when a gas is collected over water, is the gas pure?
No. It has water vapor in it.
When a gas is collected over water, it is not pure because it contains water vapor. The presence of water vapor can occur when a gas is collected by displacing water in a container or when the gas is generated by a chemical reaction involving water.
To obtain pure gas, you would need to remove the water vapor. There are several methods to achieve this:
1. Drying agents: Certain substances, such as calcium chloride or silica gel, can be used as drying agents. These materials have a high affinity for water molecules and can effectively absorb the water vapor present in the gas.
To use a drying agent, place it in a container or column in the gas collecting setup. The gas passes through the drying agent, which absorbs the water vapor, leaving behind a purer gas.
2. Condensation: Another method to remove water vapor from a gas is through condensation. This process involves cooling the gas to a temperature below its dew point, causing the water vapor to condense into liquid form. The condensed water can then be separated from the gas.
To achieve condensation, you can use a condenser in your gas collecting setup. The gas is passed through the condenser, which is typically cooled by circulating cold water or another cooling medium. As the gas cools, the water vapor condenses, and the purified gas is collected.
It is important to note that the specific method and equipment used to remove water vapor from a gas depend on the specific experimental setup and the properties of the gas being collected. Different gases may require tailor-made approaches for their purification.