Question

Oxygen \(\left(\mathrm{O}_{2}\right)\) and carbon dioxide \(\left(\mathrm{CO}_{2}\right)\) are colorless and odorless gases. Suggest two chemical tests that would allow you to distinguish between these two gases.

Short answer

Use limewater to identify \\(\text{CO}_2\\) and a glowing splint to detect \\(\text{O}_2\\).

Step-by-step solution

Test with Limewater

Limewater is a solution of calcium hydroxide \((\text{Ca(OH)}_2)\). When carbon dioxide \(\text{CO}_2\) is bubbled through limewater, it reacts to form calcium carbonate \((\text{CaCO}_3)\), turning the limewater cloudy or milky. This reaction is given by the equation: \[\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \] This test will not cause any visible change when performed with oxygen \(\text{O}_2\), so it can be used to distinguish between the two gases.

Test with a Glowing Splint

A glowing splint test can be used to test for oxygen. When a glowing wooden splint is introduced to an environment containing oxygen \(\text{O}_2\), it will reignite due to the increased availability of oxygen for combustion. This test results in no reaction when performed with carbon dioxide \(\text{CO}_2\), which does not support combustion. Thus, if the gas reignites the glowing splint, it is oxygen; if there's no reaction, it is carbon dioxide.

Key concepts

Limewater Test

The Limewater Test is a classic method used to detect the presence of carbon dioxide (\(\text{CO}_2\)). Limewater, which is a clear solution of calcium hydroxide (\(\text{Ca(OH)}_2\)), changes its appearance in the presence of carbon dioxide. What happens is quite fascinating! When you bubble carbon dioxide gas through the limewater, a chemical reaction occurs.

Here's how it works: carbon dioxide reacts with calcium hydroxide to form calcium carbonate (\(\text{CaCO}_3\)), which is insoluble in water. The formation of calcium carbonate causes the solution to turn cloudy or milky, providing visual confirmation of carbon dioxide.

• This cloudiness is practically a physical manifestation of the reaction occurring at the molecular level.
• When tested with oxygen (\(\text{O}_2\)), there is no reaction, and the limewater remains clear.

The Limewater Test is unique to carbon dioxide among common gases, making it an efficient way to distinguish this gas from oxygen.

Glowing Splint Test

The Glowing Splint Test is a simple yet effective method to detect oxygen gas (\(\text{O}_2\)). Oxygen is crucial for combustion, and this test cleverly uses that property.

To perform the test, a wooden splint is first ignited, then blown out, leaving the tip glowing. When this glowing splint is introduced into a sample containing oxygen, it will spontaneously reignite.

• This occurs because the added oxygen facilitates combustion, making the splint catch fire again.
• It's a quick indication of oxygen presence and is easily visualized as the splint returns to flame.

Contrastingly, if the same glowing splint is introduced to a container with carbon dioxide, it will not reignite.

The splint simply stops glowing because carbon dioxide is not supportive of combustion.Therefore, the Glowing Splint Test is perfect for identifying oxygen among gases.

Calcium Carbonate Formation

Calcium carbonate formation plays a pivotal role in the Limewater Test. This compound, \(\text{CaCO}_3\), emerges when carbon dioxide (\(\text{CO}_2\)) is exposed to a limewater solution containing calcium hydroxide (\(\text{Ca(OH)}_2\)). The reaction forms a white, chalky precipitate which is insoluble in water.

This reaction is an example of a precipitation reaction, where soluble substances yield an insoluble product. This physical change from a clear to a cloudy solution makes detecting carbon dioxide straightforward.

• In this state, calcium carbonate is responsible for the milky appearance during the test.
• This readily visible result demonstrates the presence of carbon dioxide effectively.

Understanding calcium carbonate's formation aids in grasping why the Limewater Test works only with carbon dioxide and not with oxygen.

Oxygen Detection

Detecting oxygen is crucial, especially in science experiments and industrial applications. While several tests exist for this purpose, the Glowing Splint Test is particularly notable for its simplicity and reliability.

Why is oxygen so pivotal? It's because oxygen supports combustion, a chemical process of burning. When testing for oxygen, you’re essentially looking at the gas's ability to keep a flame alive.

• This principle is used in the Glowing Splint Test, where oxygen causes the splint to reignite.
• Beyond visual confirmation, this test plays a key role in ensuring safety in environments where oxygen levels may vary.

Thus, efficiently detecting oxygen involves recognizing its interaction with fire, highlighted by easily observable phenomena.

Carbon Dioxide Detection

Detecting carbon dioxide (\(\text{CO}_2\)) is vital in several fields, including environmental science and industry. It is colorless and odorless, making direct detection challenging without chemical methods like the Limewater Test.

Carbon dioxide's inability to support combustion makes it unique compared to other gases such as oxygen.

• In practical settings, its detection is crucial for monitoring air quality, as excessive carbon dioxide can impact both human health and the environment.
• In chemical processes, detecting \(\text{CO}_2\) provides insights into reaction completeness and efficiency.

The combination of the Limewater Test and its lack of combustion support allows carbon dioxide to be distinguished easily from other gases.