SolveItClass 9 · NCERT

NCERT Solutions · Class 9 Science Exploring Mixtures and their Separation

25 questions · 21 still being checked

Revise, Reflect, Refine 5.2–5.3 (part 4 of 14)

  1. Exercise 5.2

    Choose the correct options, and explain the reason for the correct and incorrect options. Which among the following mixtures show the Tyndall Effect? A mixture of: (a) air and dust particles (b) copper sulfate and water (c) starch and water (d) acetone and water (i) a and b

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    NCERT’s answer
    (iii)
    Option (iii) — a and c.
    NCERT_Solution_Class9_Science_Ch5_RRR_Q5-2
    (a) Air and dust particles — shows the effect. The dust particles are large enough to scatter light, which is why a beam entering a dark room, or a stadium floodlight, becomes visible.
    (c) Starch and water — shows the effect. Starch does not dissolve into particles smaller than $\displaystyle 1$ nm; it forms a colloid with particles in the $\displaystyle 1$–$\displaystyle 1000$ nm range, and colloidal particles scatter light.
    (b) Copper sulfate and water — does not. It is a true solution with solute particles smaller than $\displaystyle 1$ nm, too small to scatter light, exactly like beaker A in Activity $\displaystyle 5.1$ where the laser path was invisible.
    (d) Acetone and water — does not. These are two miscible liquids, so the mixture is a homogeneous solution and the light passes straight through.
    So options (i), (ii) and (iv) all fail because each of them includes a true solution, and scattering happens in colloids and suspensions but not in transparent solutions.

  2. Exercise 5.3

    A mixture can be categorised as a solution, a suspension, or a colloid, each possessing distinct properties. Utilise the words or phrases provided in the box to fill in the Table 5.2. Words and phrases may be used more than once. Words and Phrases Large-sized particles; Particles remain evenly distributed; Small-sized particles (less than 1\displaystyle 1 nm diameter); Moderate-sized particles (1\displaystyle 1 - 1000\displaystyle 1000 nm); Settles down when left undisturbed (more than 1000\displaystyle 1000 nm in diameter); Does not settle down; Scatters light; Separates by filtration; Transparent; Salt solution; Milk; Sand in water; Smoke; Heterogeneous mixture; Cannot be separated by filtration; Mud; Butter; Brass. Complete the Table 5.2. Solution Properties __________________________ __________________________ Examples __________________________ __________________________

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    Solution
    NCERT_Solution_Class9_Science_Ch5_RRR_Q5-3
    Properties: Small-sized particles (less than $\displaystyle 1$ nm diameter); Particles remain evenly distributed; Does not settle down; Cannot be separated by filtration; Transparent.
    Examples: Salt solution; Brass.
    Suspension
    Properties: Large-sized particles (more than $\displaystyle 1000$ nm in diameter); Heterogeneous mixture; Settles down when left undisturbed; Separates by filtration; Scatters light.
    Examples: Sand in water; Mud.
    Colloid
    Properties: Moderate-sized particles ($\displaystyle 1$ - $\displaystyle 1000$ nm); Heterogeneous mixture; Particles remain evenly distributed; Does not settle down; Cannot be separated by filtration; Scatters light.
    Examples: Milk; Smoke; Butter.
    A colloid and a suspension both scatter light, so the Tyndall effect will not tell them apart; what does is particle size — $\displaystyle 1$ - $\displaystyle 1000$ nm against more than $\displaystyle 1000$ nm — and the two consequences of it: a suspension settles on standing and is held back by filter paper, while a colloid stays evenly dispersed and passes straight through.