Question

What is the number of moles of oxygen gas evolved in electrolysis of 180g?

Answer 1

Okay , we know the molecular weight of H2O is 18 (16+1+1). So 1 mole of water weighs 18 grams. Therefore our starting 180 grams of water represents 10 moles. The electrolysis of water is:

2 H2O → 2 H2 + O2

This tells that us it takes 2 moles of water to make 1 mole of oxygen. Therefore our 10 moles of water are going to make 5 moles of oxygen.