Solutions and Units
of Concentration
May 11, 2015
What is a Mixture?
Types of Mixtures
Definitions

A solution is a homogeneous mixture

A solute is dissolved in a solvent.
–  Solute is the substance being dissolved
–  Solvent is the liquid in which the solute is
dissolved
–  An aqueous solution has water as solvent
Definitions Continued

Dilute: a solution with a small amount of solute

Concentrated: a solution with a large amount
of solute

A saturated solution is one where the
concentration is at a maximum - no more
solute is able to dissolve

A super-saturated solution is one where the
concentration has more solute than it can
normally dissolve

Solubility: a measure of how easily a solute
dissolves in a solvent
Some Examples
Solute
Solvent
Example
solid
solid
Alloys (brass, steel)
solid
liquid
Salt water
gas
solid
liquid
liquid
Air bubbles in ice
cubes
Ethanol in water
gas
liquid
Soft drinks
gas
gas
Air
Solubility
  We
can measure how easily a
solute will dissolve in a certain
solvent.
  This measure is called solubility
Dissolution of Solid Solute
What are the driving forces which cause
solutes to dissolve to form solutions?
1. Covalent solutes dissolve by H-bonding
to water
2. Ionic solutes dissolve by dissociation
into their ions.
Solution and Concentration
WAYS OF EXPRESSING CONCENTRATION
– Molarity (M)
– Molality (m)
– Mole Fraction (X)
– Mass Percent (%)
– Parts Per… (ppm)
Molarity (M)
moles of solute (n)
M=
L of solution (V)
**concentration of solute per given amount of
volume**
Concentration measurement
  Because volume is temperature
dependent, molarity can change with
temperature

Concentration: Molarity Example
Calculate the molarity of the following
solution:
1) 2.3 moles of sodium chloride in 0.45
liters of solution
M = moles of solute = 2.3 moles = 5.11M
liters of solution
0.45 liters
Concentration: Molarity Example
2) 45 grams of ammonia (NH3) in 0.75 L of
solution.
First convert grams of NH3 to moles:
45 g / 17 g = 2.65 Moles
MM of NH3
Now plug into Molarity equation:
M = moles of solute = 2.65 moles = 3.53M
liters of solution
0.75 liters
Concentration: Molarity Example
3) What mass of LiOH would you mass to
make a 5.0 liter of 2.06 M solution
First find how many moles 5.0 L would be:
M=n
2.06 M = n
V
5.0 L
n = 10.3 moles
Now find the mass of 10.3 moles:
mass = Moles x molar mass LiOH
mass = 10.3 Moles x 23.95 g/M
mass = 246.7 grams
NOW YOU TRY
1) 0.09 moles of sodium sulfate in 12 mL
solution. (1000 mL = 1 L)
0.09 Moles / .012 L = 7.5 M
2) 0.75 moles of lithium fluoride in 65 mL
of solution. (1000 mL = 1 L)
0.75 Moles / .065 L = 11.54 M