Problem 101 - Chemistry and Chemical Reactivity

Question

You are given a stoppered flask that contains hydrogen, nitrogen, or oxygen. Suggest an experiment you could do to identify the gas.

Step-by-Step Solution

Answer

Test for hydrogen first by lighting a splint. Use a glowing splint test for oxygen. Unreactive result suggests nitrogen.

Step 1: Test for Hydrogen

Collect a small sample of the gas in a test tube. Bring a lit splint close to the opening of the test tube. If the gas is hydrogen, you'll hear a distinct 'pop' sound indicating the presence of hydrogen gas.

Step 2: Test for Oxygen

If no 'pop' sound was heard, it means the gas might be either nitrogen or oxygen. Ignite a glowing splint by extinguishing a flame and allowing it to smolder. Introduce it into the flask. If the glowing splint reignites, this confirms the presence of oxygen gas.

Step 3: Test for Nitrogen

If neither of the previous tests confirm the presence of hydrogen or oxygen, then the gas is likely nitrogen. Nitrogen is inert and will not react with the splint tests, confirming it as the remaining possibility.

Key Concepts

Hydrogen Test

To determine whether the gas in your flask is hydrogen, you can perform a simple and effective test. Hydrogen is highly flammable, and this characteristic sets it apart when tested with a flame.

Here's how you proceed: Collect a small sample of the gas in a test tube. Then, carefully bring a lit splint (which is a small piece of wood set on fire) near the opening of the test tube. The key here is the sound.

If the gas is hydrogen, it will produce a distinct 'pop' sound. This small explosive noise happens because hydrogen gas reacts with oxygen when ignited, forming water.

• Always perform this test in a controlled environment
• Hydrogen is flammable, so handle with care
• Listen carefully for the 'pop' sound to confirm hydrogen presence

Oxygen Test

If you did not hear the 'pop' sound when you tested for hydrogen, your gas could either be nitrogen or oxygen. To identify oxygen, using a glowing splint can be quite insightful.

First, you need to prepare your glowing splint. Light the splint and then extinguish it so that it glows faintly rather than giving off a flame.

Now, introduce this glowing splint into the flask containing the gas. If it bursts back into flame, it is a classic sign of oxygen presence. The reason this happens is due to oxygen’s role as a supporter of combustion—it makes the glowing splint reignite.

Here’s a reminder for the test:

• Use a glowing (not flaming) splint
• Oxygen will support the combustion of the splint
• Ensures you have not breathed into the container affecting results

Nitrogen Properties

Once both the hydrogen and oxygen tests have failed to identify the gas, you are most likely dealing with nitrogen. This gas is known for being colorless, odorless, and incredibly inert.

The inert nature of nitrogen means it doesn't react easily, which is why the hydrogen and oxygen tests won't affect it. You might reconsider the basic properties of nitrogen:

• Non-reactive under normal conditions
• Composes about 78% of Earth's atmosphere
• Commonly used to prevent oxidation in manufacturing processes

In the absence of any combustion or reaction with a splint, you can confidently conclude that the flask contains nitrogen.