Testing Ammonia Gas in Laboratory | Identify Ammonia

There are several tests for ammonia gas to identify from other gases. Ammonia is an inorganic compound which has hazardous characteristics and also a very important gas in chemistry and chemical industries. Here we are going to discuss, how we identify or test ammonia gas in the laboratory by different experiments. Doing experiments with ammonia and such other toxic gases, you should be very careful about safety of you and people around you.

Content

Lewis structure of ammonia molecule
Characteristics of ammonia gas
Experiments for testing ammonia gas
Example problems and questions, how to identify ammonia from other gases
- Sulfur dioxide (SO₂)
- Hydrogen sulfide (H₂S)
- Nitrogen dioxide (NO₂)
- Carbon dioxide (CO₂)
- Chlorine (Cl₂)
Ammonia gas can form metal hydroxide precipitates with some metal cations
Ammonia will turn red litmus to blue litmus

Lewis structure of ammonia molecule

Lewis structure of ammonia gas is a simple one because there are only two elements and four atoms in the molecule.

Before learn experiments, we should learn about characteristics of ammonia gas. It will help to understand the experiments very well.

Characteristics of ammonia gas

Colourless - You cannot see a colour such as brown colour of Nitrogen dioxide (NO₂)
Toxic - Ammonia is a highly poisonous gas. Don't try to inhale to feel the gas. Inhaling ammonia to your body may cause death.
Alkaline - Ammonia dissolves very well in water give a alkaline aqueous solution. Therefore, pH value of aqueous ammonia solution will be higher than seven.
Has an unpleasant smell - But never try to experience this.

Identify ammonia gas - experiments

Following experiments can be done to identify ammonia gas in the laboratory. But, some experiments cannot done. They are noted specially because those experiments can cause injuries to you. Those are helpful to identify when you feel like a leakage of ammonia gas.

Add nessler reagent, then it will turn into brown colour.
When get close to the concentrated HCl bottle lid, ammonium chloride (NH₄Cl ), a white solid fog will be formed.
Ammonia has an unpleasant smell and is a basic gas (form an alkaline solution in the water).
As basic characteristics, ammonia gas can behave as an acid also. As a proof, metallic sodium reacts with ammonia gas and release hydrogen gas as a typical metal - acid reaction.
Ammonia will turn red litmus to blue litmus.
NH₃ dissolve very well in water. Then check the pH of solution. You can see pH is greater than 7. It says aqueous ammonium solution is a basic one.
A colourless gas.

Testing ammonia gas from pH value

Send ammonia gas to a dilute water and measure the pH. What will you see? Obviously, you see the pH value is greater than 7.

Identify ammonia gas from other gases

In next section, we are going to discuss how to identify ammonia gas from other different gases. These gases may contain similar properties to ammonia.

Ammonia is identified from following gases in this section.

Sulfur dioxide - SO₂
Hydrogen sulfide - H₂S
Nitrogen dioxide - NO₂
Carbon dioxide - CO₂
Chlorine - Cl₂

Identify ammonia gas from Sulfur dioxide

Colour: Both ammonia gas and Sulfur dioxide gas are colourless. So, we cannot identify these two gases by observing colours.
pH: Sulfur dioxide is an acidic gas. Therefore, pH value of aqueous sulfur dioxide solution will be lower than seven while aqueous ammonia solution's pH value is higher than seven. Therefore, send both gases separately to two distilled water samples and check pH value.

Identify ammonia gas from Hydrogen sulfide gas

Colour: Both ammonia gas and Hydrogen Sulfide gas are colourless. So, we cannot identify these two gases by observing colours.
pH: Hydrogen sulfide is a weak acidic gas. Therefore, pH value of aqueous Hydrogen sulfide solution will be lower than seven while aqueous ammonia solutions pH value is higher than seven. Therefore, send both gases separately to two distilled water samples and check pH value.
Send both gases separately to separate Ferric chloride solutions. Respect to ammonia gas, a green colour precipitate (Ferrous hydroxide) is given while a black colour precipitate (Ferrous sulfide) is given respect to the Hydrogen sulfide gas.

Identify ammonia gas from Nitrogen dioxide (NO₂) gas

Colour: Though ammonia gas is a colourless gas, Nitrogen dioxide is a brown colour gas. So, those two gases can be identified easily by their colours.

Identify ammonia gas from Carbon dioxide

Colour: Both ammonia gas and Carbon dioxide gas are colourless. So, we cannot identify these two gases by observing colours.
pH: Carbon dioxide is an acidic gas and poorly dissolve in water. But, dissolved concentration of Carbon dioxide is enough to give a pH value lower than seven while aqueous ammonia solution's pH value is higher than seven. Therefore, send both gases separately to two distilled water samples and check pH value.

Testing for chlorine gas and ammonia gas

Take a concentrated HCl bottle and open it's lid. Be careful! HCl vapour immediately comes out from the bottle and remember to wear safety equipments to prevent injuries.

Send two gases close to the concentrated HCl bottle in separate occasions and observe the changes.
Respected to the ammonia gas, a white solid fog, ammonium chloride is given. No that kind of change is for chlorine gas.

Ammonia gas can form metal hydroxide precipitates with some metal cations

With some metal cations such as Al³⁺, Zn²⁺, Cu²⁺, ammonia gas can give their respective hydroxide precipitates. However, some metal hydroxide precipitates are dissolved if excess ammonia gas is fed through to the solution due to formation of coordination complexes.

Ammonia will turn red litmus to blue litmus

Red litmus papers turns blue in the presence of ammonia gas or aqueous ammonia solution. This will prove ammonia has basic characteristics.

But, do not forget ammonia has acidic characteristics too.

Ammonia releasing reactions

Add a strong base such as aqueous NaOH to any ammonium salt and heat the solution. Ammonia gas will be released from the aqueous solution.
Add magnesium nitride (Mg₃N₂) to water. It forms NH₃ and Magnesium hydroxide ( Mg(OH)₂ ). Magnesium hydroxide is a white precipitate.

Questions

How to identify ammonia from sulfur dioxide by a pH test?

Ammonia and sulfur dioxide are colourless gases cannot identify by colour differences. Therefore send both gases separately to two distilled water samples. And check the pH of the solutions.

The ammonia solution will show you higher pH value than 7 while sulfur dioxide solution will have a less pH value than 7.

Ammonia organic or inorganic?

Ammonia is an inorganic compound which is a gas at room temperature.

Where ammonia gas testing experiments are applied?

To prove, exist of nitrogen gas in the atmosphere. Heat a magnesium metal piece in the air. Then add it to the water and do ammonia gas testing. You will observe there are characteristics of ammonia from those experiments.

Propose a test for ammonia gas to identify from hydrogen sulfide

We use the forming precipitate with ammonia aqueous solution to identify hydrogen sulfide.

Send ammonia and hydrogen sulfide gases to two Al³⁺ aqueous solutions. Observe what will happen in two solutions.

In one Al³⁺ solution, a white precipitate is given due to ammonia. Ammonia produces hydroxyl ions in the water and as the white precipitate, Al(OH)₃ is given.

Testing ammonia gas and nitrogen dioxide gas

So easy to do this. Actually like nothing to do. Just observe colours of gases. Nitrogen dioxide is a brown gas and can be identified clearly from ammonia.

Identify carbon dioxide from ammonia

Both gases are colourless. So we cannot identify them by observing colours of gases. Carbon dioxide is an acidic gas.

Send carbon dioxide to calcium ion solution. It gives, a precipitate with milky colour.
Send ammonia gas to calcium ion solution, you cannot see a precipitate like given by carbon dioxide gas.