Question

Stock phosphoric acid solution is $85$% $H_{3}P{O}_4$ and has a specific gravity of $1.70$ . Hence, molarity of $H_{3}P{O}_4$ solution is:

• A. $8.51$ M
• B. $1.70$ M
• C. $14.74$ M
• D. $7.37$ M

Answer 1

Answer: (C)

$14.74$ M

$100$ g of phosphoric acid solution contains $85$ g of $H_{3}P{O}_4$.
The specific gravity is $1.7$ g/mL.
Hence, $\frac{100}{1.7}mL{H}_{3}P{O}_4$ contains $85$ g $H_{3}P{O}_4$. It is equal to $\frac{85}{98}$ moles of $H_{3}P{O}_4$.
$Molarity=\frac{85/98mol}{(\frac{100L}{1.7\times 1000})}=14.74M$.