Preparing a Molar Solution

• How many grams of sucrose (C12H22O11) 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 (C12H22O11) 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

M1V1 = M2V2

Diluting Solutions• What volume in milliliters of 2.00M calcium

chloride (CaCl2) would you use to make .50 L of .300 M calcium chloride solution?

.50 L X 1000 mL/1 L = 500 mL

M1V1 = M2V2

2.00M x V1 = .300M x 500 mL

V1 = .300M x 500 mL / 2.00M

V1 = 75 mL

Mole Fraction

• Another way to express concentration

• Need to know the number of moles of solute and solvent

• Abbreviated as X

Xa = mole fraction of solvent = na / na + nb

Xb = mole fraction of solute = nb / na + nb

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 H2O

37.5 g x 1mol / 36.46 g = 1.03 mol HCl

na / na + nb

3.47 mol H20 / 1.03 mol HCl + 3.47 mol H20

na = .771