Answer is: mass of ethanol is 52,25 grams.
b(solution) = 7,1 m = 7,1 mol/kg.
m(H₂O) = 160,0 g · kg/1000g = 0,160 kg.
n(C₂H₅OH) = b(solution) · m(H₂O).
n(C₂H₅OH) = 7,1 mol/kg · 0,160 kg.
n(C₂H₅OH) = 1,136 mol.
m(C₂H₅OH) = n(C₂H₅OH) · M(C₂H₅OH).
m(C₂H₅OH) = 1,136 mol · 46 g/mol.
m(C₂H₅OH) = 52,25 g.
