1. Introduction to Molarity
Chemistry 11
Introduction to Molarity
Lesson 1

2. Chemists need to make solutions that have precise concentrations

3. Pesticides must be in proper concentrations.
Food additives must be in correct concentrations.
A driver is legally impaired at 0.08 mg/mL blood alcohol content.
A new driver is legally impaired at 0.00 mg/mL blood alcohol content.
Chemists control the concentration of chemicals using the concepts we will develop in this unit.

4. The concentration of a solution tells you how much solute that is dissolved in a given amount of solvent (water).
The molarity is the concentration of a solution.
Moles
Molarity =
Litre

5. 1. 2. 255 moles of NaCl is dissolved in 4
moles of NaCl is dissolved in 4.0 L of water, calculate the molarity.
Molarity =
2.255 moles
4.0 L
= 0.56 moles/litre
= 0.56 M (Molar)
M means moles per 1 litre

6. 2. 5.00 g KOH is dissolved in 250. mL of water, calculate the molarity.
x 1 mole
56.11 g
Molarity =
0.250 L
= M

7. 3. How many grams are there in 205. mL of a 0.172 M solution of NaCl?
x moles
x g
= g
1 L
1 mole

8. 4. How many litres of 0.500 M MgCl2 solution contain 125 g MgCl2?
125 g x
1 mole
x 1L
= 2.62 L
95.3 g
0.500 mole

9. 5. How many grams of NaCl must be used to prepare a 100. 0 mL of 0
5. How many grams of NaCl must be used to prepare a mL of M solution. L
x moles
x g
= g
1 L
1 mole

10. 6. How many millilitres of a 0.200 M solution of CoCl2 will contain 25.0 g ?
x mole
x L
x mL
= mL
129.9 g
0.200 mol
1 L

11. 7. Describe how you would prepare 100. 0 mL of a 0
7. Describe how you would prepare mL of a M solution of CoCl2. L
x moles
x g
= g
1 L
1 mole
Weigh 2.60 g of CoCl2
Dissolve in water
Transfer and rinse to a 100 mL volumetric flask- fill to the line