Concentration of Solutions
Ch 14.2-14.3 (RB) / Chapter 16 (BB)
Heterogeneous Mixtures
A heterogeneous mixture is a mixture that
does not have a uniform composition and in
which the individual substances remain
distinct.
 Suspensions are mixtures containing
particles that settle out if left undisturbed.

Homogeneous Mixtures
Solutions are homogeneous mixtures that
contain two or more substances called the
solute and solvent.
 Most solutions are liquids, but gaseous and
solid solutions exist.

Homogenous Mixtures
Solutions



solution – a substance
dissolved in a liquid.
solvent – the liquid,
solute – the substance
being disolved.
Water—The Super Solvent!
Water is an universal solvent.
 Water dissolves more solutes than anything
else!
 A dissolved solid falls apart into its individual
constituent particles, either ions or
molecules. This explains why they are
usually transparent.


http://www.youtube.com/watch?v=EBfGcTAJF4o&playnext_from=TL&vi
deos=gRLBCOaBXS0
Factors that affect
solubility



Like tends to dissolve like.
 Polar solvent dissolves polar solutes
 Non-polar solute dissolves in non-polar solvents
Molecular Size:
 Big, heavy molecules tend to be less soluble than small
light molecules. It is harder for the solvent to “cage” the
solute.
Temperature:
 As temperature rises, agitated molecules or ions break
their bonds more easily. So as temperature goes up, so
does solubility.
Solution Equilibrium
The maximum concentration of solute that a
solvent can hold at a certain temperature is
called saturated solution.
 If large amounts of solute are added to a
solution at high temperature then allowed to
slowly cool down, then a super saturated
solution may occur.

Concentration
The concentration of a solution is a measure
of how much solute is dissolved in a specific
amount of solvent or solution.
 Concentration can be described as
concentrated or dilute.

Concentration
Concentrated vs. Dilute
 Concentrated: lots of solute per unit of
volume.
 Dilute: little solute per unit of volume.

Concentration Units
Dilute and Concentrated can be ambiguous.
 What is dilute? What is concentrated?
 Chemists like their numbers!

Example Problem p. 149
If 18.0 grams of sodium sulfate are dissolved
in 207.0 grams of water, what is the percent
concentration of this solution?
% by mass =
=
18.0g solute
225g solution
g solute
g solution
x 100
X 100
= 8.00%
Molarity

Molarity is the number of moles of solute
dissolved per liter of solution.
Example Problem #1 p. 142

Calculate the molarity of 1500 ml of solution
that contains 200.0g MgCl2.

200.0g MgCl2
1500ml
=1.40mol/L or M
1molMgCl2
95.2g MgCl2
1000 ml
1L
Example Problem #2 p. 142
Calculate the molarity of a 500 cm3 solution
that contains 10.0 g of sodium hydroxide.
 To solve: Convert 10.0 g of NaOH per 500
cm3 to moles of NaOH per dm3 of soultion.
10.0g NaOH 1 mol NaOH 1000 cm3
500 cm3
40.0 g NaOH
1dm3

Answer: 0.500 mol/dm3 = 0.500 M
Dilutions

If you want a solution of lesser concentration
you will need to dilute it!


Add more solvent!
The total number of moles of solute does not change
M1 x V1 = M2 x V2
M
= Molarity & V = Volume
 M1 and V1 = “old” or stock
 M2 and V2 = “new” or dilute
Example #1
It is necessary to make a .500M solution of HCl from
250.0 ml of a 2.00M solution of HCl. What is the
volume of the new solution?
M1 x V1 = M2 x V2
2.00M x 0.250 L = 0.500M x V2
solve for V2 = 2.00M x 0.250ml
0.500M
V2 = 1.00 L
So… you add enough solvent to bring the new volume
up to 1L. How much do you add?
1.00 L – 0.250 L = 0.750 L
THE END
Questions???
 HW
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BB
 Chpt
16: 1 (a-c), 2 (a-c), 10 (a-c), 13
 Chpt 18: 1-3 a-c, 10 a-c