Nyaw08-unit Test 3 White)

JOHN ABBOTT COLLEGE 202-NYA Winter 2008 Section 22

Unit Test 3 Name:

1. Briefly explain the following observations: (6 marks) a. The meniscus of water is concave. b. The meniscus of mercury is convex.

2. Guanine (G), cytosine (C), adenine (A) and thymine (T) are the building blocks of DNA molecules. Explain why, during the synthesis of DNA, G always binds specifically to C and A specifically to T. Provide diagrams to support your answer (5 marks).

thymine

adenine

guanine

cytosine

3. PABA (p-aminobenzoic acid, pKa = 5) was a common stabilizing ingredient in many sunscreens. Its potential as a carcinogen led to its removal form most products. The parent compound of PABA is benzoic acid (pKa = 4). Will the pKa of m-aminobenzoic acid be closer to that of PABA or benzoic acid? Explain. O

OH

O

OH

O

OH

H2N H2N

Benzoic acid

m-aminobenzoic acid

PABA

4. Sodium lauryl sulfate is a common surfactant used in many soaps and shampoos. Explain its mode of action in terms of intermolecular forces. (4 marks). O H3C

O

Sodium lauryl sulfate

S

O O

-

+

Na

5. Answer the following questions: a. Draw a fully labeled thermodynamic cycle describing ∆Hsolution for calcium chloride (4 marks). b. Would you expect ∆Hsolution for calcium iodide to be more or less exothermic than that of calcium chloride? Explain (2 marks). c. Calculate ∆Hsolution for calcium chloride using the following data (3 marks): i. ∆Hlattice = 2913 kJ/mol ii. ∆Hhydration for the fluoride ion = -431kJ/mol iii. ∆Hhydration for the magnesium ion = -1903 kJ/mol

6. Identify all the intermolecular forces present in each of the following pure substances: CH3CH2NH2, CH3CH2OH, CH3OCH3. Order these in terms of increasing vapour pressure and explain the observed trend. (6 marks)