Дано

m = 16 г

w(примесей) = 6.25% = 0.0625

Решение

w(Al2S3) = 1 - w(примесей) = 1 - 0.0625 = 0.9375

m(Al2S3) = mw(Al2S3) = 16 * 0.9375 = 15 г

n(Al2S3) = m(Al2S3) / M(Al2S3) = 15 / (2 * 27 + 3 * 32) = 15 / 150 = 0.1 моль

Al2S3 + 6H2O = 2Al(OH)3 + 3H2S

n(Al(OH)3) = 2n(Al2S3) = 2 * 0.1 = 0.2 моль

m(Al(OH)3) = n(Al(OH)3)M(Al(OH)3) = 0.2 * (27 + 3 * 16 + 3 * 1) = 0.2 * 78 = 15.6 г

Ответ: 15.6 г