Preparing a Molar Solution

1
Preparing a Molar Solution

• How many grams of sucrose (C12H22O11) is needed
  to prepare one liter of a 1.50 M solution?
• Youll need the molar mass of sucrose
• 1.5 mol 342 g
• _____________ X ___________ 513 g /
  liter
• 1 liter 1 mol

2
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

3
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

4
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

5
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

6
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