Introduction to Molarity Chemistry 11 Introduction to Molarity Lesson 1

Chemists need to make solutions that have precise concentrations

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.

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

1. 2. 255 moles of NaCl is dissolved in 4 1. 2.255 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

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 = 0.356 M

3. How many grams are there in 205. mL of a 0.172 M solution of NaCl? x 0.172 moles x 58.5 g = 2.06 g 1 L 1 mole

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

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 100.0 mL of 0.250 M solution. 0.1000 L x 0.250 moles x 58.5 g = 1.46 g 1 L 1 mole

6. How many millilitres of a 0.200 M solution of CoCl2 will contain 25.0 g ? x 1 mole x 1 L x 1000 mL = 962 mL 129.9 g 0.200 mol 1 L

7. Describe how you would prepare 100. 0 mL of a 0 7. Describe how you would prepare 100.0 mL of a 0.200 M solution of CoCl2. 0.1000 L x 0.200 moles x 129.9 g = 2.60 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