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Write all answers on this examination paper.
A periodic table and formula sheet are provided.
Nonprogrammable calculators are allowed (no organizers!)
No other aids are allowed.
1. (20 marks)
(a) (5 marks) Given the following equation for a redox reaction:
What is the oxidation number of P in Ca3(PO4)2? +5
Give the formula of the reactant that gets oxidized. C
Give the formula of the reactant that gets reduced. Ca3(PO4)2
Give the formula of the reactant that acts as the oxidizing agent. Ca3(PO4)2
Give the formula of the reactant that acts as the reducing agent. C
(b) (5 marks) Calculate the enthalpy change for the following reaction:
2 Fe + O2 ---> 2 FeO using the following equations and data:
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(c) (5 marks) Assume that 58.911 g of Fe2(SO4)3.9H2O (562.02 g/mol) is dissolved in enough water to give 500.0 mL of solution.
(i) What is the molarity of the solution? Answer: 0.2096 M
(ii) What volume of solution (mL) must be taken in order to obtain 0.05000 mol of SO42-?
(d) (5 marks) What volume (mL) of 0.1072 M KOH is required to react with 35.00 mL 0.08821 M Al(NO3)3 to produce Al(OH)3? (Hint: write the balanced equation first!)
2. (20 marks)
(a) (14 marks) Suppose you burn 1.540 g of ethylene oxide, C2H4O, in a combustion calorimeter and find that the temperature of the water in the calorimeter increases from 18.54 to 25.65°C. The calorimeter contains 1275 g of water. The heat capacity of the calorimeter is 985 J/K. Calculate the molar heat of combustion of ethylene oxide.
(b) (3 marks) Write a balanced equation for the combustion of one mole of ethylene oxide.
(c) (3 marks) The standard heat of formation of ethylene oxide is -77.8 kJ/mol Write a balanced equation for which this is the enthalpy change.
3. (15 marks)
A sample of iron ore is analyzed for its content of Fe2O3. The ore is prepared for titration by dissolving it in acid and then reducing all the iron to iron(II). If a sample of ore weighing 0.9513 g requires 38.75 mL of 0.01069 M KMnO4 for titration, what is the percentage of Fe2O3 in the sample? The balanced net ionic equation for the reaction between permanganate and iron(II) is
4. (10 marks; 2 marks each)
(a) A student states that the oxidation number of sulfur in S2O32- is +4. Briefly explain why this is incorrect, and give the correct oxidation number for sulfur in S2O32-.
Oxidation number is the property of an individual atom, not of a group of atoms. Oxidation number of each sulfur in S2O32- is +2.
(b) Define the term: specific heat capacity
Specific heat capacity, or specific heat (C), is the energy required to raise the temperature of one gram of a substance by one degree Celsius (or Kelvin, since temperature differences are the same in Celsius and Kelvin).
(c) Briefly explain Hess's Law
Hess's Law combines the law of conservation of matter and the law of conservation of energy. It states that when a reaction is the sum of two or more other reactions (conservation of mass), the enthalpy change for the overall reaction is the sum of the enthalpy changes for the constituent reactions (conservation of energy).
(d) What is a salt? Give two examples of compounds that are salts.
A salt is an ionic compound that contains cations other than the hydrogen ion, and anions other than the hydroxide ion. One way to make a salt is by the reaction of an acid with a base: the cation from the base combines with the anion of the acid.
Two examples of salts already seen on this exam are Ca3(PO4)2 and KMnO4.
(e) Define the term: standard enthalpy of formation
The standard molar enthalpy of formation of a chemical substance is the amount of energy associated with the formation of one mole of that substance in its standard state from the elements in their standard state.
5. (15 marks)
Consider these 10 compounds:
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Answer the following questions by writing the formulas of the compounds in the space provided below. Write NONE if no compound in the list is an answer to the question.
Which compound is a strong acid? HNO3
Which compound is a weak acid? CH3CO2H
Which two compounds are soluble salts? Fe(NO3)3 and Na2SO4
Which two compounds are insoluble salts? AgCl and CaCO3
Which compound is a strong base? KOH
Which compound is a weak base? NH3
Which compound is an acidic oxide? SO3
Which compound is a basic oxide? MgO
Which two compounds dissolve in water to give weakly conducting solutions? NH3 and CH3CO2H
Which compound produces no ions when it dissolves in water? None
Which two compounds react with each other to produce iron(III) hydroxide? Fe(NO3)3 and KOH
MULTIPLE CHOICE QUESTIONS. (20 marks; 10 parts, MC1 through MC10)
Choose the best answer to each of the following questions. Write the letter in the space provided for the answer. Write your letters clearly!
MC1. If iron(II) nitrate and sodium carbonate solutions are mixed, what is the formula of the precipitate formed (if any)?
(a) Na2(NO3)2
(b) Fe2CO3
(c) FeCO3
(d) NaNO3
(e) no precipitate is formed when these solutions are mixed
MC2. What are the ion concentrations in a 0.12 M solution of BaCl2?
(a) [Ba2+] = 0.12 M and [Cl-] = 0.12 M
(b) [Ba+] = 0.12 M and [Cl2-] = 0.12 M
(c) [Ba2+] = 0.12 M and [Cl-] = 0.06 M
(d) [Ba2+] = 0.060 M and [Cl-] = 0.060 M
(e) [Ba2+] = 0.12 M and [Cl-] = 0.24 M
MC3. Which of the following equations represents an oxidation-reduction reaction?
(a) 1
(b) 2
(c) 3
(d) 1 and 3
(e) 2 and 3
MC4. Identify the spectator ion or ions (if any) in the precipitation reaction of lead(II) nitrate with sodium sulfide:
(a) Pb2+ and S2-
(b) Na+ and NO3-
(c) Na+ and SO42-
(d) Pb2+ and NO3-
(e) there are no spectator ions in this reaction
MC5. Which response lists the processes that are endothermic and none that are exothermic?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 3 and 4 only
(e) 2, 3, and 4 only
MC6. Consider the thermal energy transfer during a chemical process. When heat is transferred to the system the process is said to be __ and the sign of q is __.
(a) exothermic, positive
(b) exothermic, negative
(c) endothermic, positive
(d) endothermic, negative
(e) enthalpic, negativeAnswer: (a)
MC7.
What is 
for a system which has the following two
steps:
(a) -50 J
(b) -30 J
(c) zero J
(d) 30 J
(e) 50 JAnswer: (b)
MC8. Given the following specific heats of metal:
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If the same amount of heat is added to 100.0 g samples of each of the metals which are all at the same temperature, which metal will have the lowest temperature?
(a) Mn
(b) Ba
(c) Sr
(d) Al
(e) NaAnswer: (e)
MC9. The standard enthalpy of formation of acetylene is represented by the equation
From this information, we can conclude that acetylene
1. will release energy when prepared from its elements
2. is energetically unstable with respect to its elements
3. will decompose rapidly into carbon and hydrogen
(a) 1 only
(b) 2 only
(c) 3 only
(d) 1 and 2 only
(e) 2 and 3 onlyAnswer: (b)
MC10. When two solutions are mixed, the container "feels hot." Thus,
(a) the reaction is endothermic
(b) the reaction is exothermic
(c) the energy of the universe is increased
(d) the energy of both the system and the surroundings is decreased
(e) the energy of the system is increasedAnswer: (b)
This page is
http://chemiris.labs.brocku.ca/~chemweb/courses/chem180/Midterm_Exam_2_1998.html
Created September 27, 2000 by M. F. Richardson
© Brock University, 2000