076. Solving a chemistry problem

30. A steel sample contains 0.5% silicon. What sample of steel should be dissolved in 100 ml in order to take 25 ml of this solution into a 50 ml flask to obtain a solution of β-silicon-molybdenum heteropolyacid H4(SiMo12O40)*nH2O (ε=2.2*103 l*mol-1*cm-1 at λ=400 nm), the absorption of which in a cuvette with l=1.00 cm would correspond to the minimum error of photometric measurements (Aopt=0.434)?