1. Solution Concentration (Molarity) Topic 1.5

2. Solutions
Solutions are homogenous mixtures formed when one substance disperses completely into another.
Solvent: substance in the solution found in a greater amount
Solute: substance dissolved into the solvent

3. Parts of a Solution
solute – the part of a solution that is being dissolved (usually the lesser amount)
solvent – the part of a solution that dissolves the solute (usually the greater amount)
solution = solute + solvent
Solute
Solvent
Solution Si Al
metal alloy
salt
water
salt water
CO2
carbonated water O N
air

4. Saturation and Solubility
Terminology:
1. Dissolving: the process of surrounding solute particles with solvent particles.
2. Crystallization: The process of solute particles attaching to each other

5. Saturation
Saturated: a solution in equilibrium with undissolved solute.
Unsaturated: less solute is dissolved than is required for a saturated solution.
Supersaturated: more solute is dissolved than needed for a saturated solution.
Only possible under the right environmental conditions

6. Solutions and Stoichiometry
Many times the reactants and/or products of chemical reactions are aqueous solutions.
In these cases the concentration of the solution must be determined in order to determine amounts of reactants or products
The concentration of a solution is a measure of the amount of solute that is dissolved in a given amount of solution *

7. Units of Concentration
Parts per million (ppm): grams of solute per million grams of solution
Typically used for expressing acceptable amounts of toxic substances in the environment
Mass/volume ratio (density):
Mole/unit of solvent ratio (molarity, molality, mole fraction)

8. Molarity The most common concentration unit is Molarity Molarity (M) =
Moles of solute
dm3 of solution *

9. Molarity = Molarity moles solute dm3 of solution
The number of moles of solute dissolved in cubic decimeters of solution
Molarity =
moles solute
dm3 of solution

10. 1. 0 dm3 of water was used to make 1. 0 dm3 of solution
1.0 dm3 of water was used to make 1.0 dm3 of solution. Notice the water left over dm3 of water would be too much.

11. Making a known molar solution
top off to 1 liter

12. What is the concentration of 2 moles of HCl in 4 dm3?
2 mol / 4 dm3 = 0.5 M

13. Step 1: Calculate moles of NiCl2• 6H2O in 5 g of NiCl2• 6H2O
PROBLEM: Dissolve 5.00 g of NiCl2•6 H2O in enough water to make 250 mL of solution. Calculate the Molarity.
Step 1: Calculate moles of NiCl2• 6H2O in 5 g of NiCl2• 6H2O
1.0 L = 1000 mL
.25 L = 250 mL
Step 2: Calculate Molarity

14. M = moles/V  moles = M•V USING MOLARITY
What mass of oxalic acid, H2C2O4, is required to make 250 mL of a M solution?
M = moles/V  moles = M•V
Step 1: Change mL to L.
250 mL/1000 = L
Step 2: Calculate.
moles = ( M) (0.250 L) = moles H2C2O4
Step 3: Convert moles to grams.
( mol H2C2O4) (90.00 g) = g
1 mol H2C2O4

15. Learning Check
How many grams of NaOH are required to prepare 400 mL of 3.0 M NaOH solution?
1) 12 g
2) 48 g
3) 300 g

16. Molarity Calculations
How many grams of NaOH are required to prepare 250 cm3 of M solution?
Molar Mass of NaOH = = 40.0 g/mol
250 cm3 = dm3
(0.500 mol) x
(40.0 g)
x (0.250 dm3 )
= 5.00 g
( dm ) x
( mol ) *

17. Molarity Calculations
Calculate the concentration of a NaCl solution that contains 24.5 g of NaCl in 250 cm3 of solution.
Molar mass of NaCl = = 58.5
(24.5 g NaCl) X 1
= 1.67 M
(58.5 g mol-1 )
(0.250 dm3 ) *

18. Stoichiometry Calculations Involving Solutions 1
15.0 cm3 of a M AgNO3 solution is required to precipitate the sodium chloride in 10 cm3 of a salt solution. What is the concentration of the solution?
AgNO3 (aq) + NaCl (aq) →AgCl (s) +KNO3 (aq)
Molar Mass NaCl = = 58.5 g/mol
0.500 mol AgNO3 X
dm3 x
1 mol NaCl X
58.5 g mol NaCl
dm3
1 mol AgNO3
= g of NaCl
0.439 g of NaCl x
58.5 g mol dm3
= mol dm-3 or 0.75 M *

19. Stoichiometry Calculations Involving Solutions 2
Copper metal reacts with nitric acid according to the following reaction:
8 HNO3 (aq) Cu → 3 Cu(NO3)2 (aq) H2O (l) NO (g)
What volume of M HNO3 would be required to consume a copper penny whose mass is 3.08 grams?
(3.08 g Cu )
(8 mol HNO3)
(1 dm3)
( 1000 cm3)
(63.55 g mol-1 Cu )
(3 mol Cu)
= 16.2 cm3 *

20. Molality which is mass/volume
grams/liters
or IB says g dm-3
What is the concentration of 15 g of NaCl dissolved in 500 ml of water
15g/.5L = 30 g dm-3