Question

a solution is made by dissolving 0.131 mol of sugar,C₁₂H₂₂O₁₁, in 175 g of water. the amount by which the vapor pressure is lowered is? (The vapor pressure of water is 23.76 mm Hg at 25 degrees Celcius.

please explain: thank you!

Answers:

A) 23.00 mm Hg

B) 0.316 mm Hg

C) 17.8 mm Hg

D) 3.11 mm Hg

E) 1.33 mm Hg

Answer 1

Answer - We are given the, moles of sugar = 0.131 moles

Mass of water = 175 g , vapor pressure of water = 23.76 mm Hg

First we need to calculate the moles of water

Moles of water = 175 g / 18.015 g.mol^-1

                        = 9.71 moles

Total moles = 9.71 +0.131 moles

                    = 9.84 moles

Mole fraction of water = 9.71 moles / 9.84 moles = 0.987

So, the partial pressure of water vapor = 23.76 mm Hg*0.987

                                                              = 23.44 mm Hg

So the vapor pressure is lowered = 23.76 -23.44

                                                      = 0.316 mm Hg