Final Exam

Final Exam Chem 111, Section 2 (Martin, 1:25pm) Spring 1998

Proceed immediately to the last page of the exam and follow its instructions!

1. Consider the ions Rb+, I-, Br-, Ba+2 and Cs+. The ion with the largest radius is:

(a) Rb+ (b) I- (c) Br- (d) Ba2+ (e) Cs+

2. The ground state electron configuration for Mn+3 is:

(a) [Ar]4s13d4 (b) [Ar]3d4 (c) [Ar]4s23d7

(d) [Ar]4s23d2 (e) [Ar]3d5

3. The 4p electrons on Se (selenium) "see" an effective nuclear charge of:

(a) 34 (b) 4 (c) 79 (d) 6 (e) 3

4. The highly poisonous compound brucine has the following percentage composition: 70.03% C, 6.64% H, 7.10% N and 16.22% O. The empirical formula for brucine is

(a) C21H23N3O4 (b) C24H26N2O2 (c) C22H25N3O3

(d) C23H26N2O4 (e) C21H23N3O3

. For the molecule imidazole shown at right, which statement below is true?

(a) The nitrogen on the left is sp3 hybridized

(b) The nitrogen on the right is sp3 hybridized

(d) The nitrogen on the right is sp hybridized

(e) None of the above is true

6. For the molecule imidazole (see problem above), if we take one 2p orbital from each of the 3 carbons and 2 nitrogens (5 p orbitals in all) and mix them to form molecular orbitals, we will end up with how many molecular orbitals in the end?

(a) 1 (b) 2 (c) 3 (d) 5 (e) 10

7. For IF5, the hybridization of the central atom is

(a) sp (b) sp2 (c) sp3 (d) sp3d (e) sp3d2

8. What is the (molecular) geometry for the chlorate anion, ClO3— ?

(a) linear (b) bent (c) trigonal pyramid (d) triangular-planar (e) tetrahedral

9. Which of the following is paramagnetic?

(a) Al3+, (b) Sc2+ (c) Sc3+ (d) Zn2+ (e) Sr2+

10. What is the (molecular) geometry for the perchlorate anion, ClO4— ?

(a) T-shaped (b) square planar (c) trigonal pyramid

(d) triangular-planar (e) tetrahedral

11. What is the (molecular) geometry for phosphorous pentachloride PF5 ?

(a) T-shaped (b) square planar (c) trigonal bipyramidal

(d) triangular-planar (e) octahedral

The following pertains to questions 12-14 and shows three resonance structures for HOCN. Lone pairs are present where appropriate, but are not shown.

12. What is the energy ranking of these resonance forms (lowest E< Middle E < Highest E)?

(a) B < A < C (b) A < B < C (c) C < B < A

(d) B < C < A (e) A < C< B

13. Which best describes the molecular geometry of resonance form B?

(a) Angle HOC, bent Angle OCN, bent

(b) Angle HOC, bent Angle OCN, linear

(d) Angle HOC, linear Angle OCN, linear

14. Which best describes the bond polarities of resonance form C?

(a) (b) (c)

(d) (e)

15. An unknown amino acid is found to contain 54.94% C, 9.989% H, 24.39% O, and 10.68% N. What is the empirical formula for this amino acid?

(a) C6H13O2N (b) C5H9O2N (c) C5H11O2N (d) C4H9O2N (e) C6H9O2N

16. Potassium permanganate KMnO4, oxidizes Fe2+ according to the following net ionic equation

MnO41— (aq) + 5 Fe2+ (aq) 8 H+ Æ Mn2+ (aq) + 5 Fe3+ (aq) + 4 H2O (l)

A 1.00 g sample of iron-containing ore requires 25.0 mL of 0.020 M KMnO4 to reach the equivalence point. What is the weight percent of iron in the ore?

(a) 50.0% (b) 14.0% (c) 0.250% (d) 2.00% (e) 8.52%

17. In an experiment, 1.056 g of a metal carbonate, containing an unknown metal M, is completely converted to yield the metal oxide and 0.376 g CO2 according to:

MCO3 (s) Æ MO (s) + CO2 (g)

The metal M is most likely:

(a) Fe (b) Ni (c) Cu (d) Zn (e) Ba

18. The magnesium emission spectrum has a line at 266.8 nm. Which statement below is TRUE concerning this radiation?

(a) It has a lower frequency than radiation with wavelength 315 nm

(b) It has a smaller speed in vacuum than does red light of wavelength 710 nm

(d) It has a smaller speed in vacuum than do x-rays of wavelength 0.1 nm

(e) None of the above is true

The following pertains to questions 19-20. The chromate ion, CrO42—, is present in waste water from chrome-plating plants. Sodium dithionite, Na2S2O4, can be used to reduce chromate to an insoluble hydroxide (which can then be filtered out of the wastewater) according to the following unbalanced equation:

CrO42— + S2O42— + OH^— Æ Cr(OH)3 (s) + SO32— 19. Which statement below is TRUE concerning this reaction?

(a) Cr is the oxidizing agent; S is the reducing agent

(b) S is the oxidizing agent; Cr is the reducing agent

(d) OH— and S are the oxidizing agents, Cr is the reducing agent

(e) This is not an oxidation-reduction reaction

20. Which answer below best represents the fully balanced equation for the above reaction:

(a) CrO42— + other things Æ other things + SO32-

(b) 4 CrO42— + other things Æ other things + 3 SO32-

(d) 6 CrO42— + other things Æ other things + 3 SO32-

(e) 2 CrO42— + other things Æ other things + 6 SO32-

The following information pertains to questions 21-23. Each of the four tires of a car is filled with a different gas. Each tire has the same volume and each is filled to the same pressure, 3.0 atm, at 25 °C. The tires are filled as follows:

Left front: 116 g of air

Right front: 80.7 g Ne

Left rear: 16.0 g He

Right rear: 160 g of an unknown gas

21. What is the molecular mass of the unknown gas?

(a) 160 g/mol (b) 40.0 g/mol (c) 18.4 g/mol (d) 53.3 g/mol (e) 16 g/mol

22. In which tire do the gas molecules/atoms have the greatest average speed?

(a) left rear (b) right front (c) left front (d) right rear (e) All are the same

23. In which tire do the gas molecules/atoms have the largest kinetic energy?

(a) left front (b) right front (c) left rear (d) right rear (e) All are the same

24. A sample of gas is placed in a 500. mL flask, at a pressure of 450. mm of Hg. If the sample were transferred to a flask having a volume of 2.300 L, what would the gas pressure (in mm of Hg) be?

(a) 87.2 mm of Hg (b) 97.8 mm of Hg (c) 102 mm of Hg

(d) 93.7 mm of Hg (e) 2145 mm of Hg

25. A 0.982 g sample of an unknown gas exerts a pressure of 700. mm of Hg in a 450. mL container at 23.0 °C. What is the molar mass of the gas?

(a) 741 g/mol (b) 62.4 g/mol (c) 57.5 g/mol (d) 23.6 g/mol (e) 8.22 g/mol

26. Five compounds are in the family of sulfur-fluorine compounds with the general formula SxFy. One of these compounds is 32.07% S (% by mass). If you place 0.0955 g of the compound in a 89.0 mL flask at 45.0 °C, the pressure of the gas is 98.44 mm of Hg. What is the molecular formula of SxFy ?

(a) S3F8 (b) S2F8 (c) S2F10 (d) S3F9 (e) S2F9

27. If the root mean square () speed of an oxygen molecule is 4.28 ¥ 104 cm/s at 25.0 °C, what is the root mean square speed of a SO2 molecule at the same temperature?

(a) 4.28 ¥ 104 cm/s (b) 3.89 ¥ 104 cm/s (c) 3.65 ¥ 104 cm/s

(d) 2.56 ¥ 104 cm/s (e) 3.03 ¥ 104 cm/s

28. A 0.14 g sample of a hydrocarbon is burned in oxygen to give 0.44 g CO2 (MW=44.0 g/mol) and 0.18 g H2O (MW=18.0 g/mol). Which molecular formula is most consistent with this result?

(a) C2H2 (b) C2H4 (c) C2H6 (d) C2H2O (e) C2H4O

The table below lists some standard enthalpies of formation at 298 K

Substance Hf°

(kJ/mol)

CO (g) -110.5

CO2 (g) -393.5

CH3OH (l) -238.7

H2O (l) -285.8

29. What is H° for the following reaction at 298 K:

2 CH3OH (l) + 2 O2 (g) Æ 2 CO (g) + 4 H2O (l)

(a) -157.6 kJ/mol (b) 886.8 kJ/mol (c) 157.6 kJ/mol

(d) -886.8 kJ/mol (e) insufficent information to calculate

30. Hvap for ethanol (C2H5OH, MW=46.07 g/mol) at its boiling point is 38.56 kJ/mol.
Hvap for water (H2O, MW=18.02 g/mol) at its boiling point is 40.73 kJ/mol.
Which statement below is true?

(a) Boiling 4.6 g ethanol requires more heat input than boiling 3.6 g water

(b) Boiling 4.6 g ethanol requires less heat than boiling 3.6 g water

(d) Condensing 4.6 g ethanol releases more heat than condensing 3.6 g water

(e) None of the above is true

You have exam B. Place a "2" in column "P" under "Special Codes" on your OpScan sheet. Failure to do so correctly will result in the loss of 2 points from your exam!

Left front: 116 g of air	Right front: 80.7 g Ne
Left rear: 16.0 g He	Right rear: 160 g of an unknown gas