Concentration
CALCULATING CONCENTRATION
OF SOLUTIONS
1. Mass Percent = (mass of solute/mass of
solution)100
2. Parts per million = (mass of solute/mass of
solution)106
3. Mass/volume percent = (mass of solute/mL
solution)100
4. Volume percent = (mL solute / mL solution)100
5. Molarity = n/V = moles solute / L solution
6. Molality = moles of solute / kg solvent
CALCULATING CONCENTRATION
OF SOLUTIONS
1. What is the mass percent of a solution
made by adding 25.0 g of KCl to 100.0
mL of water?
2. What is the concentration of a solution
made by mixing 25.0 g of KCl in (a)
100.0 mL and (b) 100.0 L of water in
ppm?
• The following slides are
extra worked out examples.
CALCULATING CONCENTRATION OF
SOLUTIONS
• How many grams of a solution that is
32.7% by mass NaCl would contain 45.0 g
of NaCl?
Mass % = (mass of solute /mass of solution) 100
32.7 % = (45.0 g / x )100
x = 45.0 g / 0.327
x = mass of solution = 138 g
CALCULATING CONCENTRATION OF
SOLUTIONS
• How much solute is present in 756.1 mL of
a 14.7% (mass/volume) HCl solution?
Mass/volume % = (masssolute/volumesolution) 100
14.7 % = (x / 756.1 mL )100
x = 0.147 (756.1 mL)
x = mass of solute = 111g
CALCULATING CONCENTRATION OF
SOLUTIONS
• How many grams of LiF are in 500 mL of a
solution that is 18.4% by mass and has a
density of 1.197 g/mL?
•
Masssolution = densitysolution (Volumesolution)
= 1.197 g/mL (500 mL)
= 598.5 g solution
Mass% = (masssolute/masssolution) 100
18.4 % = (x / 598.5 g )100
x = 0.184 (598.5 g)
x = mass of solute = 110 g
CALCULATING CONCENTRATION OF
SOLUTIONS
• A 350 mL sample of drinking water was analyzed
and found to contain 0.0046 g of sulfate salts.
Calculate the concentration of sulfate salts in
this water sample?
• Masswater = densitywater (Volumewater)
= 1.00 g/mL (350 mL)
= 350 g solution
ppm = (masssolute/masssolution) 106
ppm = (0.0046g / 350 g ) 106
ppm = 13 ppm
Use ppm for trace amounts of solute.
CALCULATING CONCENTRATION OF
SOLUTIONS
• Calculate the molality of a solution composed of
53.0 g of KOH in 500 mL of water.
First calculate the moles of solute:
n = 53.0 g (1 mol / 56 g) = 0.946 mol solute
Next, m = moles of solute / kg solvent
m = (0.946 mol / 0.500 kg )
m = 1.89 molal solution
PRACTICE PROBLEMS #36
calculating the CONCENTRATION OF SOLUTIONS
___1. How many grams of a 45.0 % Mg(OH)2 solution can be made
from 7.00 g of solid Mg(OH)2?
15.6 g
___2. How many kilograms of a 6.8% KC2H3O2 solution will contain 5.3
moles of KC2H3O2?
7.6 kg
___3. How many grams of KOH are needed to make 250.0 mL of a
solution that is to contain 6.70 mg/mL of potassium ion? 2.41 g
___4. If 134.5 g of a 25.0 % sucrose solution was prepared, how
many grams of a 5.00% solution of sucrose would contain the same
amount of sugar? 673 g
___5. How many grams of solution, 10.0% KOH by mass, are required
to neutralize 25.0 mL of a 2.00 M HCl solution if the moles of HCl
is equal to the moles of KOH? 28.0 g
Group study problem #36
calculating the CONCENTRATION OF SOLUTIONS
___1 How many grams of a solution, that is 76.3% by mass KBr, would
contain 38.95 g of KBr?
___2. What is the ppm and molality of a solution containing 75.0 g of
ethylene glycol, C2H6O2, in 200.0 g of water?
___3. How many grams of CuSO4 are needed to make 350.0 mL of a
solution that contains 10.5 mg/mL of Cu2+ ion? Calculate the
molarity of the resulting solution.
___4. Automobile battery acid is 38% H2SO4 and has a density of
1.29 g/mL. Calculate the molality of this solution.
___5. If 27.0 g of LiBr are dissolved in 50.0 g of water, the percent
of LiBr by mass is
___6. If 15.0 g of KNO3 is added to 75g of water, what is the mass
percent of KNO3 in the solution?