Preparing a Molar Solution

• How many grams of sucrose (C 12 H 22 O 11 ) is needed to prepare one liter of a 1.50 M solution?

• You’ll need the molar mass of sucrose: 1.5 mol 342 g _____________ X ___________ = 513 g / liter 1 liter 1 mol

Preparing a Molar Solution

• How many grams of sucrose (C 12 H 22 O 11 ) is needed to prepare 100 mL of a 1.50 M solution?

1.5 mol 342 g _____________ X ___________ = 513 g / liter 1 liter 1 mol 1 L 513 g 100 mL X __________ X _____________ = 51.3 g 1000 mL 1 L

Diluting Solutions

• Many solutions (acids) come in a concentrated liquid form called a stock solution • To dilute this solution, you add more solvent (usually water or alcohol) • The amount of solute does not change, so the amount of solution SO M 1 V 1 = M 2 V 2

Diluting Solutions

• What volume in milliliters of 2.00M calcium chloride (CaCl 2 ) would you use to make .50 L of .300 M calcium chloride solution?

.50 L X 1000 mL/1 L = 500 mL M 1 V 1 = M 2 V 2 2.00M x V 1 = .300M x 500 mL V 1 = .300M x 500 mL / 2.00M V 1 = 75 mL

Mole Fraction

• Another way to express concentration • Need to know the number of moles of solute and solvent • Abbreviated as X X a = mole fraction of solvent = n a / n a + n b X b = mole fraction of solute = n b / n a + n b

Mole Fractions

• What is the mole fraction of water in an HCl solution containing 62.5% water and 37.5% HCl by mass?

62.5 g x 1mol / 18.02 g = 3.47 mol H 2 O 37.5 g x 1mol / 36.46 g = 1.03 mol HCl n a / n a + n b 3.47

mol H20 / 1.03 mol HCl + 3.47 mol H20 n a = .771