h2 chemistry mock a level paper 2

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ABC JUNIOR COLLEGE

Mock A level Paper 2012

Higher 2

CANDIDATE

NAME

CLASS INDEX

NUMBER

CHEMISTRY 9647/02

Paper 2 Structured Questions 2 hr 00 min

READ THESE INSTRUCTIONS FIRST

Write your name, PDG and register number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a pencil for any diagrams, graphs or rough working.

Do not use staples, paper clips, highlighters, glue or correction fluid. Answer ALL questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question.

FOR EXAMINER’S USE

TOTAL / 72

This document consists of 16 printed pages.

2


Answer all questions.

1 Planning (P)

(a) Sodium hydroxide catalyses the following aldol condensation reaction (water is lost), a

powerful method for the construction of carbon–carbon bonds. In this particular

experiment, 3,4–dimethoxybenzaldehyde and 1–indanone are reacted in the absence of

a solvent as shown below. This reaction can give a yield of about 80% and you are to

prepare about 4 g of the pure organic product.

(i) Outline the four main steps required to synthesise this organic product.

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.

.

.

.

(ii) Determine the mass of each reactant needed to prepare desired amount of the pure

organic product.

[Mr: 3,4–dimethoxybenzaldehyde, 166.0; 1–indanone, 132.0.]

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(iii)Identify one important safety measure, with reason, that you would take to perform

this experiment.

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.

(iv)Suggest one reason why a student may obtain a higher yield than expected.

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[8]

(b) In inorganic qualitative analysis, sodium hydroxide is used to identify the metal cations.

In this experiment, you are only provided with four solutions, A, B, C, D, each solution

contains one of the following:

lead nitrate, Pb(NO3)2

sodium chloride, NaCl

sodium hydroxide, NaOH

zinc sulfate, ZnSO4

(i) Given that both lead and zinc ions form soluble complexes with excess sodium

hydroxide, while lead(II) chloride and sulfate are insoluble, complete the table below

to show the expected observations when pairs of the solutions are mixed by adding a

little at a time, until no further change is observed.

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(ii) Use your expected observations to explain how you could identify each of the

solutions.

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[4]

[Total: 12]

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2 Photochemical smog consists of a mixture of pollutants which includes oxides of nitrogen,

namely nitric oxide (NO) and nitrogen dioxide (NO2). The smog often has a brown haze due

to the presence of NO2. In most major cities, such as Mexico and Los Angeles, the exhaust

fumes from cars are the main sources of these oxides of nitrogen.

In car engines, nitric oxide is formed when atmospheric nitrogen reacts with oxygen:

When oxygen is present in excess, nitric oxide will be further converted to nitrogen dioxide:

The variation in equilibrium constant, Ksp, with temperature for the two equilibria is given by

the data:

(a) With reference to equilibrium (II).

(i) Write an expression for Kp for the production of NO2 from NO and O2.

(ii) At which of the above temperatures will there be maximum conversion of NO and O2

to NO2? Explain your answer.

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.

.

(iii)Calculate the mole ratio of NO2 to NO in the atmosphere at 900K given that air

consists of 20% O2 and pressure is 1 atm.

[5]

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(b) Using the values of Kp for both equilibria, explain why the formation of NO occurs mainly

in car engines while that of NO2 occurs mainly outside the engines.

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.

.

[2]

(c) The peak in the atmospheric level of NO is closely related to the peak in traffic density.

The following graph shows the concentration of atmospheric NO and NO2 in a city

measured on a particular day.

Explain why the peak of atmospheric NO2 is observed only a few hours after the peak of

atmospheric NO.

.

[1]

(d) State and explain how lowering of pressure in the engine cylinders will affect the amount

of NO produced.

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[2]

[Total: 10]

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3 (a) What do you understand by electronegativity? How does it vary in the periodic table?

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[2]

The following hard materials have all found use in body armour.

Table below gives the electronegativity values for the elements in these materials.

element electronegativity element electronegativity

Titanium 1.4 Boron 2.1

Tungsten 1.5 Carbon 2.5

Aluminium 1.6 Nitrogen 3.1

Silicon 1.9 Oxygen 3.6

(b) Plot on the van Arkel triangle the points corresponding to silicon carbide, SiC, and silicon

nitride, Si3N4. Label your points, making it clear which is which. [2]

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(c) Point A on the van Arkel triangle corresponds to metallic bonding. State the types of

bonding that correspond to points B and C.

B .

C . [1]

(d) Compare the bonding in silicon carbide, SiC, with silicon nitride, Si3N4, by circling the

correct option.

SiC is less metallic equally metallic more metallic [1]

(e) Circle the correct response about the bonding in silicon carbide, SiC. The bonding in

silicon carbide is best described as

Intermediate between metallic and covalent

Metallic

Intermediate between metallic and ionic

[1]

(f) Which of the hard materials, AlN, Al2O3 and TiB2, is the most intermediate between all

three extremes of bonding?

. [1]

(g) Scientists have recently characterised metallic behaviour in VO2 above 68°C. The same

behaviour was not found in V2O5. By considering this case and the electrical properties of

diamond and graphite suggest three general deficiencies in the predictive power of the

van Arkel triangle.

1 .

2 .

3 [3]

[Total: 11]

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4 One major difference between the properties of compounds of the transition elements and

those of other compounds is that the compounds of the transition elements are often

coloured.

(a) The following graph shows the absorption spectrum of two complexes containing copper.

(i) State the colours of the following complex ions.

[Cu(H2O)6]2+ .

[Cu(NH3)4(H2O)2]2+ .

(ii) Using the spectra above give two reasons why the colour of the [Cu(NH3)4(H2O)2]2+

ion is deeper (more intense) than that of the [Cu(H2O)6]2+ ion.

.

.

.

(iii)Predict the absorption spectrum of the complex [Cu(NH3)2(H2O)4]2+, and sketch this

spectrum on the above graph.

[6]

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(b) Copper forms a complex with chlorine according to the following equilibrium.

(i) Write an expression for the equilibrium constant, Kc, for this reaction, stating its units.

(ii) The numerical value of is 4.2 x 105. Calculate the [[CuCl4]2-]/[Cu2+] ratio when [Cl-] =

0.20 mol dm-3.

[3]

[Total: 9]

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5 A chemist designs an ion-specific probe for measuring [Ag+] in a NaCl solution saturated

with AgCl using the following set-up.

(a) (i) Given the following standard half reactions:

Obtain an overall balanced equation, including state symbols for the cell above

and state the direction of the flow of electron in the cell.

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(ii) An engineer wishes to use the probe to analyse an ore sample. After pretreating

the sample, the chemist measured the cell voltage, Ecell as 0.53V.

The Nernst equation can be used to measure the concentration of silver ions using

the probe,

Where n is the number of moles of electrons transferred in the overall reaction and

K is the equilibrium constant for the overall equation in (a)(i).

Assuming the concentration of Cl- is so high that it is essentially constant, use the

Nernst equation to calculate the concentration of silver ions in the ore sample.

(iii)Given that,

Using the half equation above and any other relevant data from the Data Booklet,

derive the for the overall reaction: and use

the equation given in (a)(ii), calculate a value of the Ksp for silver chloride at

equilibrium, if Ecell of any process at equilibrium is 0V.

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[8]

(b) (i) To prepare the saturated solution of AgCl and NaCl. AgCl is added to a 200 cm3

solution of NaCl of concentration of 1 x 10-3 mol dm-3. Using the Ksp value obtained

in (a)(iii), predict the maximum mass of AgCl to be added to obtain a saturated

solution.

(ii) The concentration of chloride ions from silver chloride in (b)(i) is less than the

square root of the Ksp value of silver chloride. Explain why this is so.

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.

.

(iii)Suggest why when aqueous sodium thiosulfate was added to the resulting solution

in (b)(i), more silver chloride was able to dissolve.

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[6] [Total: 14]

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6 The question below is about cyclic compounds.

(a) Cyclopentene undergoes the electrophilic addition reaction below to yield a few organic

products.

Draw the structural formulae of the possible products from this reaction.

[2]

(b) The structure of imidazole is shown below.

(i) Circle the most acidic hydrogen atom. Explain your answer.

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.

.

(ii) Box the most basic nitrogen atom. Explain your answer.

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.

[6]

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(c) The addition of water to alkenes can yield two kinds of product. One is the Markovnikov

product, another is the anti-Markovnikov product. The reaction that produces the anti-

Markovnikov product is also known as hydroboration.

Below shows a typical hydroboration reaction.

(i) Suggest the product when 1-Methyl-cyclopentene undergoes hydroboration.

(ii) Suggest a reason why hydroboration take place in a non-Markovnikov manner,

yielding the less highly substituted alcohol.

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[2] [Total: 8]

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7 (a) Give the reagent(s) and condition as well as the intermediates for the following organic

synthesis.

[5]

(b) Describe the mechanism for the last step of the synthesis above.

[3]

[Total: 8]

h2 chemistry mock a level paper 2

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