The mass of lithium oxide that is needed to prepare 80 g of a 20% solution of lithium hydroxide.

1. When interacting with water, lithium oxide forms hydroxide, we write down the corresponding reaction equation:

Li2O + H2O = 2LiOH;

2.Calculate the mass of hydroxide in the resulting solution:

m (LiOH) = w (LiOH) * m (solution) = 0.2 * 80 = 16 g;

3.Calculate the chemical amount of hydroxide:

n (LiOH) = m (LiOH): M (LiOH);

M (LiOH) = 7 + 16 + 1 = 24 g / mol;

n (LiOH) = 16: 24 = 0.6667 mol;

4.determine according to the ratio of the coefficients in the reaction equation the amount of reacted lithium oxide:

n (Li2O) = n (LiOH): 2 = 0.6667: 2 = 0.33335 mol;

5. find the mass of lithium oxide:

m (Li2O) = n (Li2O) * M (Li2O);

M (Li2O) = 7 * 2 + 16 = 30 g / mol;

m (Li2O) = 0.33335 * 30 = 10 g.

Answer: 10 g.