C2. Experimental Techniques

Question 1

Apparatuses used to measure volume in order of accuracy (high to low)

Answer 1

1. Graduated pipette
2. Burette
3. Graduated cylinder
4. Volumetric flask

Question 2

How many centimetres is 1 decimetre is equivalent to?

Answer 2

1 dm = 10 cm

1 cubic dm = 1 litre = 1000 cubic cm

Question 3

Rf value

Answer 3

The distance moved by the substance divided by the distance moved by the solvent

Question 4

How do melting and boiling points change when an impurity is present?

Answer 4

The melting point falls and the boiling point rises

Question 5

How do you know if a substance is pure?

Answer 5

A pure substance will have a definite/fixed melting point and boiling point

Question 6

How do you identify colourless substances when carrying out paper chromatography?

Answer 6

You spray the chromatography paper with a locating agent (eg. Ninhydrin) in a fume cupboard, and coloured spots will appear on the chromatogram

Question 7

Why does paper chromatography work as a way to purify a substance?

Answer 7

1. The substances have different solubilities in the solvent. More soluble substances will travel faster and further up the chromatography paper
2. The substances that are more attracted to the paper will travel less.

Question 8

Uses of paper chromatography

Answer 8

1. To identify substances present in a mixture
2. To check the purity of a substance
3. To separate the substances in a mixture

Question 9

Why is evaporation until dryness not allowed to be carried out on certain substances?

Answer 9

The substance will decompose or break down to form another substance

Question 10

Use of glass beads in the fractionating column (fractional distillation)

Answer 10

The glass beads provide a large surface area for evaporation and condensation of the liquid

Question 11

Use of anti-bumping granules/boiling stones (fractional distillation)

Answer 11

To calm the boiling process/for even boiling

Question 12

Why should the thermometer be placed near the mouth of the condenser during fractional distillation?

Answer 12

This is so that the temperature will be reflected accurately and that the correct vapour will be condensed

Question 13

Uses of fractional distillation

Answer 13

1. To refine crude oil into petrol and other groups of compounds
2. In producing ethanol that is made by fermentation - ethanol is separated from the fermented mixture
3. To separate gases in liquid air

Question 14

Why does crystallisation work as a way to purify a substance?

Answer 14

Crystals of the pure substance will form as the temperature falls, leaving the impurities in the solution

Question 15

What does iodine change to when heated?

Answer 15

Iodine as a black solid sublimes to a violet vapour when heated

Question 16

Volatile liquid

Answer 16

A liquid that evaporates easily

Question 17

Saturated solution

Answer 17

A solution that can hold no more solute at a given temperature

Question 18

Precipitate

Answer 18

A solid which forms when two solutions are reacted