Tarleton State University

Department of Chemistry, Geosciences, and Environmental Science

 

Chemistry 1054-010 College Chemistry Fall 2009

 

Exam 2-A

 

Name:____________________________________________________

(Please write your name legibly)

 

Read all directions and questions carefully!! This exam consists of two parts. The first part consists of 10 multiple choice questions worth four points each for a total of 40 points. The second part consists of five numerical problems worth either 10 or 15 points per question for a total of 60 points. Show all your work necessary for the numerical problems as partial credit will be given for those problems.

 

Possibly Useful Constants

 

Avogadros Number: NA = 6.022 1023 particles/mol

q = (heat capacity)T

q = (mass in grams)(specific heat)∆T

q = (number of moles)(molar heat capacity)∆T

Calorimetry: qrxn = CcalorimeterT or

qrxn = (mass of solution)(specific heat of solution)∆T

 

 

Score

 

Part 1 (40 points):_____________________

 

 

Part 2 (60 points):_____________________

 

 

Total (100 points):_____________________

 

 

Dont forget to put your name on this test!

 

Good Luck!!


Part 1

 

Multiple Choice

 

Please indicate the answer to each question by putting your choice in the space provided. There is only one correct answer for each question. There will be 10 multiple choice questions worth 4 points each.

 

1. Which of the following compounds is not a strong electrolyte.

(a) CCl4 (c) HCl

(b) NaCl (d) MgCl2

(e) All of the above are strong electrolytes

 

Answer: A

CCl4 contains only nonmetals which makes it a nonelectrolyte.

 

2. Which of the following are strong acids?

HI HNO3

HF HBr

 

(a) HF and HBr (c) HI, HNO3, and HBr

(b) HI, HNO3, HF, and HBr (d) HNO3, HF, HBr

(e) HI, HF, and HBr

 

Answer: C

The strong acids are HCl, HBr, HI, HClO4, HNO3and H2SO4

 

3. There are __________ mol of potassium ions in 0.500 L of a 0.300 M solution of K3PO4?

(a) 0.0500 (c) 0.150

(b) 0.167 (d) 0.500

(e) 0.450

 

Answer: E

 

4. In which species does sulfur have the highest oxidation number?

(a) S8 (c) H2S

(b) SO2 (d) SO32-

(e) SO42-

 

Answer: E

Sulfur has an oxidation number of +6 in SO42-

 

5. Oxidation cannot occur without ___________________.

(a) acid (c) water

(b) oxygen (d) reduction

(e) air

 

Answer: D

 

6. The DE of a system that releases 12.4 J of heat and does 4.2 J of work on the surroundings is _________ J.

(a) 16.6 (c) 4.2

(b) 12.4 (d) 8.2

(e) 16.6

 

Answer: E

DE = q + w = 12.4 J + (4.2 J) = 16.6 J

 

7. The value of DH for the following reaction is 3351 kJ:

2 Al(s) + 3 O2(g) 2 Al2O3(s)

The value of DHf for Al2O3(s) is ______________ kJ.

(a) 3351 (c) 2.86

(b) 1676 (d) 16.43

(e) 3351

 

Answer: B

DHf is defined for formation of 1 mole of Al2O3 from its elements. This would be times the above reaction.

 

8. A _____________ DH corresponds to an _______________ process.

(a) negative, endothermic (c) positive, exothermic

(b) zero, exothermic (d) negative, exothermic

(e) zero, endothermic

 

Answer: D

 

 

9. Which of the following is not considered a fossil fuel?

(a) coal (c) natural gas

(b) petroleum (d) hydrogen gas

(e) crude oil

 

Answer: D

 

10. When solutions of CaCl2 and Na2CO3 are mixed, a precipitate of CaCO3 is formed according to the reaction: CaCl2(aq) + Na2CO3(aq) CaCO3(s) + 2 NaCl(aq)

What are the spectator ions in this reaction?

(a) Ca2+ only (c) Na+ only

(b) Na+ and Cl (d) Ca2+ and CO32-

(e) Cl and CO32-

 

Answer: B

 

Total ionic equation: Ca2+(aq) + 2 Cl(aq) + 2 Na+(aq) + CO32-(aq) CaCO3(s) + 2 Na+(aq) + 2 Cl(aq)

Spectator ions are Na+ and Cl

 

 

 

 

Part 2

 

Numerical Problems

 

Solve the following problems, keeping track of significant figures where applicable. Please show all the work necessary to obtain your answer in order to receive partial credit for possibly wrong answers. Generally, full credit will not be given for the correct answer without any of the work performed to obtain the answer being shown on the paper. Each question is worth either 10 or 15 points.

 

11. (10 points) Calculate the volume in milliliters of 1.25 M (NH4)2SO4 solution that contains 35 g of (NH4)2SO4.

 

Calculate moles of (NH4)2SO4:

Calculate the volume of the solution in liters:

Convert to milliliters:


 

12. (15 points) What is the molarity of a H2SO4 solution if it requires 26.36 mL of the H2SO4 solution to neutralize 58.46 mL of 0.1376 M NaOH? The acid-base neutralization reaction is:

H2SO4(aq) + 2 NaOH(aq) Na2SO4(aq) + 2 H2O(l)

 

Known: 58.46 mL of 0.1376 M NaOH

Unknown: 26.36 mL of ?? M H2SO4

 

Calculate moles of NaOH from the volume and the molarity:

Convert to moles of H2SO4 using the balanced chemical equation:

Calculate molarity of H2SO4 solution:

(4 sig figs)

 

 

 

13. (10 points) Calculate DH for the following reaction given the table of thermodynamic data on the back of this exam:

2 NO2(g) + 7 H2(g) 2 NH3(g) + 4 H2O(g)

 

DHf values: For NO2(g): 33.84 kJ/mol; For NH3(g): 46.19 kJ/mol; For H2O(g): 241.82 kJ/mol; For H2(g): 0 kJ/mol

 

DH = (2 mol NH3)(46.19 kJ/mol) + (4 mol H2O)(241.82 kJ/mol) (2 mol NO2)(33.84 kJ/mol) (7 mol H2)(0 kJ/mol)

 

= 92.38 kJ 967.28 kJ 67.68 kJ = 1127.34 kJ

14. (10 points) Write the net ionic equation for each of the following reactions:

 

(a) 2 HI(aq) + Ba(OH)2(aq) BaI2(aq) + 2 H2O(l)

 

Total ionic: 2 H+(aq) + 2 I(aq) + Ba2+(aq) + 2 OH(aq) Ba2+(aq) + 2 I(aq) + 2 H2O(l)

 

Net ionic: 2 H+(aq) + 2 OH(aq) 2 H2O(l)

 

 

(b) Ca(NO3)2(aq) + Na2CO3(aq) CaCO3(s) + 2 NaNO3(aq)

 

Total ionic: Ca2+(aq) + 2 NO3(aq) + 2 Na+(aq) + CO32-(aq) CaCO3(s) + 2 Na+(aq) + 2 NO3(aq)

 

Net ionic: Ca2+(aq) + CO32-(aq) CaCO3(s)

 

 

 

(c) Zn(s) + Sn(NO3)2(aq) Zn(NO3)2(aq) + Sn(s)

 

Total ionic: Zn(s) + Sn2+(aq) + 2 NO3(aq) Zn2+(aq) + 2 NO3(aq) + Sn(s)

 

Net ionic: Zn(s) + Sn2+(aq) Zn2+(aq) + Sn(s)

 

 

 

15. (15 points) When 50.0 mL of 0.10 M HCl is mixed with 50.0 mL of 0.10 M NH3 in a coffee cup calorimeter, the temperature of the solution upon mixing increases from 21.2C to 26.4C. Assuming that the density of the solution is equal to 1.00 g/mL and that the heat capacity of the solution is 4.18 J/gC, calculate the heat of this reaction and the heat of reaction per mole of HCl.

 

qrxn = (mass of solution)(specific heat)DT

 

mass of solution = (50.0 mL + 50.0 mL)(1.00 g/mL) = 100.0 g

DT = 26.4C 21.2C = 5.2C

qrxn = (100.0 g)(4.18 J/gC)(5.2C) = 2.2 103 J (2200 J) 2 sig figs

 

Moles of HCl =

 

Heat of reaction per mole of HCl =


 

(10 points extra credit) Give the complete definition for 2 out of the 3 terms below. 5 points will be given for each correct complete definition. Clearly note which 2 definitions you want graded, if you write three definitions without a clear notation, only the first two will be graded.

 

Oxidation: the loss of electrons by a substance

 

 

 

 

Specific heat: the amount of heat required to raise the temperature of one gram of a substance by 1C (or 1 K)

 

 

 

 

Exothermic reaction: a reaction that releases heat.