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
|Colour and smell
|Hold a glowing splint in gas
|relights/rekindles glowing splint
|Hold a lighted splint in a gas
|Burns with a squeaky pop sound
|Green Choking smell
|Hold damp litmus paper in gas
|Bleaches litmus paper
|Colourless Pungent /choking
|Hold damp red litmus paper
|Turns litmus blue
|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.