Chemistry 65.100 A and V

Second Test - November 8, 1996 5:00 - 6:30 PM

Calculators permitted. Answer all questions in the exam booklets provided. You may keep this question paper. (xx) are the marks for each question.

1. (6) Write the oxidation numbers of each of the atoms in each of the following compounds:

(a) COCl₂ (b) CrO₄^-2 (c) NH₂OH

2. (16) For each of the following reactions,

(i) state which species is the OXIDIZING AGENT and which is the REDUCING AGENT:

(ii) Balance the reaction

(a) I₂ + H₅IO₆ ® IO₃^- + H₂O + H⁺ (in acidic solution)

(b) CrO₄^-2 + AsH_3(g) + H₂O ® Cr(OH)_3(s) + As_(s) + OH^- (in basic solution)

3. (3) What is meant by the term "formal charge"?

4. (12) Using VSEPR theory, predict the shapes of each of the following species:

(a) CrO₄^-2 (b) SiCl₄ (c) I₃^-

The periodic group numbers for the elements are Cr and O(group 6); Si(group 4); I and Cl(group 7)

5 (9) Using data from the table below, calculate the quantity of heat released (in kJ) when 1 kg of sulfur dioxide is reacted with excess oxygen at 25^oC and 1 atm pressure:

SO_2(g) + ½ O_2(g) ® SO_3(g)

6. (4) For each of the following reactions, predict whether DS is positive or negative, and briefly state why:

(a) dissolving NaCl_(s) in water

(b) Cl_2(l) ® Cl_2(g)

7. (10) A molecular orbital diagram for C₂ is shown below.

(a) What is the bond order of C₂?

(b) What would be the bond order of C₂⁺?

(c) Is it possible for C₂⁺⁴ to exist? Why?

(d) Which would have the higher bond energy, C₂ or C₂⁺²? Why?

(e) Is C₂⁺ paramagnetic? Why?