SolveItClass 9 · NCERT

NCERT Solutions · Class 9 Science Exploring Mixtures and their Separation

25 questions · 21 still being checked

Revise, Reflect, Refine 5.5–5.6 (part 8 of 14)

  1. Exercise 5.5

    The label on a cooking oil pack says one litre (910\displaystyle 910 g). If this oil is mixed with water, will it form a separate layer? If so, which substance will be on top? How will you separate the two layers? Also, draw the diagram of the apparatus used.

    Not cross-checked

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

    Yes, two separate layers form, with the oil on top, and the two are separated using a separating funnel.
    NCERT_Solution_Class9_Science_Ch5_RRR_Q5-5
    Oil and water are immiscible, so they never form a single uniform liquid however much they are shaken.
    One litre of the oil has a mass of $\displaystyle 910$ g while one litre of water has a mass of about $\displaystyle 1000$ g, so the oil is the lighter liquid: \(\displaystyle \text{density of oil} = \dfrac{910\ \text{g}}{1000\ \text{mL}} = 0.91\ \text{g/mL} \) against \(\displaystyle 1\ \text{g/mL} \) for water.
    The less dense liquid floats, so oil is the upper layer and water the lower layer.
    Method: pour the mixture into a separating funnel, close the stopper and let it stand undisturbed until the boundary between the layers is sharp; open the stopcock slowly and run the lower water layer into a beaker; close the stopcock when the water is almost drained; discard the small middle portion that contains both liquids; then open the stopcock again and collect the oil in a separate vessel.
    Diagram to draw: a pear-shaped separating funnel clamped upright in a laboratory stand, a glass stopper at the top, the funnel showing two layers separated by a straight horizontal boundary — the upper one labelled oil and the lower one labelled water — the narrow stem below carrying the stopcock, and a conical flask placed under the stem to receive the liquid that is run off. Every one of those seven parts must be labelled with a leader line.

  2. Exercise 5.6

    Assertion (A): Solutions do not exhibit the Tyndall effect. Reason (R): The particles in solutions are larger than 100\displaystyle 100 nm, so they cannot scatter light. Choose the correct option: (i) Both A and R are true, and R is the correct explanation of A. (ii) Both A and R are true, but R is not the correct explanation of A. (iii) A is true, but R is false. (iv) A is false, but R is true.

    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 is true, but R is false.
    Assertion is true: a solution does not show the Tyndall effect, which is why the laser beam left no visible path through the salt solution in Activity 5.1.
    Reason is false on the number: the particles in a solution are the smallest of all — less than $\displaystyle 1$ nm in diameter, not larger than $\displaystyle 100$ nm. Particles larger than $\displaystyle 1000$ nm are found in suspensions.
    The correct reason is the opposite of the one given: solution particles are too small to scatter light, so the beam passes straight through and the solution looks transparent.