Concentration of solutions
CONCENTRATED = Lots of solute in the solution
DILUTE = Not much solute in the solution
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 = 4 M
1 liter
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 M
2 liter
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 = .33 M
6 liters
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 = 4 M
.5 liters
Molarity ProblemsWhat 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 so 40 g = 1 mole
H = 1 g/mol
40 g/mole GFM
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 M
1 liters
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 = 2 M
1 liters
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 = 0.045 M
2 liters
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 = Liter x Molarity
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 x 100
Mass of whole
% 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 x 100 (2.5 + 50g)
% mass = (2.5 / 52.5) x 100 = 4.76% solution
% Volume
Uses the same formula as % composition
(See Table T)
Percent volume = volume of part x 100
volume of whole
% 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) x 100 volume of whole (solution)
% volume = 20 ml x 100 (20 ml + 300 ml)
% volume = (20 / 320) x 100 = 6.25% solution
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?
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