Concentration units
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Concentration Units. Percent by mass, mole fraction, molarity, and molality. Percent by mASS. PERCENT BY MASS =. MASS OF SOLUTE. X 100%. MASS OF SOLUTION. 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?.

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Concentration Units

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Concentration units

Concentration Units

Percent by mass, mole fraction,

molarity, and molality


Percent by mass

Percent by mASS

PERCENT BY MASS =

MASS OF SOLUTE

X 100%

MASS OF SOLUTION

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 =

X 100%

0.892g + 54.6g

= 1.61%


Concentration units1

Concentration Units

Percent by mass, mole fraction,

molarity, and molality


Mole fraction x

Mole fraction (x)

MOLE FRACTION OF COMPONENT A = XA =

Moles of A

Σ all moles in solution

Your solution contains 5 moles of KCl and 15 moles of water.

What is the mole fraction of KCl?

5 moles KCl

XKCl =

= 0.25

5 moles KCl + 15 moles H2O

What is the mass percent of KCl?

74.55 g

5 molKCl x

Mass percent of KCl =

1 molKCl

= 58%

74.55 g

18.02 g

15 mol H2O x

5 molKCl x

+

1 molKCl

1 mol H2O


Concentration units2

Concentration Units

Percent by mass, mole fraction,

molarity, and molality


Molarity and molality

Molarity and molality

Moles of solute

Moles of solute

MOLALITY = m =

MOLARITY = M =

Kg of solvent

Liters of solution

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.

1 mol H2SO4

24.4 g H2SO4 x

mH2SO4 =

98.09 g

= 1.26m = 1.26 “molal”

0.198 kg H2O

What is the molarity of the solution? (d = 1.84 g/mL)

1 mL

= 120.87 mL

Volume of solution =

(24.4g + 198g)

1.84g

0.2487 mol H2SO4

Molarity = M =

= 2.06M = 2.06 “molar”

0.12087L solution


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