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IBH 1996 Mock Examination Paper 1

Only those questions that relate to the new IB syllabus have been included.

1. The nucleus of a radon atom, 222 86 Ra contains

A. 222 protons and 86 neutrons.

B. 86 protons and 136 neutrons.

C. 86 protons and 222 neutrons.

D. 86 protons, 136 neutrons and 86 electrons.
 
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2. A mass spectrum of a sample of naturally occurring magnesium produced the following results.
 

Mass/charge % abundance
26.0 11.29 
25.0 10.11 
24.0 78.60 
Based on this information, one can deduce that the relative atomic mass, of magnesium is

A. 24.0

B. 24.3

C. 25.0

D. 25.7
 
 
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3. How many unpaired electrons are present in an atom of element number 23 in its ground state ?

A. 1

B. 3

C. 5

D. 7

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4. Which pair of elements is most likely to form a covalently-bonded compound ?

A. Li and F

B. P and O

C. Ca and O

D. Zn and Br

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5. Some of the more common oxides of nitrogen which contribute to the problems of smog and air pollution around the world are NO2, N2O and N2O4. Which of these molecules violate(s) the 'octet rule' ?

A. NO2 only

B. N2O only

C. NO2 and N2O4 only

D. NO2, N2O and N2O4

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6. How many bonds are present in CO2 ?

A. One

B. Two

C. Three

D. Four

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7. The F-B-F bond angle in the BF3 molecule is most similar to the bond angle in

A. C2F2

B. C2F4

C. CF4

D. C2F6

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8. In which of the following structures do all the carbon atoms lie in one plane ?

I. C6H5 CH3

II. CH3CH=CHCH3

III. C(CH3)4

A. I only

B. II only

C. I and II only

D. II and II only

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9. Which of the following chlorides would be expected to have the highest melting point ?

A. NaCl

B. MgCl2

C. SiCl4

D. PCl5

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10. The boiling point of iodine monochloride, ICI, is about 40 0C higher than the boiling point of bromine, Br2 , even though the two substances have nearly identical relative molar masses. Which one of the following statements best accounts for this observation ?

A. The I--Cl bond is stronger than the Br--Br bond.

B. The ionisation energy of iodine is lower than that of bromine or chlorine.

C. The number of neutrons in ICl is greater than that in Br2 .

D. ICl is a polar molecule while Br2 is non-polar.

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11. Given the following information :
 
Metal  Specific Heat Capacity (J g-1 K-1
lead 0.129 
magnesium  1.02 
mercury 0.138 
silver 0.237 
While metal will reach the highest temperature when 100 kJ of heat is transferred to 10.0 g samples of the above metals at an initial temperature of 250C ?

A. Lead

B. Magnesium

C. Mercury

D. Silver

12. The bond dissociation energy of hydrogen iodide, HI, is the enthalpy change associated with the reaction

A. HI(g) ----->     1/2 H2(g)  +    1/2 I2(g)

B. HI(g) ----->     1/2 H2(g)  +     1/2 I2(s)

C. HI(g) ----->      H(g)        +       I(g)

D. HI(g) ----->      H(g)        +      I(s)

13. All of the following explanations contribute to the observation that magnesium oxide, MgO, has a larger lattice enthalpy than sodium chloride, NaCl, except

A. the distance between the ions in sodium chloride is greater than that between the ions in magnesium oxide.

B. the charge of the magnesium ion is twice that of the sodium ion.

C. the charge of the oxide ion is twice that of the chloride ion.

D. the magnesium oxide lattice has a higher degree of ionic character than the sodium chloride lattice.

14. For which of the following processes, carried out at 25 0C, is the value of S positive ?

I.   H2O(I) ------>  H2O(g)

II.   F2(g )  ------> 2F(g)

III. KBr(s) ---------> KBr(aq)

IV. O2(g, 1 atm) -------> O2(g, 2 atm)

A. I, II and III

B. I, II and IV

C. IV only

D.  III only

15. If it is necessary to employ an electric current continuously in order for a reaction to take place, which one of the following must always be true for that reaction?

A.  /\  H = 0

B.  /\  H < 0

C.  /\  G = 0

D.  /\ G < 0

16. A 1.0 dm3 bulb containing hydrogen gas at 2.4 atm pressure is connected to a 2.0 dm3 bulb containing helium gas at 1.2 atm pressure. Assuming no change in temperature, what will be the final pressure of the gas mixture when the valve connecting the bulbs is opened ?
 

A. 0.8 atm

B.  1.6 atm

C. 1.8 atm

D. 3.6 atm

17. Real gases deviate from ideal behaviour under most conditions. This deviation is a result of the space occupied by the gas molecules themselves and

A. attractive forces between the gas molecules.

B. molecular vibrations of the gas molecules.

C. changes in bond enthalpy with changes in temperature.

D. variations in molecular velocities.

18. Which one of the following substances is most likely to be found in the gaseous state at 25 0C and 101.3 kPa (1 atm) pressure ?

A. LiH

B. P4O10

C C8H18

D. SiH4

19. The numerical value of the equilibrium constant for a chemical change may be altered by changing the

A. pressure on the system.

B. temperature of the system.

C. concentration of the products in the system.

D. concentration of the reactants in the system.

20. Which one of the following reactions involves neither oxidation nor reduction ?

A. Fe(s) + Cu2+(aq) ------ Fe2+(aq) + Cu(s)

B. 2CrO4 2-(aq) + 2H+(aq) ------- Cr2O72-(aq) + H2O(l)

C. C2H4(g) + H2(g) ------- C2H6(g)

D NH4NO2(s) ------- N2(g) + 2H2O(g)

The following questions have not been edited yet. Back to past papers?

21.    Zn2+(aq) + 2e ==== Zn(s) E0 = -0.762 volt

       Mg2+(aq) + 2e ==== Mg(s) E0 = -2.357 volt

Use the half-cell potentials above to predict which one of the following results will be observed when metallic zinc is added to an aqueous solution of magnesium nitrate.

A. Solid zinc will dissolve and solid magnesium will be precipitated.

B. Solid zinc will dissolve in the solution and the magnesium will be unchanged.

C. Aqueous zinc chloride will form and solid magnesium will be precipitated.

D. There will be no reaction.
 
 

22. Only one of the following substances cannot function as a Lewis acid or a Lewis base. Identify that substance on the basis of its structure.

A. H2O

B. CH4

C. NH3

D. BF3

23. A student determined the concentration of a solution of hydrochloric acid by an acid-base titration. When a 45.0 cm3 sample of the acid was titrated to a phenolphthalein endpoint, 36.0 cm3 of 0.15 M KOH was required. What was the molarity of the hydrochloric acid solution ?

A. 0.30

B. 0.24

C. 0.12

D. 0.060

24. A solution is prepared by adding 0.25 mol of ethanoic acid, CH3COOH, to sufficient water to give 1.0 dm3 of solution. The pH of this solution is 2.67 and the percent ionization 0.848%. What will happen to the pH and the percent ionization of this solution as it is diluted with water to a volume of 2.0 dm3 ?

A. The pH will increase; the % ionization will increase.

B. The pH will decrease; the % ionization will increase.

C. The pH will increase; the % ionization will decrease.

D. The pH will decrease; the % ionization will decrease.
 

25. Equal concentrations of ammonia and ammonium chloride were mixed to give an aqueous buffer solution with a pH = 9.3. Which one of the following action would not reduce the pH of this solution to 9.0 ?

A. Adding some solid ammonium chloride.

B. Adding some concentration hydrochloride acid.

C. Diluting the solution with distilled water.

D. Boiling briefly to evaporate some of the ammonia.

26. The number of moles of a solid weak organic acid is to be determined by titrating a solid sample with 0.1280 M sodium hydroxide solution. Which one of the following will always give results that are too high ?

A. The solid acid is dissolved in 75 cm3 of water rather than in 50 cm3 of water.

B. The wet buret is not rinsed with the standard NaOH solution.

C. Methyl orange (PKa 3.4) is used as an indicator instead of phenolphthalein (pKa 9.4).

D. A concentration of 0.1208 M is used for the base in the calculations.
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27. An energy diagram for a chemical reaction is shown below. Which letter correctly represents the activation energy for the catalyses reaction in the forward direction ?
 
 
 
 
 
 
 
 
 

A. W

B. X

C. Y

D. Z
 
 

38. Which one of the following graphs represents the plot of In[X] against time, t, for the first-order reaction, X ---- Y ?
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

39. The conversion of NO to NO2 was studied at 250 0C in the gas phase. The following kinetic data were obtained.

[NO] mol dm3 [O2] mol dm-3 Initial rate (mol dm-3 s-1)

1.6 x 10-1 2.4 x 10-1 1.5 x 10-4

3.2 x 10-1 2.4 x 10-1 6.0 x 10-4

3.2 x 10-1 4.8 x 10-1 1.2 x 10-3

The value for the order of the reaction with respect to NO and O2 are
 

40. Some information regarding the catalysed and uncatalysed decomposition of HI is given below :

Reaction Eactivation(kJ mol-1) Rate

2HI ----- H2 + I2 190 R1

2HI ----- H2 + I2 (catalysed) 95 R2

Based on this information, which of the following statements is true ?

A. R1 = 2R2 at all temperatures.

B. R1 = R2 2 at all temperatures.

C. An increase of 10 0C will cause the rates of both reactions to double.

D. R1 increases more rapidly with temperature than R2 does.

41. When oxides of magnesium and sulphur are dissolved in water and the resulting solutions are tested with litmus, an acid-base indicator, it is evident that

A. magnesium forms an acidic oxide and sulphur forms an acidic oxide.

B. magnesium forms a basic oxide and sulphur forms an acidic oxide.

C. magnesium forms an acidic oxide and sulphur forms a basic oxide.

D. magnesium forms a basic oxide and sulphur forms a basic oxide.

42. The litmus ion, Li+, has a very large negative enthalpy of hydration because

A. it has a very high charge density.

B. it is an alkali metal.

C. it is very easily reduced by water.

D. lithium reacts with water to form hydrogen gas.
 

43. Which one of the following names would be the most acceptable IUPAC name for the molecules
 
 
 

A. 2-ethyl-3-methyl-5-tert-butylhexane

B. 2-ethyl-3,5,6,6-tetramethylheptane

C. 2,2,3,5,6-pentamethyloctane

D. 3,4,6,7,7-pentamethyloctane

44. Which pair of compounds may be described as 'functional group isomers'?
 
 

A. I and II

B. I and III

C. II and IV

D. III and IV
 
 

45. Which one of the following sets of reagents will react by an electrophilic substitution mechanism ?

A. CH3CH2 CH2Br + NaOH(aq)

B. CH3CH=CHCH3 + Br2

C. CH3CH=CHCH3 + HBr

D. C6H6 + Br2/FeBr3

46. A sample of the compound shown below is added to an aqueous solution of sodium hydroxide and stirred well. How many of the chlorine atoms will be removed from the molecule by hydrolysis ?
 

A. Zero

B. One

C. Two

D. Three
 
 

47. When propan-1,3-diol is refluxed with an excess of acidified aqueous potassium dichromate(VI), the most likely reaction product is
 
 

48. Chlorine reacts with methylbenzene in the presence of ultraviolet light. What is the active chlorine species and the organic product ?

Cl species Product

A. Cl+ ClC6H4CH3

B. Cl+ C6H5CH2Cl

C. Cl. C6H5CH2Cl

D. Cl- ClC6H5CH3
 
 

49. How does the melting point range of a pure sample of a compound compare with that of an impure sample of the same compound ? The melting point range of the pure compound is

A. lower and over a narrower range.

B. lower and over a wider range.

C. higher and over the same range.

D. higher and over a narrower range.

50. A 20 cm3 sample of 0.1 M HCl is added to a 10 cm3 sample of 0.1 M NaOH. which graph best represents the electrical conductivity of the solution during this addition ?