Let's have 100 ml of concentrated hydrochloric acid (HCl) solution (W = 36%, density = 1,18 g/ml)
W(HCl)= x g HCl / 100 ml of solution = x/118 g = 36%
Hence m(HCl) equals x = 0,36•118 = 42,48 g
To prepare 10% solution of HCl we should add to concentrated HCl y grams(ml) of water. Then, we have the proportion:
0,1 = 42,48 g of HCl/118 g of first solution + y grams of H2O
Or 0,1 = 42,48/118+y
y = 306,8 g(ml) of H2O
SO, to prepare 10% solution of HCl we should add 306,8 ml of H2O to 100 ml of concentrated HCl. OR, to prepare 100 cm3 of 10% solution of HCl we should add to 23,54 cm3 of concentrated HCl 76,46 cm3 of water.
To prepare 100 ml(cm3) of 10% solution of NaCl:
0,10 = x g NaCl/100 cm3 of solution
x = 10 g
You should take a 10 g of NaCl and 90 g of water.