Chemistry Chapter 14.2
Solution Concentration
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Definition: the measure of how much
_______________ is dissolved in a specific
amount of solvent
Solutions can be described quantitatively
using words concentrated and dilute
o Concentrated – a lot of solute
compared to the amount of solvent
 Example:
o
Dilute – very little solute compared to
the amount of solvent
 Example:
Expressing Concentration
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Percent by mass
Percent by volume
Molarity
Concentration
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Expressed as a percent in a ratio of measured
amount of solute to a measured amount of
solution
o Percent by mass = solid dissolved in a
liquid
 Example:
o Ratio of solute’s mass to the solution’s
mass
o Mass of solution = masses of solute +
mass of solvent
Formula used to represent percent by
mass/volume:
Molarity: takes into account the number of
particles (atoms and molecules ) present in
the solution
Percent by Mass Examples:
Solution Concentration
Solution Concentration Practice I
1. What is the % concentration by mass of 8.3 g of NaCl dissolved in 300 g of water? (2.7%)
2. What is the % concentration by mass of 65 g of C6H12O6 dissolved in 500 g of water? (11.5%)
3. You have a 1000 g bleach solution. The % concentration by mass of the solute NaOCl is 6.02 % . How many
grams of the NaOCl are in the solution? (60.2 g)
4. How many grams of water would you have to add to 50 g of NaCl to produce a solution concentration of 5%?
(950 g)
5. What is the solution concentration by mass of 12 grams of NaCl dissolved in 300 grams of water? (3.8%)
6. If you need to produce 500 grams of an 8.3% saline solution, how many grams of salt and how many grams of
water would you use to form the solution? (41.5 g of salt, 458.5 g H2O)
Percent by Volume Examples:
1. What is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL of
water?
2. If you have 100 mL of a 30% aqueous solution of ethanol, what volumes of ethanol and water are in the
solution?
3. What is the percent by volume of isopropyl alcohol in a solution that contains 24 mL of isopropyl alcohol in
1.1 L of water?
4. What is the percent by volume of 140 mL of isopropyl alcohol dissolved in 60 mL of water?
23.3%, 30 mL/70 mL, 2.1%, 70%
Dilution Solutions
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Concentrated stock solutions of chemicals are purchased in the laboratory because they are much more
economical to buy
These solutions are diluted to desired concentrations that are required by the labs we perform in class
To properly dilute solutions we use the following equation:
o
o
Where ‘M’ =
Where ‘V’ =
Diluting Solutions Examples:
5. What volume of a 3M KI solution would you use to make .3 L of a 1.25M KI solution?
6. How many milliliters of a 5M H2SO4 solution would you need to prepare 100 mL of .25 M H2SO4?
7. If you dilute 20 mL of a 3.5M solution to make 100 mL of solution, what is the molarity of the dilute solution?
125 mL, 5 mL, .7M
Molarity
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When chemists are working with a reaction in an aqueous solution, they must know the number of particles
(atoms, molecules) that are present
Since we count the number of particles present using moles, then the number of moles of solute dissolved
per liter of solution is referred to as ____________ (M), or molar concentration
The unit ‘M’ is read as molar
A liter of solution containing one mole of solute is read as a 1 Molar Solution
The following formula is used to calculate the molarity of a solution:
Molarity Practice I
1) 58 g NaCl
1 Liter
1 molar
2) ____ g NaCl
1 Liter
2 molar
(116 g)
3) 58 g NaCl
.5 Liter
________
(2 M)
4) ____ g NaCl
5) 232 g NaCl
1 Liter
1 Liter
.5 Molar
__________
(4 M)
6) _____g LiCl
1 Liter
7) 200 g CaCO3
1 Liter
___________
(2 M)
8) 98 g CCl4
1 Liter
____________
(.64 M)
9) 27 g CaCO3
500 mL
____________
(.54 M)
10) _____g CaSO4
1 Liter
2 Molar
(29 g)
2.3 Molar
(84 g)
(312.8 g)
11) _____g NaCl
350 mL
.8 Molar
(16.24 g)
12) 87 g LiCl
_______
1 molar
(2.07 L)
13) ______ g C6H12O6
800 mL
1.5 molar
( 216 g)
14) 58 g H2SO4
300 mL
________
(1.97 M)
15) 128 g CO2
_______
3.2 M
16)______g NaSO4
1.8 L
2.7 M
(578.3 g)
17) 12.6 g KCl
5.4 L
______
( .03 M)
18) 172 g NaHCO
19) _____ g NaCl
____________
1.7 M
(.9 L)
(1.95 L)
2.7 L
4.2 M
(657.7 g)
20) 43 g HCl
225 mL
_______
(5.3 M)
21) 183 g K2SO4
________
3.6 M
(.29 L)
This is a typical molarity problem:
1.
What is the molarity of a solution containing 58 grams of salt in 1 Liter of solution?
2.
What is the molarity of a glucose solution containing 12.8 g of glucose in 1.5 liters of an aqueous solution?
3.
Calculate the molarity of 100 mL of a solution containing 50 g of H 2SO4.
4.
What is the molarity of 500 mL of a solution containing 125 g of MgSO 4?
5.
What is the solution concentration of 45 g of NaCl in 350 mL of water?
6.
How many grams of salt would be dissolved in 1.0 L of a 0.5M solution of NaCl?
7.
If the solubility of O2 is 8.3 g/L at 3 atm, how many g/L will dissolve at 10 atm?
8.
How many grams of CaCO3 are contained in one liter of a 4M CaCO3 solution?
9.
How many grams of Na3PO4 should be dissolved in 800 mL of water to make a .3M solution of Na 3PO4?
10. How many grams of LiCl are in 750 mL of a 4.0M LiCl solution?
11. If the solubility of N2 is 2.3 g/L at 3 psi, how much pressure is needed to dissolve 8.0 g/L?
12. How many grams of water must be added to 12 grams of salt to make a 15% solution concentration?
13. How many grams of C6H12O6 are needed to make a 600 mL of .3M aqueous solution of C 6H12O6?
14. How many grams of CCl4 are in 300 mL of a 5M CCl4 solution?
15. How many grams of NH3 can be produced with 500 g of N2 and an unlimited amount of H2?
Molality
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concentration expressed as the number of moles of solute dissolved in 1 kilogram of solvent
volume can change with temperature but mass does not so molarity can change if temperature changes but not
molality
use m, Molal
ex. 1.3 m solution is a 1.3 molal solution
Conversion reminder: to convert g to kg, you must divide by 1000 (1000 g = 1 kg)
𝑴𝒐𝒍𝒂𝒍𝒊𝒕𝒚 =
𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
𝒌𝒈 𝒐𝒇 𝒔𝒐𝒍𝒗𝒆𝒏𝒕
Example Problem #1
Calculate the molality of a solution that contains 15.7 g of NaCl in 100 g of water.
Example Problem #2
Calculate the molality of a solution that contains 20.0 g CaCl2 in 700 g of H2O.
Molality Practice Problems
Solve the following problems. Show all work!
1. What is the molality of a solution in which 3.0 moles of NaCl are dissolved in 1.5 kg of water?
2. What is the molality of a solution in which 55 g of NaBr is dissolved in 2.0 kg of water?
3. What is the molality of a solution in which 15 g of I2 is dissolved in 500 g of water?
4. If 13.8 g of KCl is dissolved in 750 g of water, then what is the molality of the solution?
5. A solution contains 25 g of LiCl in 135 g of water. What is the molality of the solution?
Molarity and Molality Practice Problems
I.
Molarity Problems
Be sure to show all your work!!
1. What is the molarity of an aqueous solution that contains 14.2 g NaCl dissolved in 2.35 L of solution?
2. How many grams of NaCl would be contained in 1.00 L of the solution in #1?
3. A solution is made by dissolving 17.0 g of lithium iodide (LiI) in enough water to make 387 mL of solution.
What is the molarity of the solution?
4. How many grams are contained in 150 mL of a 0.20 M solution of K2SO4?
5. Calculate the molarity of a water solution of CaCl2, given that 5.04 L of the solution contains 612 g of CaCl2.
6. Suppose you wish to make 0.85 L of a 0.25 M solution of silver nitrate, AgNO3? How many grams of the
AgNO3 would you need to prepare the solution?
II.
Molality
Be sure to show all work!!!
1. What is the molality of a solution that contains 16.3 g of potassium chloride, KCl, dissolved in 845 g of water?
2. What is the molality of a solution formed by mixing 104 g of silver nitrate, AgNO3, with 1.75 kg of water?
3. Suppose that 5.25 g of sulfur, S8, is dissolved in 682 g of the liquid solvent carbon disulfide, CS2. What is the
molality of the sulfur solution?
4. What is the molality of a solution that contains 25 g of NaCl in 2.2 kg of water?