Separation Techniques

Question 1

What is a pure substance?

Answer 1

A pure substance is a single substance not mixed with anything else. They can be elements or compounds

Question 2

How is a pure substance identified?

Answer 2

Melting/Boiling Points:
Pure substances have a fixed melting/boiling point whereas mixtures boil over a range of temperature

Chromatography:
Pure substances only have 1 spot on the chromatogram.

Question 3

Which method of separation do we use to separate a solid-solid mixture that contains a magnetic solid?

Answer 3

Magnetic attraction

Question 4

Which method of separation do we use to separate a solid-solid mixture that contains a solid which sublimes?

Answer 4

Sublimation

Question 5

Which method of separation do we use to separate an insoluble solid-liquid mixture?

Answer 5

Filtration

Question 6

Which method of separation do we use to separate soluble solid-liquid mixture where solid doesn’t decompose to get a solid?

Answer 6

Evaporation

Question 7

Which method of separation do we use to separate a soluble solid-liquid mixture where the solid decomposes to get a solid?

Answer 7

Crystallisation

Question 8

Which method of separation do we use to separate a soluble solid-liquid mixture where we want to obtain the liquid?

Answer 8

Distillation

Question 9

Which method of separation do we use to separate a liquid-liquid mixture with miscible liquids?

Answer 9

Fractional distillation

Question 10

Which method of separation do we use to separate a liquid-liquid mixture with immiscible liquids?

Answer 10

Separating funnel

Question 11

What are the substances that can undergo sublimation?

Answer 11

1. Solid carbon dioxide (dry ice)
2. Iodine
3. Ammonium chloride

Question 12

What is the difference between evaporation and crystallisation in terms of heating

Answer 12

In evaporation, we heat the mixture until all liquid evaporates but in crystallisation, we heat until we obtain a saturated solution and allow it to cool.

Question 13

How are the different liquids in a mixture separated?

Answer 13

Separation is based on the fact that different liquids boil at different temperature. Liquid with lowest BP boils first hence will also be collected first.

Question 14

Why is chromatography used?

Answer 14

To determine the number and identity of
components in a mixture

Question 15

When can chromatography be used?

Answer 15

Can be used for very small amounts of
samples

Question 16

Real life examples of chromatography being used

Answer 16

number of and the colours present in substances such as food dyes, ink, paint, and the chemicals used in a drug.

Question 17

Why do we draw the line in pencil when doing chromatography?

Answer 17

Because
ink will dissolve in the
solvent.

Question 18

What does the spot staying on the line indicate?

Answer 18

It’s insoluble in the solvent

Question 19

What is a locating agent used for?

Answer 19

To identify colourless substances