Final answer:
Gases that are produced in laboratory experiments can be collected using a technique called water displacement. This involves filling a bottle with water, inverting it in a pan of water, and allowing the gas to displace the water in the bottle. The collected gas may be mixed with vapor from the evaporation of the water, so Dalton's Law can be used to calculate the amount of the desired gas.
Step-by-step explanation:
Gases that are produced in laboratory experiments are often collected by a technique called water displacement. In this process, a bottle filled with water is placed upside-down in a pan of water. The reaction flask is fitted with rubber tubing, which is fed under the bottle of water. As the gas is produced in the reaction flask, it exits through the rubber tubing and displaces the water in the bottle. When the bottle is full of the gas, it can be sealed with a lid.
The reason this technique works is because as the gas pushes out the water, it is also pushing against the atmosphere, so the pressure inside the bottle is equal to the pressure outside. However, because the gas is collected over water, it is not pure and is mixed with vapor from the evaporation of the water. Dalton's Law can be used to calculate the amount of the desired gas by subtracting the contribution of the water vapor.
A pneumatic trough is a common setup used for collecting gases over water. It involves inverting a tube or bottle filled with water into a larger container of water. As the gas enters the bottle, it displaces the water and becomes trapped in the upper part of the bottle. This arrangement allows for the collection of gases that do not react with water.