Hi!
In practice, why is the volume of oxygen obtained from the electrolysis of water LESS THAN half the volume of hydrogen obtained?
I'm guessing it might have to do with gases escaping? Help!
Hello! You're correct, the volume of oxygen obtained from the electrolysis of water is indeed less than half the volume of hydrogen obtained. This can be attributed to a few factors, including the properties of water and the nature of gases.
When water is electrolyzed, it splits into its component elements, hydrogen (H2) and oxygen (O2), through the process of electrolysis. The balanced chemical equation for this reaction is as follows:
2H2O(l) → 2H2(g) + O2(g)
As per the stoichiometry of this equation, for every 2 moles of water molecules (H2O) that are electrolyzed, we expect 2 moles of hydrogen gas (H2) and 1 mole of oxygen gas (O2) to be produced.
However, the actual volume of gases obtained can vary due to a couple of reasons. One significant factor is the difference in molar volume between hydrogen and oxygen gases. At the same temperature and pressure conditions, 1 mole of any gas occupies the same volume, known as the molar volume. According to Avogadro's law, at standard temperature and pressure (STP), 1 mole of a gas occupies 22.4 liters of space.
Since hydrogen gas (H2) is diatomic (consists of two atoms), it occupies the same volume as 1 mole of any other gas (22.4 liters at STP). However, oxygen gas (O2) is also diatomic, meaning it consists of two oxygen atoms. Thus, to obtain 1 mole of oxygen gas (O2), two water molecules (2 moles) must be electrolyzed. This means that the actual volume of oxygen gas produced will be less than half the volume of hydrogen gas produced.
Another contributing factor is the escape of gases during the electrolysis process. Gases, being highly mobile, can escape from the system before they are collected or measured. This can result in a loss of gases, further reducing the volume of oxygen obtained compared to hydrogen.
Therefore, the combination of differences in molar volume between hydrogen and oxygen gases, along with the potential escape of gases during the process, leads to the volume of oxygen obtained being less than half the volume of hydrogen obtained during the electrolysis of water.