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. Molarity= Moles Litre

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

=0.356 M L g x 1 mole5.00 g Molarity = g KOH is dissolved in 250. mL of water, calculate the molarity.

3.How many grams are there in 205. mL of a M solution of NaCl? 1 L x moles0.205 Lx 58.5 g 1 mole = 2.06 g

=2.62 L mole x 1L1 mole 95.3 g 125 g x 4.How many litres of M MgCl 2 solution contain 125 g MgCl 2 ?

5.How many grams of NaCl must be used to prepare a mL of M solution. = 1.46 g 1 mole x 58.5 gx moles 1 L L

6.How many millilitres of a M solution of CoCl 2 will contain 25.0 g ? = 962 mL 1 L x 1000 mL mol x 1 L g x 1 mole25.0 g

7.Describe how you would prepare mL of a M solution of CoCl 2. Transfer and rinse to a 100 mL volumetric flask- fill to the line Dissolve in water Weigh 2.60 g of CoCl 2 = 2.60 g 1 mole x g 1 L x moles L