chem 127 Final Exam December 16, 2004

Tables of data are found on the last pages; you can detach them.

You are permitted a card with equations-- it must be stapled to your completed exam.

As a rule, you must show your work or logic to get credit for an answer (unless the answer is pretty direct.)

Part I -- Problems

Do any 9 of the problems 1-12 .

1. Evaluate the voltage of the cell

Cu| Cu²⁺ (0.25M) || HCl (0.5 M) | Cl₂ (1 atm) |Pt

the net reaction is Cu (s) + Cl₂ (g) ---> Cu²⁺ + 2 Cl-

a. What’s E^o, the cell potential at standard conditions

b. What’s E at the concentration in the cell

(start by writing the Nernst Equation)

2. Here's a cell notation

Pt| Fe²⁺, Fe³⁺ || Mn⁺², MnO₄^-, H⁺ |Pt

write the balanced chemical reaction in this cell

3. Faraday's law

How long would it take to electroplate 63.5 mg (0.0010 moles) of Copper metal from a 0.25 M Cu²⁺ solution at a current of 150 milliampere.

4. Electrolytic Cell: Two copper wires are connected to a power supply. The wires are dipped into a solution containing 1M CuSO₄, 1 M HCl and 1 M Ni(NO₃)₂

a. what reaction can you expect at the anode? (briefly why?)

b. what reaction can you expect at the cathode ?

c. Is the anode connected to the (+) or the (-) terminal of the power supply?

5. Nuclear Chemistry-- supply the missing items in the equations below (a box-- on the Web this may be out of position)

6. Half life of a nuclear decay

You go to Egypt and are offered a papyrus scroll, supposedly created at the time of the Pharaoh Ramses II (1279-1233 B.C) You ask to see the results of a C-14dating process, knowing that the half life of C-14 is 5730 years.

The report says that the C-14 level is 64 % of that of the C-14 content of modern paper.

What can you conclude about the authenticity of the scroll ?

7. Thermochemistry

The reaction H₂(g) + I₂(g) --> 2 HI (g)

has DH^o = 53.0 kJ/mol and DS^o= +21.8 J/K-mol

a. is the reaction spontaneous at 27 ^oC ?

b. what is Keq for the reaction at 400^oC?

8. Kinetics -- Initial rate problem, reagent and catalyst (see table-- may be elsewhere on Web page)

oxalate ion ( C₂O₄^2-) reacts with permanganate ion (MnO₄^-)

5 C₂O₄^2- +2 MnO₄^- + 16 H⁺ ----> 10 CO₂ (g) + 2 Mn²⁺ + 8 H₂O

run	initial [oxalate]	initial [MnO4-]	initial [H+]	rate of CO2 formation (mol/liter)
A	0.100	0.050	1.000	2.4 x 10^-4
B	0.300	0.050	1.000	7.3 x 10^-4
C	0.300	0.050	0.500	1.8 x 10^-4
D	0.200	0.100	1.000	9.6 x 10-4

What is the order of the reaction with respect to each species?

What is the rate constant for the reaction ?

9. What is the pH of a 0.150 M solution of potassium acetate, K (CH₃CO_{2 .})

Acetic Acid is a weak acid with Ka = 1.8 x 10^-5

10. The vapor pressure of propane is 10.0 atm at 27^oC; the vapor pressure of butane is 2.56 atm at the same temperature. If you were to mix 2.0 moles of propane and 5.0 moles of butane, what would be the (total) vapor pressure of this liquid at the given temperature?

(The exam had a section of graph paper)

11. The gas SO₂ reacts with oxygen, in the presence of a Platinum metal catalyst, to form SO₃.

2 SO₂ (g) + O₂ (g) ----> 2 SO₃ (g)

We start with a 2 liter container that has 2.5 moles of pure SO₃ gas. When equilibrium is reached, we only have 1.73 moles of SO₃ in the container. What is Kc for this reaction?

12. The vapor pressure of Hydrogen peroxide, H₂O₂, changes with temperature. Use the table below to determine either the vapor pressure of H₂O₂ at 90 ^oC OR DHvaporization of. H₂O₂ .

(You may use an equation or, hint, a suitable graph)

T(^oC)	P (torr)
15.3	1
50.4	10
77	40

Short Answers (you do not need to justify your answers here)

15 questions, 5 points each

1. A solution is prepared by mixing 1.5 mole of alcohol and 25.0 moles of water ( 450 g = 450 ml of water.) This solution has an alcohol concentration of ___________ m (molality).

2. Which solution freezes at the lowest temperature:

0.5 M NaCl 0.3 M CaCl₂ 0.2 M AlCl₃ pure water

3. In the phase diagram on the right (graph omitted on the web page)

label the LIQUID phase

use an arrow to show the process called sublimation

4. In osmosis water moves across a membrane. If side A of the membrane has 0.01 M sugar solution and side B has 1.0 M sugar, will water move from A to B or from B to A ?

5. Label these statements as true (T) or false (F)

_____ A catalyst will shift the equilibrium of a reaction to the right

_____ A catalyst functions by increasing DS for the reaction

_____ A catalyst will decrease the activation energy required for a reaction

6. Write the equilibrium expression (Ksp) for the ionic salt Ag₂SO₄ dissolving in water.

7. In the reaction HCN + H₂O ----> H₃O⁺ + CN^-

what term(s) describe the relationship between the species HCN and CN-

8. Does adding Ca(OH)₂ , also known as lime, to the soil raise or lower the soil pH (select one)

9. Copper metal is typically produced by the reaction of copper oxide with hot _____________.

10. A buffer could be prepared by mixing which of these species

a. sodium acetate and sodium hydroxide

b. acetic acid and sodium hydroxide

c. acetic acid and hydrochloric acid

11. What is the pH of these solution of a strong acid or a strong base

0.055 M Ca(OH)₂

0.55 M HNO₃

12. What is the [H+] and [OH-] in a solution at pH 4.65

13. A bidentate ligand is a ligand that .........

14. A metal like Copper can be described with an "electron-sea model." with a regular crystal lattice. What is located at the lattice points of the crystal lattice?

15. Sketch a diagram showing several water molecules interacting through hydrogen bonds.