дано
m(NaOH) = 0.4 g
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N(CuCL2)-?
CuCL2+2NaOH-->Cu(OH)2+2NaCL
M(NaOH) = 40 g/mol
n(NaOH) = m/M = 0.4 / 40 = 0.01 mol
n(CuCL2) = 2n(NaOH)
n(CuCL2) = 0.01/2= 0.005 mol
N(CuCL2) = n(CuCL2) *N(A)= 0.005*6.02*10^23 = 0.0301*10^23 молекул
ответ 0.0301*10^23 молекул