Mixtures

Question 1

What is a pure substance?

Answer 1

A substance that consists of only one element or compound

Question 2

What is a mixture?

Answer 2

Contains two or more different substances, NOT chemically joined together

Question 3

What is filtration used for?

Answer 3

To separate an insoluble solid from a liquid

Question 4

You want to separate sand from water.

Which method should you use?

Answer 4

Filtration

Question 5

Describe the setup for filtration.

Answer 5

• Put a funnel in a conical flask
• Put folded filter paper into the funnel
• Pour a beaker containing a mixture through the filter paper / funnel

Question 6

What is crystallisation?

Answer 6

Producing crystals from a solution by evaporating the solvent

Question 7

You want to separate copper sulfate from copper sulfate solution.
Which method should you use?

Answer 7

Crystallisation

Question 8

Describe the three steps to crystalisation.

Answer 8

1. put the solution in an evaporating basin
2. warm the solution by placing the evaporating basin over a boiling water bath
3. stop heating when crystals begin to form around the edge of the basin

Question 9

When is simple distillation used?

Answer 9

To separate a solvent from a solution

Question 10

You want to produce pure water from seawater.

Which method should you use?

Answer 10

Simple distillation

Question 11

Explain how simple distillation works to separate a solvent from a solution.

Answer 11

The dissolve solute has a much higher boiling point than the solvent

Question 12

Give the three steps to simple distillation of salty water.

Answer 12

1. Salty water is heated.
2. The water vapour cools in the condenser and drips into a beaker.
3. Pure water has condensed into the beaker, and salt stays behind.

Question 13

What is the name of this process?

Answer 13

Simple distillation

Question 14

What is condensation?

Answer 14

The change from a gas to a liquid

Question 15

When is fractional distillation used?

Answer 15

To separate different liquids from a mixture of liquids

Question 16

You want to separate out the different fractions of crude oil.
Which method should you use?

Answer 16

Fractional distillation

Question 17

Why does fractional distillation work to separate out different liquids in a mixture?

Answer 17

Because the different liquids have different boiling points

Question 18

Explain what happens when a liquid is heated in fractional distillation.

Answer 18

• vapours rise through a column which is hot at the bottom, and cooler at the top
• vapours condense when they reach a part of the column that is below the temperature of their boiling point
• each liquid is led away from the column

Question 19

Which process does this show?

Answer 19

Fractional distillation

Question 20

When is paper chromatography used?

Answer 20

To separate mixtures of soluble substances

Question 21

What are the two different phases of paper chromatography?

Answer 21

• stationary phase

- mobile phase (solvent moves through paper)

Question 22

Why should pencil be used in paper chromatography?

Answer 22

Because pencil is insoluble

Question 23

Look at this chromatogram.

How many coloured dyes are in brown ink?

Answer 23

Three

Question 24

What is the name for this process?

Answer 24

Filtration