Question Paper 2[1]

8/3/2019 Question Paper 2[1]

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SECTION A

Answer all question in this section

1. The reaction between hydrogen and iodine can be represented by the followingequation:

H2(g) + I

2(g) 2HI(g) H= +52 kJ mol1

Kinetic data are available for both forward and reverse reactions. A series ofexperiments to investigate the kinetics of the forward reaction was carried out ata constant temperature. The results are shown in Figure 1.

Experiment Initialconcentration of

H2 / mol dm

3

Initialconcentration of

I2 / mol dm

3

Initial rate

/ mol dm3 s1

1 2.0 103 3.0 103 l.2 106

2 6.0 103 3.0 103 3.6 106

3 6.0 103 6.0 103 7.2 106

Figure 1

(a) Explain the meaning of each of the following terms:

(i) rate constant;

(1)

(iii) overall order of reaction.

(2)


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(b) (i) Use the results in Figure 1 to work out the order of the forwardreaction with respect to both hydrogen and iodine, explaining yourreasoning.

(3)

(ii) Write the rate equation for the reaction between hydrogen andiodine.

(1)

(iii) Calculate the value of the rate constant for the forward reaction andgive its units.

(2)

(c) The experiment was repeated with the following initial concentrations forreactants:

[H2] = 4.0 103 mol dm3 [I2] = 5.0 10

3 mol dm3

Calculate the initial rate of the reaction.

(1)

(Total 10 marks)


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2. (a) Write an equation for the reaction which occurs when the weak acid HA isadded to water.

........................................................................................................................

(1)

(b) Write an expression for the dissociation constant, Ka, for the weak acid

HA.

........................................................................................................................(1)

(c) The dissociation of the acid HA is an endothermic process. Deduce theeffect, if any, of

(i) an increase in temperature on the value of the dissociation constant,Ka

..............................................................................................................

(ii) an increase in temperature on the pH of an aqueous solution of theacid

..............................................................................................................

(iii) an increase in the concentration of the acid on the value of Ka

...............................................................................................................

(3)

(d) Identify a compound which could be added to aqueous ethanoic acid sothat the pH of the resulting solution would not change significantly if a smallvolume of dilute hydrochloric acid were added. State the name given tosolutions which behave in this way.

Compound......................................................................................................

Name..............................................................................................................


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(2)

(e) The diagram below shows the trend in the first ionisation energies of theelements from neon to aluminium.

Ne Na Mg Al Si P S

Firstionisationenergy

Element

(i) Draw crosses on the graph to show the first ionisation energies of silicon,

phosphorus and sulphur.(1)

(ii) Explain why the first ionisation energy of neon and that of magnesium areboth higher than that of sodium.

Explanation for neon

.......................................................................................................................

Explanation for magnesium

...................................................................................................................... (2)

(Total 10 marks)


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3. a. The ionic radius of the Group 2 element is given in the table below.

Ion Be2+ Mg2+ Ca2+ Sr2+ Ba2+Ionic radius (nm) 0.027 0.072 0.099 0.113 0.136

(i) Write the electronic configuration of Mg2+ ion and Sr2+ ion.

Mg2+ ion :....................................................................................................................

Sr2+ ion :.....................................................................................................................

(ii) How would you expect the ionic radius of Al3+ ion to be compared to that of Mg2+

ion. Explain your answer.

...................................................................................................................................

..................................................................................................................................

..................................................................................................................................

(iii) The hydrated Be2+ ion has the formula, [Be(H2O)4]2+. State one property shown by

beryllium salts in water.

..................................................................................................................................

(5)

b. The carbonates of the Group 2 elements decompose on heating.

(i) Write the chemical equation for the decomposition of magnesium carbonate.

...................................................................................................................................

(ii) Explain why magnesium carbonate does not decompose spontaneously.

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

(iv) The thermal stability of the carbonates increases with the proton number of the

element. Suggest an explanation for the effect of the size of the cation on the

thermal stability of the carbonates.

..................................................................................................................................

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..................................................................................................................................

(5)

4. a. Benzene undergoes electrophilic substitution reaction. In the nitration process,

nitrobenzene is obtained by the mixture of two acids and benzene.

(i) Name the two acids, the condition and write a balanced equation for the reaction.

Name of acids:............................................................................................................

Condition:...................................................................................................................

Equation:....................................................................................................................

(3)

(ii) State the electrophile in the above reaction.

...................................................................................................................................

(iii) Using balanced equations, describe the mechanism for the substitution reaction.

(iv) State one importance of benzene in the chemical industry.

.......................................................................................................................................

(4)

b. Give the structural formulae of the organic products formed from the following

reactions.

(i) CH3COCl + C6H5NH2

(ii) CH3 + H2SO4 conc

(iii) (CH3)2CCHCH3 + Br2(aq)

H20


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(3)

SECTION B

Answer any 4 question in this section.

5. (a) Define the term electronegativityand explain why the electronegativityvalues of the Group II elements BeBa decrease down the group.

(4)

(b) Name the strongest type of intermolecular force between hydrogen fluoridemolecules and draw a diagram to illustrate how two molecules of HF areattracted to each other.In your diagram show all lone pairs of electrons and any partial charges.Explain the origin of these charges.

Suggest why this strong intermolecular force is not present between HImolecules.(7)

(c) Crystals of sodium chloride and of diamond both have giant structures.Their melting points are 1074 K and 3827 K, respectively. State the type ofstructure present in each case and explain why the melting point ofdiamond is so high.

(4)

6. Methanol, CH3OH, is a convenient liquid fuel.

(a) An experiment was conducted to determine the enthalpy of combustion ofliquid methanol. The energy obtained from burning 2.12 g of methanol wasused to heat 150 g of water. The temperature of the water rose from 298

(i) Define the term standard enthalpy of combustion.

(ii) Use the data above to calculate a value for the enthalpy ofcombustion of one mole of liquid methanol.

(7)

(b) Methanol can be synthesised from methane and steam by a process thatoccurs in two stages.

Stage 1 CH4(g) + H2O(g) 3H2(g) + CO(g) is

H = +206 kJ mol1

Stage 2 CO(g) + 2H2(g) CH3OH(g)

H = 91 kJ mol1

(i) Explain why, in Stage 1, a higher yield of hydrogen and carbonmonoxide is not obtained if the pressure is increased.

(ii) Stage 2is carried out at a compromise temperature of 500K. Byconsidering what would happen at higher and lower temperatures,explain why 500 K is considered to be a compromise for Stage 2.

(5)


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(c) The standard enthalpies of combustion of carbon monoxide and of hydrogen

are 283 kJ mol1 and286 kJ mol1, respectively. Use these data and theenthalpy change for Stage 2to calculate a value for the standard enthalpy of

combustion of gaseous methanol. (3)

7. (a) An solution of sodium chloride of concentration 2.00 mol dm-3 is electrolysed for 25minutes using graphite electrodes. The resulting solution is then treated withhydrochloric acid of concentration 0.25 moldm-3. If the volume of hydrochloric acidneeded to complete titration is15.50 cm3, calculate the magnitude of the currentused during the electrolysis. (7)

(b) the partition coefficient for a solute S between ether and water is 12.50.

(i) Referring to solute S, ether and water, explain what is meant t by

partition law.

(ii) suggest the conditions at which the partition law holds true.

(iii) calculate the mass of S remaining in 25.0 cm3 of water that originallycontains 8.00 g of S after separate extraction with 25.0 cm3 of ether andtwo separated portion of 12.50 cm3 of ether. (8)

8. (a) By referring to the physical and chemical properties of aluminium, describe theproperty of an aqueous solution of aluminium salt. (5)

(b) By writing equations for the reactions involved, explain;

(i) the reaction of anhydrous aluminium chloride with water.(2)

(ii) why aluminium carbonate cannot be prepared from a solution containing

the Al3+ ion. (4)

(iii) Aluminium chloride is a white solid that fumes in moist air and sublimes at 180

C. (4)

9. (a) The table below shows the molecular formulae and dissociation constants, Kb at250C for ammonia, ethylamine and phenylamine.

Compound Formula Kb / moldm-3

Ammonia NH3 1.8 x 10-5

Ethylamine CH3CH2NH2 5.4 x 10-4

Phenylamine C6H5NH2 5.0 x 10-10

(i) Arrange the compounds according to increasing basic strength.

(ii) Discuss the factors that determine the relative base strength of the compounds

above. (5)


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b. Give reagents, condition, and equations to show how each of the following compounds

can be prepared from methylbenzene in the laboratory.

(i) CONH2

(ii) CH2OH

Explain one simple test to show the presence of hydroxyl group, -OH in compound (ii).

Write equations for reactions occurred. (10)

10. a. A sweet smelling liquid organic compound X has a molecular formula of C10H12O2undergoes acidic hydrolysis to produce an acid and an alcohol,Y. The alcohol Y reacts

with bromine water to produce a white precipitate. Reduction of X with lithium

tetrahydridoaluminate (III) followed by acid hydrolysis produces two alcohols Y and Z.

On dehydration by concentrated sulphuric acid, Z produces 2-methylpropene.

Determine the structures of X, Y and Z. Write equation for all the reactions involved.

Name compound X. (11)

b. Grignard reagents are organometallic compounds that are very important in the

synthesis of organic compounds.

(i) State how ethyl magnesium bromide can be prepared from a named haloalkane.(ii) Write the reaction sequence in the preparation of 2-methyl-2-butanol from ethyl

magnesium bromide. (4)

END OF THE QUESTION PAPER

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