Borax decahydrate reacts with hydrochloric acid: $Na X_{2} B X_{4} O X_{7} \cdot 10 H X_{2} O + 2 HCl 4 H X_{3} BO X_{3} + 2 NaCl + 5 H X_{2} O$ . Use atomic masses Na = 23, B = 11, O = 16, H = 1. Calculate the mass of boric acid (in grams, two decimals) obtained from 20.0 g of borax decahydrate, assuming complete reaction.

Numerical answer type, answer in g, tolerance 0.01.

Answer: 12.98 g

Molar mass of borax decahydrate = 2(23) + 4(11) + 7(16) + 10(18) = 382 g/mol. Moles = 20.0/382 = 0.05236 mol. Four moles of

H X_{3} BO X_{3}

(62 g/mol) form per mole of borax, so mass = 0.05236 x 4 x 62 = 12.98 g.