to prevent osmosis and the inward flow of solvent molecules.

Question 12

A solution prepared by dissolving 34.2 g of sucrose (C₁₂H₂₂O₁₁) in 200 mL of water has what approximate mass percentage of sucrose? (Molar mass of sucrose = 342 g/mol; assume density of solution ≈ 1 g/mL)

Accepted Answer

Mass % = (mass of solute / total mass of solution) × 100 = (34.2 / 234.2) × 100 ≈ 14.6%.

Question 13

The van't Hoff factor (i) for a 0.1 m CaCl₂ solution is approximately 3. What is the freezing point depression of this solution? (Kf = 1.86 K·kg·mol⁻¹)

Accepted Answer

ΔTf = i × Kf × m = 3 × 1.86 × 0.1 = 0.558°C (CaCl₂ dissociates into 3 ions, hence i ≈ 3).

Question 14

A solution is prepared by dissolving 6.84 g of a solute in 100 g of water at 25°C. If the relative molecular mass of the solute is 228 and the density of the solution is 1.08 g/mL, calculate the molality of the solution.

Accepted Answer

Molality = moles of solute / mass of solvent in kg = (6.84/228) / 0.1 = 0.03 / 0.1 = 0.3 mol/kg.

Question 15

At 20°C, the solubility of KNO₃ is 13.3 g per 100 g of water. What is the mass percentage of KNO₃ in a saturated solution at this temperature?

Accepted Answer

Mass percentage = (mass of solute / mass of solution) × 100 = (13.3 / (100 + 13.3)) × 100 = 11.7%.

Question 16

An aqueous solution contains 5.85 g of NaCl (M = 58.5 g/mol) dissolved in 500 mL of water. Assuming the density of the solution is 1.02 g/mL, calculate the molarity of the NaCl solution.

Accepted Answer

Molarity = moles of solute / volume of solution in liters = (5.85/58.5) / 0.5 = 0.1 / 0.5 = 0.20 M.

Agniveer Army Technical Solutions

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