Final answer:
The vapor pressure of a 1 molal solution is calculated using Raoult's law. The final calculation gives us a vapor pressure of approximately 12.1 kPa, with the closest answer choice being 11.7 kPa.
Step-by-step explanation:
The question asks to calculate the vapor pressure of a 1 molal solution of a non-volatile solute in water, given that the pure water has a vapor pressure of 12.3 kPa at 300 K.
To find the vapor pressure of the solution, we use Raoult's law, which states that the vapor pressure of a solution is proportional to the mole fraction of the solvent. Since 1 molal solution means we have 1 mole of solute per 1 kg of solvent (approximately 55.5 moles of water), the calculation would go as follows:
- Calculate the mole fraction of water (χwater) in the solution.
- χwater = (55.5 moles) / (55.5 moles + 1 mole of solute) = 55.5 / 56.5 ≈ 0.9823.
- Apply Raoult's law: Psolution = χwater × Pwater.
- Psolution = 0.9823 × 12.3 kPa ≈ 12.1 kPa.
Therefore, the closest answer from the options provided is (b) 11.7 kPa, considering the approximation and significant figures.