Textbook: Chapter 15
Reference Table: F, G, & T www.regentsprep.org


A solution is a homogenous mixture
 homogeneous mixture of substances in the same physical state
 contains atoms, ions, or molecules of one substance spread uniformly throughout a second substance
When salt (NaCl) is stirred into water, the individual Na+ and Cl- ions separate and uniformly spread throughout the water, forming a solution
 appears to be one substance


A solid may be dissolved in another solid

Brass is a solution of zinc and copper

When metals are mixed together to form a solution, the result is called an
ALLOY


Air is an example of a mixture of gases that form a solution

Although solutions exist in all three states the most common type of solution is one in which a solid or a liquid is dissolved in another liquid


Solution: a homogenous mixture made up of two or more substances. A solution is made up of a solute and a solvent.

Solute: a substance like salt or sugar that dissolves in a solvent like water.

Solvent: usually a liquid, for example water. If the solvent is water, then the solution is called an aqueous solution (aq).


Precipitate: a substance that is caused to become
by heat or chemical reagent and separate out from a solution.
Example: salt and water, boil, evaporate water, and the salt that remains are known as the precipitate.

Solubility: the most substance that can dissolve in the water (a solvent) at a specific temperature. Different substances react differently (TABLE G).


The solvent molecules have enough attraction for the solute particles to break the intermolecular forces between solute particles.

Solvent particles are attracted to the solute particles and bring the solute into the solution.


Three important factors that affect rate of dissolving are surface area, stirring, and temperature.
SURFACE AREA:

The greater the SA, the faster the substance will dissolve.

More solute particles can come in contact with the solvent and be pulled into solution.

This is why granulated sugar will dissolve faster than a cube of sugar.

STIRRING:

Increased stirring causes a substance to dissolve faster.

More solute particles can come in contact with the solvent and be pulled into solution.

This is why people stir lemonade or iced tea mixes.
TEMPERATURE:

For solids and liquids, increasing temperature increases the rate of dissolving.

This allows more solvent particles to collide with the solute.


For gases, increasing the temperature
the rate of dissolving.

The gas is more able to evaporate out of the solution.

This is why soda should be refrigerated and why it becomes flat if left open.




Polar solutes will solvents.
dissolve in polar
Non-polar solutes will polar solvents.
dissolve in non-
Polar in Polar Non-polar in Polar

HCl
NH
3
SO
2


TABLE G: Solubility Curve, the horizontal line in the graph shows temperature, and the vertical line shows how many grams of a solute is the most that can dissolve in 100 grams of water.

The various compounds on the graph (solutes) dissolve differently at different temperature, and for a given temperature only a certain amount of the solutes can dissolve in 100 grams of water.

Some of the solutes on the graph are in solid form, and some are in gas form.

This graph represents that temperature does have an effect on solubility.


Solubility of a solid (KNO
3
, NaNO
3
) increases as temperature increases.

Solubility of a gas (NH
3 temperature increases.
, HCl) decreases as
HCl
NH
3
SO
2


Concentrated: a large amount of solute per grams of solvent; there is a large concentration of solute.

Dilute: a small amount of solute per grams of solvent.

There are three types of solutions:


 saturated unsaturated supersaturated


Contains the most solute that can dissolve at a given temperature. If you added anymore of the solute it would not dissolve.

When you graph the solubility of a solvent, the line on the graph represents saturated; all the lines on Table G are saturated!!!

Example: Look at KNO
3 at 70 ° C, the maximum amount of the salt that can dissolve in 100 grams of water is about 134 grams, so the line for saturated can only hold 134 grams of KNO
3
.


Contains less solute than a saturated solution. You can still add more salt and it will dissolve.

Example: At 70 ° C, if you have 130 grams of KNO
3
, this would be an unsaturated solution because you can still add 4 grams of KNO
3 before the solution is saturated.


This is only a temporary situation caused by slowly cooling a saturated solution. It has more solute than in a saturated solution.

A supersaturated solution is very unstable and the amount in excess can precipitate or crystallize.

Example: At 70 ° C, if you have 137 grams of
KNO
3
, this would be an supersaturated solution because you have more than 134 grams of solute per 100 grams of water.


We have already learned that temperature has an affect on solubility, and that the nature of the solute/solvent has an affect on solubility (polar vs. nonpolar)

Pressure also has an effect on solubility.

Pressure makes gases more soluble, and has almost no effect of liquids or solids.

Example: High pressure forces carbon dioxide gas into water to make soda; makes carbon dioxide more soluble. When you open the cap of soda, there is less pressure, the soda fizzes, and gas escapes.

NH
4
+


Ions that are soluble (have the highest concentration of dissolved ions) can conduct electricity (are electrolytes)

Ions that are insoluble (have the lowest concentration of dissolved ions) cannot conduct electricity (are non-electrolytes or poor electrolytes)

Electrical conductivity decreases when the concentration of ions decreases.

Remember that a precipitate is insoluble.
always considered


Question: Are the following soluble? NaCl, AgBr,
CaCO
3
, (NH
4
)
2
S

Question: Based on Table F, which of the following saturated solutions has the lowest concentration of dissolved ions? (meaning insoluble) NaCl, MgCl or AgCl?
2
, NiCl
2


Sometimes it is adequate to refer to a solution as dilute or concentrated, but dilute and concentrated are solute involved relative terms and are not precise with regards to the amount of

In most cases it is very important to know the specific amount of solute (the concentration) of a solution

There are several methods of expressing the specific concentration of a solute in a solution

You can describe the concentration of a solution by molarity, molality, percent by mass, or parts per million.


The molarity of a solution is the number of moles of solute in one liter of a solution.
WARNING!!! Triple Threat:
1.
2.
3.
May not give you moles (given/GFM)
May not give you liters (convert mL  L)
Liters of solution (solute + solvent; may have to add them together)

Question: How many grams of NaCl would you need for a .5M solution?
Question: How many moles of solute are contained in
200 mL of a 1M solution?
Question: If you have 50 moles of a solute in 25 liters of solution, what is the molarity?

We said before that the higher the concentration of ions (more ions), the better the solution conducts electricity. When comparing a 1M solution of NaCl to a 5M of NaCl, the 5M of NaCl is a better conductor of electricity than the 1M of NaCl.



There are certain situations in which we must know how much solvent is present in a solution.
Molality is defined as the number of moles of solute dissolved in 1 kilogram of solute.
WARNING!!! Double Threat:
1.
May not give you moles (given/GFM)
2.
May not give you Kg (convert g  Kg)

Question: Sucrose (table sugar) as a molar mass (GFM) of 342 grams per mole. What is the molality of a solution prepared by dissolving 34.2 grams of sucrose in 200 grams of water?
Question: What is the molality of a solution prepared by dissolving 51 grams of NH
3 in
2.0 kilograms of H
2
O?


A unit of concentration that expresses the mass of a solute dissolved in 1 million parts of a very diluted solution.
WARNING!!! Triple Threat:
1.
2.
3.
May not give you grams of solute (given/GFM)
May not give you grams of solution (mg  g)
Grams of solution (solute + solvent; may have to add them together)


Similar concept as percent composition (part/whole x 100).
Looking to calculate the percent mass of solute in the whole solution.
% Mass = grams solute x 100 grams solution
WARNING!!! Triple Threat:
1.
2.
3.
May not give you grams of solute (given/GFM)
May not give you grams of solution (convert mg  g)
Grams of together) solution (solute + solvent; may have to add them

Question: A CuSO
4 solution contains .05g of CuSO solution in parts per million?
4 in
1000g of solution. What is the concentration of the
Question: What are the grams of solute required to make a
3 ppm solution when the amount of water is 150g?
Question: In percent by mass, what is the concentration of
85.6g of hydrochloric acid in 356g of solution?

Question: What are the parts per million if a solution contains 75g of solute in 150g of solution?
Question: 8 grams of NaCl is dissolved in 100 grams of solution, what is the percent by mass of NaCl?


Dilution - the process of adding more solvent to a solution.
**Important**
We’re not changing the number of moles, just the volume of solvent. The moles of solute are equal in the concentrated and dilute solutions
.
Before Dilution After Dilution

1
1
2
2




M
1
V
1
= initial concentration (molarity)
= initial volume
M
2
V
2
= final concentration (molarity)
= final volume

Question: A teacher wants to prepare 500. mL of
1.00 M solution of acetic acid from 17.5 M stock solution. What volume of the stock solution is required?
Question: What volume of 16M sulfuric acid must be used to prepare 1.5L of a 0.10 M solution?
Question: What volume of 12 M HCl must be taken to prepare 0.75 L of 0.25M HCl?

Boiling Point Elevation:

Rule: The presence of a solute (salt or sugar) raises the
 boiling point of the solvent.
The greater the concentration of the solute, the more it raises the boiling point.


Water boils at 100 ° C, by adding glucose to water; it will raise the boiling point of water slightly. The greater the concentration of solute, the higher the boiling point becomes.
Freezing Point Depression:

Rule: The presence of any solute (salt or sugar) lowers the freezing point of the solvent.
The freezing point of water is 0 ° C, by adding glucose to water it lowers the freezing point slightly. The greater the concentration of the solute, the lower the freezing point becomes.
HOT GET HOTTER; COLD GET COLDER

∆T b
= (i)(+k b
)(m)
∆T f
= (i)(-k f
)(m)




∆T b
& ∆T f
= changes in BP & FP i – ions (in ionic  dissociation; covalent  1)
+k b
& -k f
= constants representing the number of degrees that the BP and FP of a solvent is raised when 1 mole of a molecular, non-volatile (does not evaporate with the solvent) solute is dissolved in 1 kilogram of the solvent m = molality


 k b k f
= +0.513 ° C/m
= -1.86 ° C/m
Question: What is the boiling point of a
2.0m solution of ethylene glycol in water at 1 atm?
Question: What is the boiling point of a
2.0m aqueous solution of NaCl?
Question: What is the freezing point of a
2.0m solution of ethylene glycol in water?

1) What is the molarity of a solution of NaOH if 2 liters of the solution contains 4 moles of NaOH?
A) 2 M B) 8 M C) 80 M D) 0.5 M
2) How many moles of solute are contained in 200 milliliters of a 1 M solution?
A) 1 B) 0.2 C) 200 D) 0.8
3) What is the total number of grams of NaI(s) needed to make 1.0 liter of a 0.010 M solution?
A) 15 B) 0.15 C) 0.015 D) 1.5

4) At standard pressure when NaCl is added to water, the solution will have a
A) lower freezing point and a lower boiling point than water
B) higher freezing point and a higher boiling point than water
C) higher freezing point and a lower boiling point than water
D) lower freezing point and a higher boiling point than water
5) According to the table, which of these compounds is the water?
A) K
2
CO
B) Ca
3
C) KC
2
3
(PO
4
)
2
H
3
O
2
D) Ca(NO
3
)
2
Solubility Guidelines chemistry reference least soluble in

6) How many liters of a 0.5 M sodium hydroxide solution would contain 2 moles of solute?
A) 1 L B) 2 L C) 3 L D) 4 L
7) How many grams of KOH are needed to prepare 250 milliliters of a 2.00 M solution of
KOH (formula mass = 56.0)?
A) 112 g B) 28.0 g C) 2.00 g D) 1.00 g
8) A solution of KCl(aq) contains 15 grams of solute in 85 grams of water. What is the concentration of the solution in percent by mass?
A) 0.20% B) 2.0% C) 15% D) 6.0%

9) Based on the Solubility Curves chemistry reference table, which substance is most soluble at 60 °C?
A) NH
3
B) KCl C) NH
4
Cl D) NaCl
10) A solution contains 90 grams of a salt dissolved in 100 grams of water at 10 °C.
The solution could be an unsaturated solution of
A) KI B) KCl C) NaCl D) KNO
3

Questions 11 and 12 refer to the following:
The graph below represents the solubility curves for solute and solute B .
A
11) Compare the solubility of solute and at 80DC.
A and solute B at 20DC
12) At what temperature are solute soluble in 100. grams of water?
A and solute B equally