Question

A 500ml sample of effluent from a water softener required 6 drops of standard soap solution to produced permanent leather. The soap solution had been calibrated against an artificial hard water solution contAining 0.136g of CaCL2 /l. 28drops of standard soap solution is required to lather 500ml of artificial solution. WhAt is the hardness of effluent sample in terms of ppm of CaCO3?

Answer 1

Dear Student,

$$\begin{gathered} \mathrm{The}\mathrm{hardness}\mathrm{of}\mathrm{the}\mathrm{effluent}\mathrm{sample}\mathrm{is}\frac{6}{28}\mathrm{th}\mathrm{of}\mathrm{the}\mathrm{hardness}\mathrm{of}\mathrm{the}{\mathrm{CaCl}}_2\mathrm{solution}. \\ \mathrm{Hardness}\mathrm{of}{\mathrm{CaCl}}_2\mathrm{solution}=? \\ 111\mathrm{parts}\mathrm{of}{\mathrm{CaCl}}_2=100\mathrm{parts}{\mathrm{CaCO}}_3 \\ 0.136\mathrm{parts}(\mathrm{mol}.\mathrm{wt})\mathrm{of}{\mathrm{CaCl}}_2=\frac{100}{111}\times 0.136 \\ =0.123\mathrm{parts}\mathrm{of}{\mathrm{CaCO}}_3 \\ 0.136\mathrm{g}\mathrm{of}{\mathrm{CaCl}}_2\mathrm{in}1000\mathrm{parts}\mathrm{of}{\mathrm{H}}_2\mathrm{O}=0.123\mathrm{in}{10}^6 \\ =123\mathrm{parts} \\ \mathrm{Hardness}\mathrm{of}{\mathrm{CaCl}}_2=123\mathrm{ppm} \\ \mathrm{Hardness}\mathrm{of}\mathrm{effluent}\mathrm{sample}=\frac{6}{28}\times 123=26\mathrm{ppm} \end{gathered}$$