Question

An isotonic solution will produce an osmotic pressure of $10.00$ atm measured against pure water at ${37}^o$C. How many grams of NaCl must be dissolved in one litre of water to produce an isotonic solution?

• A. $11.46$g
• B. $0.196$g
• C. $9.01$g
• D. $10$g

Answer 1

The correct option is A $11.46$g

An isotonic solution will produce an osmotic pressure of $10.00$atm measured against pure water at ${37}^o$C.
Let W grams of NaCl must be dissolved in one litre of water to produce an isotonic solution.
The molar mass of NaCl is 58.5 g/mol.

The molar concentration
$C=\frac{\text{W g}}{\text{58.5 g/mol}\times \text{1 L}}$

$C=\frac{\text{W}}{\text{58.5}}$ M.

The isotonic solutions have same osmotic pressure.

$\pi =iCRT$

$\text{10 atm}=2\times \frac{\text{W}}{\text{58.5}}M\times \text{0.08206 L atm/ mol /K}\times (37+273)\text{K}$

$W=11.4$ g.

$11.46$g grams of NaCl must be dissolved in one litre of water to produce an isotonic solution.

Note: The vant Hoff factor 'i' for NaCl is 2 as one molecule of NaCl dissociates to give 2 ions.

$NaCl\rightleftharpoons N{a}^{+}+C{l}^{-}$