Transcript Concentration Units

CONCENTRATION UNITS
PERCENT BY MASS, MOLE FRACTION,
MOLARITY, AND MOLALITY
PERCENT BY MASS
MASS OF SOLUTE
PERCENT BY MASS =
MASS OF SOLUTION
X 100%
A sample of 0.892g of potassium chloride is dissolved in 54.6g of water.
What is percent by mass of KCl in the solution?
0.892g
Percent by mass of KCl =
0.892g + 54.6g
= 1.61%
X 100%
CONCENTRATION UNITS
PERCENT BY MASS, MOLE FRACTION,
MOLARITY, AND MOLALITY
MOLE FRACTION (X)
Moles of A
MOLE FRACTION OF COMPONENT A = XA = Σ all moles in solution
Your solution contains 5 moles of KCl and 15 moles of water.
What is the mole fraction of KCl?
XKCl =
5 moles KCl
5 moles KCl + 15 moles H2O
= 0.25
What is the mass percent of KCl?
5 mol KCl x
Mass percent of KCl =
74.55 g
1 mol KCl
5 mol KCl x 74.55 g
1 mol KCl
18.02 g
+ 15 mol H2O x
1 mol H2O
= 58%
CONCENTRATION UNITS
PERCENT BY MASS, MOLE FRACTION,
MOLARITY, AND MOLALITY
MOLARITY AND MOLALITY
MOLARITY = M =
Moles of solute
MOLALITY = m =
Liters of solution
Moles of solute
Kg of solvent
Calculate the molality of a sulfuric acid solution containing 24.4g of sulfuric acid in
198g of water. The molar mass of sulfuric acid is 98.09 g/mol.
mH2SO4 =
24.4 g H2SO4 x
1 mol H2SO4
98.09 g
= 1.26m = 1.26 “molal”
0.198 kg H2O
What is the molarity of the solution? (d = 1.84 g/mL)
Volume of solution = (24.4g + 198g)
Molarity = M =
0.2487 mol H2SO4
0.12087L solution
1 mL
1.84g
= 120.87 mL
= 2.06M = 2.06 “molar”