Chem 109 Final Exam Fall 2008 (Form 1)

CHEM 109 FINAL EXAM FALL 2008 (FORM 1)

Part 1. Free Response. Answer each question below as completely as possible. Be sure to show all math steps. No work, no credit.

1. (15 pts.) A reaction that occurs in a blast furnace, where iron ore is converted to cast iron, is shown below:

Compound Molar Mass (g/mol)

Fe2O3 159.6

Fe2O3 + 3 CO → 2 Fe + 3 CO2 CO 28.0

Use this information to answer the following questions:

(a) Suppose 86.7 grams of Fe2O3 are mixed with 100.5 g of CO. Which is the limiting reagent? (Work must support answer!)

86.7 g Fe2O3(1mol Fe2O3/ 159.7 g Fe2O3)(2 mol Fe/ 1 mol Fe2O3)(55.845 g Fe/ 1 mol Fe) = 60.7 g Fe

100.5 g CO(1mol CO/ 28.0 g CO)(2 mol Fe/ 3 mol CO)(55.845 g Fe/ 1 mol Fe) = 133.629 g Fe

Limiting Reagent: Fe2O3

(b) What mass of Fe, in grams, will be produced when this reaction takes place?

Work shown above

60.7 g Fe

(c) In a separate experiment, 25.4 g of Fe are produced, yet it was calculated that 42.3 g Fe should have been produced. Calculate the percent yield.

25.4 g/ 42.3 g x 100 = 60.0 %

60.0 %

2. (10 pts.) Ethylene glycol (C2H6O2), a substance primarily used as auto antifreeze, has a density of 1.11 g/cm3. Acetone (C3H6O), a substance used in paints, glues and nail polish remover, has a density of 0.7857 g/cm3.

(a) If 100.0 mL of each liquid are placed in separate containers, which weighs more? (Must show work to justify answer, circle your choice below)

100.0 mL(1.11 g/ mL) = 111 g ethylene glycol

100.0 mL(0.7857 g/ mL) = 78.57 g acetone

ethylene glycol acetone

(b) Determine the number of hydrogen atoms in 335.0 grams of ethylene glycol, C2H6O2.

335.0 g C2H6O2 (1 mol C2H6O2/ 62.066 g C2H6O2)(6.022 x 1023 molecules/ mol)(6 H atoms/1 molecule) = 1.95 x 1025

1.95 x 1025 H atoms

4.7 x 1030 molecules C3H6O (1 mol/ 6.022 x 1023 molecules)(58.077 g C3H6O/ 1 mol) = 4.53 x 108 g

4.53 x 108 g

3. (10 pts.) (a) Estradiol is a female sexual hormone. Elemental analysis of estradiol gave the following mass percent composition: C 79.37%, H 8.88%, O 11.75%. Use these data to determine the empirical formula for estradiol.

79.37 g C (1 mol C/ 12.011 g C) = 6.614 moles C/ 0.7348 = 9.00

8.88 g H (1 mol H/ 1.0079 g H) = 8.8183 moles H/ 0.7384 = 12.00

11.75 g O (1 mol O/ 15.9994 g O) = 0.7348 moles O/ 0.7384 = 1.00

Empirical formula: C9H12O

(b) Fructose is a common sugar found in fruit. If the empirical formula for this compound is CH2O and the molar mass of fructose is 180.16 g/mol, what is the molecular formula for this compound?

180.16/30.0 = 6 C6H12O6

Molecular formula: C6H12O6

4. (a) (10 pts.) A 7.25 g chocolate-chip cookie is burned in a bomb calorimeter to determine its energy content. The heat capacity of the calorimeter is 39.97 kJ/0C. During combustion, the temperature of the calorimeter increases from 25.00 0C to 28.90 0C. What is ΔErxn in kJ/gram for the combustion of the cookie?

q = (39.97 kJ/ °C)(3.9 °C) = 155.883 kJ

∆Erxn = 155.883 kJ/ 7.25 g = 21.50 kJ/ g

21.5 kJ/g

(b) The thermite reaction is used to produce molten iron to weld railroad rails together. Calculate the standard enthalpy change, ΔH0rxn, for following target reaction:

2Al (s) + Fe2O3 → 2Fe (s) + Al2O3 (s) ΔH0rxn = ?

Given that:

2Al (s) + 3/2O2 (g) → Al2O3 (s) ΔH0rxn = –1601 kJ

4Fe (s) + 3O2 (g) → 2Fe2O3 (s) ΔH0rxn = –1642 kJ x (– ½)

2Al (s) + 3/2O2 (g) → Al2O3 (s) ΔH0rxn = –1601 kJ

2Fe2O3 (s) →4Fe (s) + 3O2 (g) ΔH0rxn = + 821 kJ

–780 kJ

q = (255 g)(1.84 J/ g°C)(124.3 – 107.5) = 7883 J

q = 7883 J (1 kJ/ 1000 J)

q = 7.88 kJ

7.88 kJ

5. (10 pts.) The molecule testosterone is shown below. Use it to answer parts (a) – (d).

(a) Identify two functional groups present in this molecule.

(1) ketone (2) alcohol .

(b) How many pi bonds are present in this molecule?

120°

(d) What is the hybridization of the atom labeled “B”?

sp3

(e) Please give the name of the following compound:

1,4 – dimethylhexene

(f) Please draw the structure of cis-2-butene.

(g) Please give the name of the following compound:

1 – butanol

(h) Please draw the structure of ethyl ethanoate.

(i) Please draw the structure of a possible product of the reaction between valine and glycine.

Part 2. Multiple Choice/Fill in the Blank. (3 pts. each) Circle the ONE BEST answer or fill in the blank where appropriate.

6. Which of the following samples has the greatest density at STP?

(d) SF6

7. Which of the following is an example of a physical change?

(a) dew forms on a blade of grass

8. Which of the following statements is false?

(d) The halogens tend to form +1 ions.

9. Which of the following compounds is insoluble in water?

(a) Hg2I2

10. What volume of 0.305 M AgNO3 is required to react completely with 155.0 mL of 0.274 M Na2SO4 solution?

(e) 278 mL

11. Give the net ionic equation for the reaction (if any) that occurs when aqueous solutions of Na2CO3 and HCl are mixed.

12. A large balloon is initially filled to a volume of 25.0 L at 353 K and a pressure of 2575 mmHg. What volume of gas will the balloon contain at 1.35 atm and 253 K?

(d) 45.0 L

13. Calculate the energy of the orange light emitted by a neon sign with a frequency of 4.89 x 1011 kHz

14. Which of the following transitions (in a hydrogen atom) represents absorption of the smallest frequency photon?

(a) n = 5 to n = 6

15. Which of the following quantum numbers describes the shape of an orbital?

(e) angular momentum quantum number

16. Which of the following could represent the ground state electron configuration for the ion Ba2+.

(e) [Kr]5s24d105p6

17. Choose the bond that is most polar.

18. Draw the best Lewis structure for I3–. What is the formal charge on the central I atom? Hint: use only single bonds!

(a) –1

19. What is the molecular shape of iodine pentachloride, ICl5?

(d) square pyramidal

20. How many of the following molecules have sp3d2 hybridization on the central atom?

SeCl6 XeF4 IF5 AsCl5

(b) 3