$(7)($iii$)$ The average analysis in terms of $Ca,Mg$ and $Cu$ results of lake water near a coppe

refining operation is given below. Calculate the hardness of the lake water in $m\frac{g}{L}$

as $CaC{O}_3,$ assuming that the atomic weights are: $Ca=40$;$Mg=24$;$Cu=64$;$H=$

$C=12$ and $O=16$ and indicate how you would classify this water $($i$.$e$.,$ soft,

moderately hard or hard$)$:

$C{a}^{2+}=20m\frac{g}{L}$

$M{g}^{2+}=30m\frac{g}{L}$

$C{u}^{2+}=50m\frac{g}{L}$