Chemical analysis

Question 1

What is a pure substance?

Answer 1

A substance that only contains one element or compound

Question 2

How can you identify a pure substance?

Answer 2

By its melting/boiling point

Question 3

How can you tell if a substance is impure?

Answer 3

If its melting/boiling point is over a range of temperatures

Question 4

What is chromatography used for?

Answer 4

The separation of mixtures to identify their components

Question 5

What is the stationary phase in chromatography?

Answer 5

The paper

Question 6

What is the mobile phase in chromatography?

Answer 6

The water or solvent

Question 7

How do you calculate the Rf value in chromatography?

Answer 7

Distance moved by substance / distance moved by solvent

Question 8

How do you test for hydrogen?

Answer 8

A burning splint is held at the open end of a test tube of the gas, if hydrogen is present it will make a squeaky pop sound

Question 9

How do you test for oxygen?

Answer 9

A glowing splint is inserted into a test tube of the gas, the splint will relight if oxygen is present

Question 10

How do you test for carbon dioxide?

Answer 10

Bubbling the gas through limewater (calcium hydroxide), the limewater will turn from clear to cloudy if carbon dioxide is present

Question 11

How do you test for chlorine?

Answer 11

Damp litmus paper is put into the gas, it will bleach and turn white if chlorine is present

Question 12

What are the two ways you can test for metal ions?

Answer 12

Flame tests and drops of sodium hydroxide solution

Question 13

What colour does each metal burn:
Lithium
Sodium
Potassium
Calcium
Copper

Answer 13

Crimson
Yellow
Lilac
Orange-red
Green

Question 14

Why might a flame test not work?

Answer 14

If the substance is impure then some colours can be masked by other brighter colours

Question 15

What is the method for a flame test?

Answer 15

1) Dip the end of the wire in concentrated hydrochloric acid and heat it in a bunsen flame to clean it
2) Put the wire into the solid/compound
3) Hold the wire in the flame to see what colour is produced

Question 16

When a few drops of sodium hydroxide are added, which metals produce a white precipitate?

Answer 16

Aluminium, calcium and magnesium

Question 17

When a few drops of sodium hydroxide are added, what colour precipitate does iron (II) produce?

Answer 17

A green precipitate

Question 18

When a few drops of sodium hydroxide are added, what colour precipitate does iron (III) produce?

Answer 18

A brown precipitate

Question 19

When a few drops of sodium hydroxide are added, what colour precipitate does copper produce?

Answer 19

A blue precipitate

Question 20

What metal produces a precipitate that then dissolves if sodium hydroxide is added in excess?

Answer 20

Aluminium

Question 21

How would you produce ammonia?

Answer 21

By adding sodium hydroxide and warming the solution gently; the ammonium ions should produce ammonia

Question 22

How would you test for ammonia / tell if it’s present?

Answer 22

It has a very strong smell however is colourless
It would also turn damp litmus paper blue

Question 23

How would you test for a carbonate?

Answer 23

Any carbonate will produce CO2 when a dilute acid is added and then you would use the limewater test

Question 24

What is the word equation for the limewater test?

Answer 24

Calcium hydroxide + carbon dioxide → calcium carbonate + water

Question 25

Why does the limewater turn from clear to cloudy when CO2 is present?

Answer 25

Because calcium carbonate is produced which is a solid, turning it cloudy

Question 26

How do you test for a halide ion?

Answer 26

You add silver nitrate solution (with dilute nitric acid) to a sample of the halide

Question 27

What precipitate is formed when silver nitrate solution is added to chlorine?

Answer 27

A white precipitate of silver chloride

Question 28

What precipitate is formed when silver nitrate solution is added to bromine?

Answer 28

A cream precipitate of silver bromide

Question 29

What precipitate is formed when silver nitrate solution is added to iodine?

Answer 29

A yellow precipitate of silver iodide

Question 30

How do you test for sulphates?

Answer 30

You add hydrochloric acid and barium chloride solution, a white precipitate of barium sulphate will form if the sulphate is present

Question 31

What are some examples of instrumental analysis?

Answer 31

Mass spectrometry Flame emission spectroscopy Gas chromatography

Question 32

What are the pros and cons of instrumental analysis?

Answer 32

Pros- Uses smaller samples Fast Accurate Gives a lot of information Cons- Machines / instruments can be expensive

Question 33

What are the pros and cons of chemical analysis?

Answer 33

Pros- Often simple to do Cons- It uses up the sample

Question 34

What is flame emission spectroscopy used for and how is it better than a flame test?

Answer 34

To identify different ions in mixtures; this makes it more useful than flame tests which only work for substances that contain a single metal ion

Question 35

How does flame emission spectroscopy work?

Answer 35

By measuring the specific wavelength of the light emitted by each ion

Question 36

What is a formulation?

Answer 36

A mixture of different substances that forms a useful product

Question 37

What is each part of a formulation called?

Answer 37

A component