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An aqueous HCl solution has molar concentration 10⁻⁵ M and density 1 g/cc. Which of the following statements is correct?

1. The molality of HCl is approximately 10⁻⁵ m
2. The mole fraction of HCl is about 1.8 x 10⁻⁷
3. The concentration of HCl is 3.65 ppm
4. The (w/v)% of the solution is 3.65 x 10⁻⁵ %

Correct answer: The molality of HCl is approximately 10⁻⁵ m

Solution

Since the solution is extremely dilute and density is 1 g/cc, 1 L contains ~1 kg of water, so molality is approximately equal to molarity = 10⁻⁵ m. The ppm value would be 10⁻⁵ * 36.5 * 1000 = 0.365 ppm, not 3.65, so that option is wrong.

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