дано
m(K) = 10 g
η = 90%
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V прак (H2)-?
2K+2HOH-->2KOH+H2↑
M(K) = 39 g/mol
n(K) = m/M =10 / 39 = 0.26 mol
2n(K) = n(H2)
n(H2) = 0.26 / 2 = 0.13 mol
V теор (H2) = n*Vm = 0.13 * 22.4 = 2.912 L
Vпракт (H2) = 2.912 * 90% / 100% = 2.62 L
ответ 2.62 л