AP Chapter 4: Reactions in Aqueous Solution
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AP Chapter 4: Reactions in Aqueous Solution
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AP Chapter 4: Reactions in Aqueous Solution
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Warm-ups and problems will be collected before you take the test.
Read Chapter 4: Reactions in Aqueous Solution and Chapter 19.1
Know selected solubility rules
Know metal activity series
Answer the following problems in the space provided. For problems involving an equation, carry out the
following steps: 1. Write the equation. 2. Substitute numbers and units. 3. Show the final answer with units.
There is no credit without showing work.
Electrolytes
1. Identify each of these substances as a strong electrolyte (S), weak electrolyte (W), or nonelectrolyte (N):
(a) Ba(NO3)2,
(b) Ne,
(c) NH3,
(d) NaOH
(e) CH3COOH
2. Identify the species that carry the electric current when electricity is passed through an aqueous electrolyte
solution.
Solubility & Precipitation Reactions
3. Characterize the following compounds as soluble (S) or insoluble (I) in water:
(a) Ca3(PO4)2,
(b) Mn(OH)2, (c) AgC1O3,
(d) Al(NO3)3
(e) K2S.
4. Write balanced “molecular” and net ionic equations for the following reactions. Show states.
(a) AgNO3(aq) + Na2SO4(aq) 
(b) BaCl2(aq) + ZnSO4(aq) 
(c) (NH4)2CO3(aq) + CaCl2(aq) 
5. A student found that a sulfuric acid solution conducts, however, after the addition of a certain amount of a
barium hydroxide solution to the sulfuric acid solution, the light began to dim, even though Ba(OH)2 is also a
strong electrolyte. Write a balanced equation for this reaction and explain why the light dims as the reaction
proceeds.
AP Chapter 4: Reactions in Aqueous Solution
Acids & Bases
6. Identify each of the following species as a Bronsted acid (A), base (B), or both(AB):
(a) PO 4 3(b) ClO 2 (c) NH 4 +
(d) HCO3(e) HBr
Redox
7. Give oxidation number for the underlined atoms in the following molecules and ions:
(a) Cr2O72(b) CaI2
(c) A1203
(d) H3As03
(e) TiO2,
8. Identify which reactions are redox:
(a) 2AgNO3(aq) + Na2SO4(aq)  Ag2SO4(s) + 2NaNO3(aq)
(b) 2NO2(g)  N2O4(g)
Balancing Complex Redox Equations
9. Balance the following redox equations:
(a) H2O2 + Fe2+  Fe3+ + H2O (in acidic solution)
(b) CN- + MnO4-  CNO- + MnO2 (in basic solution)
(c) Br2  BrO3- + Br- (in basic solution)
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AP Chapter 4: Reactions in Aqueous Solution
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10. Predict the outcome of the reactions represented by the following equations by using the activity series, and
balance the equations. Also for each equation, write the balanced oxidation half-reaction.
(a) Cu(s) + HCl(aq) 
(b) Br2(s) + NaI(aq) 
(c) Mg(s) + CuSO4(aq) 
(d) Cl2(g) + KBr(aq) 
Concentration
11. Calculate the molarity of each of the following solutions:
(a) 6.57 g of methanol (CH3OH) in 1.50 X 102 mL of solution
(b) 7.82 g of naphthalene (C10H8) in 85.2 mL of benzene solution.
12. Calculate the volume in mL of a solution required to provide the following:
(a) 2.14 g of sodium chloride from a 0.270 M solution
(b) 4.30 g of ethanol from a 1.50 M solution
13. Water is added to 25.0 mL of a 0.866 M KNO3 solution until the volume of the solution is exactly 500 mL.
What is the concentration of the final solution?
14. A 46.2 mL, 0.568 M calcium nitrate solution is mixed with 80.5 mL of 1.396 M calcium nitrate solution.
Calculate the concentration of the final solution.
AP Chapter 4: Reactions in Aqueous Solution
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15. Given a stock solution of 1.26 M HCl, how many milliliters of the stock solution are needed to make:
(a) 32.0 mL of 0.41 M HCl
(b) 410 mL of 0.075 M HCl
Gravimetric Analysis
16. A sample of 0.6760 g of an unknown compound containing barium ions is dissolved in water and treated with
an excess of Na2SO4. If the mass of the BaSO4 precipitate formed is 0.4105 g, what is the percent by mass of Ba
in the original unknown compound?
17. Commercial marble contains a high percentage of calcium carbonate. A 5.37 Kg sample of marble is
dissolved in excess HCl, and the resulting solution is reacted with sodium phosphate. The resulting
precipitate is collected by filtration and found to weigh 4730 g.
(a) Write a balanced equation for the reaction of calcium carbonate and HCl.
(b) Write a balanced equation for the precipitation reaction.
(c) What is the percentage of calcium in the marble sample?
Acid-Base Titration
18. What volume of a 0.50 M HC1 solution is needed to neutralize completely each of the following:
(a) 10.0 mL of a 0.30 M NaOH solution
(b) 10.0 mL of a 0.20 M Ba(OH)2 solution
AP Chapter 4: Reactions in Aqueous Solution
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Redox Titration
19. The SO2 present in air is mainly responsible for the acid rain phenomenon. Its concentration can be determined
by titrating against a standard potassium permanganate solution. The unbalanced half reactions for this titration
are:
SO2  SO42and
MnO4 -  Mn2+
(a) Write the balanced redox equation
(b) Calculate the number of grams of SO2 in a sample of air if 7.37 mL of 0.00800 M KMnO4 solution are
required for the titration.
20. Oxalic acid (H2C2O4) is present in many plants and vegetables. If 24.0 mL of 0.0100 M KMnO4 solution is
needed to titrate 1.00 g of impure H2C2O4 sample to the equivalence point, what is the percent by mass of
H2C2O4 in the sample? The net ionic equation is
2MnO4- + 16H+ + 5C2O42-  2Mn2+ + 10CO2 + 8H2O
Visible Spectroscopy
21. A commonly used dye in the food industry is called “brilliant blue.” This dye has a molar absorptivity of
130,000 cm-1M-1 at 630nm.
(a) What color does this dye absorb?
(b) Describe the physical process within the dye that is responsible for the absorption of light?
(c) If the pathlength of a spectrophotometer is 1.0 cm, what concentration of a brilliant blue solution would
have a transmittance of 0.32 (32%)?
AP Chapter 4: Reactions in Aqueous Solution
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How to Balance Complicated Redox Reactions
Many redox reactions cannot be balanced by “inspection”. When inspection does not work, the following process
will give a properly balanced equation. Although the process is not difficult, all the steps must be done correctly
and in the proper order.
1. Write the unbalanced reaction and, if aqueous, note whether it is acidic or basic.
Example:
S + HNO3  SO2 + NO + H2O (obviously acidic)
2. If the reaction is in aqueous solution, break ionic substances into their ions. Do not break-up molecular
substances, weak acids, weak bases, polyatomic ions or oxides.
Example:
S + H+ + NO3-  SO2 + NO + H2O
3. Determine which atoms are oxidized or reduced by assigning oxidation numbers.
0
+5
+4 +2
Example: S + H+ + NO3-  SO2 + NO + H2O
Therefore S is oxidized and N is reduced.
4. Write separate half reactions for the oxidation and reduction steps.
Oxidation:
S  SO2
Reduction: NO3-  NO
5. Balance each half reaction using “X,O,H,e” in order.
X: balance atoms other than O & H
O: balance O using water
H: balance H using H+
E: balance charge using electrons
Oxidation:
S  SO2
X: S already balanced
O: 2H2O + S  SO2
H: 2H2O + S  SO2 + 4H+
e: 2H2O + S  SO2 + 4H+ + 4eReduction:
NO3-  NO
X:
N already balanced
O:
NO3-  NO + 2H2O
+
H:
4H + NO3-  NO + 2H2O
e: 3e + 4H+ + NO3-  NO + 2H2O
AP Chapter 4: Reactions in Aqueous Solution
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6. Multiply each half reaction by a number to make the number of electrons equal.
In this example, the lowest common denominator is 12.
Oxidation: 3x (2H2O + S  SO2 + 4H+ + 4e-)
6H2O + 3S  3SO2 + 12H+ + 12eReduction: 4x (3e- + 4H+ + NO3-  NO + 2H2O)
12e- + 16H+ + 4NO3-  4NO + 8H2O
7. “Add” the two half reactions and cancel anything that is exactly the same on both sides.
6H2O + 3S  3SO2 + 12H+ + 12e12e + 16H+ + 4NO3-  4NO + 8H2O
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3S + 4H+ + 4NO3-  3SO2 + 4NO + 2H2O
8. If the reaction is in basic solution, add the same number of OH- ions to both sides of the equation as there are
H+ ions. Combine OH- and H+ ions to form water and cancel water molecules if appropriate.
This example is NOT in basic solution, but if it were, this is what would happen.
Add OH-:
4OH- + 3S + 4H+ + 4NO3-  3SO2 + 4NO + 2H2O + 4OH+
Combine H & OH to form H2O: 4H2O + 3S + 4NO3-  3SO2 + 4NO + 2H2O + 4OHCancel H2O:
2H2O + 3S + 4NO3-  3SO2 + 4NO + 4OH-
9. Double check.