Aluminium
The Blast Furnace
Purification of Copper
Crude Oil
Electrolysis
Analysing Gases
Haber Process
Solubility of Salts
Steel
Test for Anions
Test for Cations
Titration

Other Section

Applied
Fundamental
Inorganic
Organic
Physical

Analysing Gases

Methods of Collection

One way for gases to be collected is over water. But this can only be done with gases that are insoluble or only slightly soluble in water (else they would dissolve and you wouldn't collect them. For example: carbon dioxide, oxygen and hydrogen.

In this method a container is filled with water, a test tube is also partially filled with water and inverted and submerged in the water - it remains full. A pipe is put under the test tube, and as gas bubbles up into the test tube, it forces water from it; so that the gas is collected in the tube.

the collection of gas over water

Another, more simple method is to displace air rather than water. If the gas has a density lower than that of air, it can be collected by upward delivery. But if, on the other hand, the gas has a density higher than air, it must be collected by downward delivery, or it would escape.

collection of gas by upward and downward delivery

The next method of collection, the gas syringe, is not only for collection but also for measuring the volume of gas collected.

Testing

GasTesting Method
Hydrogen
H2
Collect gas
Put in a burning match
It will pop.
Oxygen
O2
Collect gas
Put in a glowing match
It will reignite.
Carbon dioxide
CO2
Bubble gas through lime water (CaOH)
The water will turn cloudy
Sulphur dioxide
SO2
Collect gas
Bubble through orange potassium dichromate solution
Solution turns green.
Hydrogen Chloride
HCl
Collect gas
Mix with ammonia gas
Forms dense white fumes.
Ammonia
NH3
Collect gas
Add damp red litmus paper
Paper turns blue.