Molarity

Calculating Molarity and Molality

Concentration

• measure of the amount of solute in a given amount of solvent or solution

• 2 ways to measure

• molarity- mol/L of solution

• molality- mol/ g of solvent

Molarity

• number of moles of solute in one liter of solution

• How to make

• 1. Determine desired molarity i.e. .5 M, 1 M

• 2. determine the mass needed by converting mol to gram

• 3. dissolve in less solvent than 1 L

• 4. Bring total solution to 1 L

Molarity Problem #1

You have 3.5 L of solution that contains 90 g of sodium chloride, NaCl. What is the molarity of that solution?

Problem #2

You have .8 L of a .5 M HCl solution. How many moles of HCl does this solution contain?

Problem #3

A 23.4 g sample of potassium chromate is needed to carry out a reaction in aqueous solution of silver chromate. All you have on hand is 5 L of a 6.0M K2CrO4 solution. What volume of the solution is needed to give you the 23.4 g K2CrO4 needed for the reaction?

Molality

• Second way to express concentration of a solution

• Moles of solute/ mass of solvent in kg

• expressed by m

Problem #1

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.

Problem #2

A solution of iodine, I2. in carbon tetrachloride, CCl4, is used when iodine is needed for certain chemical test. How much iodine must be added to prepare a .480 m solution of iodine in CCl4 if 100 g of CCl4 is used?

Problem #3

What is the molality of acetone in a solution compose of acetone, dissolved in 200 g of water?