Concentration of solutions
CONCENTRATED = Lots of solute in the
solution
DILUTE = Not much solute in the solution
Ways to express concentration
numerically
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Molarity
% by Mass
% by Volume
Parts per million
MOLARITY
Molarity = # of moles of solute in 1
liter of solution
See Table T
Molarity Problems
What is the molarity of a solution of NaOH if
there are 4 moles of NaOH dissolved
water to make 1 liter of solution?
4 moles
1 liter
= 4M
Molarity Problems
What is the molarity of a solution of NaOH if
there are 4 moles of NaOH dissolved
water to make 2 liters of solution?
4 moles
2 liter
= 2M
Molarity Problems
What is the molarity of a solution of NaOH if
there are 2 moles of NaOH dissolved
water to make 6 liters of solution?
2 moles
6 liters
= .33 M
Molarity Problems
What is the molarity of a solution of NaOH if
there are 2 moles of NaOH dissolved
water to make .5 liters of solution?
2 moles
.5 liters
= 4M
Molarity Problems
What is the molarity of a solution of NaOH if
there are 40 grams of NaOH dissolved
water to make 1 liters of solution?
First, convert grams to moles:
Na = 23 g/mol
O = 16 g/mol
H=
1 g/mol
40 g/mole GFM
so 40 g = 1 mole
Molarity Problems
What is the molarity of a solution of NaOH if
there are 40 grams of NaOH dissolved
water to make 1 liters of solution?
1 moles
1 liters
= 1M
Molarity Problems
What is the molarity of a solution of NaOH if
there are 80 grams of NaOH dissolved
water to make 1 liters of solution?
80g/40g/mol = 2 moles
2 moles
1 liters
= 2M
Molarity Problems
What is the molarity of a solution of NaOH if
there are 3.6 grams of NaOH dissolved
water to make 2 liters of solution?
3.6g/40g/mole = 0.09 moles
0.09 moles
2 liters
= 0.045 M
In General….
Concentrations < 1M are considered weak,
or dilute
Concentrations > 1M are considered strong,
or concentrated
Always know the concentration of your
solution before you use it!!!! (read the
label)
Can you….
Rearrange the molarity equation to solve for
moles?
Molarity = Moles
Liter
moles = ?
Can you….
Rearrange the molarity equation to solve for
moles?
Molarity = Moles
Liter
moles = Liter x Molarity
Can you….
Rearrange the molarity equation to solve for
Liters?
Molarity = Moles
Liter
Liters = ?
Can you….
Rearrange the molarity equation to solve for
Liters?
Molarity = Moles
Liter
Liters = Moles
Molarity
Example
How many moles of NaOH do you have if
you have 3 liters of a 0.5M NaOH
solution?
Moles = Molarity x Liters
Moles = 0.5M x 3 liters
Moles = 1.5
% Mass
Uses the same formula as % composition
(See Table T)
Percent mass = mass of part
Mass of whole
x 100
% Mass
What is the % mass of NaOH if 2.5 g of NaOH are added to
50 g of water?
Percent mass = mass of part (solute)
x 100
Mass of whole (solution)
% mass = 2.5g
(2.5 + 50g)
x
% mass = (2.5 / 52.5) x 100
= 4.76% solution
100
% Volume
Uses the same formula as % composition
(See Table T)
Percent volume = volume of part
volume of whole
x 100
% Volume
What is the % volume of NaOH if 20 ml of NaOH are added
to 300 ml of water?
Percent volume = volume of part (solute)
volume of whole (solution)
% volume = 20 ml
(20 ml + 300 ml)
% volume = (20 / 320) x 100
= 6.25% solution
x
100
x 100
Parts per million
ppm = grams solute x 1,000,000
grams solution
This is used when the amount of solute is
very very small
Parts per million
ppm = grams solute x 1,000,000
grams solution
.0043 g of oxygen gas dissolve in 100 ml of
water at 20 degrees celsius. What is the
concentration in ppm?
Parts per million
ppm = .0043g
x 1,000,000
(100 g + 0.0043g)
Concentration = 43 ppm