QA Part I

Question 1

What is the colour and odour of hydrogen gas (H2)?

Answer 1

Colourless and odourless

Question 2

What is the result of the litmus test for hydrogen gas?

Answer 2

Nothing. No effect.

Question 3

What confirmation test do we use for hydrogen gas?

Answer 3

Lighted splint test. Place a lighted splint a test tube containing the gas. The lighted splint will extinguish with a ‘pop’ sound.

Question 4

What is the colour and odour of carbon dioxide?

Answer 4

Colourless and odourless

Question 5

What is the litmus test result for carbon dioxide?

Answer 5

Turns moist blue litmus paper red.

Question 6

What is the confirmation test for carbon dioxide gas?

Answer 6

Bubble the gas into limewater (calcium
hydroxide). A white precipitate of Calcium
Carbonate will form. Calcium carbonate will
dissolve in excess carbon dioxide gas.

If the limewater becomes chalky then carbon dioxide is present.

Question 7

What is the colour and odour of oxygen gas?

Answer 7

Colourless and odourless.

Question 8

What is the litmus test result for oxygen gas?

Answer 8

No effect.

Question 9

What is the confirmation test for oxygen gas?

Answer 9

Place a glowing splint (like a joss stick) in the gas

and the glowing stick will relight.

Question 10

What is the colour and odour of ammonia gas?

Answer 10

It is a colourless and pungent smelling gas.

Question 11

The confirmation test for ammonia is litmus test. What is the result of the test and why do we only need to perform a litmus test?

Answer 11

Turns moist red litmus paper blue (ammonia is the only alkaline gas in this list)

Question 12

What is the colour and odour of chlorine gas?

Answer 12

Greenish-yellow colour and irritating smell.

Question 13

What is the litmus test result for chlorine gas (it is also the only the confirmation test).

Answer 13

Bleaching effect on litmus paper. Turn moist blue litmus paper red and then bleach the litmus paper, turning it white.

Question 14

What is the colour and odour of sulfur dioxide gas?

Answer 14

Colourless and choking-smelling gas

Question 15

What is the litmus test result for sulfur dioxide gas?

Answer 15

Turns moist blue litmus paper red.

Question 16

What is the confirmation test for sulfur dioxide gas?

Answer 16

Place a piece of paper soaked with acidified
potassium manganate (VII)/ potassium
dichromate in the gas.
The acidified potassium manganate (VII) will turn
from purple to colourless. The acidified potassium dichromate will turn from orange to green.

Question 17

What is the colour and odour of water vapour?

Answer 17

Colourless and odourless.

Question 18

What is the litmus test result for water vapour?

Answer 18

Nothing you balless boy

Question 19

What is the confirmation test for water vapour?

Answer 19

Turns cobalt(II) chloride paper from blue to pink.

Question 20

Why does a white precipitate form in the limewater test for carbon dioxide?

Answer 20

Calcium hydroxide reacts with carbon dioxide to form insoluble calcium carbonate. The insoluble calcium carbonate will react with excess carbon dioxide to form soluble calcium hydrogen
carbonate/calcium bicarbonate

Question 21

How do you conduct tests for aqueous cations?

Answer 21

1. Add a few drops of sodium hydroxide solution/aqueous ammonia and observe the colour of the precipitate.
2. Add excess of sodium hydroxide solution/aqueous ammonia and observe if the precipitate dissolves.

Question 22

How do you test for ammonium ion with sodium hydroxide (no visible change with aq ammonia)

Answer 22

No precipitate forms. On heating, a pungent-smelling gas (Ammonia) which turns moist red litmus
paper blue is produced.

Question 23

How do you test for lead (II) ion in sodium hydroxide and aq. ammonia?

Answer 23

White ppt. of Pb(OH)2 is formed in both.

Pb(OH)2 dissolves in excess NaOH to form a colourless solution.

Pb(OH)2 is insoluble in excess aq. ammonia.

Question 24

How do you test for aluminium ion in NaOH and aq. ammonia?

Answer 24

White ppt. of Zn(OH)2 is formed in both.

Zn(OH)2 dissolves in excess NaOH to form a colourless solution.

Zn(OH)2 is insoluble in excess aq. ammonia.

Question 25

How do you test for zinc ion?

Answer 25

White precipitate of Zn(OH)2 | is formed which dissolves in excess NaOH/ excess NH3 to form a colourless solution.

Question 26

How do you test for copper (II) ion?

Answer 26

Light blue precipitate of Cu(OH)2 is formed in both. Cu(OH)2 is insoluble in excess NaOH, but dissolves in excess NH3 to form a dark blue solution.

Question 27

How do you test for Calcium ion?

Answer 27

White precipitate of Ca(OH)2 is formed which is insoluble in excess NaOH. There is no visible changes in aq. ammonia as no precipitate is formed.

Question 28

How do you test for iron (II) ion?

Answer 28

Green precipitate of Fe(OH)2 is formed which is insoluble in excess NaOH/ excess NH3 . The precipitate turns brown on standing (when you leave it alone forlong enough.)

Question 29

How do you test for iron (III) ion?

Answer 29

Reddish-brown precipitate of Fe(OH)3 is formed which is insoluble in excess NaOH/ excess NH3. The precipitate turns brown on standing because it oxidises into iron (III) ions.