Transcript Ways to express the concentration of a solution

Concentration – amount of solute per
quantity of solvent
Ways to express the concentration of a solution
1. Concentration as a Mass/Volume Percent
2. Concentration as a Mass/Mass Percent
3. Concentration as a Volume/Volume Percent
Mass/Volume Percent
• Mass of solute dissolved in a volume of
solution, expressed as a %
Mass/volume percent =
Mass of solute (in g)
Volume of solution (in mL)
x 100%
Example: Saline solution contains 0.9g of sodium chloride
dissolved in 100 mL of solution or 0.9%
A pharmacist adds 2.00 mL of distilled water
to 4.00g of a powdered drug. The final
volume of the solution is 3.00 mL.
a. What is the percent (m/v) of the solution?
mass of solute (in g)
Mass/volume percent=
x 100%
Volume of solution (in mL)
= 4.00 g
x 100%
3.00 mL
= 133%
b. What is the concentration of the drug in
g/100 mL of solution?
133% means 133g/100 mL of solution
Use ratios or cross out units to solve
for the mass of solute in 100 mL
x
100 mL
=
x=
4.00 g
3.00 mL
4.00g x 100 mL
3.00 mL
= 133 g
X = 4.00g x 100ml x
= 133 g
1
3.00ml
Many people use a solution of trisodium phosphate to
clean walls before putting up wall paper. The
recommended concentration is 1.7% (m.v). What mass
of TSP is need to make 2.0 L solution?
(m/v) percent =
Mass of solute (g)
x 100%
Volume of solution (in mL)
rearrange the equation to solve for mass of solute
Mass of solute= (m/v) percent x volume of solution
100%
= 1.7% x 2000 mL
100%
= 34 g
Concentration as a
Mass/Mass percent
Mass/mass percent gives the mass of a
solute divided by the mass of a
solution
- also referred to as percent (m/m)
Mass/mass percent =
Mass of solute (in g)
x 100 %
Mass of solution (in g)
Calcium chloride can be used instead of road salt to melt the
ice on roads during the winter. To determine how much
calcium chloride had been used on a road, a student took a
sample of slush to analyze. The sample had a mass of 23.47 g.
When the solution was evaporated, the residue had a mass of
4.58 g. What was the mass/mass percent of calcium chloride
in the slush?
Mass of solute (in g)
Mass/mass percent =
x 100%
Mass of solution (in g)
=
4.58 g
23.47 g
x 100%
= 19.5 %
The mass/mass percent was 19.5% (m/m)
19.5 g of calcium chloride was dissolved in 100 g of
solution
Concentration as a Volume/Volume
Percent
Volume/volume percent gives the volume of
solute divided by the volume of solution
• Also referred to as percent (v/v), volume
percent concentration
volume of solute (in mL)
Volume/volume percent = Volume of solution (in mL)
x 100%
Rubbing alcohol is commonly used as an antiseptic for
small cuts. It is sold as 70% (v/v) solution of
isopropyl alcohol in water. What volume of isopropyl
alcohol is used to make 500 mL of rubbing alcohol?
Using this equation,
Volume/volume percent = volume of solute
Volume of solution
x 100 %
Rearrange to solve for volume of solute:
Volume/volume % x volume of solution
100%
70% x 500 mL
=
100%
Volume of solute =
= 350 mL
350 mL of isopropyl alcohol is used to make 500 mL of 70% (v/v)
rubbing alcohol.
Concentration in parts per
million or parts per billion
ppm – parts per million (106)(one part solute per
million parts of solution)
ppb – parts per billion (109)(one part solute per billion
parts of solution)
Usually mass/mass relationships ie. The mass of
solute compared with the mass of solution.
mass of solute (g) x 106
ppm =
Mass of solution (g) OR
Mass of solute
Mass of solution
=
xg
106 g of solution
Mercury poisiong becomes apparent when a
person build up more than 20.mg of Mercury in
their body. Express this amount as ppm for a
60.kg person
You must first convert everything into grams
• 20mg/1000g = 2.0 x 10-2 g
• 60kg x 1000g = 6.0 x 104 g
• Ppm = mass solute
x 106
mass solution
= 2.0 x 10-2 g
x 106
6.0 x 104 g
= (3.33 x 10-7g) x 106
= .33 ppm
Homework
• Pg 376 #21-30, pg 378 #31,39