дано
m(C6H6) = 117 g
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m(CaC2)-?
CaC2+2H2O-->Ca(OH)2+C2H2
3C2H2-->C6H6
M(C6H6) = 78 g/mol
n(C6H6) = m/M = 117 / 78 = 1.5 mol
3n(C2H2) = n(C6H6)
n(C2H2) = 3*n(C6H6) = 3*1.5 = 4.5 mol
n(CaC2) = n(C2H2) = 4.5 mol
M(CaC2) = 64 g/mol
m(CaC2) = n*M = 4.5 * 64 = 288 g
ответ 288 г