CONCENTRATION OF SOLUTIONS

Chapter 13.3

Objectives1. Given the mass of solute and

volume of solvent, calculate the concentration of a solution

2. Given the concentration of a solution, determine the amount of solute in a given amount of solution

3. Given the concentration of a solution, determine the amount of solution that contains a given amount of solute

Concentration Measure of the amount of solute in a

given amount of solvent or solution Solutions

Dilute or concentrated Dilute – relatively small amount of solute in

a solvent Concentrated – relatively large amount of

solute in a solvent Measure of the amount of solute in a given

Molarity Number of moles of solute in one

liter of solution M - Symbol Written as 1 M NaOH

One molar solution of sodium hydroxide One mole NaOH in 1 liter of solution

molarity = amount of solute (mol)

volume of solution (L)

Units are mol/L

Making a 0.500 M Solution of NaOH Step 1: Determine mass needed

M =

0.500 M =

mol solute =

mass of NaOH needed = 0.500 mol NaOH x

mol solute

L solution

mol solute

1.00 L

0.500 M 1.00 LX = 0.500 mol NaOH

40.0 g NaOH

1 mol NaOH

= 20.0 g NaOH

Step 2: Measure out 20.0 g NaOH using a balance

Step 3: Add less than one Liter of water to a volumetric flask.

Step 4: Dissolve 20.0 g (0.500 mol) of NaOH in the water.

Step 5: Fill volumetric flask to the line.

Practice Problems1. You have 3.50 L of solution that contains 90.0

g of sodium chloride, NaCl. What is the molarity of that solution?

2. You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain?

3. To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in solution as a reactant. All you have on hand in the stock room is 5 L of 6.0 M K2CrO4 solution. What volume of the solution is needed to give you the 23.4 g K2CrO4 need for the reaction?

Molality Concentration of a solution

expressed in moles of solute per kilogram of solvent. m - symbol Written as 1 m solution of NaOH

One molal solution of sodium hydroxide 1 mol NaOH in 1 kg of solvent

molality = moles solute (mol)

mass of solvent (Kg)

Practice Problems1. A solution was prepared by dissolving

17.1 g of sucrose (table sugar, C12H22O11) in 125 g of water. Find the molal concentration of this solution.

2. A solution of iodine, I2, in carbon tetrachloride, CCl4, is used when iodine is needed for certain chemical tests. How much iodine must be added to prepare a 0.489 m solution of iodine in CCl4 if 100.0 g of CCl4 is used?