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
1L
100 mL X
__________
1000 mL
513 g
X
_____________
1L
= 51.3 g
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