How do you identify a gas?

Identifying a gas involves a lot of steps though there is a basic chemical test for each gas which we will cover in this article. However, we can suspect the presence of gas by some basic physical properties though it won’t be conclusive.

This is because some gases have similar physical properties, for example, oxygen and nitrogen are colorless but they have different chemical tests.

Why do we need to identify a gas?

Identifying a gas is very important because it will enable us to know the specific gas we should prepare in the fume chamber because some gases are poisonous and also enable avoid mishaps in the laboratory..

Another reason to identify gases is that the explosion of gases is very fatal and consequently care needs to be taken in the storage and reaction of some gaseous industrial processes and the condition of the surrounding.

I am going to summarize the test for the common gases in olevel chemistry and still explain them in detail.

What are the tests for gases?

Carbon dioxide gas is colorless and odorless but it has a refreshing taste and that is why it is used in carbonated drinks to preserve the taste of drinks.

1. Test for carbon iv oxide gas

The test for carbon iv oxide gas is called the lime water test.. the lime water test for carbon iv oxide is used to indicate the presence of carbon iv oxide.

Lime water test for carbon dioxide equation

The lime water test has two steps

Bubbling of carbon iv oxide over lime water

Test: When you bubble carbon iv oxide over lime water, it turns the lime water milky due to the precipitation of calcium carbonate (CaCO₃)

This is the test for carbon dioxide equation

CO₂ + Ca (OH)₂ ==CaCO₃ + H₂O

On continuous bubbling of carbon IV oxide, the milky color disappears.

CaCO₃ + H₂O + CO₂== Ca (HCO₃)₂

Result: lime water turns milky and disappears after continuous bubbling

2. Test for Hydrogen

Test for hydrogen gas equation

The test for the hydrogen gs equation is the combustion of hydrogen in air to give a pop sound.

This is the hydrogen pop test equation or the burning splint test for hydrogen gas

Test: Pop test equation (burning splint test for hydrogen gas equation)

2H₂ + O₂ === 2H₂O

Result: Bring the hydrogen gas in the test tube close to a splint; hydrogen will burn with a pop sound.

3. Test for Oxygen gas

What is the test for oxygen gas called? The test for oxygen gas is called the glowing splint test.

The test for oxygen gas in chemistry is the test using a glowing splint.

Test: Bring the gas close to a splint; the oxygen gas will rekindle the glowing splint.

Result: oxygen gas relights or rekindles a glowing splint

4. Test for chlorine gas

There are two tests for chlorine gas; the litmus paper test and the starc-iodide paper test.

How do you test if chlorine is present in a sample?

First test for chlorine

The first test is the test for chlorine gas using litmus paper. This test can also serve as the confirmatory test for chlorine.

Test: Litmus paper test

Bring or hold a damp blue litmus paper close to a test tube containing chlorine gas. The chlorine gas bleaches the damp litmus paper.

Result: chlorine gas bleaches litmus paper

Second test for chlorine gas

Test: starch-iodide paper test

Bring the starch iodide close or in a test tube containing chlorine gas, the chlorine gas will displace the iodine which will turn the starch iodide paper dark blue.

The test for chlorine gas equation is thus written,

Cl₂ + 2KI == 2KCl + I₂

It is the iodine displaced that turns the starch to blue-black.

Result: The chlorine gas will turn the starch iodide paper dark blue

5. Test for ammonia gas

There are two basic tests for ammonia gas. Ammonia gas is the only alkaline gas so it can change litmus paper.

First test for ammonia gas

Test: litmus paper test

Hold a damp rd litmus paper close to the test tube containing the ammonia gas. Ammonia gas changes red litmus paper blue.

Result: ammonia changes damp red litmus paper blue

Second test for ammonia gas

Test: Dip a glass rod in concentrated acid and then insert in a gas jar or test tube containing the ammonia gas.

Result: white dense fumes of ammonium chloride will be formed

The test for ammonia gas equation is thus written;

NH₃ + HCl === NH₄Cl

6. Test for sulphur IV oxide

There are two basic chemical tests for sulphur iv oxide

We can use the acidified potassium permanganate or acidified potassium dichromate VI.

First test for sulphur iv oxide

Test: Potassium permanganate (KMnO₄) test

Bubble the sulfur IV oxide gas over acidified potassium permanganate. The gas turns the purple potassium permanganate to colourless.

Result : Sulphur iv oxide decolorizes acidified potassium permanganate from purple to colorless.

Second test for sulphur iv oxide

Test: Potassium dichromate VI test

Bubble the sulfur IV oxide gas over acidified potassium dichromate. The gas turns the orange potassium dichromate to green.

How do you test for gases collected?

The tests for gases are very simple and whether the gas is collected dry immediately from the preparation, the test result will be the same.

Summary of gas table analysis

Gas	Colour and smell	Test	Result
Oxygen	Colourless odourless	Hold a glowing splint in gas	relights/rekindles glowing splint
Hydrogen	Colourless odourless	Hold a lighted splint in a gas	Burns with a squeaky pop sound
Chlorine	Green Choking smell	Hold damp litmus paper in gas	Bleaches litmus paper
Ammonia	Colourless Pungent /choking	Hold damp red litmus paper	Turns litmus blue
Carbon dioxide	Colourless odourless	Bubble gas through lime water	Turns lime water milky
Sulphur IV dioxide	Colourless Choking smell	Bubble gas through acidified aqueous potassium mangannate VII	Turns acidified potassium mangannate vii from purple to colourless

To identify a gas, there is a need to carry out the above tests and master the results gotten from each specific test.

How do you identify a gas?