Calculate the amount of the substance and the mass of water if 3 moles of oxygen O2 enter during its decomposition.

When water is decomposed by an electric current, molecular oxygen is released at the anode, and molecular hydrogen at the cathode. The equation can be written as:

2 H2O = 2 H2 + O2

As can be seen from the reaction equation, the amount of oxygen is 2 times less than the amount of hydrogen and water. This means that for the formation of 3 moles of oxygen, you need to decompose 6 moles of water.

Now you can find the mass of water by the formula:

m = n * M, where n is the amount of the substance, M is the molar mass of the substance.

M (H2O) = 18 g / mol;

m (H2O) = 6 * 18 = 108 g.

Answer: 6 mol, 108 g of water.