Mixtures and Separation of Mixtures (Advanced)

CBSE Science. Optional Advanced level: column chromatography, simple and fractional distillation from boiling points, crude oil fractions, percentage composition. Every sheet has 20 questions in three sections and an answer key, and the numbers change every time.

Open a printable sample sheet Cheat sheet: formulas and key points

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.
Methanol (b.p. 65 °C) and water (b.p. 100 °C) mix completely. The best way to separate them is:
1. fractional distillation
2. simple distillation
3. using a separating funnel
4. filtration
Answer
(b) simple distillation
the boiling points differ by 35 °C, which is at least 25 °C
2.
A mixture of ethanol (b.p. 78 °C) and toluene (b.p. 111 °C) is distilled. Which collects first in the receiver?
1. ethanol
2. neither: they cannot be separated
3. both together
4. toluene
Answer
(a) ethanol
the liquid with the lower boiling point, 78 °C, vaporises first
3.
A mixture of three dyes is separated on a silica gel column. How strongly each is held by the silica gel (1 weakest, 9 strongest): brown 8, pink 4, orange 1. Which dye comes out of the column first?
1. the brown dye
2. the pink dye
3. all three together
4. the orange dye
Answer
(d) the orange dye
the least strongly adsorbed component moves fastest with the solvent

Section B · short answer

4.
Name the method you would use to separate benzene (b.p. 80 °C) from toluene (b.p. 111 °C), which mix completely.
Answer
simple distillation
difference 31 °C: at least 25 °C
5.
Methanol boils at 65 °C and water at 100 °C. Find (a) the difference in their boiling points and (b) which liquid distils over first.
Answer
(a) 35 °C; (b) methanol
(a) 100 − 65; (b) the lower boiling point

Section C · long answer

6.
A mixture of heptane (b.p. 98 °C) and octane (b.p. 126 °C) is to be separated. (a) What is the difference in their boiling points? (b) Name the best method. (c) Which liquid is collected first? (d) Explain why repeated condensation and vaporisation in a fractionating column improves separation.
Answer
(a) 28 °C; (b) simple distillation; (c) heptane; (d) each time the vapour condenses and boils again on the column's surfaces it becomes richer in the lower-boiling liquid, so the vapour reaching the condenser is nearly pure
(a) 126 − 98; (b) at least 25 °C; (c) lower boiling point

Fresh sheets for your child

In the app, every Mixtures and Separation of Mixtures (Advanced) sheet is new: the app remembers the questions your child has already had and leaves them out. Print the sheet as a PDF, or use notebook mode and write the answers in a notebook.

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