AP Chemistry Unit 4- Homework Problems Chemical Equations and ...

AP Chemistry
Unit 4- Homework Problems
Chemical Equations and Electrochemistry
Types of Reactions & Balancing
1. For each of the equations below, decide whether the reaction is an example of: synthesis,
decomposition, single replacement, double replacement, or combustion
a. CaI 2 + Br 2 CaBr 2 + I 2
b. CH 4 + 2 O 2 CO 2 + 2 H 2 O
c. 2 Al + 3 Cl 2 2 AlCl 3
d. 6 K + N 2 2 K 3 N
e. 3 MgCl 2 + 2 K 3 PO 4 Mg 3 (PO 4 ) 2 + 6 KCl
f. CaCO 3 CaO + CO 2
g. NH 4 OH NH 3 + H 2 O
h. 2 Li + F 2 2 LiF
i. CS 2 + 3 O 2 CO 2 + 2 SO 2
j. Zn + Cu(NO 3 ) 2 Zn(NO 3 ) 2 + Cu
2. Balance the following equations:
a. Fe 2 O 3 + Mg MgO + Fe
b. SF 4 + H 2 O SO 2 + HF
c. BF 3 + H 2 O HF + H 3 BO 3
d. C 6 H 5 CH 3 + O 2 H 2 O + CO 2
e. Fe + H 2 O Fe 3 O 4 + H 2
3. Predict the products and balance the equation:
a. Si + Cl 2
b. Na 2 SO 4 + BaCl 2
c. CaO
d. Zn + AgNO 3
e. C 8 H 18 + O 2

Stoichiometry
1. For the reaction:
4 Al + 3 O 2 2 Al 2 O 3
a. How many moles of Al are needed to react with 9 moles of O 2 ?
b. How many moles of Al 2 O 3 can be made from 3.2 moles of O 2 and excess Al?
c. How many grams of O 2 are needed to react with 100 grams of Al?
d. How many grams of Al 2 O 3 can be produced from 75 grams of Al and excess O 2 ?
2. For the reaction:
2 B 4 H 10 + 11 O 2 4 B 2 O 3 + 10 H 2 O
a. How many moles of O 2 are needed to react with 3.7 moles of B 4 H 10 ?
b. How many moles of B 2 O 3 can be made from 0.075 moles of O 2 and excess B 4 H 10 ?
c. How many grams of B 4 H 10 are needed to react with 0.25 grams of O 2 ?
d. How many grams of water will be made from 0.43 grams of B 4 H 10 and excess O 2 ?
3. For the reaction:
Na 2 SO 4 (s) + 4 C (s) Na 2 S (s) + 4 CO (g)
a. If you mix 15 g of Na 2 SO 4 with 7.5 g of C, how many grams of Na 2 S can be made?
b. If you mix 10 g of Na 2 SO 4 with 14.2 g of C, how many grams of CO can be made?
4. For the reaction:
2 Al + 3 Cl 2 2 AlCl 3
a. If you mix 2.7 g Al and 4.05 g Cl 2 , which reactant is limiting?
b. What mass of AlCl 3 can be made?
c. What mass of the excess reactant remains?
5. For the reaction:
CaO + 2 NH 4 Cl 2 NH 3 + H 2 O + CaCl 2
a. If 112 g of CaO and 224 g of NH 4 Cl are mixed, what is the theoretical yield of NH 3 ?
b. If only 16.3 g of NH 3 is actually made, what is the % yield?

6. For the reaction:
CuSO 4 + 4 NH 3 Cu(NH 3 ) 4 SO 4
a. If you react 25 mL of 1.25 NH 3 with 7.5 grams of CuSO 4 , what is the theoretical yield of
the product in grams?
b. If you only get 0.63 grams of the product, what is the % yield?
7. For the reaction:
2 NaN 3 2 Na + 3 N 2
What mass of NaN 3 is required to give 75 L of N 2 at a pressure of 1.3 atm and 25 o C?
8. For the reaction:
2 C 8 H 18 + 25 O 2 16 CO 2 + 18 H 2 O
a. If 0.095 g of C 8 H 18 burns in O 2 , what will be the pressure of water vapor in a 4.75 L flask
at 30 o C?
b. If the O 2 gas needed for complete combustion was in the 4.75 L flask at 22 o C, what would
its pressure have been?
9. For the reaction:
4 KO 2 + 2 CO 2 2 K 2 CO 3 + 3 O 2
What mass of KO 2 is required to react with 8.90 L of CO 2 at 30 o C and 780 mm Hg?
10. For the reaction:
Na 2 CO 3 + 2 HCl 2 NaCl + CO 2 + H 2 O
If 38.55 mL of HCl is needed to titrate 2.150 g of Na 2 CO 3 , what is the M of HCl?
11. For the reaction:
H 2 A + 2 NaOH Na 2 A + 2 H 2 O
If 36.04 mL of 0.509 M NaOH is needed to reach the endpoint of 0.954 g of H 2 A, what is the
molar mass of H 2 A?

Redox
1. What are the oxidation numbers of the atom that is bolded in each of the following:
a. Na
b. Cl 2
c. S 8
d. Na +1
e. Cl -1
f. S -2
g. BrO 3
-1
h. H 4 SiO 4
i. HSO 4
-1
j. PF 6
-1
k. UO +2
l. N 2 O 5
m. C 2 O 4
-2
2. For each of the following reactions, identity the oxidizing agent and reducing agent:
a. C 2 H 4 + 3 O 2 2 CO 2 + 2 H 2 O
b. Si + 2 Cl 2 SiCl 4
c. Cr 2 O 7 -2 + 3 Sn +2 + 14 H + 2 Cr +3 + 3 Sn +4 + 7 H 2 O
d. FeS + 3 NO 3 -1 + 4 H + 3 NO + SO 4 -2 + Fe +3 + 2 H 2 O
e. MnO 4 -1 + 5 Fe +2 + 8 H + Mn +2 + 5 Fe +3 + 4 H 2 O
3. Balance the following reactions in a neutral solution:
a. Fe +3 + I -1 Fe +2 + I 2
b. Fe +2 + Cu +2 Cu + Fe +3
c. Al + Sn +4 Sn +2 + Al +3
4. Balance the following reactions in an acidic solution:
a. MnO 4 -1 + HSO 3 -1 Mn +2 + SO 4
-2
b. CH 2 O + Ag +1 HCO 2 H + Ag
c. Cr 2 O 7 -2 + Fe +2 Cr +3 + Fe +3
d. CrO 4 -2 + HNO 2 Cr +2 + NO 3
-1
5. Balance the following reactions in a basic solution:
a. CrO 4 -2 + SO 3 -2 Cr(OH) 3 + SO 4
-2
b. Zn + Cu(OH) 2 [Zn(OH) 4 ] -2 + Cu
c. HS -1 + ClO 3 -1 S + Cl -1
d. NiO 2 + Zn Ni(OH) 2 + Zn(OH) 2

Chemical Analysis
1. A mixture of CuSO 4 and CuSO 4 *5H 2 O has a mass of 1.245 g. After heating to drive off the
water, the mass is only 0.832 g. What was the mass % of CuSO 4 and CuSO 4 *5H 2 O in the
original mixture?
2. For the reaction:
2 NaHCO 3 Na 2 CO 3 + CO 2 + H 2 O
Heating a 1.7184 g sample of impure NaHCO 3 gives 0.196 g of CO 2 . What was the mass
percent of NaHCO 3 in the original sample?
3. For the reaction:
BeC 2 O 4 *3 H 2 O (s) BeC 2 O 4 (s) + 3 H 2 O (g)
a. If 3.21 g of BeC 2 O 4 *3H 2 O is heated, calculate:
i) the mass of BeC 2 O 4 (s) formed
ii) the volume of H 2 O (g) released at 220 o C and 735 mm Hg
b. A 0.345 g of BeC 2 O 4 which contained an inert impurity was dissolved in enough water to
give 100 mL of solution. A 20 mL portion of this was titrated with 0.0150 M KMnO 4 and
required 17.80 mL to reach the endpoint. The equation is as follows:
16 H + + 2 MnO 4 -1 + 5 C 2 O 4 -2 2 Mn +2 + 10 CO 2 + 8 H 2 O
i) Identify the reducing agent
ii) Calculate the number of moles of each of the following at the endpoint of the titration:
• MnO 4
-1
• C 2 O 4
-2
iii) Calculate the total moles of C 2 O 4 -2 that were in the 100 mL sample
iv) Calculate the mass % of BeC 2 O 4 in the impure 0.345 g sample
4. For the following reaction:
Fe 2 O 3 (s) + 3 CO (g) 2 Fe (s) + 3 CO 2 (g)
A 16.2 L sample of CO (g) at 1.5 atm and 200 o C is combined with 15.39 g of Fe 2 O 3
a. How many moles of CO are present?
b. What is the limiting reagent? Prove it with calculations.
c. How many grams of Fe are made?
d. How many L of CO 2 are made?

5. For the reaction:
3 Ba(NO 3 ) 2 (aq) + 2 H 3 PO 4 (aq) Ba 3 (PO 4 ) 2 (s) + 6 HNO 3 (aq)
If 200 mL of 3 M Ba(NO 3 ) 2 are mixed with 300 mL of 1 M H 3 PO 4 , calculate the following:
a) The mass of Ba 3 (PO 4 ) 2 (s) formed
b) The final concentration of the NO 3 -1 ion in solution
6. For the reaction:
MnO -1 4 + 5 Fe +2 + 8 H + Mn +2 + 5 Fe +3 + 4 H 2 O
A 0.598 g sample of an iron-containing compound was analyzed. It required 22.25 mL of
0.0123 M KMnO 4 to reach the equivalence point. What is the mass % of iron in the
sample?
Battery Basics
1. What are two other terms to describe a battery?
2. What are the three necessary parts of a battery?
3. What charge is the cathode?
4. What reaction takes place at the cathode?
5. What charge is the anode?
6. What reaction takes place at the anode?
7. What purpose does the salt bridge serve?
8. Write the following equations in shorthand notation:
a. Cu +2 + Mg Mg +2 + Cu
b. 2 Ag +1 + Sn Sn +2 + 2 Ag
c. 2 Al + 3 Pb +2 3 Pb + 2 Al +3
9. Write the two possible equations for the standard electrode:
a.
b.
10. All ½ reactions are tabulated as what kind of reactions?
11. What does it mean that voltage E o is an intensive property?
12. Give the voltages for the following ½ reactions as written:
a. Ca +2 + 2 e - Ca
b. Br 2 + 2 e - 2 Br -1
c. Na Na +1 + e -
d. 2 I -1 I 2 + 2 e -
13. Calculate the E o values for each of the following reactions as written. Which will be
spontaneous?
a. 2 Fe +3 + Cd Cd +2 + 2 Fe +2
b. Zn +2 + Hg Hg +2 + Zn
c. O 2 + 4 H +1 + 2 Ni 2 Ni +2 + 2 H 2 O
d. 6 Br -1 + 2 Au +3 2 Au + 3 Br 2

14. In each of the reactions above in #13, which species is the cathode and which is the anode?
a. Cathode = Anode =
b. Cathode = Anode =
c. Cathode = Anode =
d. Cathode = Anode =
15. A battery is made from using the following ½ reactions:
Cu +2 + 2 e - Cu E o = +0.36 V
V +2 + 2 e - V E o = -1.18 V
Knowing that Cu +2 ions are blue and V +2 ions are purple, answer the following questions
about a voltaic cell using Cu, Cu +2 , V, and V +2 ions.
a. Write the equation that occurs at the cathode.
b. Write the equation that occurs at the anode.
c. Write the shorthand notation for the cell.
d. What is the voltage under standard conditions.
e. As the reaction progresses, what should happen to:
i) The size of the copper electrode
ii) The size of the vanadium electrode
iii) The intensity of the blue color from the copper ion
iv) The intensity of the purple color from the vanadium ion
f. Which species is the oxidizing agent?
g. Which species is the reducing agent?

Nernst Equation & Non-Standard Conditions
1. What are the conditions for the following that are considered to be standard?
a. Concentration
b. Pressure
c. Temperature
2. What is the equation for non-standard voltages?
3. What is n?
4. Write the equations for Q for each of the following reactions:
a. Cu +2 + Mg Mg +2 + Cu
b. 2 Ag +1 + Sn Sn +2 + 2 Ag
c. 2 Al + 3 Pb +2 3 Pb + 2 Al +3
5. What is n for each of the equations in problem #4?
a.
b.
c.
6. A battery is made from Ag, Ag +1 , Pb, and Pb +2 .
a. What is the E o ?
b. Write the balanced equation for the battery.
c. What is the equation for Q?
d. If the [Ag +1 ] is made to 0.25 M and the [Pb +2 ] is made to 2.5 M, what is the new
voltage?
e. What would the effect of having a large Pb electrode have on the voltage? Why?
7. A battery is made from Cu, Cu +2 , Sn, Sn +2 .
a. What is the E o ?
b. Write the balanced equation for the battery.
c. What is the equation for Q?
d. If the [Cu +2 ] is made to 1.75 M and the [Sn +2 ] is made to 0.025 M, what is the new
voltage?
e. What would the effect of having a large Cu electrode have on the voltage? Why?
8. A battery is made from Zn, Zn +2 , Fe, Fe +2 . Describe what effect each of the following will
have on the standard voltage of the battery.
a. Increasing [Zn +2 ]
b. Decreasing [Fe +2 ]
c. Increasing the size of the Zn electrode
d. Decreasing the size of the Fe electrode
9. A battery is made from Cd, Cd +2 , Ag, Ag +1 . Describe what effect each of the following will
have on the standard voltage of the battery.
a. Decreasing the [Cd +2 ]
b. Increasing [Ag +1 ]
c. Decreasing the size of the Ag electrode
d. Increasing the size of the Cd electrode

Electrolysis
1. What is electrolysis?
2. Answer the following questions about electrolysis:
a. What reaction takes place at the cathode?
b. What is the polarity of the cathode?
c. What reaction takes place at the anode?
d. What is the polarity of the anode?
3. For each of the following molten salts, predict what species will be produced at each
electrode:
Cathode Anode
a. NaCl
b. CaBr 2
c. Ag 2 O
d. ZnI 2
e. AlF 3
4. How is an aqueous solution different than a molten salt?
5. Write the equation for the reduction of water during electrolysis.
6. Write the equation for the oxidation of water during electrolysis.
7. For each of the following aqueous solutions, predict what species will be produced at each
electrode:
Cathode Anode
a. KBr
b. CuF 2
c. NaI
d. SnCl 2
e. KF

Electrolysis Calculations
1. What is a Faraday?
2. How many F are needed to produce:
a. 1 mole of Na from Na +1
b. 1 mole of Ca from Ca +2
c. 1 mole of Al from Al +3
d. 0.25 moles of Mg from Mg +2
e. 0.075 moles of Cl 2 from Cl -1
f. 0.175 moles of I 2 from I -1
3. How many F are needed to produce:
a. 10 grams of Na from Na +1
b. 50 grams of Sr from Sr +2
c. 75 grams of F 2 from F -1
4. A solution of Cu +1 is electrolyzed with 0.08 F. How many moles of Cu are formed?
5. A solution of Cr +3 is electrolyzed with 1.2 F. How many moles of Cr are formed?
6. A solution of Pb +2 is electrolyzed with 2.4 F. How many grams of Pb are formed?
7. A solution of Cl -1 is electrolyzed with 0.046 F. How many grams of Cl 2 are formed?
8. How many moles of Sn can be made by electrolyzing a solution of Sn +2 with 0.50 amps for
1000 seconds?
9. How many moles of Ag can be made by electrolyzing a solution of Ag +1 with 2.7 amps for 4
hours?
10. How many grams of Ca can be made by electrolyzing Ca +2 with 0.25 amps for 78 minutes?
11. How many grams of Al can be made by electrolyzing Al +3 with 12,000 amps for 2.5 hours?
12. How long can a battery last if it’s limiting reagent is 2.2 grams of Cd going to Cd +2 at 1.5
amps?
13. How long can a battery last it it’s limiting reagent is 0.75 grams of Hg going to Hg +2 at 0.25
amps?

Electrochemistry Analysis
1. For the reaction:
2 Ag +1 (aq) + Zn (s) Zn +2 (aq) + 2 Ag (s)
a. A 1.50 g sample of Zn is combined with 250 mL of 0.110 M AgNO 3
i) What is the limiting reagent? Show proof.
ii) Assuming the reaction goes to completion, what is the [Zn +2 ] after the reaction
is complete?
b. What is the E o for the above reaction?
2. In an electrolytic cell, a current of 0.250 amps is passed through a solution containing Cl -1 and
iron ions producing Cl 2 (g) and Fe (s).
a. Write the half-reaction that occurs at the anode.
b. When the cell operates for 2 hours, 0.521 g of iron is deposited at an electrode.
Determine the formula of the chloride of iron.
c. What is the overall balanced reaction that occurs in the cell.
d. How many Liters of Cl 2 (g) are produced if the cell is at 25 o C and 750 mm Hg.
e. Calculate the current that would produce Cl 2 gas at a rate of 3 grams per hour.
3. A solution is electrolyzed such that water is both oxidized and reduced so that O 2 (g) and H 2
(g) are produced at 298 K and 1.0 atm. The solution was electrolyzed for 5.61 minutes at 0.513
amps.
a. Write the balanced equation for the ½ reaction that occurs at the anode.
b. Calculate the amount of electric charge, in coulombs, that passed through the solution.
c. Why is the volume of O 2 different from the volume of H 2 gas collected?
d. Calculate the number of moles of H 2 produced.
e. Calculate the volume of H 2 produced.
4. An electrochemical cell is constructed so that a strip of Sn and unknown metal X are used as
electrodes. Each is submerged in a 1.0 M solution of its ion. When the battery is connected,
it is noticed that the mass of the Sn electrode increases. Knowing that and using the halfreactions
below, answer the following questions:
Sn +2 (aq) + 2 e -1 Sn (s) E o = -0.14 V
X +3 (aq) + 3 e -1 X (s) E o = ???
a. Which electrode is the cathode? Justify your answer.
b. If the E o cell is +0.60 V, what is the reduction potential for the X +3 /X electrode?
c. Identify metal X
d. Write a balanced net-ionic equation for the overall reaction.
e. In the cell, the concentration of Sn +2 is changed from 1.0 M to 0.50 M and the
concentration of X +3 is changed from 1.0 M to 0.10 M. Calculate the new voltage of the
cell.