4.6 - Chemical analysis

Question 1

Test for hydrogen

Answer 1

1. Collect sample of gas in test tube
2. Ignite using lit splint
3. Result = squeaky pop

Question 2

Test for oxygen

Answer 2

1. Collect a sample of gas in test tube
2. Place glowing splint in test tube
3. Result = splint relights

Question 3

Chemical test for water

Answer 3

1. Add anhydrous copper sulfate
2. Result = Changes from white to blue

Question 4

Physical test for water

Answer 4

1. Measure BP
2. Result = BP is 100 degrees

Question 5

Test for carbon dioxide

Answer 5

1. Bubble a sample of the gas through limewater.
2. Result = solution turns cloudy

Question 6

Test for chlorine

Answer 6

1. Place damp blue litmus paper in a sample of gas.
2. Result = it turns white (bleaches).

Question 7

Test for ammonia

Answer 7

1. Place damp red litmus paper in a sample of gas.
2. Result = it turns blue

Question 8

How to conduct a flame test.

Answer 8

1. Dip a piece of nichrome / platinum wire into hydrochloric acid. These wires don’t colour the flame, and the acid cleans the wire.
2. Dip the wire into a sample of solid or solution. This causes some of the sample to stick onto the wire.
3. Place the tip of the wire into a non-luminous Bunsen flame.

Question 9

What does a flame test test for?

Answer 9

What type of metal cation is in a substance

Question 10

Flame colour of lithium (Li) ?

Answer 10

Red

Question 11

Flame colour of sodium (Na) ?

Answer 11

Yellow

Question 12

Flame colour of potassium (K) ?

Answer 12

Lilac

Question 13

Flame colour of calcium (Ca) ?

Answer 13

Orange-red

Question 14

Flame colour of copper (Cu) ?

Answer 14

Blue-green

Question 15

How do you conduct a sodium hydroxide (NaOH) test?

Answer 15

1. Dissolve the sample in water.
2. Add a few drops of NaOH(aq).

Question 16

What is a sodium hydroxide test testing for?

Answer 16

To see in Cu, Fe(II) or Fe (III) is present

Question 17

What colour precipitate is formed with Cu?

Answer 17

Blue

Question 18

What colour precipitate is formed with Fe(II) ?

Answer 18

Green

Question 19

What colour precipitate is formed with Fe(III) ?

Answer 19

Brown

Question 20

How to conduct an ammonium test

Answer 20

1. Dissolve the sample in water.
2. Add some NaOH(aq) and warm it.
3. Test the gas evolved with damp red litmus paper

Question 21

What happens if ammonium ions are present?

Answer 21

Litmus will turn blue.

Question 22

How to conduct a halide test?

Answer 22

1. Dissolve the sample in water.
2. Add nitric acid (HNO3).
3. Add silver nitrate (AgNO3) solution.

Question 23

What are we testing for with a halide test?

Answer 23

If Cl−, Br− or I− ions are present

Question 24

What colour precipitate does Cl form?

Answer 24

White

Question 25

What colour precipitate does Br form?

Answer 25

Cream

Question 26

What colour precipitate does I form?

Answer 26

Yellow

Question 27

Why do we add HNO3 in the halide test?

Answer 27

1. Ag ions also form precipitates with OH and CO3.
2. The HNO3 reacts with those anions and prevents false positives

Question 28

How to conduct a test for carbonates?

Answer 28

1. Add hydrochloric acid (HCl), look for effervescence.
2. If there is effervescence, bubble the gas through limewater

Question 29

If carbonate ions are present what colour does the limewater go?

Answer 29

Cloudy

Question 30

Why do we check the gas is CO2 in the carbonate test?

Answer 30

To prevent false positives

Question 31

How to conduct a test for sulfates?

Answer 31

1. Add hydrochloric acid (HCl), look for effervescence.
2. If there’s no effervescence, add barium chloride (BaCl2) solution.

Question 32

What happens if sulfate ions are present?

Answer 32

White precipitate will be formed

Question 33

Why do we add HCl is the sulfate test?

Answer 33

Because carbonate atoms also form a white precipitate white Ba ions. So we prevent false positives.