Chemical Reactions and Equations - double of the amount collected in the other? Name this gas.
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Electrolytic Decomposition: This is a type of decomposition reaction where a compound is broken down into simpler substances by passing an electric current through its molten state or aqueous solution. A prime example is the electrolysis of acidified water.
Stoichiometry of Water: A water molecule () is composed of two atoms of Hydrogen and one atom of Oxygen. During electrolysis, the decomposition follows the ratio of its constituent elements.
Gas Collection at Electrodes: During the electrolysis of water, Hydrogen gas () is liberated at the cathode (negative electrode), and Oxygen gas () is liberated at the anode (positive electrode).
Volume Ratio: According to Avogadro's Law, the volume of a gas is proportional to the number of moles. Since the balanced equation produces 2 moles of for every 1 mole of , the volume of Hydrogen is exactly double the volume of Oxygen.
📐Formulae
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💡Examples
Problem 1:
During the electrolysis of water, why is the amount of gas collected in one of the test tubes double the amount collected in the other? Name this gas.
Solution:
The gas collected in double the amount is Hydrogen (). This occurs because water () contains two parts of hydrogen and one part of oxygen by volume. When water decomposes via electricity, the balanced chemical reaction is: From this equation, it is clear that 2 moles of Hydrogen gas are produced for every 1 mole of Oxygen gas.
Explanation:
Since the number of molecules (or moles) of Hydrogen produced is twice that of Oxygen, and according to gas laws, equal volumes of gases contain equal numbers of molecules at the same temperature and pressure, the volume of Hydrogen gas collected is double the volume of Oxygen gas.