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Chemistry
Worksheet/notes : Ch. 15-16 ; Obj. 35-39
Name :
Date :
A. Mole fraction :
1. Equations for mole fraction (ratio of moles of solute and solvent to moles of solution) :
a. mole fraction of solute (A):
b. mole fraction of solvent (B):
2. What are the mole fractions of solute and solvent of a solution formed by dissolving 2.00 moles of MgCl2 in
400.0 moles of water?
3. What is the mole fraction of Cl- ions in the above solution ?
4. What are the mole fractions of a solution formed by dissolving 25.0 g of MgCl2 (molar mass = 95.21 g/mol) in
1.20 kg of water?
B. Colligative properties :
5. _____________________________ properties are properties which depend on the number of solute particles
dissolved in a given mass of solvent.
6. _____(T/F) The above type of property depends, to a large extent, on the type of solute.
7. List three important colligative properties.
8. _____(T/F)A nonvolatile solute, such as magnesium chloride, would increase the vapor pressure of a solvent
such as water.
9. _____ (T/F) Carbon dioxide, as a solute, would decrease the vapor pressure of water.
10. Explain why nonvolatile solutes decrease vapor pressure.
11. _____(T/F) A one molar solution of sodium fluoride (NaF) would lower the vapor pressure of water to the
same extent that a one molar solution of magnesium chloride (MgCl2).
12. _____(T/F) Elevation of the vapor pressure due to the increase in the number of nonvolatile solute particles
will not affect the boiling point of a liquid.
13. ____________________________________________ is the difference in temperature between the boiling
points of a pure solvent and a solution.
14. ______________________________________________ is the difference in temperature between the
freezing points of a pure solvent and a solution.
15. Why does salt cause ice to melt?
16. The ________________________________________ is equal to the change in the boiling point for a 1 molal
solution of a nonvolatile molecular solute.
17. The ________________________________________ is equal to the change in the freezing point for a 1
molal solution of a nonvolatile molecular solute.
18. ________ are the units for the answers to numbers 16 and 17.
19. ____________ = Kb
_________________ = Kf
20. Finish the following equations :
ΔTb =
; ΔTf =
21. What will the boiling point of a solution be if you add 130.0 g of glucose (molar mass = 180.18 g/mol) to
750.0 g of water? (Assume 1 atm. of pressure)
22. What will the freezing point of a solution be if you add 2.2 grams of urea (CH4N2O, molar mass = 60.07
g/mol) to 750 grams of water?
23. What will the freezing point of a solution be if you add 12.2 grams of magnesium chloride (MgCl2, molar
mass = 95.21 g/mol) to 1,250 grams of water?
24. Calculate the freezing-point depression of an aqueous solution containing that is 50.0 % ethanol (C2H5OH)(a
nonelectrolyte) . (Kf for water = 1.86 ºC/m).
25. Calculation of molar mass from freezing point and boiling point data :
Four steps : 1. Determine change in f.p. or b.p.
2. Calculate molality (e.g. m = ΔTb/Kb) - rearranged from ΔTb = Kbm
3. Calculate moles from molality equation (moles = Kg solvent x m)
4. Calculate molar mass (g/mol) of solute.
a. A solution contains 22.5 grams of a nonvolatile, nonelectrolyte solute in 500.0 grams of water. If the
solution freezes at -0.89 ºC, what is the molecular mass of the solute?
b. A solution contains 115.5 grams of a nonvolatile, nonelectrolyte solute in 750.0 grams of water. If the
solution boils at 101.2 ºC at 1 atm, what is the molecular mass of the solute?