What mass of copper (II) oxide can be formed by the interaction of 84 g of copper containing 15%

What mass of copper (II) oxide can be formed by the interaction of 84 g of copper containing 15% of impurities with oxygen, if the yield is 89% of the theoretical?

Given:
m tech. (Cu) = 84 g
ω approx. = 15%
η (CuO) = 89%

Find:
m pract. (CuO) -?

1) 2Cu + O2 => 2CuO;
2) ω (Cu) = 100% – ω approx. = 100% – 15% = 85%;
3) m clean. (Cu) = ω * m tech. / 100% = 85% * 84/100% = 71.4 g;
4) n clean. (Cu) = m pure. / M = 71.4 / 64 = 1.1 mol;
5) n theory. (CuO) = n (Cu) = 1.1 mol;
6) n practical (CuO) = η * n theory. / 100% = 89% * 1.1 / 100% = 1 mol;
7) m practical. (CuO) = n practical * M = 1 * 80 = 80 g.

Answer: The mass of CuO is 80 g.