qualitative analysis: test for gases

Question 1

Hydrogen
Colour and odour
Test
Observation

Answer 1

colourless and odourless

Place a lighted splint into the gas
Lighted splint extinguishes with a ‘pop’ sound

Question 2

Oxygen
Colour and odour
Test
Observation

Answer 2

Colourless and odourless
Place a glowing splint into the gas
glowing splint is rekindled/reignites

Question 3

Carbon Dioxide
Colour and odour
Test
Observation

Answer 3

colourless and odourless
pass the gas into limewater (calcium hydroxide)
gas evolved forms a white ppt with limewater

**white ppt dissolves when more CO2 is continuously passes into limewater to form soluble calcium hydrogen carbonate

Question 4

Chlorine
Colour and odour
Test
Observation

Answer 4

greenish-yellow gas with a pungent smell
use a piece of moist blue litmus paper
moist blue litmus paper turns red, then bleached (white)

Question 5

Sulfur dioxide
Colour and odour
Test
Observation

Answer 5

colourless gas with a pungent smell
i) pass the gas into acidified potassium manganate(VII)

purple solution decolourises (turns from purple to colourless)
or
ii)use a piece of moist blue litmus paper

moist blue litmus paper turns red

Question 6

Ammonia
Colour and odour
Test
Observation

Answer 6

colourless gas with a pungent smell
i)use a piece of moist red litmus paper (at the mouth of the test tube)
moist red litmus paper turns blue
or
ii) with hydrogen chloride (gas)
white smoke is observed

Question 7

water vapour
Colour and odour
Test
Observation

Answer 7

colourless and odourless (condenses on the cooler part of the test tube)
I) use anhydrous copper(II) sulfate
anhydrous copper(II) sulfate changes from white to blue
II) use cobalt(II) chloride paper
cobalt(II) chloride paper changes from blue to pink