Solutions and Units of Concentration FUNDAMENTALS May 11, 2015
Dec 24, 2015
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
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 Air bubbles in ice cubes
liquid liquid 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.
moles of soluteL of solution
M =
Concentration of moles of solute per given amount of volume
Concentration measurement Because volume is temperature
dependent, molarity can change with temperature
Concentrations: MOLARITY (M)
n (moles)
M V (liters)
Concentration: Molarity Example #1Calculate 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 liters of solution 0.45
M = [ 5.11 M ]
n (moles)
M V (liters)
Concentration: Molarity Example #2Calculate the molarity of the following
solution:
2) 10.3 moles of LiOH in 250 mL in solution.
**Need to convert mL to L (÷ by 1000) M = moles of solute = 10.3 moles = 41.2M
liters of solution 0.250 liters
Concentration: Molarity Example #3
Calculate the moles of the following solution:
3) How many moles are needed to make 2 L of a [5.5 M] solution of NaOH?
M = n (moles)
V (liters)
[5.5M] = n (moles)
2 Liters
n = 5.5 x 2 = 11 moles
n (moles)
M V (liters)