Question 73

The osmotic pressure of a living cell is 12 atm at 300 K. The strength of sodium chloride solution that is isotonic with the living cell at tltis temperature is __________ $$g L^{-1}$$.
(Nearest integer)
Given: R = 0.08 L atm $$K^{-1} mol^{-1}$$
Assume complete dissociation of NaCl
(Given : Molar mass of Na and Cl are 23 and 35.5 g $$mol^{-1}$$ respectively.)


Correct Answer: 15

Solution

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Osmotic pressure of cell = 12 atm at 300 K. For isotonic NaCl solution:

$$\pi = iCRT$$ where $$i = 2$$ for NaCl (complete dissociation).

$$12 = 2 \times C \times 0.08 \times 300$$

$$C = \frac{12}{48} = 0.25$$ mol/L

Strength = $$0.25 \times 58.5 = 14.625 \approx 15$$ g/L

The answer is 15 g/L.

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