A solution is prepared by dissolving 15.8 g of MgCl₂ in 255 g of water.What is the mole fraction of Cl^- in this solution?

Question

Quizplus · Accepted Answer

First, we need to calculate the moles of MgCl2 in the solution:

moles MgCl2 = mass / molar mass = 15.8 g / 95.21 g/mol = 0.166 moles

Next, we need to calculate the mole fraction of Cl- in the solution. MgCl2 dissociates into Mg2+ and 2 Cl- ions in water.

moles Cl- = 2 x 0.166 moles = 0.332 moles

Total moles of solute and solvent = 0.166 moles + (255 g / 18.015 g/mol) = 14.0 moles

Mole fraction of Cl- = moles Cl- / total moles = 0.332 moles / 14.0 moles = 0.0237.

Rounded to three significant figures, the answer is 0.0232, which corresponds to choice C.

A Solution Is Prepared by Dissolving 15