The mole fraction of NaCl, in a solution containing 1 mole of NaCl in 1000g of water is:
Correct answer: A. 0.0177
- A. 0.0177
- B. 0.001
- C. 0.5
- D. 0.244
Explanation
Mole fraction of a component X in a solution is defined as the ratio of the number of moles of X to the total number of moles of all components in the solution.Mole fraction of NaCl = moles of NaCl / (moles of NaCl + moles of water)In this case, 1 mole of NaCl is dissolved in 1000 g of water. We can calculate the number of moles of water as follows:moles of water = mass of water / molar mass of water = 1000 g / 18.015 g/mol = 55.49 molSo, the total number of moles of all components in the solution is:moles of NaCl + moles of water = 1 mol + 55.49 mol = 56.49 molTherefore, the mole fraction of NaCl is:mole fraction of NaCl = moles of NaCl / (moles of NaCl + moles of water) = 1 mol / 56.49 mol = 0.0177 (rounded to four significant figures)Hence, the correct answer is A) 0.0177.
This question appeared on the NUMS 2019 (cancelled sitting) paper, which you can sit online with every answer explained.
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