дано
m(K) = 11.7 g
η(K2S) = 70%
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m( практ K2S)-?
2K+S-->K2S
M(K) = 39 g/mol
n(K) = m/M = 117 / 39 = 0.3 mol
2n(K) = n(K2S)
n(K2S) = 0.3 / 2 = 0.15 mol
M(K2S) = 110 g/mol
m теор (K2S) = n*M = 0.15 * 110= 16.5 g
m практ(K2S) = mтеор(K2S) * η(K2S) / 100% = 16.5 * 70% / 100% = 11.55 g
ответ 11.55 г