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Q.
Concentrated hydrochloric acid contains $37\%HCl $ (by mass). The density of this solution is $1.18\, g/mL$. The molarity of the solution is:
BHUBHU 2001
Solution:
Calculate the molarity of solution by using formula,
Molarity $=\frac{\text { moles of solute }}{\text { volume of solution in litre }}$
Given : Mass of solute (by mass) $=37 \%$
$d=1.18\, g / mL$
Molecular mass of $HCl =1+35.5$
$=36.5 \,g / mol$
Volume of solute $=\frac{\text { mass of solute }}{\text { density of solution }}$
$=\frac{100\, g }{1.18 \,g / mol }=85\, mol $
$=85\, cm ^{3}=0.85 \,dm ^{3}$
Moles of solute $( HCl )$
$=\frac{\text { mass of solute }}{\text { molecular mass of solute }}$
$=\frac{37\, g }{36.5\, g / mol }$
$=1.01\, mol$
$\therefore $ molarity of solution $=\frac{1.01 \,mol }{0.085\, dm ^{3}}$
$=12.0 \,mol\, dm ^{3}$
$=12.0 \,M$