Chemical Test

Question 1

Test for hydrogen gas

Answer 1

Hold a lighted splint to the mouth of test tube. It explodes with a squeaky pop sound.

Question 2

Test for oxygen gas

Answer 2

A glowing splint is put into the test tube. It relights.

Question 3

Test for carbon dioxide gas

Answer 3

Bubble the gas through limewater. The limewater turns milky.

Question 4

Test for chlorine gas

Answer 4

Test the gas with a damp litmus paper. The litmus turns red then white.

Question 5

Test for ammonia gas

Answer 5

Add sodium hydroxide solution. A gas with pungent smell is produced.
Test the gas with a damp red litmus paper. Litmus paper turns blue.

Question 6

Test for water

Answer 6

Add anhydrous copper (II) sulfate. The solution turns blue.

Question 7

Test for pure water

Answer 7

Measure boiling point
It boils exactly at 100 degrees celsius
Measure melting point
It melts exactly at 0 degree celsius
If it is impure, it boils at a higher temperature and melts at a lower temperature.

Question 8

Test for cations

Answer 8

Flame Test
Precipitation

Question 9

Test for anions

Answer 9

Precipitation

Question 10

Lithium flame colour

Answer 10

Red

Question 11

Sodium flame colour

Answer 11

Yellow

Question 12

Potassium flame colour

Answer 12

Lilac

Question 13

Calcium flame colour

Answer 13

Orange-red

Question 14

Copper flame colour

Answer 14

Blue-green

Question 15

How to test cations using flame test

Answer 15

• a platinum or nichrome wire is dipped into concentrated hydrochloric acid
• dip the salt with the wire
• hold the wire and salt just within a non-luminous (roaring) bunsen burner flame
• observe the flame colour

Question 16

Why is it important to clean the wire?

Answer 16

To prevent any other substances interrupting the flame colour

Question 17

Why is important to use platinum or nichrome wire?

Answer 17

Unreactive and have high melting points

Question 18

Why does the bunsen burner flame need to be non-luminous?

Answer 18

To observe the flame colour clearly

Question 19

Copper precipitate colour

Answer 19

Blue

Question 20

Iron (II) precipitate colour

Answer 20

Green

Question 21

Iron (III) precipitate colour

Answer 21

Orange-brown

Question 22

Test for carbonates

Answer 22

• add dilute hydrochloric acid
• a gas is given off as fizzing occurs
• bubble the gas through limewater
• limewater turns milky

Question 23

Test for sulfates

Answer 23

• add dilute hydrochloric acid followed up by barium chloride solution
• white precipitate is formed

Question 24

Why is acid needed in testing sulfates?

Answer 24

To remove other anions which might also produce white precipitate

Question 25

Why is sulfuric acid unsuitable for sulfate test?

Answer 25

- it contains sulfate ions - barium sulfate will be produced because of the sulfate ions from the sulfuric acid

Question 26

Test for halides

Answer 26

- add dilute nitric acid followed by silver nitrate solution chloride ions : white precipitate bromide ions : cream precipitate iodide ions : yellow precipitate