"Chem 20 Review Sheet - Unit: Aqueous Solutions, Lesson: #1"

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Unit: Aqueous Solutions
Lesson: #1
Aqueous Solutions
 A solution is a mixture made up of a solvent and at least one solute.
 Solutes and solvents may be gases, liquids or solids.
 An aqueous solution is any solution where water is the solvent.
 All aqueous solutions are transparent and may be colored or colorless.
 Electrolytes are soluble compounds which conduct electricity when dissolved. All soluble
ionic compounds are electrolytes, acids are also electrolytes.
 When an ionic compound dissolves, the + and – ions separate from each other. Electricity is
conducted from one free ion to another.
 Non-electrolytes are soluble compounds which do not conduct electricity when dissolved.
Molecular compounds are non-electrolytes.
Formation of Solutions
 When a solid dissolves, the individual particles separate from each other and spread out in
solution.
 Separation is the spreading out of individual molecules that takes place when a molecular
compound is dissolved in water.
 A soluble molecular compound disperses electrically neutral molecules throughout the
solution.
 EX. dissolving sugar
C
H
O
C
H
O
12
22
11 (s)
12
22
11 (aq)
NOTE: no ions are present in solution  solution will not conduct electricity
 The crystals of soluble ionic compounds break apart into individual ions that spread
throughout the solution. This process is known as dissociation.
 Ex. dissolving sodium chloride
Unit: Aqueous Solutions
Lesson: #1
Aqueous Solutions
 A solution is a mixture made up of a solvent and at least one solute.
 Solutes and solvents may be gases, liquids or solids.
 An aqueous solution is any solution where water is the solvent.
 All aqueous solutions are transparent and may be colored or colorless.
 Electrolytes are soluble compounds which conduct electricity when dissolved. All soluble
ionic compounds are electrolytes, acids are also electrolytes.
 When an ionic compound dissolves, the + and – ions separate from each other. Electricity is
conducted from one free ion to another.
 Non-electrolytes are soluble compounds which do not conduct electricity when dissolved.
Molecular compounds are non-electrolytes.
Formation of Solutions
 When a solid dissolves, the individual particles separate from each other and spread out in
solution.
 Separation is the spreading out of individual molecules that takes place when a molecular
compound is dissolved in water.
 A soluble molecular compound disperses electrically neutral molecules throughout the
solution.
 EX. dissolving sugar
C
H
O
C
H
O
12
22
11 (s)
12
22
11 (aq)
NOTE: no ions are present in solution  solution will not conduct electricity
 The crystals of soluble ionic compounds break apart into individual ions that spread
throughout the solution. This process is known as dissociation.
 Ex. dissolving sodium chloride
+
-
NaCl
Na
+ Cl
(s)
(aq)
(aq)
 Ex. dissolving magnesium fluoride
2+
-
MgF
Mg
+ 2 F
2 (s)
(aq)
(aq)
NOTE: ions are present in solution  solution will be able to conduct electricity
 Most bases are ionic compounds that contain the OH
-
-
ion. When bases dissociate, the OH
ion is responsible for the properties of bases (eg. turning litmus paper blue)
 Ex.
2+
-
Ba(OH)
Ba
+ 2 OH
2 (s)
(aq)
(aq)
 Most acids are molecular compounds  only neutral molecules are present. However, when
acids dissolve in water, they become electrolytes.
 Acids separate into individual molecules and ionize into positive hydrogen ions and negative
anions.
 Ionization is the reaction of neutral atoms or molecules to form charged ions.
 Ex.
+
-
HCl
H
+ Cl
(g)
(aq)
(aq)
 Acids can be classified as strong or weak.
 Strong acids will completely ionize in solution. They are very good electrical conductors.
 Strong acids include sulfuric acid, nitric acid, and hydrochloric acid.
 Weak acids will only partially ionize in solution. They will not conduct electricity as well as
strong acids.
 Common weak acids include:
 Acetic acid -- CH
COOH
3
 Citric acid -- H
C
H
O
3
6
5
7
 Benzoic acid -- C
H
COOH
6
5
Selective Precipitation
 Some ionic compounds have very low solubility and will form a solid precipitate when the
two ions are mixed together in a solution.
 The solubility chart is used to predict whether a precipitate will form or not.
 EX. Demonstrate the mixing together of lead (II) nitrate and potassium iodide.
Pb(NO
)
+
2 KI
2KNO
+ PbI
3
2 (aq)
(aq)
3 (aq)
2 (s)
2+
+
+
-
Pb
K
K
NO
(aq)
(aq)
(aq)
3
(aq)
+
-
-
NO
I
PbI
3
(aq)
(aq)
2 (s)
2+
+
+
-
Pb
K
K
NO
(aq)
(aq)
(aq)
3
(aq)
-
-
NO
I
PbI
3
(aq)
(aq)
2 (s)
 Selective precipitation can be used to confirm the presence or absence of a particular ion in
an unknown solution.
 To test for a certain ion in a solution, you must an oppositely charged ion to it that would
react to produce an insoluble precipitate if the original ion was indeed present.
 EX. How could you test for the presence of Br
-
?
(aq)
 EX. How could you test for the presence of Mg
2+
?
(aq)
 If you are testing for more than one ion, you must ensure that only one possible precipitate
can be produced in each step.
 EX. How could you test for the presence of CH
-
-
COO
and OH
?
3
(aq)
(aq)
 EX. How could you test for the presence of Sr
2+
2+
and Pb
?
(aq)
(aq)