Chemistry
Worksheet : Molality
Name :
Date :
A. Answer the following as we go over them in class :
1. ______________________ ( ___ ) is the ratio of the number of moles of solute to the number of kilograms
of solvent.
2. _____ (T/F) A .50 m ( read "point five molal") solution is made by dissolving 0.50 moles of solute in one
kilogram of solvent.
3. _____ (T/F) A .50 m solution is formed by dissolving 0.50 moles of solute in a mass of solvent which is less
than one kilogram, and then diluting so that the total mass of the solution (solute and solvent) equals
one kilogram.
4. Write the mathematical equation for calculating molality and rearrange this equation to solve for moles and
kilograms of solvent.
5. Change the equation for the calculation of moles of solute to calculate grams of solute.
B. Sample problems : Solve the following problems dealing with molality.
6a. A solution contains 0.60 mol of glucose in 500.0 g of the solvent. What is the molality of this solution?
6b. A solution contains 2.36 g of NaI in 155 g of solvent. What is the molality of this solution?
6c. How many grams of NaI are needed to make a 1.2 m solution of NaI using 568 grams of water?
C. Group Problems :
7. What is the molality of a solution formed by dissolving 1.2 moles of solute in 1.20 kg of solvent ?
8. What is the molality of a solution formed by dissolving 0.50 moles of solute in 250.0 grams of solvent ?
9. What is the molality of a solution formed by dissolving 25.0 grams of magnesium nitrate in 500.0 grams of
solvent?
10. What is the molality of a solution formed by dissolving 40.0 grams of methanol (CH3OH) in 100.0 grams
of water?
11. How many moles of sucrose are needed to form a 0.20 m solution using 500.0 grams of water ?
12. How many grams of glucose are needed to form a 0.50 m solution of glucose in 1500 grams of water
(C6H12O6, molar mass = 180.18 g/mol) ?
13. How many grams of ethylene glycol (HOCH2CH2OH, molar mass = 62.08 g/mol) are needed to form a
0.80 m solution of ethylene glycol in 755 grams of water ?
14. How many kilograms of solvent are needed to form a .15 m solution of glucose using .50 moles of
glucose?
15. How many grams of water are needed to form a .25 m solution of urea (CH4N2O, molar mass = 60.07
g/mol) using 25.0 grams of urea?
Answers : 7. 1.0 m 8. 2.0 m 9. 0.337 m Mg(NO3)2
14. 3.3 kg 15. 1,700g
10. 12.5 m
11. 0.10 mol
12. 140 g 13. 37 g