7 g of technical calcium containing 20% of impurities was dissolved in 100 g of water.

7 g of technical calcium containing 20% of impurities was dissolved in 100 g of water. Determine the mass fraction of calcium hydroxide in the resulting solution.

Given:
mCa = 7g
ω = 20%
mH2O = 100g
Find: ω r.v. (Ca (OH) 2) -?
Decision:
1) 7 * 0.2 = 1.4 g – the mass of impurities
2) 7 – 1.4 = 5.6 g – Ca
determine the molar masses M (Ca) = 40 M (Ca (OH) 2) = 74
by proportion we find the mass of hydroxide
40 – 74
Ca + 2H2O = Ca (OH) 2 + H2 ↑
5.6 – x
x = 10.36 g
3) 100 + 7 = 107 g – solution
4) 107 – 100%
10.36 x%
x = 9.68%
Answer: 9.68% Ca (OH) 2 in the resulting solution.