Chem1012+-NOV+2014 - can be used for practice PDF

Preview

Summary

can be used for practice...

Description

CHEM1012

NOVEMBER 2014

PAGE 1 OF 21 PAGES

Please fill in your name if you want to:

SURNAME ..............................................

INITIALS ..........

PART A RECOMMENDED TIME: 70 - 80 MINUTES A.

Part A consists of 35 multiple choice questions, each worth 2 marks.

B.

Study the following questions and the suggested answers, only one of which is correct. When you have decided on the correct answer, mark the question paper accordingly. After answering all the questions, fill in the computer card supplied. Use pencil only. If you make a mistake, ask for a new card. The computer card must be filled in during the allocated test time and no further time will be allowed.

C.

Only one answer per question is permitted. incorrect answer.

1.

The heat of sublimation can be approximated by adding together: A. B. C. D. E.

2.

heat of fusion and heat of condensation. heat of freezing and heat of condensation. heat of freezing and heat of vaporization. heat of fusion and heat of vaporization. heat of deposition and heat of vaporization.

Which one of the following molecules is polar? A D.

3.

No marks are subtracted for an

XeF4 BCl3

B. E.

AsH3 Cl2

C.

CO2

For each of the following pairs predict which compound in the pair will have the higher freezing point:

.

(i) HF and HBr A. B. C. D. E.

HF, LiF and CO HBr, CaF2 and CO HF, CaF2 and SiO2 HF, LiF and SiO2 HBr, LiF and SiO2

(ii) CaF2 and LiF

(iii) SiO2 and CO

CHEM1012 4.

0.0589

B. 0.0626

44

B. 88

E. 4.14

C. 500

D. 11

E. 22

B. E.

0.1023 0.1023

C. 0.2046

Consider a certain compound that decomposes by a first-order process. Determine the half-life of the compound in minutes, if 25.0% of the compound decomposes in 60.0 minutes. A.

8.

D. 1.00

Calculate the freezing point (°C) of a 0.05500 m aqueous solution of KNO3. The molal freezing- point -depression constant of water is1.86 ºC/m. A. 0.0286 D. 0.05628

7.

C. 0.259

A solution is prepared by dissolving calcium chloride in water and making it up to 500.0 mL. If this solution contains 44 ppm chloride ions, the concentration of calcium ions in ppm is: A.

6.

PAGE 2 OF 21 PAGES

Calculate the mole fraction of phosphoric acid in a 25.4% (by mass) aqueous solution. (Molar mass H3PO4 = 97.99 g mol1) A.

5.

NOVEMBER 2014

65

B. 120

C. 198

D. 180

E. 145

Nitric oxide reacts with bromine to form nitrosyl bromide, NOBr. Use the following data for the initial rate of appearance of NOBr, to determine the rate equation for the reaction: 2 NO(g) + Br2(g)  2 NOBr(g) Concentration (mol L1) [NO] [Br2] 0.10 0.20 0.30 0.20 0.10 0.50 A. B. C. D. E.

rate = k[NO] rate = k[NO]2[Br2] rate = k[NO][Br2] rate = k[NO][Br2]½ rate = k[NO]2[Br2]2

Initial rate (mol L1 s1) 24 216 60

CHEM1012 9.

NOVEMBER 2014

PAGE 3 OF 21 PAGES

Consider the following reaction: CH3COCH3 + I2 + H+

→

ICH2COCH3 + H+ + I

It was experimentally found that this reaction is first-order with respect to both propanone and the hydrogen ion, and that the reaction is independent of the iodine concentration. Which of the following statements is/are CORRECT? (i) (ii) (iii) (iv) A. B. C. D. E.

10.

Iodine was the catalyst used. H+ was the catalyst used. Iodine is involved in the rate determining step. The overall reaction order is 2.

Statement (i) only is correct. Statements (ii) only is correct. Statements (i) and (iv) only are correct. Statement (ii) and (iv) only are correct. All the statements are correct.

A sample of pure POCl3(g) was allowed to decompose according to the following reversible reaction: POCl3(g)

⇋

POCl(g) + Cl2(g)

Kc = 0.450

At equilibrium, the concentrations of POCl(g) and Cl2(g) were each 0.150 M. What was the initial concentration of POCl3(g)? A.

11.

0.200 M

B. 0.225 M

C. 0.633 M

D. 0.483 M

E. 0.350 M

Consider the following endothermic reaction: S2Cl2(l) + CCl4(l)

⇌

CS2(g) + 3 Cl2(g)

Given that the system is at equilibrium in a closed vessel the number of moles of CS2(g) can be increased most by: (i) (ii) (iii) (iv) (v) A. B. C. D. E.

adding some Cl2 to the system. adding some S2Cl2 to the system. increasing the size of the reaction vessel. Increasing the temperature of the reaction. Adding a catalyst.

(ii) only (ii), (iii) and (iv) (ii) and (iv) (iii) and (iv) (v) only

CHEM1012 12.

NOVEMBER 2014

PAGE 4 OF 21 PAGES

Consider the following equilibrium reaction at 300 K. Br2(g) + Cl2(g)

⇋

2 BrCl(g)

Kp = 7.0

A closed vessel is initially charged with 1.00 atm of Br2(g), 1.00 atm of Cl2(g) and 2.00 atm of BrCl(g). Which one of the statements below is TRUE? A. B. C. D. E.

13.

The equilibrium partial pressure of BrCl(g) will be greater than 2.00 atm. The equilibrium partial pressures of Br2(g), Cl2(g) and BrCl(g) will be the same as the initial values. The equilibrium partial pressure of Br2(g) will be greater than 1.00 atm. At equilibrium the total pressure in the vessel will be less than the initial total pressure. The reaction will go to completion since there are equal amounts of Br2(g) and Cl2(g).

Using the following information decide which one of the corresponding conjugate acids for the given bases will be the strongest. Base HONH2 CH3NH2

14.

Kb 1.1 x 108

C 5H 5N NH3

4.4 x 104 1.7 x 109 1.8 x 105

H2NNH2

1.3 x 106

A.

NH4+

B.

C5H5NH+

D.

H2NNH3+

E.

HONH3+

C.

CH3NH3+

Which of the following will be basic aqueous solutions? (i) Mg(C2H3O2)2(aq)

(ii) SrCl2 (aq)

(iii) Na2CO3(aq) C.

A.

(i) only

B.

(ii) only

D.

(i) and (ii) only

E.

(i) and (iii) only

(iii) only

CHEM1012 15.

NOVEMBER 2014

Which of the following species can behave as Lewis acids? (i) NH3 A. B. C. D. E.

16.

(iv) Cu2+

(iii) BF3

What is the concentration (M) of hydroxide ions in a solution at 25 ºC with pH = 4.282? B. 1.91 x 1010

C. 9.72

D. 5.22 x 103

E. 1.66 x 104

What is the percent ionization of a 0.20 M weak monoprotic acid solution at 25 ºC? (Ka = 1.5 x 105) A. D.

18.

(ii) FeCl3

(i) only (i) and (ii) only (iii) and (iv) only (ii), (iii) and (iv) only All can behave as Lewis acids

A. 4.28

17.

PAGE 5 OF 21 PAGES

1.5 x 103 % 4.3 %

B. E.

7.5 x 103 % 0.87 %

C.

0.038 %

Which of the following could be added to a solution of acetic acid solution to prepare a buffer? (i) Sodium hydroxide A. B. C. D. E.

(ii) More acetic acid

(iii) Calcium acetate

(i) only (ii) only (iii) only (i) and (iii) only None of the above can be added to acetic acid to prepare a buffer.

CHEM1012 19.

21.

0.020 M BaCl2 0.020 M KCl 0.015 M Pb(NO3)2 pure water 0.015 M NaCl

The pH of an ammonia/ammonium chloride buffer system could easily be expressed as which one of the following options? (Kb NH3 = 1.8 x105) A.

pH = 4.74 + log [NH3] / [NH4+]

B.

pH = 4.74 + log [NH4+] / [NH3]

C.

pH = 9.25 + log [NH4+] / [NH3]

D.

pH = 14.0 + log (1.8 x 105)

E.

pH = 9.25 + log [NH3] / [NH4+]

Which one of the following statements is TRUE? A. B. C. D. E.

22.

PAGE 6 OF 21 PAGES

In which one of the following aqueous solutions would you expect PbCl2 to have the lowest solubility? A. B. C. D. E.

20.

NOVEMBER 2014

Enthalpy is an intensive property. The enthalpy change for a reaction depends on the pathway and not the final state of the products. H is the value of q measured under constant pressure. S universe is always negative for a spontaneous process. A reaction that is spontaneous in one direction is also spontaneous in the reverse direction.

For which one of the following reactions is Hrxn equal to the standard enthalpy of formation of the product?

A.

12 C(g) + 11 H2(g) + 11 O(g)  C6H22O11(g)

B.

N2(g) + 3 H2(g)  2 NH3(g)

C.

C(g) + O2(g)  CO2(g)

D.

I(g) + I(g)  I2(g)

E.

Ca(s) + Cl2(g)  CaCl2(s)

CHEM1012 23.

NOVEMBER 2014

PAGE 7 OF 21 PAGES

Consider the following reaction: Ag+(aq) + Cl(aq) → AgCl(s) Determine G (kJ mol1) for the reaction, given the following thermodynamic data at 25 °C: Hf (kJ mol1) 105.90

Substance Ag+(aq) Cl(aq) AgCl(s)

A. B. C. D. E.

24.

S (J K1 mol1) 73.93 56.5 96.11

167.2 127.0

1.02 x 104 –55.5 6.72 x102 –65.7 –64.8

Consider the information given for the following reaction: C2H6(g) → C2H4(g) + H2(g) H = +137 kJ mol1

S = +120 J K1 mol1

One can conclude that this reaction is: A. B. C. D. E.

25.

exothermic and spontaneous only at low temperature. endothermic and spontaneous at all temperatures. endothermic and non-spontaneous at all temperatures. endothermic and spontaneous only at low temperatures. endothermic and spontaneous at high temperature.

How many nucleophilic sites are there in each of the following two molecules? (i)

A. B. C. D. E.

CH3CH2COCH3

(i) 1 1 1 3 3

(ii) C6H5CONH2

(ii) 2 3 1 1 2

CHEM1012 26.

PAGE 8 OF 21 PAGES

Which one of the following molecules CAN react with an electrophile at a carbon atom? A. B. C. D. E.

27.

NOVEMBER 2014

CH3CH2COCH3 CH3CH2COOCH2CH3 CH3CH2CH2Li CH3CH2CH2OH CH3CH2CHO

Which one of the following reactions is CORRECTLY classified?

A. Substitution B. CH3CH2CONH2 → CH3CH2COCl

Elimination

C. Substitution D. (CH3)3Cl → (CH3)2CCH2

Substitution

E. Addition

28.

If the compound below is reduced, which one is the most likely product to form? CH3C(CH3)2CH2COCH3 A.

CH3C(CH3)2CH2CH(OH)CH3

B.

CH3C(CH3)2CH2COOH

C.

CH3C(CH3)2CH2COCH3

D.

CH3C(CH3)2CH2CH2CH3

E.

CH3C(CH3)2CH2CH2CH2OH

CHEM1012 29.

NOVEMBER 2014

PAGE 9 OF 21 PAGES

Which one of the reaction schemes below is INCORRECT? (i.e. the depicted product is not formed)

A.

B.

C.

D.

E.

30.

Which one of the following options represents the products of the hydrolysis of the ester ethylpentanoate? A.

Ethanoic acid and pentanol.

B.

Pentanoate and ethanol.

C.

Pentanoyl chloride and ethanoic acid.

D.

Butanoic acid and pentanol.

E.

Pentanoic acid and ethanol.

CHEM1012 31.

32.

33.

NOVEMBER 2014

PAGE 10 OF 21 PAGES

A certain alkene is polymerized and the resulting polymer is represented below. The monomer from which this polymer is obtained is:

A.

CH3CH2CH2CN

B.

NCCH2CH2CH3

C.

CH3CH2CHCN

D.

CNCHCHCH2CH3

E.

CH3CHCHCN

Which one of the reactions represented below is expected to give a carboxylic amide as a product? A.

CH3CH2COOH + NH3

B.

CH3COCl + CH3OH

C.

CH3NH2 + HCl

D.

CH3COCl + CH3NH2

E.

CH3COOH + PCl3

Which one of the following is a redox reaction? A. B. C. D. E.

Pb2+ + 2Cl  PbCl2 AgNO3 + HCl  HNO3 + AgCl NaOH + HCl  NaCl + H2O 4Fe + 3O2  2Fe2O3 NaCl + H2O  NaOH + HCl

CHEM1012 34.

NOVEMBER 2014

PAGE 11 OF 21 PAGES

Identify the reducing agent in the following equation: Pb + PbO2 + 2H2SO4  2PbSO4 + 2H2O

A. D.

35.

Pb PbO2

B. E.

H2SO4 H 2O

C.

PbSO4

How many minutes will it take to plate out 4.56 g of Ni metal from a solution of Ni2+ using a current of 45.5 amperes in an electrolytic cell? A. D.

5.49 155

B. E.

2.75 330

C.

4.55

TOTAL MARKS FOR PART A: [35 x 2] = [70]

CHEM1012

NOVEMBER 2014 PART B

PAGE 12 OF 21 PAGES 30 MARKS

Answer the following questions in the space provided. Show all working for calculations. Just writing down a numerical answer is not acceptable. Pay particular attention to the use of units and significant figures. QUESTION 1 The bicarbonate buffer system helps the body to restore the pH of blood to normal. a)

What mass of NaHCO3 (in grams), must be added to 1.00 L of 0.10 M carbonic acid to obtain a solution with pH of 7.20? Clearly write the equation involved. (Given: Ka H2CO3 = 4.3 x 107; Molar mass of NaHCO3 = 84.01 g mol1)

(5)

b)

Write down the equation that takes place if a small amount of a strong base, NaOH, is added to the bicarbonate buffer solution and explain how a nearly constant pH is maintained. (2)

[7]

CHEM1012

NOVEMBER 2014

PAGE 13 OF 21 PAGES

QUESTION 2 (a) The decomposition of N2O5 to NO2 is first order with a rate constant of 4.80 x 104 s1 at 45°C. If the initial concentration is 1.65 x 102 mol L1, what is the concentration after 835 seconds? (2)

(b)

Consider the reaction: CH3Br(aq) + OH(aq)  CH3OH + Br(aq) The rate law for this reaction is first order in both [CH3Br] and [OH]. When [CH3Br] is 5.0 x 103 M and [OH] is 0.050 M, the reaction rate is 0.043 M s1 at 298 K. (i)

(ii)

What are the value and units of the rate constant?

(1.5)

By what factor would the rate change if the concentrations of both reactants were tripled?

(0.5)

[4]

CHEM1012

NOVEMBER 2014

PAGE 14 OF 21 PAGES

QUESTION 3 Consider the following reaction at 298 K: 3 CH4(g)

 C3H8(g) + 2 H2(g)

Given the thermodynamic data below: Substance CH4(g) C3H8(g)

Gf (kJ mol1) 50.8 23.47

Calculate G at 298 K if the reaction mixture consists of 40.0 atm of CH4(g), 0.0100 atm of C3H8(g) and 0.0180 atm of H2(g).

[5]

CHEM1012

NOVEMBER 2014

PAGE 15 OF 21 PAGES

QUESTION 4 Answer the questions below based on the following reaction scheme:

a)

Using curly arrow notation, provide a detailed stepwise mechanism of the reaction leading to ONLY the MAJOR product expected. (5)

b)

What type of reaction took place? ______________________________

(1)

c)

Using IUPAC rules, name the product obtained in part (a)

(1)

[7]

CHEM1012

NOVEMBER 2014

PAGE 16 OF 21 PAGES

QUESTION 5 (Standard reduction potential table provided) A voltaic cell consists of a strip of cadmium metal in a solution of Cd(NO3)2 in one compartment, and a platinum (Pt) electrode in NaCl solution, with Cl2(g) bubbled around the electrode in the other compartment. A general voltaic cell diagram is provided.

(i) Write the two half reactions involved.

(ii)

(2)

Which reactions in part (i) occur at the anode and the cathode respectively? (2)

(iii)

Write the overall cell reaction and calculate the emf generated by the cell under standard conditions? (3)

[7]

TOTAL MARKS OF PART B: [30] TOTAL MARKS: [100] FULL MARKS: [100]

CHEM1012

NOVEMBER 2014

PAGE 17 OF 21 PAGES

Standard Reduction Potentials at 25 C

CHEM1012

NOVEMBER 2014

PAGE 18 OF 21 PAGES

CHEMISTRY DATA SHEET Physical Constants Gas constant

R

= 8.315 J K1 mol1 = 8.315 kPa dm3 K1 mol1 = 8.315 Pa m3 K1 mol1 = 8.206 x 102 L atm K1 mol1

Boltzmann constant

k

= 1.381 x 1023 J K1

Planck constant

h

= 6.626 x 1034 J s

Faraday constant

F

= 9.649 x 104 C mol1 = 9.649 x 104 JV1 mol1

Avogadro constant

L or NA

= 6.022 x 1023 mol1

Speed of light in vacuum

c

= 2.998 x 108 m s1

Mole volume of an ideal gas

Vm

= 22.41 L mol1 (at 1 atm and 273.15 K) = 22.71 L mol1 (at 1 bar and 273.15 K)

Elementary charge

e

= 1.602 x 1019 C

Rest mass of electron

me

= 9.109 x 1031 kg

Rest mass of proton

mp

= 1.673 x 1027 kg

Rest mass of neutron

mn

= 1.675 x 1027 kg

Permitivity of vacuum

o

= 8.854 x 1012 C2 J1 m1 (or F m1)

Gravitational acceleration (at sea level)

g

= 9.807 m s2

Conversion Factors 1W

= 1 J s1

1J

= 0.2390 cal = 1 N m = 1 V C = 1 Pa m3 = 1 kg m2 s2

1 cal

= 4.184 J

1 eV

= 1.602 x 1019 J

1 L atm

= 101.3 J

1 atm 1 bar

= 1.013 x 105 N m2 = 1.013 x 105 Pa = 760 mmHg = 1 x 105 Pa

1L

= 103 m3 = 1 dm3

1 Ångstrom

= 1 x 1010 m = 0.1 nm = 100 pm

1 micron ()

= 106 m = 1 m

1 Poise

= 0.1 Pa s = 0.1 N sm2

1 ppm

= 1 g g1 = 1 mg kg1 = 1 mg L1 (dilute aqueous solutions only)

1 dyn cm1

= 103 J m2

CHEM1012

NOVEMBER 2014

PAGE 19 OF 21 PAGES

CHEM1012 For Rough Work

NOVEMBER 2014

PAGE 20 OF 21 PAGES

CHEM1012 For Rough work

NOVEMBER 2014

PAGE 21 OF 21 PAGES...