Practice Test

Section

II

Free-Response Questions

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Part B: Question 5 and 6

Directions:No Calculators may be used with Part B. Your responses to the rest of the ques-
tions in this part of the examination will be graded on the basis of the accurancy and relevance
of the information cited. Explanations should be clear and well organized. Examples and equa-
tions may be included in your responses where appropriate. Specific answers are preferable to
brad, diffuse responses. Answer both Question 5 and 6. Both of these questions will be graded.
The Section II score weighting for this question is 30% (15% each).

5. Give a brief explanation for each of the following:

(a) Water can act either as an acid or as a base.

(b) HF is a weaker acid than HC1.

(c) For the triprotic acid H 3 PO 4 , Ka1is 7.5 × 10 –3whereas Ka2is 6.2 × 10 –8.

(d) Pure HCl is not an acid.

(e) HClO 4 is a stronger acid than HClO 3 , HSO 3 - , or H 2 SO 3.

6. Interpret each of the following four examples using modern bonding principles.

(a) C 2 H 2 and C 2 H 6 both contain two carbon atoms. However, the bond between the two

carbons in C 2 H 2 is significantly shorter than that between the two carbons in C 2 H 6.

(b) The bond angle in the hydronium ion, H 3 O+, is less than 109.5°, the angle of a tetra-

hedron.

(c) The lengths of the bonds between the carbon and the oxygens in the carbonate ion,

CO 32 - , are all equal and are longer than one might expect to find in the carbon

monoxide molecule, CO.

(d) The CNO–ion is linear.