Honors Chemistry, Chapter 13

1
Chapter 13 Solutions
2
Solutions

• If you put sugar in water, it is soluble and will
  form a solution. Soluble means that a substance
  is capable of being dissolved in another
  substance.
• Water and sugar form a solution. A solution is a
  homogeneous mixture of two or more substances in
  a single phase.

3
Components of a Solution

• The simplest type of solution, like sugar in
  water consists of
• The dissolving medium is called the solvent.
• The substance being dissolved is called the
  solute.

4
Solute-Solvent Combinations
5
Suspensions and Colloids

• If particles in a solute are so large that they
  settle out unless the mixture is constantly
  stirred or agitated, the mixture is called a
  suspension. Particles over 1000 nm in diameter
  (1000 X the size of atoms or molecules) form
  suspensions.
• Particles that are intermediate in size between
  those in solution and suspensions form mixtures
  known as colloidal dispersions, or simply
  colloids. Particles between 1 nm and 1000 nm in
  diameter may form colloids.

6
Classes of Colloids
7
Solutions, Colloids, Suspensions
8
Solutes Electrolytes vs. Nonelectrolytes

• A substance that dissolves in water to make a
  solution that conducts electric current is called
  an electrolyte.
• A substance that dissolves in water to make a
  solution that does not conduct an electric
  current is called a nonelectrolyte.

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Chapter 13, Section 1 Review

• Distinguish between heterogeneous and homogeneous
  mixtures.
• List three different solute-solvent combinations.
• Compare the properties of suspensions, colloids,
  and solutions.
• Distinguish between electrolytes and
  non-electrolytes.

10
Factors Affecting the Rate of Dissolution

• What can be done to increase the rate of
  dissolution?
• Increasing the surface area of the solute
• Agitating the solution
• Heating the solvent

11
Solubility Characteristics

• Solution equilibrium is the physical state in
  which the opposing process of dissolution and
  crystallization of a solute occur at equal rates.
• A solution that contains the maximum amount of
  dissolved solute is described as a saturated
  solution.

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Solubility Characteristics

• A solution that contains less solute than a
  saturated solution under the existing conditions
  is an unsaturated solution.
• The solubility of a substance is the amount of
  that substance required to form a saturated
  solution with a specific amount of solvent at a
  specified temperature.

13
Dissolving Ionic Compounds in Aqueous Solution

• Water tends to surround charged ions. This
  solution process is referred to as hydration.
• When a crystalline compound incorporates water
  into the crystal structure, the compound is known
  as a hydrate. (Example CuSO4.5H2O)

14
Nonpolar Solvents

• Nonpolar solvents are covalently bonded solvents
  without strong molecular dipoles.
• Ionic compounds are generally not soluble in
  nonpolar solvents such as carbon tetrachloride
  and toluene because they differ widely in
  bonding, polarity, and intermolecular forces.

15
Liquid Solutes and Solvents

• Liquid solutes and solvents that are not soluble
  in each other are immiscible.
• Liquids that dissolve freely in one another in
  any proportion are said to be completely
  miscible. (There is no partially miscible.)
  Examples Water and Ethanol Hexane and
  Octane Benzene and CCl4

16
Effects of Pressure on Solubility

• Pressure has very little effect on the
  solubilities of liquids and solids in liquid
  solvents. However, increases in pressure
  increase gas solubilities in liquids.
• Gas solvent solution

17
Henrys Law

• Henrys Law states that the solubility of a gas
  in a liquid is directly proportional to the
  partial pressure of that gas on the surface of
  the liquid.
• When the pressure over a liquid with dissolved
  gas is reduced, bubbles of gas begin to form in
  the solution. The rapid escape of gas from a
  liquid in which it is dissolved is known as
  effervescence.

18
Three Steps In Dissolving

• Solute particles become separated from the solid.
  (Requires addition of energy.)
• Solvent particles must move aside to make room
  for the solute particles. (Requires addition of
  energy.)
• Solvent particles are attracted to and solvate
  solute particles. (Releases energy.)

19
Heat of Solution

• The net amount of heat energy absorbed or
  released when a specific amount of solute
  dissolves in a solvent is the heat of solution.
• Heats of solution may be either negative
  (exothermic, heat is released) or positive
  (endothermic, heat is required).

20
Chapter 13, Section 2 Review

• List and explain three factors that affect the
  rate at which a solid solute dissolves in a
  liquid solvent.
• Explain solution equilibrium, and distinguish
  among saturated, unsaturated, and supersaturated
  solutions.
• Explain the meaning of like dissolves like in
  terms of polar and non-polar substances.

21
Chapter 13, Section 2 Review

• List three interactions that contribute to the
  heat of solution, and explain what causes
  dissolution to be exothermic or endothermic.
• Compare the effects of temperature and pressure
  on solubility.

22
Concentration of Solutions

• The concentration of a solution is a measure of
  the amount of solute in a given amount of solvent
  (molality) or solution (molarity).

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Molarity

• Molarity is the number of moles of solute in one
  liter of solution.
• Example 0.5 mole of NaOH in 1 liter of solution
  is 0.5 molar NaOH
• To prepare 0.5 molar NaOH, 20.0 g (0.5 mole) of
  NaOH is dissolved in less than a liter of water,
  then the volume is carefully brought up to 1
  liter.

24
Sample Problem 13-1

• You have 3.50 L of solution that contains 90.0 g.
  of sodium chloride, NaCl. What is the molarity
  of the solution?
• Given 90.0 g of NaCl
• 3.5 liter of solution
• 90.0 g of NaCl x 1 mole of NaCl 1.54 mol
  58.44 g NaCl

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Sample Problem 13-1
1.54 mol NaCl 0.440 M NaCl 3.50 L of
solution
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Sample Problem 13-2
You have 0.8 L of 0.5 M HCl solution. How many
moles of HCl does this solution contain? Given
0.8L of HCl Solution 0.5 M HCl is the
solution Concent. 0.5 mole of HCl x 0.8 L
0.4 mole HCl 1 L of Solution
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Sample Problem 13-3

• To produce 40 g. of Ag2CrO4, you will need at
  least 23.4 grams of K2CrO4 in solution as a
  reactant. All you have on hand in the stock room
  is 5 L of a 6 M K2CrO4 solution. What volume of
  the solution is needed to give you the 23.4 g of
  K2CrO4 needed for the reaction?

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Sample Problem 13-3
Given 5 L of 6.0 M K2CrO4 Mass needed 23.4
g of K2CrO4 Mass of product 40.0 g
Ag2CrO4 1 mol K2CrO4 194.2 g. 23.4 g K2CrO4
x 1 mol K2CrO4 1.20 mol 194.2 g K2CrO4
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Sample Problem 13-3
1.20 mol K2CrO4 6.0 M K2CrO4 x L of K2CrO4 x
0.020 L K2CrO4 Solution
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Molality

• Molality is the concentration of a solution
  expressed in moles of solute per kilogram of
  solvent.
• Example 40.0 g of NaOH (1 mole) dissolved in 1
  kg of water would make a 1 m NaOH solution

31
Sample Problem 13-4

• A solution was prepared by dissolving 17.1 g of
  sucrose (C12H22O11) in 125 g of water. Find the
  molal concentration of this solution.
• Given 17.1 g of C12H22O11
• 125 g of H2O
• 1 mol of C12H22O11 342.34 g

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Sample Problem 13-4
342.34 g C12H22O11 x 1 mol C12H22O11
342.34 g C12H22O11 0.0500
mol C12H22O11 125 g H2O x 1 kg H2O 0.125
kg H2O 1000 g H2O
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Sample Problem 13-4
0.0500 mol C12H22O11 0.400 m C12H22O11
0.125 kg H2O
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Sample Problem 13-5

• A solution of iodine, I2, in CCl4 is used when
  iodine is needed for a certain chemical test.
  How much iodine must be added to prepare a 0.480
  m solution of iodine in CCl4 if 100.0 g of CCl4
  is used?
• Given 0.480 m I2
• 100 g of CCl4
• 253.8 g of I2 1 mole

35
Sample Problem 13-5
100.0 g CCl4 x 1 kg CCl4 0.100 kg CCl4
1000 g CCl4 0.48 m x mol I2
0.100 kg CCl4 x 0.0480 mol I2
36
Sample Problem 13-5
0.0480 mol I2 x 253.8 g I2 12.2 g I2
1 mol I2
37
Chapter 13, Section 3 Review

• Given the mass of solute and volume of solvent,
  calculate the concentration of a solution.
• Given the concentration of a solution, determine
  the amount of solute in a given amount of
  solution.
• Given the concentration of a solution, determine
  the amount of solution that contains a given
  amount of solute.