21. Solving a chemistry problem

4.7 To determine lead, a 100 ml sample of waste water is evaporated to 30 ml, neutralized with ammonia to a clear alkali reaction and extracted with a solution of dithizone in carbon tetrachloride. The solution is brought to 100 ml and colorimetric at λ=520 nm. The lead content in the sample was 0.01 mg/l. Determine the content of lead in the initial solution in mg/l.