Chemistry for biology exam semester 2 2015/16 PDF

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SEMESTER II RESIT EXAMINATIONS 2015/16

CHEM 20090 Chemistry for Biology Professor Riley Professor Redmond Dr Buckin* Dr Morgan

Time Allowed: 2 Hours Instructions for Candidates Answer both questions 1 and 2. All questions carry equal marks; the approximate assignment of marks to parts of a question is indicated (as a percentage) in parentheses. Use a separate answer book provided for each question. No loose rough work sheets are to be used. The rough work for each question should be included in the answer book for that question. Instructions for Invigilators The use of non programmable electronic calculators is permitted A Periodic Table of the Elements is attached to these sheets

Page 1 of 7

Gas constant, R = 8.315 J K-1 mol-1 Faraday constant, F = 96485 C mol-1 Absolute zero temperature -273.15 oC 1atm = 100000Pa

Question 1. Answer any three of the following parts (a) - (d). (a)

A vessel is separated into two parts, A and B, by a bilayer lipid membrane containing Na+ channels. Part A holds an aqueous solution of NaCl with concentration 0.15 mol L-1 and of disaccharide sucrose with concentration 0.01 mol L-1 . Part B holds an aqueous solution of NaCl with concentration 0.015 mol L-1. Calculate the electrical potential between the two sides of the membrane at 30 oC and at 50 o

C.

Neglect the effect of temperature on the molarity of the solutions. Assume that the membrane is not permeable for glucose and for Cl- ions. (33.3)

(b)

The pH in an aqueous solution of a protein is 6.6. (i) Calculate the concentration of hydronium ions and hydroxide ions in the solution. (ii) Will the protein molecules in the solution have overall positive, negative or neutral charge if the isoelectric point of the protein is 8.1? Explain your answer. (iii) Explain the expected effect on the protein charge, of a gradual addition of the following compounds to the solution: HCl; NaOH; Glucose.

(33.3) Question 1 continues on the following page… Page 2 of 7

(c) (i)

Calculate the equilibrium constant K at temperature 25oC for the reaction in an aqueous solution outlined below if the standard molar Gibbs energy of the reaction, Go, at 25oC is 12 kJ mol-1. Creatine + ATP  Creatine-Phosphate + ADP

(ii) Outline the equilibrium expression for the above reaction. (iii) Calculate the molar Gibbs energy of the reaction, G, at concentration of Creatine 0.03 mol L-1, ATP 0.002 mol L-1, creatine-phosphate 0.01 mol L-1, and ADP 0.02 mol L-1. (33.3) (d) (i)

Calculate the number of moles of nitrogen released from a scuba diver’s blood following surfacing from 50 m depth. Assume that the volume of blood is 5L, the air pressure at 50 m depth is 5 atm and Henry’s law constant for nitrogen in blood (at 37 °C) is 6.4×10−4 mol L-1 atm-1 .

(ii) Calculate the volume occupied by the gas released. Assume that the gas is ideal and the temperature of the gas is 37 °C. Nitrogen represents 80% of molecules of air.

(33.3)

Page 3 of 7

Question 2. Answer all parts (a) - (d).

(a)

Use the VSEPR method to predict the shapes of any four of the following molecules and ions, clearly indicating the orientation of any lone pairs:

SiCl4

SO2

SF4

IF5

PCl3 (20)

(b)

Write short notes on any two of the following sections (i) - (iii)

(i)

Variable oxidation states, Lewis structures and shapes in oxoanions of sulfur.

(ii) Preparation of some elements (iii) Energy storage in battery packs. Your answer should include redox equations. (20)

(c)

Electrochemical cells may be described as voltaic or electrolytic. Explain the general principle behind an electrochemical cell and the differences between a voltaic cell and an electrolytic one. (10)

(d)

Answer section (i) or section (ii).

(i)

A voltaic cell is constructed with a Zn/Zn2+ half cell and a Ag/Ag+ half cell. The zinc electrode is negative. Draw a diagram of the cell, labeling the electrodes with their charges and showing the direction of electron flow in the circuit and of cation and anion flow in the salt bridge. Identify the anode and cathode half-reactions and show the shorthand notation.

Calculate the standard potential in volts for the reaction at room temperature. (ii) An electrolysis cell is constructed with a Mg/Mg2+ half-cell and a Cl/Cl2 half cell at a graphite electrode. The graphite electrode is positive. Write balanced half-reactions and the overall reaction. How many grams of magnesium are produced if a constant current of 15 A is passed through the cell for 2 hours? (Charge on 1 mol electrons = 96 500 Coulombs) (25)

Question 2 continues on the following page… Page 4 of 7

(e)

Answer section (i) or section (ii).

(i)

Assign oxidation numbers to all elements in the following, balance the equation and calculate the number of moles of sodium sulfate produced if 10 cm 3 of 0.35 M sodium nitrate are consumed in the reaction. NO3-(aq) + SO2(g)

→

SO4

2(aq)

+ NO2(g) (acidic conditions)

(ii) Assign oxidation numbers to all elements in the following, balance the equation and calculate the volume of 0.15 M potassium permanganate required to react with 10 cm 3 of 0.2 M potassium iodide. MnO4 -(aq) + I-(aq) →

MnO2(s) + I2(aq) (basic conditions) (25)

oOo

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Page 6 of 7

Periodic Table of the Elements 1 I

2 II

Group (new notation) Group (old notation)

1 Hydrogen

N Name

Atomic number Name

H

El

Symbol

Mass

Atomic mass

1.0079 3 Lithium

13 III

Li

Be

B

6.941 11 Sodium

9.0122 12 Magnesium

10.811 13 Aluminium

Mg

3

4

24.305 20 Calcium

21 Scandium

22 Titanium

5

6

K

Ca

Sc

Ti

V

Cr

39.0983 37 Rubidium

40.08 38 Strontium

44.956 39 Yttrium

47.87 40 Zirconium

50.942 41 Niobium

51.996 42

Rb

Sr

Y

Zr

Nb

Mo

87.62 56 Barium

88.905 57 Lanthanum

91.224 72 Hafnium

92.906 73 Tantalum

95.94 74 Tungsten

La

Hf

Ta

Cs

Ba

132.905 87 Francium

137.34 88 Radium

W

Fr

Ra

Ac

Rf

Db

223

226

227

261

262 58 Cerium

59

28 Nickel

29 Copper

Co

Ni

Cu

58.933 45 Rhodium

58.69 46 Palladium

Fe

Tc 98 75 Rhenium

Ru 101.07 76 Osmium

Rh 102.905 77 I ridium

Re

Os

Ir

190.2 108 Hassium

192.22 109 Meitnerium

Sg

Bh

Hs

Mt

266

264

269

268

60 61 62 Praesodymium NeodymiumPromethium Samarium

Pr

140.12 140.907 90 91 Thorium Proactinium

Actinides

9 27 Cobalt

186.207 107 Bohrium

138.91 178.49 180.948 183.85 89 104 105 106 Actinium Rutherfordium Dubnium Seaborgium

Ce

Mn

8 26 I ron

54.938 55.847 43 44 MolybdenumTechnetium Ruthenium

85.468 55 Cesium

Lanthanides

7

23 24 25 Vanadium Chromium Manganese

Nd 144.24 92 Uranium

Pm

Sm

10

Pd 106.42 78 Platinum

Th

Pa

U

Np

231.036

238.03

237.048

Pu 244.064

11

63.546 47 Silver

Ag

12 30 Zinc

Zn 65.39 48 Cadmium

Cd

Al

6 Carbon

7 Nitrogen

C

N

12.0112 14.0067 14 15 Silicon Phosphorus

Si

17 VII

18 VIII

Ga 69.723 49 Indium

In

Ar 39.948 36 Krypton

As

Se

Br

Kr

74.922 51 Antimony

78.96 52 Tellurium

79.904 53 I odine

83.80 54 Xenon

Sn

Sb

Te

118.71 82 Lead

121.75 83 Bismuth

Ge 72.61 50 Tin

Hg

Tl

Pb

Bi

200.59

204.38

207.19

208.98

157.25 96 Curium

20.18 18 Argon

Cl

Au

65 66 67 Terbium Dysprosium Holmium

Dy

Ne

35.453 35 Bromine

196.967

Tb

F 18.9984 17 Chlorine

S

Pt

Gd

O 15.9994 16 Sulfur 32.066 34 Selenium

195.09

Eu

4.0026 10 Neon

P

112.411 80 Mercury

63 64 Europium Gadoloinium

114.82 81 Thallium

9 Fluorine

8 Oxygen

30.9738 33 Arsenic

26.9815 28.086 31 32 Gallium Germanium

107.868 79 Gold

144.913 150.35 151.96 93 94 95 Neptunium Plutonium Americium

232.038

16 VI

He 5 Boron

Na

15 V

2 Helium

4 Beryllium

22.989 19 Potassium

14 IV

Ho

127.60 84 Polonium

Po 209

I 126.904 85 Ast atine

At 210

Xe 131.29 86 Radon

Rn 222

68 Erbium

69 Thulium

70 Ytterbium

71 Lutetium

Er

Tm

Yb

Lu

158.925 162.50 164.93 167.26 168.934 173.04 174.97 97 98 99 100 101 102 103 Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium

Am

Cm

Bk

243

247

247

Cf 242.058

Es 254

Fm

Md

No

257.095

258.10

259.101

Lr 260.105

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