Autumn Examinations 2009-2010: Chemistry Exam Questions, Exams of Chemistry

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Autumn Examinations 2009 / 2010

Exam Code(s) 1MR, 1HF, 1BP, 1EG, 1BEE, 1BN, 1BEI, 1BSE Exam(s) 1 st^ Science, 1st^ Engineering

Module Code(s) CH Module(s) Fundamentals of Chemistry

External Examiner(s) Professor Richard Taylor Internal Examiner(s) Professor P.V. Murphy *Dr. P. O’Leary

I I NNSSTTRRUUCCTTIIOONNSS :: Answer Four questions: one question must be attempted

from each section (A, B, C and D) Separate Answer Books are not required for each section. All questions carry 25 marks distributed as shown.

Leave the front page of the Answer Book blank and clearly list on it the numbers of the questions attempted.

Duration No. of Pages

2hrs 4 (including this front page) Department(s) Chemistry

Requirements Log Tables

All questions carry equal marks. Atomic masses: H: 1.01; C: 12.01; O. 16. Molar volume at STP= 22.4 dm^3 , Avogadro’s Number 6.02 x 10 23 , R=0.08206 dm 3 atm/mol K

Section A

1. Answer each of the following: (i) An ester was found to contain 54.52% C, 9.17% H the remainder being O. Using this information along with the atomic weights above calculate its empirical formula? [7 Marks] (ii) If its molecular mass is 88.12 amu what is its molecular formula? [3 Marks] (iii) Draw the structure of one possible ester with these characteristics. [3 Marks]

(iv) Write a chemical formula for each of the following compounds: (a) Oxygen (b) magnesium oxide (c) Sodium iodide (d) potassium sulfate [8 Marks]

(v) Correct any errors in the formula of sodium nitrate below. NANo3 [4 Marks]

2. Answer each of the following: (i) A balloon containing 253 dm 3 of helium is released at the north pole (Temp -25 o^ C, Pressure 0.98 atm) (a) How many moles of helium are contained in the balloon. [10 Marks] (b) How many molecules of gas are present in the sample [4 Marks] (c) If the balloon rises to a point where the temperature is -45o^ C and the pressure is 0.83 atm. What is the volume of the balloon at this stage? [5 Marks]

(ii) Classify the following gases in order of increasing density Ne, N 2 , CH 4 , He, Ar, O 2 , Cl 2. Indicate the basis for your decision [6 Marks]

Section B

3. Answer each of the following: (i) Write out the electronic configuration of the following elements. (a) Magnesium, (b) Bromine [8 marks] (ii) Discuss with reference to the electronic configurations above what compound is likely to form when Calcium and chlorine react [4 Marks] (iii) In the compounds below identify the types of bonding present (ionic, polar covalent or covalent). (a) H 2 O (b) C 3 H 8 (c) NaF [6 Marks]

(iv) One isotope of bromine has a mass of 79 and is 50% abundant the second isotope of chlorine has a mass of 81 and is 50% abundant (i) explain the term isotope (ii) What is the average atomic mass of bromine? Show how you calculate your answer and indicate appropriate units [7 Marks]

4. Answer each of the following: (i) Discuss the factors which can effect the rate of a reaction. [6 Marks] (ii) Write a balanced equation for the reaction of H 2 SO 4 and Mg(OH) 2. [4 Marks] (iii) 15 cm 3 of a 0.1 M solution of H 2 SO 4 are reacted with 20 cm 3 of a 0.5 M solution of Mg(OH) 2 .. Given this information calculate the following: (a) Which is the limiting reagent? (b) How many moles of the excess reagent are left unreacted at the end of the reaction? (c) What is the concentration of the excess reagent at the end of the reaction? [15 Marks]

Section C

5. Answer each of the following: (i) Draw structural formulae showing all the atoms of both of the following: (a) 2-Ethyloct-1-ene, (b) 3- Ethyl-nonane. [8 marks] (ii) Name each molecule and indicate the functional group present in the following molecules (a)-(e): [2×6 marks]

O OH

O

H

O

O

NH 2

(a) (b) (^) (c)

(d) (e)^ (f)

(iii) Describe the structural features of DNA and how these relate to genetic coding and replication [5 marks]

6. Answer each of the following: (i) What is the Keq for the following process

Heat + 2CO 2 (g) 2CO(g) + O 2 (g) [5 Marks] (ii) Describe in your own words Le Chatelier’s principle [5 Marks] (iii) Discuss the reaction above in the context of Le Chatelier’s principle with respect to the following headings  Temperature  Pressure  Removal of product as it is formed [15 Marks]

Section D

7. Write an essay on the ozone layer and its depletion (the essay should discuss the chemistry of the subject and include structures of the chemicals involved and their role etc) [25 marks]

8. Write an essay on sources and effects of carbon dioxide and methane in the atmosphere (the essay should discuss the chemistry of the subject and include structures of the chemicals involved and their role etc) [25 marks]