Practice Calculations
Percent Solutions
1. If you dissolved 25.0 grams of HCl in enough water to make 300.0 grams of solution, what is the
percent HCl in this solution?
Ans: 8.3%
2. You have 250.0 grams of a salt solution and you slowly heat the solution to boil the water away. You
find that there is 16.0 grams of salt left behind. What was the percent salt in the original solution?
Ans: 6.4%
3. How much sugar would be needed to make 3500.0 grams of a 12.5% solution?
Ans: 437.5 g
4. Find the percent by mass of the following:
a) 10.0 grams of sugar dissolved in 40.0 grams of water.
Ans: 20%
b) 0.63 grams of AgNO3 dissolved in 12.0 grams of water.
Ans: 5%
c) How many grams of sugar are in a 35% solution if the sugar is dissolved
in 25.0 grams of water?
Ans: 13.5 g.
Molarity of Solutions
1. How many moles of NaOH would be needed to make 2.5 liters of a 0.4M solution? How many grams
would this be?
Ans: 1.0 mol; 40 g.
2. A solution is made by dissolving 25.0 grams of LiF in enough water to make 800.0 ml of solution.
What is the molarity of this solution?
Ans: 1.2M
3. What is the molarity of a solution that contains 50.0 grams of KOH in 900.0 ml of solution?
Ans: 0.99M
4. Assume you have 250.0 ml of a 0.6M solution of NaOH. What would the concentration be if you were
to add 100.0 ml of water to this solution?
Ans: 0.429M
5. If you have 2.5 liters of a 0.4M solution of KNO3, what would the concentration be if you added 500.0
ml of water?
Ans: 0.33M
6. Let's say that you have 25.0 ml of a 2M solution of MgSO4. If you add 5.0 ml of water to this solution
then what would the concentration become?
Ans: 1.67M
7. You have dissolved 10.0 grams of NaOH in enough water to make 400.0 ml of solution. What is the
molarity of this solution? What would the concentration be if you added 250.0 ml of water to the
solution?
Ans: .625M; .382M
1
8. How much concentrated sulfuric acid would be needed to make 3.0 liters of a 0.60M solution?
(concentrated sulfuric acid, H2SO4, is 18M)
Ans: 0.1L or 100mL
9. How much concentrated sulfuric acid would be needed to make 400.0 ml of a 0.2M solution?
Ans: 4.4mL
10. How much concentrated nitric acid would be needed to make 300.0 ml of a 0.25M solution?
(concentrated nitric acid, HNO3, is 15M)
Ans: 5.0mL
11. How much concentrated HCl would be needed to make 880.0 ml of a 2M solution? (concentrated,
HCl, is 12M)
Ans: 147mL
12. Suppose that 200.0 ml of 0.5M HCl is mixed with 300.0 ml of a 0.8M HCl solution. What is the
molarity of the final solution?
Ans: 0.68M
13. Imagine mixing 4.0 liters of 0.3M HNO3with 7.0 liters of a 0.4M HNO3 solution. What is the final
concentration?
Ans: 0.364M
14. Suppose that you mixed the three following solutions together...
100.0 ml of water
300.0 ml of 0.4M HCl
500.0 ml of 0.5M HCl
Calculate the molarity of the final concentration.
Ans: 0.41M
15. Calculate the volume of a solution of LiOH that contains 6.70 mol LiOH having
a concentration of 0.0025M.
Ans. 2.68 x 103 L
Molality of Solutions
1. What mass of HNO3 is present in 140.0 g of a solution that is 12.5% HNO3 by mass?
Ans: 17.5 g
2. What is the molality of a solid solution containing 0.125 g of chromium and 81.3 g of iron?
Ans: 0.03m
3. If 18.6 g of methanol is used to dissolve 2.68 g of Hg(CN)2, what is the molality of the solution?
Ans: 0.57m
4. Calculate the molality of a solid solder wire made from 68.7 g of lead dissolved in 117 g of tin?
Ans: 2.84m
5. Calculate the molality of a solution containing 75.2 g of AgClO4 dissolved in 885 g of benzene?
Ans: 0.41m
6. What is the freezing point depression of 210.0 g of glycerol (92.1g/mol) dissolved
in 350.0 g of water? What is the new freezing point of water? (Kf for water = -1.86oC/molal)
Ans: T = -12.05oC; freezing point = -12.05oC
2
7. A solution containing 3.39 g of a compound in 10.0 g of water has a freezing point depression of
-7.31oC. What is the molar mass of the compound? (Kf for water = -1.86oC/molal)
Ans: 86.3 g.
8. Calculate the boiling point of a solution containing 34.3 g of a the ionic compound
magnesium nitrate, Mg(NO3)2, dissolved in 0.107 kg of water? (Kb for water = 0.51oC/molal)
Ans: Tb = 3.29oC
BP = 103.29oC
9. A solution of 0.827 g of a substance in 2.5 g of water has a freezing point of -10.18oC.
Calculate the molar mass of the compound. (Kf for water = -1.86oC/molal)
Ans: 60.4 g/mol
10. An unknown compound has an empirical formula of C2H2O. A solution of 3.775 g of the unknown
compound dissolved in 12.0 g of water freezes at -4.72oC. Determine the molar mass and the
molecular formula of the compound.
Molar mass = 124 g/mol
o
(Kf for water = -1.86 C/molal)
Molecular formula = C6H6O3
11. How many grams of a solute having a molar mass of 41.9 g/mol must be added to 1000.0 ml of water
to produce a boiling point elevation of 0.84 oC? Kb = 0.51oC/mole
Ans: 69 g
Heating and cooling curve calculations
Given for Water:
1. Heat of vaporization and condensation (Hv) = 2.3 x 103 J/g.
2. Heat of fusion and crystallization (Hf) = 3.4 x 102 J/g
3. Specific heats (Cp):
Cp ice = 2.1 J/goC
Cp water = 4.2 J/goC
Cp water vapor = 1.87 J/goC
q = mcpT
q = mH
1. Calculate the total heat required to vaporize 1.5 kg of water at 100oC to water vapor at 100oC.
Ans: 3.45 x 106 J
2. Calculate the total energy required to heat 600 g of water from 80oC to 140oC.
Ans: 1.48 x 106 J
3. Calculate the total heat required to bring 80 g of water at 4oC to a vapor temperature of 120oC.
Ans: 2.19 x 105 J
4. Calculate the total heat required to raise the temperature of 6.0 kg of an equilibrium
mixture of ice and water from 0oC to 106oC. The mixture is 40% ice. Ans: 1.72 x 107 J
5. Calculate the total heat required to raise the temperature of 250 g of water from –15oC to 156oC.
Ans: 7.99 x 105 J
3
6. Calculate the heat lost when 2.2 kg of steam at 130oC is condensed to water at 35oF.
Ans: 6.09 x 106 J
7. Given a 200 g equilibrium mixture of ice and water which is composed of 85% ice:
a) calculate the total heat required to raise the temperature of the mixture to 60oC.
Ans: 1.08 x 105 J
b) calculate the total heat required to vaporize half of this mixture. Ans: 3.72 x 105 J
(starting with original mixture in “a” above)
c) calculate the heat required to be removed in order to freeze the entire mixture.
Ans: 1.02 x 104 J
4