In a science experiment showing the splitting of water into Oxygen and hydrogen, two inverted test tubes of water were placed over the site of the reaction. (see the pic) How can you tell which one was catching the oxygen and which one was catching the hydrogen?

The hydrogen is a positive ion and will be located close to the negative terminal of the battery.

The oxygen is a negative ion which will be located next to the negative terminal of the battery.

There are 2 hydrogen atoms for every oxygen atom. The hydrogen will take up more space and is pushing the water lower in the test tube.

The hydrogen, being a smaller atom, will take up less space than the oxygen. It will push the water down less.

There are 2 hydrogen atoms for every oxygen atom. The hydrogen will take up more space and is pushing the water lower in the test tube.

Explanation:

Electrolysis refers to the decomposition of a solution (electrolyte) owing to the passage of direct current through the solution.

Water is decomposed into its constituents; hydrogen and oxygen by electrolysis. However, a battery is connected to drive the process and other electrolytes such as dilute acids are added to improve the conductivity of water.

In the electrolysis of water, two moles of hydrogen gas is produced for each mole of oxygen gas produced. Hence the ratio of hydrogen to oxygen gas produced is 2:1 by volume. This implies that the space occupied by oxygen is half the space occupied by hydrogen. The hydrogen will thus occupy more space, pushing the water much lower than oxygen.