C12: Chemical Analysis

Question 1

What is a pure substance in chemistry?

Answer 1

A single element or compound, not mixed with any other substance

Question 2

What can be used to distinguish pure substances from mixtures?

Answer 2

Melting and boiling points

Question 3

What is a pure substance in everyday language?

Answer 3

A substance that has had nothing added to it

Question 4

What is a formulation?

Answer 4

A mixture that has been designed as a useful product

Question 5

How are formulations made?

Answer 5

By mixing the components in carefully measure quantities to ensure that the product has the required properties

Question 6

What 7 things to formulations include?

Answer 6

Fuels, cleaning agents, paints, medicine, alloys, fertilisers and food

Question 7

Give 2 reasons why chromatography is useful

Answer 7

It can separate mixtures and can give information to help identify substances

Question 8

What does the separation of mixtures depend on?

Answer 8

The distribution of substances between the phases

Question 9

What is the Rf value in words?

Answer 9

The ratio of the distance moved by a compound to the distance moved by a solvent

Question 10

What is the formula for the Rf value?

Answer 10

Distance by substance/distance by solvent

Question 11

How can you identify a pure substance using paper chromatography?

Answer 11

If it produces a single spot in all solvents

Question 12

What is the test for hydrogen?

Answer 12

The use of a burning splint held at the open end of the test tube of the gas. Hydrogen burns rapidly with a squeaky pop sound

Question 13

What is the test for oxygen?

Answer 13

The use of a glowing splint is inserted into a test tube of gas. The splint relights in oxygen

Question 14

What is the test for carbon dioxide?

Answer 14

The use of an aqueous solution of calcium hydroxide (limewater). When carbon dioxide is shaken with or bubbled through limewater, the limewater turns milky

Question 15

What is the test for chlorine?

Answer 15

The use of damp litmus paper being put into chlorine gas. It is bleached and turns white

Question 16

What are flame tests used for?

Answer 16

To identify some metal ions (cations)

Question 17

What colour is the flame when lithium compound is used?

Answer 17

Crimson red

Question 18

What compound produces a yellow flame?

Answer 18

Sodium

Question 19

What colour is the flame when calcium compound is used?

Answer 19

Orange-red

Question 20

What compound produces a lilac flame?

Answer 20

Potassium

Question 21

What colour is the flame when copper compound is used?

Answer 21

Green

Question 22

What elements in sodium hydroxide form a white precipitate?

Answer 22

Aluminium, calcium and magnesium

Question 23

What happens to aluminium hydroxide in excess sodium hydroxide?

Answer 23

The precipitate dissolves

Question 24

What colour is the copper(II) precipitate when sodium hydroxide is added in excess?

Answer 24

Blue

Question 25

What element forms a green precipitate when sodium hydroxide is added in excess?

Answer 25

Iron (II)

Question 26

What colour is the iron (III) precipitate when sodium hydroxide is added in excess?

Answer 26

Brown

Question 27

What 2 things react to form a salt, carbon dioxide gas and water?

Answer 27

Carbonates and dilute acids

Question 28

What is the test for carbonate ions?

Answer 28

Add dilute hydrochloric acid and take gas produced. Run through limewater to observe carbon dioxide production

Question 29

What is the test for sulfate ions?

Answer 29

Adding dilute hydrochloric acid, removing carbonate and sulfite ions. Add barium chloride solution to produce a white precipitate

Question 30

What is the test for halide ions?

Answer 30

Add dilute nitric acid to remove impurities. Add silver nitrate afterwards so that the silver can react with the halide ions, producing a precipitate

Question 31

What colour is the precipitate from silver chloride?

Answer 31

White

Question 32

What compound's precipitate is cream?

Answer 32

Silver bromide

Question 33

What colour is the precipitate from silver iodide?

Answer 33

Yellow

Question 34

In paper chromatography, how would you know if any of the chemicals are soluble in the solvent?

Answer 34

Then they won't be able to dissolve and move up the paper

Question 35

What is the mobile phase?

Answer 35

The solvent used

Question 36

What is the stationary phase?

Answer 36

The paper

Question 37

How do impurities affect melting and boiling points?

Answer 37

They decrease MP but increase BP

Question 38

What is the main advantage of flame emission spectroscopy?

Answer 38

The line spectrum shows lines for all elements of a compound

Question 39

What are advantages of manual methods, i.e. flame tests?

Answer 39

Basic and cheap

Question 40

What are advantages of instrumental methods?

Answer 40

Accurate, sensitive and very fast