UNIVERSITI TEKNOLOGI MARATEST 1

COURSE:PROCESS CHEMISTRY

COURSE CODE:CHE434

EXAMINATION:APRIL 2014

TIME:1 HOURS

INSTRUCTIONS TO CANDIDATES

1.This question paper consists of three (3) questions.

2.Answer ALL questions in the Answer Booklet. Start each answer on a new page.

3.Do not bring any material into the examination room unless permission is given by the invigilator.

4.Please ensure that this examination pack consists of:

i) the Question paperii) an Answer Booklet provided by the Faculty

Question 1

Using a molecular orbital diagram, arrange C2, molecules in order of increasing bond length (Assuming that the 2p MO is lower in energy than the 2py and 2pz MOs) (10 marks)

Question 2

a) A typical weak acid, HA, is prepared in such a way as to have an initial concentration in water of 0.100 M. At equilibrium the solution has pH = 2.87, what is Ka for this acid? (2 marks)

b) The conjugate base of the above acid exists as a sodium salt, NaA. What is Kb for this conjugate base? (1 mark)

c) For a 0.100 M solution of the conjugate base in part b, what is the [OH-] at equilibrium AND what is the pH? (4 marks)

d) For the same pair of weak acid and conjugate base in the questions above, what is the pH of a buffer in which [HA] = [A-] = 0.25 M? (1 mark)

e) For the same pair of weak acid and conjugate base to form a buffer with pH = 5.00 when [HA] = 0.25, what does [A-] have to be?(2 marks)

Question 3

A voltaic cell with Mn/Mn2+ and Cd/Cd2+ half-cells has the following initial concentrations [Mn2+]=0.09M , [Cd2+]=0.06M.

a) Write a balanced spontaneous equation for the reaction (1 mark)b) Determine the initial Ecell at 25oC(4 marks)

c) Determine the [Mn2+] when Ecell reaches 0.055V(5 marks)

END OF QUESTION PAPER