Chemistry 40s
Midterm Review Part 2
October 2011
Aqueous Solutions Unit
Midterm Review
Solubility and Solutions
A solution is a homogenous mixture of a solvent and one or more solutes. Some substances
dissolve (dissociate) when mixed in a solution, some substances do not dissolve in a solution.
Solvent is a substance that has other substances dissolved in it. A solvent is more abundant
than the solute in a solution.
Solute is a substance that is dissolved in a solution.
Concentration of a solution is the amount of solute in a solution.
Saturated Solution is the point when no more solute can be dissolved in the solution.
Aqueous Solution is a solution that has water as the solvent.
Soluble means that a solvent will dissolve in a solvent.
Insoluble means that the substance will not dissolve in a solution.
Precipitate a solid that results from a displacement reaction in a solution.
Double Displacement Reactions
A double displacement reaction takes place when two cations switch anions. It has the general
formula of
WX + YZ  WZ + YX
Example:
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
We can use the solubility rules chart to determine which state the products are in after the
reaction (i.e. if it is a liquid or if it is still in its aqueous form). If water is a product of the
reaction it is noted as a liquid and not as aqueous.
The above example is a molecular equation. To help with balancing the equation you can write
out the ionic equation, as follows:
Ag+ (aq) + NO3− (aq) + Na+(aq) + Cl−(aq) → Na+(aq) + NO3−(aq) + AgCl(s)
The precipitate, AgCl, is still written in its ionic form because it is a solid and does not dissociate
into ions in the solution. We can cancel out the spectator ions, which are the ions that are
present for the reaction but do not contribute to in. In this case the spectator ions are Na and
NO3. After cancelling out the spectator ions you can write the net ionic equation, as shown
below.
Ag+ (aq) + Cl−(aq) → AgCl(s)
Chemistry 40s
Midterm Review Part 2
October 2011
Acids and Bases
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The Arrhenius Theory of Acids and Bases
o An acid is a substance that dissociates in water to produce one or more
hydrogen ions, H+.
o A base is a substance that dissociates in water to form one or more hydroxide
ions, OH−.
The Bronsted-Lowry Theory of Acids and Bases
o An acid is a substance from which a proton (H+ ion) can be removed.
o A base is a substance that can remove a proton (H+ ion) from an acid.
Strong Acid completely dissociates when placed in water.
Strong Base completely dissociates when placed in water.
There are only 6 strong acids,
 HCl, hydrochloric acid
 HBr, hydrobromic acid
 HNO3, nitric acid
 HClO4, perchloric acid
 HI, hydroiodic acid
 H2SO4, sulphuric acid
When a strong acid and base are combined they react to form a salt and water in what is called
a neutralization reaction. In a neutralization reaction all of the H+ ions from the acid combine
with all of the OH- from the base to form water.
In a titration, the concentration of one solution is determined by adding a solution of known
concentration and watching for a reaction with the aid of an indicator. By performing the
titration you can find the equivalence point, at which the number of moles of the equal to the
original number of moles of the unknown solution. At the equivalence point, all the moles of
hydrogen ions that were present in the original volume of one solution have reacted with an
equal number of moles of hydroxide ions from the other solution.
To calculate the concentration of the unknown solution in a titration you must follow these
rules:
1. Write out the balanced equation.
Chemistry 40s
Midterm Review Part 2
October 2011
2. Calculate the number of moles of the known solution by manipulating the formula
c= n/v
3. Using the mole ratio 1:1, 1:2, etc. calculate the number of moles for the unknown
solution.
4. Use the number of moles and the given volume or concentration of the unknown
solution to determine the unknown value.
Oxidation Numbers
Oxidation is the loss of electrons in a reaction.
Reduction is the gain of electrons in a reaction.
OIL RIG
Zn (s) + Cu2+(aq)  Cu(s) + Zn2+(aq)
copper gains 2 electrons, zinc loses 2 electrons
Zinc is oxidized, copper is reduced. We call this a redox reaction.
An oxidizing agent is the reactant that oxides the other reactant. In the above example copper
is the oxidizing agent.
A reducing agent is the reactant that reduces the other reactant. In the above example zinc is
the reducing agent.
When we have a reaction that takes place between compounds we assign each element an
oxidation number. Oxidation Numbers are a representation of the electron transfer and are
assigned using a set of rules. The rules are as follows: