Download 4/15/2015 1 CONCENTRATION OF SOLUTIONS

4/15/2015
CONCENTRATION
• In chemistry we often refer to solutions
as dilutes or concentrated
CONCENTRATION OF
SOLUTIONS
• Refers to the amount of solute involved
• Express concentration using different
calculations
MOLARITY
EXAMPLE
• Number of moles of solute per liter
of solutions
• What is the molairty of a solution that
contains 4.0 mol of NaOH in .50L of solution?
• To calculate use the formula
• Substitute in the formula
• Molarity = Moles of Solute
Liters of solution
• Molarity = Moles of Solute
Liters of solution
Molarity = 4.0 moles NaOH
.50 liter
•
M = 8.0
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EXAMPLE
• What is the molarity of a solution containing
82.0 g of Ca(NO3)2 in two liters of solution?
• Step 1 Covert grams to moles
• GFM= 164 g/m of Ca(NO3)2
• Moles= 82.0
164
= .500 mols
CONT…….
• Step 2 Calculate molarity
• M = .500 mol
2.0 liters
M = .250
REMINDER
• Answers need to be calculated
using liters
• If a question uses ml instead of liters
divide by 1,000
• Ex. 500 ml = 0.5 L
TRY
• Find the molarity of 100 mL of a
solution that contains 0.25 moles of
dissolved solute
• M = .25
.100
2.5M
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PARTS PER MILLION
PARTS PER MILLION
• Is the ratio between the mass of a solute and
the total mass of the solutions
• This is used when the concentrations are low
or diluted (difficult to calculate)
• Ppm = grams of solute x 1,000,000
grams of solution
• Ex. Swimming pools
• 2 grams of Cl per 1,000,000 grams of water
• Or particles in the air
EXAMPLE
• Approximately .0043 g of oxygen can
be dissolved in 100.00ml of water at 20
degrees. Express this in parts per
million
EXAMPLE
• Ppm = .0043 g x 1,000,000
100.0043 g
Ppm = 43
• Grams of solute = .0043 g
• Grams of solution = 100.0043 g
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TRY
CHALLENGE QUESTION
• What is the ppm of a solution containing .008
g NaOH dissolved in 1000 grams of H2O?
• How many grams of NaCl are needed
to be dissolved in water to make 100
grams of a 250 ppm solution?
• Answer = .025g
• Ppm = .008g
x 1,000,000
1000.008
• 250 = x_
x 1,000,000
100
• Divide 250/1,000,000 =.00025
• Multiply .00025*100
= 8 ppm
PERCENT BY MASS
• Is the mass of an ingredient divided by
the total mass as a percent
• %mass = Mass of part x 100
mass of whole
EXAMPLE
• What is the percent mass of NaOH if
2.50g of NaOH are added to 50.00
grams of H2O?
• Use the formula
• %mass = Mass of part x 100
mass of whole
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EXAMPLE
• % mass = 2.50 grams NaOH
x 100
(2.50 + 50.00) g solution
•
= 4.76%
TRY
• What is the percent by mass of a
solution containing 12.3 g of
caffeine dissolved in 100.0 g of
water?
• Step 1: Find the mass of the solution
• 100.0 g + 12.3 g = 112.3 g
TRY
PERCENT VOLUME
• Step 2: Divide the mass of the solute by
the mass of the solution and multiply
by 100 %
• Sometimes we might not have solids, but
liquids
• Ratio of the volume of an ingredient by the
total volume expressed as a percent
• (12.3 / 112.3) x 100
• 11.0%
• Ex. Rubbing Alcohol
70% Ethanol
• This means 70% is Alcohol, 30% is water
• % volume = volume of solute
Volume of solution
x100
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EXAMPLE
• What is the percent by volume of
alcohol if 50.0 ml of ethanol is diluted
with water to form a total volume of
300.0 ml?
50.0 ml x100
300.0ml
= 16.7 % alcohol
TRY
• If 19 mL of alcohol are dissolved in 31
mL of water, what is the percentage
by volume of alcohol?
• (19/50)
=
x 100
38%
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