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