2012 Y6 H2 Chem T3 CT Question Paper

7/27/2019 2012 Y6 H2 Chem T3 CT Question Paper

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Raffles Institution 2012 9647/Y6/T3/12 [Turn Over

RAFFLES INSTITUTION2012 YEAR 6 TERM 3 COMMON TEST

Higher 2

CHEMISTRY 964728 June 2012

2 hours 45 minutes

Additional Materials: OMR Answer SheetAnswer PaperData Booklet

READ THESE INSTRUCTIONS FIRST

DO NOT open this booklet until you are told to do so.

Write your name and civics tutorial group in the spaces provided on the cover sheet onpage 10.

This paper consists of three sections A, B and C.

Section A (20 marks) consists of 20 multiple-choice questions.Record your answers to this section in soft pencil on the separate OMR Answer Sheet.

Section B (42 marks) consists of 4 structured questions.Answers to this section are to be written in the spaces provided in the question paper.

Section C (40 marks) consists of 3 free-response questions.Answer question C1 and one other question from this section. Answers to this section are tobe written on the writing paper provided. You are to begin each question on a fresh sheet ofpaper.

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.

Write in dark blue or black pen. You may be subject to penalty for writing answers in pencil.

This document consists of 27 printed pages.


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Section A (20 marks)

For each question, there are four possible answers, A, B, C, and D. Choose the one youconsider to be correct and record your choice on the OMR Answer Sheet provided.

1 Which ion will be deflected the least in an applied electric field?

A Br+ B 1Br+ C 1Br + D Br +

2 Which of the following statements is true?

A SF4 is a non-polar molecule.B Propanoneis immiscible with water.C I3

has a larger bond angle than N3

.

D CH2=C=CH2 is not a planar molecule.

3 With reference to the Data Booklet, which of the following predictions regarding Cu+and Sn2+ ions can we make?

A Only Cu+ undergoes disproportionation.B Only Sn + undergoes disproportionation.C Both Cu+ and Sn + undergo disproportionation.D Neither Cu+ nor Sn + undergoes disproportionation.

4 In the electrolysis of aqueous chromium(III) sulfate, how much time is taken to form1.04 g of chromium at the cathode when a current of 5 A is passed through thesolution?

A 129 s B 386 s C 1158 s D 5790 s

5 A sparingly soluble aluminium salt ionises in aqueous solution according to theequation given:

AlY3(s) Al3+(aq) + 3Y(aq)

Given that the solubility product of AlY3 is K, what is the value of the concentration ofY(aq) at equilibrium?

A1

2( )K B1

23( )K C1

4(3 )K D

1

4

27

K


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6 The graph below shows how the pH changes when 0.05 mol dm3 CH2ClCOOH isadded dropwise to 5.0 cm3 of 0.10 mol dm3 KOH(aq).

At which point on the graph does pH = pKa, where Ka is the acid dissociation constantof CH2ClCOOH?

7 For the chlorides of Period 3 elements, from Na to P, which of the followingstatements is true?

A All the chlorides dissolve in water to give HCl.B The ionic chlorides give a neutral solution in water.C None of the chlorides exists as a giant covalent structure.D The electrical conductivity of the molten chlorides increases across the period.

8 The reaction conditions for four different transformations are given. Whichtransformation has the correct conditions?

A

B

CCl2(g)

(l)HO HO

Cl

uv light

D

Br

heat

Na(s)/CH3CH2OH(l)(l)

Volume of

0.05 mol dm3CH2ClCOOHadded / cm

3

pH

105 15 200

A

B

CD


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9 In an attempt to distinguish between compounds P and Q,2,4-dinitrophenylhydrazineand alkaline aqueous iodine are used separately. Which reagents can distinguishbetween P and Q?

P Q

A alkaline aqueous iodine onlyB 2,4-dinitrophenylhydrazine onlyC both 2,4-dinitrophenylhydrazine and alkaline aqueous iodineD neither 2,4-dinitrophenylhydrazine nor alkaline aqueous iodine

10 Phenyl benzoate was heated with concentrated sulfuric acid under reflux. Theorganic products were dissolved in CCl4 and then transferred to a separatory funnelcontaining excess aqueous sodium carbonate. The funnel was then stoppered andshaken thoroughly. After some time, two immiscible layers were obtained.

separatory funnel

What were the predominant species found in the organic and aqueous layers?

organic (CCl4) layer aqueous layerA C6H5ONa C6H5COOHB C6H5OH C6H5COONaC C6H5COONa C6H5OHD C6H5COOH C6H5ONa

aqueous layer

organic (CCl4)

layer


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11 Ciprofloxacin, an antibacterial agent, is an inhibitor of bacterial topoisomerase.

ciprofloxacin

Which of the following gives the correct order of increasing pKb values of the N atomsin ciprofloxacin?

A N(I) < N(II) < N(III)

B N(I) < N(III) < N(II)

C N(II) < N(III) < N(I)

D N(III) < N(II) < N(I)

12 A tripeptide was isolated after an enzymatic hydrolysis of an animal protein.

H2N C C N C C N C C OH

H H

O OH H H

CH2

COOH

CH2 CH2

OH

OH

O

Which compound could be obtained when the tripeptide reacts with hot dilute NaOH?

AH2N C C

OH

CH2

COOH

O

B

C DH2N C C

OH

CH2

OH

O


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For each of the following questions, one or more of the three numbered statements 1 to 3may be correct. Decide whether each of the statements is or is not correct (you may find ithelpful to put a tick against the statements that you consider to be correct).

The responses A to D should be selected on the basis of

A B C D1, 2 and 3

arecorrect

1 and 2only arecorrect


1 onlyis

correct

No other combination of statements is used as a correct response.

13 Which of the following diagrams correctly describes the behaviour of a fixed mass ofan ideal gas? ( = density)

1

2

3

at constant P

T

at constant

1/P

1/T

at constant V

PV

T


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14 A concentration cell is a non-standard galvanic cell that has two equivalent half-cellsof the same substance differing only in concentrations. A concentration cell producesa small voltage as it attempts to reach equilibrium. This equilibrium occurs when theconcentrations of reactants in both cells are equal.

Which of the following statements are correct?

1 The electrons flow from the right half-cell to the left half-cell.2 The copper electrode on the left half-cell functions as a cathode.3 The Cu + concentration on the left half-cell gradually reduces and stabilises at

approximately 0.5 mol dm3.

15 The graph below shows the variation of pH when 25 cm3 of a 0.1 mol dm3 weakbase is titrated against aqueous HCl solution until the acid is in excess.

Which of the following statements are correct?

1 The mixture is a buffer solution when 25 cm of HCl is added.2 Methyl orange is a suitable indicator for the titration.3 The base used in the experiment could be H2NCH2CH2NH2.

pH

Vol. of HCl

added / cm350

[Cu +(aq)]= 1.0 mol dm3

[Cu +(aq)]= 0.01 mol dm3

Temperature= 25 oC

Salt bridge

Cu Cu

V


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The responses A to D should be selected on the basis of

A B C D

1, 2 and 3are

correct



1 onlyis

correct

16 Which of the following trends concerning Period 3 elements from Na to Cl are correct?

1 When the highest oxides of the elements are separately added to water, thepH values of the solutions formed generally decrease across the period.

2 The reducing powers of the elements in their standard states increase acrossthe period.

3 The electrical conductivities of the elements decrease steadily across theperiod.

17 Sustained heating is required to decompose Group II carbonates completely intotheir respective oxides and carbon dioxide. Which of the following statementsregarding the thermal decomposition of Group II carbonates are correct?

1 When equal masses of MgCO3 and BaCO3 are heated under the sameconditions, the time taken to collect a fixed volume of CO2 is shorter for MgCO3.

2 The decomposition process is driven by an overall increase in entropy of thesystem.

3 The standard enthalpy change for the thermal decomposition reaction is greaterthan zero.

18 Progesterone and aldosterone are steroid hormones which can be synthesised fromcholesterol in the human body.

Which reagents can distinguish between progesterone and aldosterone?

1 alkaline aqueous iodine2 Fehlings solution3 sodium hydrogen carbonate

progesterone aldosterone


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19 Aspirin is a painkiller which can be synthesised from salicylic acid.

Which of the following statements are incorrect?

1 Salicylic acid reacts with ethanoic acid to form aspirin.2 Both aspirin and salicylic acid give a violet complex with neutral FeCl3(aq).3 Both aspirin and salicylic acid react with the same amount of PCl3.

20 Leupeptin is a naturally occurring protease enzyme inhibitor, which is often used in

experiments involving enzymatic reactions. It contains a guanidino group with onlyone pKa value of 12.5.

leupeptin

Which properties does leupeptin possess at pH 7?

1 It reacts with ethanoyl chloride.2 The predominant form is singly protonated.3 In aqueous solution, it migrates to the cathode of an electrolytic cell.

aspirin salicylic acid

OHO

O

O

OHO

OH

guanidino

group


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RAFFLES INSTITUTION2012 Year 6 Term 3 Common Test

H2 Chemistry

COVER SHEET

Name: ( ) CT Group:

For Examiners Use Only

Section Marks

A / 20

B

Q1 / 12

Q2 / 11

Q3 /14

Q4 / 5

C

(circle the questionsyou have answered)

Q1(compulsory)

/ 20

Q2 / 20

Q3/ 20

Total / 102

Overall Percentage / 100


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Section B (42 marks)

This section consists of four questions.Answer all questions in the spaces provided in the question paper.

B1 Planning (P)The solubility of cerium(IV) sulfate, at a particular temperature, is defined as:the mass of cerium(IV) sulfate that will dissolve in and justsaturate100 g of solventat that temperature.

Cerium(IV) sulfate will dissolve in water.A saturated solution is one in which no more solid can dissolve at a particulartemperature.In a saturated solution in contact with undissolved solid, the followingequilibrium is established.

Ce(SO4)2(s) + aq Ce4+(aq) + 2SO42(aq)Cerium(IV) sulfate is unusual as its solubility decreases when the temperatureof the solution increases.

Cerium(IV) sulfate crystals also dissolve in dilute sulfuric acid, H2SO4, a corrosiveaqueous solution.

You are to plan an experiment to investigate how the solubility of cerium(IV)sulfate crystals in dilute sulfuric acid depends on the concentration of the acid.

(a) By considering the ions present in a solution of cerium(IV) sulfate in sulfuricacid, predict and explain how the solubility of the cerium( IV) sulfate will beaffected by the concentration of the acid.

Prediction .

...

Explanation .

...

Display your prediction in the form of a graph.

[2]

solubility ofcerium(IV)sulfate

concentration of sulfuric acid

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(b) Besides concentration of dilute sulfuric acid and mass of cerium(IV) sulfate,identify another variable which needs to be controlled when you plan theexperiment.

[1]

(c) Design a two-part laboratory experiment to investigate your prediction in (a).

Part 1 solubility of cerium(IV) sulfate in water

In addition to the standard apparatus present in a laboratory, you areprovided with the following materials.

60 cm3 distilled watersolid cerium(IV) sulfate, Ce(SO4)2

Give a step-by-step description of how you would

prepare a saturated solution using all of the 60 cm3 of distilled water

separate the saturated solution from undissolved solid

control the variable identified in (b) obtain the mass of cerium(IV) sulfate and mass of water in the saturated

solution calculate the solubility of cerium(IV) sulfate from the experimental results

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[4]

Part 2 solubility of cerium(IV) sulfate in varying concentrations ofsulfuric acid

Give a step-by-step description of how you would prepare a range ofstandard solutions of sulfuric acid of four different concentrations. Thesesolutions could then be used to investigate the solubility of cerium(IV) sulfatein sulfuric acid of different concentrations.

In addition to the standard apparatus present in a laboratory, you areprovided with the following materials.

5 mol dm3 sulfuric aciddistilled water

Your plan should include details of the following.

the number and concentrations of the solutions to be prepared

the volumes of acid and water used to prepare the solutions

the apparatus and method you would use in their preparation

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[4]

(d) State a risk that must be taken into consideration when planning theexperiment.

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[1]

[Total: 12]

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B2 (a) This question concerns the rechargeable lead-acid battery. The standardelectrode potentials of the reactions involved are shown below.

E / VPbO2(s) + 4H

+(aq) + SO42(aq) + 2e PbSO4(s) + 2H2O(l) + 1.69

PbSO4(s) + 2e Pb(s) + SO4

2(aq) 0.36

(i) Suggest a suitable electrode at the negative terminal duringdischarging.

(ii) Determine the e.m.f. of the cell.

(iii) A storage cell, as used in the lead-acid battery, is a simple cell inwhich the reactions are reversible, i.e. once the chemicals have beenused up they can be re-formed. Write an equation for the chemicalreaction which occurs during charging.

[3]

(b) A cell is constructed with zinc and graphite electrodes, each weighing 40 g,partly immersed in aqueous NaOH. Oxygen is supplied in the half-cellcontaining the graphite electrode by bubbling air into it.

When connected in a circuit, some zinc passes into the solution aszincate(II) ions, [Zn(OH)4]

2(aq).

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(i) Write the equation for the reaction occurring in each half-cell, andhence, write a balanced equation for the overall reaction which takesplace.

(ii) The standard cell potential was found to be +1.62 V. With reference tothe Data Booklet, calculate the standard electrode potential of the[Zn(OH)4]

2(aq) / Zn(s) system.

(iii) The value obtained in (b)(ii) can be measured with the help of thestandard hydrogen electrode. Draw a fully labelled sketch of how youwould determine the standard electrode potential of the[Zn(OH)4]

2(aq) / Zn(s) system.

(iv) The cell delivers a current of 13.7 mA. The zinc electrode is replacedonce 60% of it is used up. Calculate the quantity of electricity passingthrough the cell and the length of time the cell can last beforereplacement becomes necessary.

[8]

[Total: 11]

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B3 Collagen, a component of bone and connective tissue, is the most abundant proteinin vertebrates. It exists as water-insoluble fibres of great strength.

Five of the most common amino acids in the collagen obtained from human skin arelisted below.

Amino acid Formula of side chain

(R in RCH(NH2)COOH)

Number of amino acid

residues per 1000residues in collagen

glycine (gly) H 329

alanine (ala) CH3 109

glutamic acid (glu) CH2CH2COOH 74

serine (ser) CH2OH 36

lysine (lys) (CH2)4NH2 29

(a) There are three pKa values associated with glutamic acid: 2.1, 4.1 and 9.5.

(i) Sketch the titration curve obtained when 10 cm3 of 0.1 mol dm3

protonated glutamic acid is titrated against 0.1 mol dm

3

NaOH(aq)until 40 cm3 of NaOH(aq) is added.

(ii) Suggest the two major forms of glutamic acid present at pH 2.5, and

calculate the ratio in which the two species are present at pH 2.5.

[5]

pH

Volume of

NaOH(aq) / cm3

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(b) In addition to the five common amino acids, proline (pro) is also present insignificant amounts in the collagen.

HN

O

OH

Draw the structural formula of gly-pro-ser.

[1]

(c) Suggest one type of interaction responsible for holding the tertiarystructure ofcollagen together and state the amino acid(s) that give rise to this interaction.

[2]

It is found that the polypeptide chains in collagen contain a repeating sequence ofgly-pro-X, where X refers to an amino acid residue other than glycine and proline.

A collagen fibre consists of three polypeptide chains wrapped around one another ina rope-like twist known as the triple helix.

collagen triple helix

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(d) What level of structure, primary, secondary, tertiaryor quaternary, in collagendoes the triple helix describe?

[1]

(e) The third amino acid in each chain must be occupied by glycine. Whatstructural feature of glycine allows the chains to be tightly held in the triplehelix?

[1]

In collagen from meat of animals, reactions of the side chain R groups of the aminoacids result in intramolecular and intermolecular covalent bonds known as cross-links.The amount of cross-linking increases with age and hence meat from older animalsis tougher than meat from younger animals.

(f) Raw papaya juice can be used to soften or tenderise meat tissues. However,boiled papaya juice is ineffective as a tenderiser. Explain why that is so.

[2]

(g) Suggest another method to soften or tenderise meat for cooking.

[1]

In human hair, the cysteine (R = CH2SH) residues, can form disulfide bridges, whichare responsible for cross-linking.

(h) Write a balanced equation to show the formation of a cross-link formed

between two cysteine molecules.

[1]

[Total: 14]

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B4 In an experiment, a mixture containing magnesium nitrate and barium nitrate washeated in a boiling tube and the gaseous products evolved were collected in a gassyringe under constant pressure.

(a) Explain which nitrate decomposed at W. Write a balanced equation, includingstate symbols, for this decomposition.

[3]

(b) (i) Assuming the gases behave ideally, explain why there is a slightincrease in volume from X to Y.

(ii) Explain why the gradient of the graph changes non-linearly from

W to X.

[2]

[Total: 5]

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Section C (40 marks)

This section consists of threequestions. Answer two questions from this section.Answer question C1 and one other question.

Begin each question on a fresh sheet of paper.

It is compulsory to answer question C1.

C1 (a) When treated with lithium aluminium hydride, LiAlH4, esters are reduced toyield alcohols. LiAlH4 functions as a delivery agent of the nucleophile, H:

.

RCOOR RCH2OH + ROH (R, R : alkyl group)

The simplified version of the mechanism of this reaction is shown below.

R

O

OMe

Al HH

H

H

RH

O

OMe R

O

H

Al HH

H

H

RH

O

H

H

O

H

RH

O

H

H

I II

III

IV

(i) Explain what is meant by the term nucleophile.

(ii) State the type of reactions that take place in Steps I, II and IV

respectively in the above mechanism.

(iii) Explain why water is an unsuitable solvent and suggest a suitablesolvent for this reduction.

(iv) Explain why this reduction reaction cannot be achieved by usingsodium hydride, NaH, instead of LiAlH4.

[7]


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Cyanoacrylate is the generic name for cyanoacrylate based fast-acting glues such asethyl 2-cyanoacrylate.

(b) The skeletal formula of ethyl 2-cyanoacrylate is given below.

(i) State the molecular formula of ethyl 2-cyanoacrylate.

(ii) State the bond angles labelled x and y.

(iii) Name the respective functional groups of the carbon atoms labelled1, 2, and 3.

[5]

(c) Ethyl 2-cyanoacrylate rapidly undergoes addition polymerisation in thepresence of a suitable nucleophile to form long, strong chains that join thebonded surfaces together. The presence of moisture can cause a tube orbottle of glue to become unusable over time.

Identify the nucleophile that causes the glue to harden over time.[1]

(d) The reduction of ethyl 2-cyanoacrylate with LiAlH4 produces two compounds,Q and R.Q reacts with ethanoyl chloride in a 1:2 molar ratio to form S.R reacts with ethanoyl chloride in a 1:1 ratio to form T.

If ethyl 2-cyanoacrylate is instead reduced with hydrogen using a nickelcatalyst, then there is only a single product, U.

Draw the structural formula of each of the compounds Q, R, S, T and U.Explain the reactions.

[7]

[Total: 20]


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Answer one of the following questions. You may choose eitherquestion C2orquestion C3.

C2 (a) Pentan-2-one and pentan-3-one both react with 2,4-dinitrophenylhydrazine toform an orange precipitate.

(i) Write a balanced equation for the reaction of pentan-2-one with2,4-dinitrophenylhydrazine.

(ii) Suggest how the two compounds can be identified by reacting with2,4-dinitrophenylhydrazine.

(iii) Suggest another simple chemical test to distinguish pentan-2-onefrom pentan-3-one. State the reagents you would use, what you wouldobserve and give the structural formulae of all the organic productsformed.

(iv) What type of reaction is undergone when pentan-2-one reacts withhydrogen cyanide, and what conditions are necessary for the reactionto take place? Briefly describe the steps in the mechanism of thisreaction.

[10]

(b) But-2-ene-1,4-dioic acid, HOOCCH=CHCOOH, exists as two stereoisomers.Explain why trans-but-2-ene-1,4-dioic acid has a higher melting point thancis-but-2-ene-1,4-dioic acid.

[2]

(c) Crown ethers were discovered by Pedersen who won the Nobel Prize inChemistry in 1987. Crown ethers are cyclic polyethers with oxygen atomsconnected by CH2CH2 bridges. Three examples are shown below.

12-crown-4 15-crown-5 18-crown-6

The oxygen atoms in crown ethers act as Lewis bases by donating a lone pairof electrons to alkali metal ions to form complexes. The stability of eachcomplex depends largely on the correlation between the internal cavity size ofthe crown ether and the ionic radius of the cation. The table below shows the

crown ethers most suitable to complex with Group I metal ions.

Cation Crown etherLi+ 12-crown-4Na+ 15-crown-5K+ 18-crown-6


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(i) Explain why the cationic radius increases from Li+ to K+.

(ii) Draw a diagram to suggest how an 18-crown-6 molecule can beattached to a potassium cation. Label your diagram to show the typeof interaction involved.

Potassium manganate(VII) does not dissolve in organic solvents. However, inthe presence of 18-crown-6, KMnO4 dissolves readily in benzene, formingpurple benzene.

(iii) Explain why KMnO4 is soluble in benzene only in the presence of18-crown-6.

Purple benzene, in contrast to aqueous KMnO4, readily oxidises alkenes,alcohols and aldehydes to form carboxylic acids with 100% yield.

(iv) Give the structural formula of the product formed when cyclohexene isreacted with purple benzene.

(v) Suggest why purple benzene behaves as a more powerful oxidisingagent than KMnO4 in aqueous medium.

[6]

(d) A Lewis acid is a species that accepts a lone pair of electrons.

(i) In the following reaction scheme, state the reagent that acts as aLewis acid.

(ii) Explain why the reaction in (d)(i) cannot be carried out in an aqueousmedium.

[2]

[Total: 20]


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C3 The use of chemicals has improved the quality of our lives to some extent. However,the improper use of some chemicals can lead to undesirable consequences.

(a) Titanium dioxide (TiO2), oxybenzone, octocrylene and phenylbenzimidazolesulfonicacid are common ingredients found in sunscreens.

oxybenzone octocrylene

phenylbenzimidazole sulfonic acid

(i) Explain why titanium dioxide (b.p 2972 C) has a higher boiling pointthan octocrylene (b.p 218 C).

(ii) An athlete has been training for the Standard Chartered Marathon. Heneeds a sunscreen that is highly water resistant.

Suggest why the sunscreen he used should contain octocrylene, but

not phenylbenzimidazole sulfonic acid.

(iii) Give the structural formulae of the organic products obtained whenoctocrylene reacts with hot aqueous sodium hydroxide.

(iv) Describe a simple chemical test to distinguish between oxybenzoneand octocrylene.

[8]

(b) Melamine is chosen for a self-assembly network which has useful applicationsin nanotechnology.

1,3,5-triazine-2,4,6-triamine(melamine)


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(i) State the type of hybridisation of the circled carbon atom in melamine.

(ii) A molecule of melamine and a molecule of PTCDI attach togetherstrongly via three hydrogen bonds.

Suggest where these three hydrogen bonds would be formed bydrawing the melamine attached to PTCDI in the correct orientation,with the hydrogen bonds connecting the relevant atoms.

perylene-3,4,9,10-tetracarboxylic diimide (PTCDI)

You may use to represent PTCDI.

[3]

(c) There is a recent claim of the discovery of an isotope of a new element withan atomic number of 122. The existence of this new element will require anew block in the periodic table, corresponding to the occupancy of a gsubshell, beyond the s, p, dand f. This gsubshell is predicted to be found inthe 5th shell of an atom, i.e. the 5gsubshell.

(i) Based upon the sequence of subshells in the Periodic Table s, p, d, f,predict how many orbitals there are in a gsubshell.

(ii) Below is a scheme of the 17 lowest energy subshells, which can beused to show the order in which the subshells are filled by electrons(the Aufbau principle).

1s 2s 3s 4s 5s 6s 7s

2p 3p 4p 5p 6p

3d 4d 5d

4f 5f

Predict how many elements there would be in the first row of theg-block.

HN NH

O O

O O

R

R


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(iii) List the order of filling subshells from 4pto 5d.

(iv) The subshells in the scheme above are those that are occupied by theelements up to uranium. List the next four subshells that would beexpected to be filled for element 122.

(v) Write down the number of electrons in the 5g subshell that theelement 122 would be expected to have.

[6]

(d) Tetrachloroethene, Cl2C=CCl2, is a colourless, volatile and non-flammableliquid widely used for the dry cleaning of fabrics.

A sampling was carried out to monitor the current level of tetrachloroethene inthe air of a laundry room to ensure that it does not exceed the PermissibleExposure Limit (PEL) of 100 ppm.

Calculate the maximum mass of tetrachloroethene which can be used in alaundry room which has a capacity of 25.5 m3 at 30 C at a pressure of101 kPa. Assume that all tetrachloroethene vapourises and it behaves like anideal gas under these conditions.[1 ppm (by volume) is equal to 1 m3 of a given gas in 106 m3 of air.]

[3]

[Total: 20]

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2012 Y6 H2 Chem T3 CT Question Paper