Transcript Slide 1

PACKET #9
Solutions
Textbook: Chapter 15
Reference Table: F, G, & T
www.regentsprep.org
Let’s Review a little . . .

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
Solid Solutions:

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
Gaseous Solutions:

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 insoluble 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).
Dissolving
 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.
Factors Affecting the Rate of
Dissolving

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
decreases 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.
Remember . . .
 “Likes
dissolve in likes”
 Polar solutes will only dissolve in polar
solvents.
 Non-polar solutes will only dissolve in nonpolar solvents.
Polar in Polar
Non-polar in Polar
Table G: Solubility Curve
HCl
NH3
SO2

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 (KNO3, NaNO3)
increases as temperature increases.
 Solubility of a gas (NH3, HCl) decreases as
temperature increases.
HCl
NH3
SO2
Table G: Solubility Curve

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
Saturated Solution

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 KNO3 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 KNO3.
Unsaturated Solution
 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 KNO3, this would be an unsaturated
solution because you can still add 4 grams
of KNO3 before the solution is saturated.
Supersaturated Solution

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
KNO3, this would be an supersaturated solution
because you have more than 134 grams of solute
per 100 grams of water.
Pressure Affects Solubility

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.
Soluble or Insoluble? (Table F)
Soluble
Insoluble
Insoluble
Soluble
NH4+

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 always considered
insoluble.

Question: Are the following soluble? NaCl, AgBr,
CaCO3, (NH4)2S

Question: Based on Table F, which of the following
saturated solutions has the lowest concentration of
dissolved ions? (meaning insoluble) NaCl, MgCl2, NiCl2
or AgCl?
Be Specific . . .

Sometimes it is adequate to refer to a solution as dilute or
concentrated, but dilute and concentrated are relative
terms and are not precise with regards to the amount of
solute involved

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.
Molarity (Table T)

The molarity of a solution is the number of
moles of solute in one liter of a solution.
Molarity (M) = moles of solute
liters of 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)
Molarity (Table T)
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.
Molality


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.
Molality (m) = moles of solute
Kg of solvent
WARNING!!! Double Threat:
1.
2.
May not give you moles (given/GFM)
May not give you Kg (convert g  Kg)
Molality
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 NH3 in
2.0 kilograms of H2O?
Parts Per Million (ppm) (Table T)

A unit of concentration that expresses the mass of
a solute dissolved in 1 million parts of a very
diluted solution.
ppm = grams of solute x 1,000,000
grams of 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)
Percent by Mass

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 solution (solute + solvent; may have to add them
together)
Parts Per Million & % Mass
Question: A CuSO4 solution contains .05g of CuSO4 in
1000g of solution. What is the concentration of the
solution in parts per million?
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?
Parts Per Million & % Mass
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?
Molarity by Dilution

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
Molarity by Dilution
M 1V 1 = M 2V 2
 M1
= initial concentration (molarity)
 V1 = initial volume
 M2 = final concentration (molarity)
 V2 = final volume
Molarity by Dilution
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?
Colligative Properties
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
Calculating the Freezing and Boiling
Points of Solutions
∆Tb = (i)(+kb )(m)
∆Tf = (i)(-kf )(m)
∆Tb & ∆Tf = changes in BP & FP
 i – ions (in ionic  dissociation; covalent  1)
 +kb & -kf = 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

 kb
= +0.513 °C/m
 kf = -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?
Review Questions
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 Solubility Guidelines chemistry reference
table, which of these compounds is the least soluble in
water?
A) K2CO3
B) Ca3(PO4)2
C) KC2H3O2
D) Ca(NO3)2
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) NH3 B) KCl C) NH4Cl 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) KNO3
Questions 11 and 12 refer to the following:
The graph below represents the solubility curves for solute A
and solute B.
11) Compare the solubility of solute A and solute B at 20DC
and at 80DC.
12) At what temperature are solute A and solute B equally
soluble in 100. grams of water?