Solution Chemistry
TOPICS:
Solution Formation
Solubility
Solution concentration
Mass Percent
Molarity
Dilution
*Solution Stoichiometry(HP)
Standards Addressed:
6. Solutions are homogeneous mixtures of two or more substances. As a basis for understanding this concept:
a. Students know the definition of solute and solvent
b. Students know how to describe the dissolving process at the molecular level by using the concept of random
molecular motion
c. Students know temperature, pressure, and surface area affect the dissolving process
d. Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per
million, and percent composition.
Objectives:
By the end of the lesson, the student will:
 Understand the dissolving process at the molecular level.
 Understand how the structure of the water molecule allows it to dissolve many substances
 Know the factors which influence:
o solubility and why
o dissolving rate and why
 Know how to calculate the concentration of a solution
SOLUTION FORMATION
Solution:
Solvent:
Solute:
Soluble:
Insoluble:
You can find examples of solutions in all three states of matter:
Gas in Gas
Gas in Liquid
Liquid in Liquid
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Solid in Solid
The dissolving process at the molecular level:

To understand how dissolving works, let’s first look at the structure of the water molecule:

The structure of the water molecule creates a polar molecule due to the differences in
electronegativities of the oxygen and hydrogen atoms.
 The partial negative charge on the oxygen attracts a positive charge, while the partial
positive charge on Hydrogen attracts to a negative charge. Molecules arrange themselves
so as to have opposite charges aligned, pulling the ion away from its ‘structure’, “one ion
at a time”
Dissolving process:


Once released, the ions are surrounded by water molecules; this is called “solvation.”
The dissolving process is reversible
o The dissolved solute moves around in the solution and when it comes into contact
with undissolved solute particles it recrystallizes, meaning it returns to the solid
state. And the process repeats itself.
o
o NaCl
Na+(aq) + Cl- (aq)
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
When the rates of the dissolving and recrystallization become the same, the solution is
saturated at that temperature.

A dynamic
o
is reached
meaning the rate of the forward and reverse reaction is the same.
Dissolving Process Animations:
http://www.youtube.com/watch?v=EBfGcTAJF4o (53 sec)
http://www.youtube.com/watch?v=CLHP4r0E7hg&feature=related (42 sec)
http://www.youtube.com/watch?v=xdedxfhcpWo&feature=related (1:35)
Factors Affecting Dissolving Rate
Where does dissolving occur?

3 common ways to increase the collisions between solute and solvent:
1. Temperature: raising the temperature increases the kinetic energy of the particles, resulting
in more frequent and forceful collisions.
Animation:http://www.kentchemistry.com/links/Kinetics/FactorsAffecting.htm
2. Amount of Surface Area Exposed: breaking the solute into smaller pieces increases its surface area. A
greater surface area allows more collisions to occur and therefore, faster dissolving.
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3. Agitation: stirring moves dissolved solute particles away from the contact surfaces more quickly and
thereby allows new collisions between solute and solvent particles to occur. Without stirring, solvated
particles move away from the contact areas slowly.
SOLUBILITY: the maximum amount of solute that will dissolve in a given amount of solvent at a
specified temperature and pressure
Saturated solution: contains the maximum amount of solute. You cannot dissolve
any more solute in the solvent.
Unsaturated solution: contains less than the maximum amount of solute. You can
dissolve more solute in the solvent.
Supersaturated solution: contains more than the normal maximum amount of solute. This is
usually achieved by heating the solution in order to dissolve more solute, then the solution is
cooled. This makes a supersaturated solution. (ie.Rock candy; hot mineral springs)
Factors affecting solubility:
1. Temperature: many substances are more soluble at high temperatures than low
temperatures. Exception: Gases
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2. Pressure: affects the solubility of gaseous solutes. The solubility of a gas in any solvent
increases as the pressure above the solution increases
3. Intermolecular forces:
o meaning polar substances dissolve polar substances and non-polar substances
dissolve non-polar substances.
 Miscibility: the ability to mix without separating into two phases
o Miscible:
o Immiscible:
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SOLUTION CONCENTRATION:
Dilute solution:
Concentrated solution:
Mass Percent:
Mass Percent = mass of solute x 100%
mass of solution
1. Calculate the mass percent of NaCl in a solution containing 15.3 g of NaCl and 155.0 g water.
(8.98%NaCl)
2. Calculate the mass percent of a solution containing 27.5 g of ethanol and 175 mL of water.
The density of water is 1.0 g/mL. (13.6%)
3. You have 1,500 g of a bleach solution. The percent by mass of the solute sodium
hypochlorite, NaOCl, is 3.62%. How many grams of NaOCl are in the solution?
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(54.3 g)
Molarity (M):
Molarity (M)=
M is pronounced “molar”
moles of solute
Liters of solution
1) Calculate the molarity if water is added to 2.0 mol of glucose to give 5.0 L of solution. (0.40 M)
2) A solution contains 0.900 g of NaCl per 100 mL of solution. What is the molarity? (0.154 M)
3) How many moles of Na2SO4 are needed to prepare 1.5L of 0.20 M Na2SO4? (0.30 moles solute)
4) How many grams of solute are contained in 250 mL of 3.0 M NaOH? (30. g NaOH)
5)
How would you prepare 250 mL of a 0.500 M NaCl solution? (7.31 g NaCl)
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Solution Dilution:


Use the dilution equation
o
1. How many milliliters of 12.0 M HCl are needed to prepare 750. mL of 0.250 M HCl? (15.6 mL)
2. How would you prepare 5.00 L of a 1.50 M KCl solution from a 12.0 M stock solution? (0.625L)
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3. What is the resulting molarity of the solution when the following mixture is prepared:
150.0 mL of water is added to 55.0 mL 6.50 M NaOH . (1.74 M)
4. How much water must be added to 125 mL of a 4.50 M NaCl solution to produce a 2.75 M solution? (80. mL)
Summary of Steps:
1.
2.
3.
4.
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SOLUTION STOICHIOMETRY
There are several different ways to solve solution stoichiometry problems. Here are a few
guidelines/suggestions to get you started:

Write a balanced chemical equation

use Molarity as mol…allows conversion between moles and volume or concentration and volume
L
use a mol-mol ratio, if necessary


there may be limiting reagent problems…in this case determine how many moles there are for
each substance

sample mini road map:
o from moles you can go to L instead of g or moles to particles via avogadro’s #
Sample problems
1) Calculate the mass of solid NaCl that must be added to 1.50 L of a 0.100 M AgNO3 solution to
precipitate all the Ag+ ions in the form of AgCl
2) How many milliliters of 0.0500M Pb(NO3)2 are needed to react with 2.00L of a 0.0250M Na2SO4
solution in order to produce a precipitate? How many grams of precipitate are formed?
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