Chem 1151Exam 2A-1 (40 pts)March 27, 2007

1.(4) Consider a 1.00 L solution that is 0.150 M in NaCl and 0.060 M in Na2S. What is the concentration of sodium ions? Prob 4.32

molarity of soln, identification of soluble salts, these strong electrolytes ionize 100%, molarity of ions in soln

2.(4)2Na3PO4(aq) + 3Pb(NO3)2  6NaNO3(aq) + Pb3(PO4)(s)

How many mL of 0.245 M sodium phosphate are required to precipitate all of the lead(II) ions from 200 mL of a 0.165 M solution of lead(II) nitrate? Prob 4.48

Stoichiometry, precipitation, solubility rules, M x V = # mol

3.(2) This equation is balanced in acid. Now balance it in base.

16H+ + 7S2- + 2MnO4-  5S + 2MnS + 8H2O

Prob 4.76b

4.(4)Consider this balanced acid-base reaction.

2HCl(aq) + Ba(OH)2(aq)  2H2O(ℓ) + BaCl2(aq)

When 250 mL of 0.100 M acid reacts with 200 mL of 0.050 M base, how many moles of water are produced? Prob 4.64

Stoichiometry, net ionic eqn, limiting reactant, M x V = # mol, acid + base rxn

5.(8)When 0.75 mol of oxygen, 1.40 mol of Ar and 0.45 mol CO are placed in a 10.0 L flask at 300 K, Sample Ex 5.15

ideal gas law, Dalton’s Eqn for gas mixtures, relationship between effusion rate and molar mass

a.(3) What is the total pressure in the flask?

b.(3) What is the partial pressure of Ar in the flask?

c.(2) Which gas has the highest effusion rate under these conditions? Prob 5.88

6.(4)A sample of ideal gas in a 2.50 L container at 30 oC and 1.00 atm is cooled to 15 oC and compressed to 1.75 L. What is the final pressure of the gas?

Ideal gas law, convert temp in Celsius to K. P vs T and P vs V

7.(4)When a 0.513 g piece of solid at 200 oC is placed 5.0 g of water at 25 oC, the final temperature of the mixture is 28 oC. What is the specific heat of the solid? What is the solid? Prob 6.49

answer / A / B / C / D / E
metal / H2O(ℓ) / Fe(s) / Ag / Al(s) / C(s)
Specific heat
J/g- oC / 4.18 / 0.45 / 0.24 / 0.89 / 0.71

Calorimetry, q = ms ΔT, conservation of energy (heat lost by hot metal = heat gained by cold water)

8.(4)4Fe(s) + 3O2(g)  2Fe2O3(s)ΔH = -1652 kJ

How many grams of iron must burn to produce 500 kJ of energy? Probl 6.36

Thermochemical eqn, enthalpy depends on amount of reactant,

9.(6)Select the correct answer.

a.When a gas expands, work is [positive, zero, negative]. Sample Ex 6.2

b.If w = +113 kJ and q = -72 kJ, then

∆E = [+185 kJ, +41 kJ, -41 kJ, -185 kJ]. Prob 6.21

c.OMIT When one mol of propane burns, 2221 kJ of energy is produced. If the reaction is only 75% efficient, how much energy will be produced? Prob 6.37

[-2961 kJ, +2221 kJ, -2221 kJ, -1666 kJ, +1666 kJ]

Chem 1151Exam 2B-2 (30 pts)March 28, 2007

1.Which statements are true about this redox reaction

redox defns, Ch 4

3As2O3(s) + 4NO3-(aq) + 7H2O(ℓ) + 4H+(aq)  6H3AsO4(aq) + 4NO(g)

I.As2O3(s) is the reducing agent.

II.NO3-(aq) is the reducing agent.

III.As gains 2 electrons.

IV.As loses 2 electrons.

V.A total of 12 electrons are transferred.

VI.This reaction occurs in base.

2.Which statement is not a postulate of the Kinetic Molecular Theory?

KMT Ch 5

3.Which species has ∆Hfo = 0?

Defn of std enthalpy of formation Ch 6

4.All of the following are weak acids except

Memorize strong acids, Ch 4

5.Consider these chemical equations. Combine Rxns (1), (2) and (3) to describe Rxn (4). Prob 6.61 Hess’s Law

(1)2O3(g)  3O2(g)

(2)O2(g)  2O(g)

(3)NO(g) + O3(g)  NO2(g) + O2(g)

(4)NO(g) + O(g)  NO2(g)

6.Consider this decomposition reaction 2HN3(g)  3N2(g) + H2(g)

If all of the reactant decomposes, the mole fraction of nitrogen in the product gases is

Dalton’s Law Ch 5

7.Which graph correctly describes the relationship between volume of a gas and its temperature at constant number of moles and pressure?

Charles’ Law Ch 5

8.All of the following are endothermic except

Defn of endo- and exo-thermic, Ch 6

9.The correct net ionic equation for the reaction between Al(NO3)3 and Ba(OH)2 is net ionic eqn, solubility rules Ch 4

10. Consider two identical 2.00 L flasks. Flask A contains F2 and Flask B contains O2. Both gases are at STP. Which statements are true about the gas in Flask A compared with the gas in Flask B. dRT = PM

I.Flask A has more molecules.

II.The molecules in Flask A are, on average, moving faster.

III.The molecules in Flask A are, on average, moving slower.

IV.The average kinetic energy in Flask A is higher.

V.The density of the gas in Flask A is larger.

VI.The density of the gas in Flask B is larger.

Ch 5 ideal gases

11.If a gas is compressed and gives off heat, then the signs of w and q are

w / q
A / + / -
B / - / +
C / + / +
D / - / -
E / 0 / +

Ch 6 sign convention of work and heat

12.Arrange the following in order of increasing sulfur oxidation state.

Ch 4 assigning oxidation states or numbers

13.The chemical equation correctly associated with the standard enthalpy of formation, ∆Hfo, of Cl3PO(g) is

application of std enthalpy of formation Ch 6

14.All of the following are units of pressure except

Def of pressure units Ch 5

15.The correct net ionic equation for the reaction between HNO3(aq) and Fe(OH)2(s) is

net ionic eqn for strong acid and weak base. Ch 4

Part A: Calculations

Quest. / Question Topic / Version 1 answers / Version 2 answers
1 / Ion concentration / C / C
2 / Stoichio of ppt rxn / 89.8 mL / 183 mL
3 / Redox in base / 8H2O +7S2- + 2MnO4-
5S + 2MnS + 16OH- / Same as V1
4 / Stoichio of acid-base rxn / 0.020 mol water / 0.25 mol water
5 / Gas mixture / a. 6.4 atm
b. PAr = 3.45 atm
c. CO (lowest mass has highest effusion rate) / a. 6.65 atm
b. . PO2= 2.34 atm
c. Ar (highest mass has lowest effusion rate)
6 / Ideal gas law / B / D
7 / calorimetry / 0.71 J/(g-C), C(s) / 0.89 J/(g-C), Al(s)
8 / Thermochem eqn / 67.6 g / 81.1 g
9 / thermochem / a. negative
b. +41 kJ
c. -1666 kJ / a. positive
b. +17 kJ
c. -1444 kJ

Part B:Multiple Choice

Question / Version 1 / Version 2
1 / C / E
2 / B / A
3 / A / B
4 / E / C
5 / E / C
6 / D / D
7 / B / B
8 / A / D
9 / C / B
10 / A / E
11 / D / A
12 / B / E
13 / E / D
14 / D / A
15 / D / A

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