Vidaara.orgClass 9 · Chemistry
CodeVID-C9-02-T1-01
Assignment — Mixtures, Solutions & Concentration
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Which is a pure substance?
- A.Air
- B.Brass
- C.Distilled water
- D.Soil
2.
The size of particles in a true solution is:
- A.less than 1 nm
- B.1 to 100 nm
- C.more than 100 nm
- D.more than 1 mm
3.
Milk is an example of a:
- A.true solution
- B.suspension
- C.colloid
- D.element
4.
The maximum amount of solute that dissolves in 100 g of solvent at a given temperature is called:
- A.concentration
- B.solubility
- C.saturation point
- D.mass percentage
5.
A solution that can still dissolve more solute at a given temperature is:
- A.saturated
- B.unsaturated
- C.colloidal
- D.heterogeneous
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Distinguish between a homogeneous and a heterogeneous mixture with one example each.
7.
Define solute and solvent using the example of a copper sulphate solution.
8.
15 g of urea is dissolved in 85 g of water. Find the mass percentage of urea.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Compare a true solution, a colloid and a suspension on the basis of particle size, settling and the Tyndall effect.
10.
Calculate the mass of sugar and water needed to make 400 g of a 5% (by mass) sugar solution.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Explain what is meant by a colloid. Describe the Tyndall effect with a daily-life example, and classify fog, milk and jelly by naming the dispersed phase and dispersion medium.
Answer Key
Section A — Multiple Choice Questions
- (C) Distilled water
- (A) less than 1 nm
- (C) colloid
- (B) solubility
- (B) unsaturated
Section B — Short Answer (2 marks)
- A homogeneous mixture has uniform composition with no visible parts (e.g. salt solution); a heterogeneous mixture has non-uniform composition with visible parts (e.g. sand and salt).
- The solvent is the larger component (water) that dissolves the solute; the solute is the dissolved component (copper sulphate), present in smaller amount.
- Mass of solution = 15 + 85 = 100 g; mass % = (15 / 100) x 100 = 15%.
Section C — Short Answer (3 marks)
- True solution: particles < 1 nm, do not settle, no Tyndall effect. Colloid: 1-100 nm, do not settle, shows Tyndall effect. Suspension: > 100 nm, settle on standing, scatter light strongly.
- Mass of sugar = (5 / 100) x 400 = 20 g; mass of water = 400 - 20 = 380 g.
Section D — Long Answer (5 marks)
- A colloid is a heterogeneous mixture whose particles (1-100 nm) appear evenly spread but actually form a separate phase. The Tyndall effect is the scattering of light by these particles, making the beam visible — seen when sunlight enters a dusty room or headlights cut through fog. Fog is an aerosol (liquid droplets dispersed in gas); milk is an emulsion (liquid fat dispersed in liquid water); jelly is a gel (liquid dispersed in a solid).
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