1 Elements, Compounds and Mixtures

Question 1

What is an element?

Answer 1

Substances that can’t be split into anything simpler by chemical means. It contains only one type of atom.

Question 2

What is a compound?

Answer 2

When two or more elements are chemically combined and are always in fixed proportion.

Question 3

How do we seperate the elements in a compound?

Answer 3

With a chemical reaction.

Question 4

What is a mixture?

Answer 4

Different elements or compounds not chemically combined together.

Question 5

How can mixtures be seperated?

Answer 5

By physical means.

Question 6

What kind of things melt and boil at a fixed temperature?

Answer 6

• Pure substances
• Elements
• Pure compounds

Question 7

What happens to the melting and boiling point of mixtures?

Answer 7

They melt and boil over a range of temperatures.

Question 8

How does the presence of impurities affect the melting and boiling points?

Answer 8

• They lower the melting point
• They raise the boiling point

Question 9

What are physical separation techniques used for?

Answer 9

To separate mixtures.

Question 10

What are the separation techniques used for?

Answer 10

• Simple distillation
• Fractional distillation
• Filtration
• Crystallisation
• Paper chromatography

Question 11

What does insoluble mean?

Answer 11

That the solid won’t dissolve in a liquid.

Question 12

What does soluble mean?

Answer 12

That the solid will dissolve in a liquid.

Question 13

What is an aqueous solution?

Answer 13

It means that the substance is dissolved in water.

Question 14

What is filtration?

Answer 14

It is used to separate an insoluble solid from a liquid.

Question 15

What is the residue?

Answer 15

The substance left in the filter paper.

Question 16

What is the filtrate?

Answer 16

The liquid that comes through.

Question 17

What is an example of the substances that could be used in filtration?

Answer 17

Silver chloride (AgCI) and water (H2O).

Question 18

What are the results found from using filtration?

Answer 18

The insoluble solid will be on top of the filter paper, and the liquid will be in the beaker at the bottom.

Question 19

What is crystallisation?

Answer 19

It is used to separate a soluble liquid from a liquid.
(Solute from a solution).

Question 20

What is an example of substances that can be used in crystallisation?

Answer 20

Sodium chloride and water.

Question 21

How does crystallisation work?

Answer 21

The water evaporates and leaves behind the soluble solid in a crystal form.

Question 22

How can you make crystallisation happen faster?

Answer 22

You can gently heat the solution to make the water evaporate faster.

Question 23

What is simple distillation?

Answer 23

Used to separate a liquid from a solid when we want to keep the liquid.

Question 24

How does simple distillation work?

Answer 24

We evaporate the liquid by heating it and then the vapour turns back into the liquid by condensing it.

Question 25

What does the condenser do?

Answer 25

Turns the gas into a liquid.

Question 26

What is an example of substances that can be used in simple distillation?

Answer 26

Obtaining drinking water from sea water.

Question 27

What is fractional distillation?

Answer 27

Separates a mixture of liquids.

Question 28

What needs to be special about the liquids?

Answer 28

They need to have different boiling points.

Question 29

What does the fractionating column contain?

Answer 29

Glass beads.

Question 30

How do the glass beads help in fractional distillation?

Answer 30

Their high surface area in the column help with the separation of the vapours.

Question 31

What is chromatography?

Answer 31

It allows us to separate substances based on their different solubilities.

Question 32

How does chromatography work?

Answer 32

The solvent makes its way up the paper and brings the ink with it.

Question 33

What does the line on the chromatography paper have to be made out of and how much further up does it have to be from the bottom of the paper?

Answer 33

Pencil and 10cm up.

Question 34

Why does it have to be pencil?

Answer 34

Because if it was pen, the ink would move up the paper with the solvent.

Question 35

What does it mean if there are multiple spots?

Answer 35

It is a mixture of substances.

Question 36

What does it mean if there is only one spot?

Answer 36

The substance is pure - only made up of one colour.

Question 37

What is the solvent front?

Answer 37

The highest level of the solvent on the paper at any time.

Question 38

What is the solvent usually made from?

Answer 38

A non-aqueous solution.

Question 39

What affects the result found in chromatography?

Answer 39

- Their affinity (stickiness to the paper) - How soluble they are (moves up the paper)

Question 40

What is a chromatogram?

Answer 40

The pattern you get.

Question 41

What does it mean if the dye doesn't move?

Answer 41

It is not soluble in the solvent.

Question 42

What does it mean if the dye moves too much up the paper?

Answer 42

It is too soluble in the solvent.

Question 43

What does the retardation factor show?

Answer 43

It is a value to describe how far the spots move.

Question 44

How do you work out the retardation factor?

Answer 44

Distance moved by a spot (from the pencil line) / Distance moved by the solvent front (from the pencil line)