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Mr (CaO) = 40 + 16 = 56
W (Ca) = Ar (Ca) / Mr (CaO) = 40 / 56 = 0.7143 = 71.43%
X - m (CaO)
100% - Xг
71.43% - 3г
71.43х = 300
х = 4.2г
Ответ: m (CaO) = 4.2г
N2+3H2=2NH3
280-100%
x-10%
x=(280*10):100=28
M(N2)=28
252:28=x:44.8
x(252*44/8):28=403.2л