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Class 12 Solutions worksheet
CBSE Chemistry. Concentration terms, Raoult's and Henry's laws, colligative properties, van't Hoff factor. Every sheet has 20 questions in three sections and an answer key, and the numbers change every time.
Sample questions
Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.
Section A · multiple choice
- 1.
Molality is the number of moles of solute per:
- litre of solvent
- kilogram of solution
- litre of solution
- kilogram of solvent
Answer
(d) kilogram of solvent
- 2.
60 g of urea (molar mass 60 g/mol) is dissolved in 500 g of water. The molality of the solution is:
- 2 mol/kg
- 0.002 mol/kg
- 0.12 mol/kg
- 4 mol/kg
Answer
(a) 2 mol/kg
m = moles ÷ kg of solvent = 1 ÷ 0.5
- 3.
A solution of 46.5 g of ethylene glycol (M = 62 g/mol) in 200 g of water freezes at: (Kf of water = 1.86 K kg/mol, Kb = 0.52 K kg/mol)
- −1.95 °C
- −13.95 °C
- 6.975 °C
- −6.975 °C
Answer
(d) −6.975 °C
ΔTf = Kf m = 1.86 × 3.75
Section B · short answer
- 4.
Define molarity and molality. Which of them changes with temperature, and why?
Answer
Molarity is moles of solute per litre of solution; molality is moles of solute per kilogram of solvent. Molarity changes with temperature because the volume of a solution changes; molality does not.
- 5.
13.8 g of glycerol (C₃H₈O₃, M = 92 g/mol) is dissolved in water to make 500 mL of solution. Find its molarity.
Answer
0.3 M
M = moles ÷ litres = 0.15 ÷ 0.5
Section C · long answer
- 6.
Explain the four colligative properties and write the expression for each.
Answer
Relative lowering of vapour pressure: (p° − p)/p° = x(solute). Elevation of boiling point: ΔTb = Kb m. Depression of freezing point: ΔTf = Kf m. Osmotic pressure: π = CRT. All depend only on the number of solute particles; for electrolytes each is multiplied by the van't Hoff factor i.
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