STPM Trials 2009 Chemistry Answer Scheme (SMJK Sam Tet Ipoh)

8/3/2019 STPM Trials 2009 Chemistry Answer Scheme (SMJK Sam Tet Ipoh)

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CHEMISTRY PAPER 1

1 B 26 D

2 A 27 C

3 C 28 A

4 B 29 A

5 B 30 A

6 D 31 A7 C 32 B

8 A 33 C

9 D 34 C

10 D 35 C

11 D 36 B

12 C 37 C

13 C 38 C

14 A 39 C

15 C 40 B16 A 41 D

17 A 42 B

18 D 43 D

19 B 44 B

20 A 45 D21 C 46 B

22 C 47 A

23 C 48 C


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Name:

SMJK SAl'" TET IPORCHEMISTRYPAPER 2

Class:

Section A [40 ma rks)An swer all quest ions in this section

1 a. The electron in a hydrogen atom finds Itself In the forth energy level.A radiation with frequency v is emitted when the hydrogen atom re gai nsground state.State,; list of all the orbitals that the electron can po!.sibly ue found whileit is in the forth energy level.4S, 4p, 4d , 4f

li; :;:;.;;w a n ;;r rGW o n the diag(,a, {. LdvoN ~ 1 l 5 0 ; , v w hll-N llh:: Cll.oJfI. 1t:6C1il'!Iground sta te.

Ii) Determine v = cR. (l/n , ' - l/n, ')= 3 .0 x 10' )(1.097 x101' ) (1/1' - 1/4 ' )"l.1,rt"S"

2009 STPM CHEMISTRY TR IAL

n =6

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b. Beryllium chloride, BeCi l,. is an electrondeficient compound. In the gasphase, it exists both as a linear monomer and a bridged dlmer.

(I) Draw a dot and cross diagram to show the electronic structure of the ;monomer of beryllium chloride. Explain why beryllium chloride isconsidered an electrondeficient compound?

empty""",,

It hastwo empty orbitals at thebonding levelfnot achieved octet.

(Ii) Draw a dot and cross diagram to show the chemical bonding of the dimerof beryllium chloride. Predict the bond angle of CIBe-C I.

(iii)= -""""

-,,,,,I ond angle of CI-6e-CI = 20'

Both beryllium and magnesium are group 2 elements. Beryllium chloride,BeCl u melts at 405C and boils at 520C whereas magnesium chloride,714Cand 141rC respectively. Comment and explain on the data.Substance Comments Explanation

MgCI, mp and bp much higher Ionic cpdstrong ionic bond holding the ions

BeCI, mp and bp much lower Cova len t cpdweak IMF holding the molecules

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2009 STPM CHEMISTRY TRIAL Page 2


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2 a. Bromoethane reacts with potassium cyanide in a solution of ethanol andwater. The rate of this reaction was studied and the results are recordedIn the tabl b Ieow.

Experiment (CN'] (C,H.Br] Initial rate(moldm" ) (mol dm:') (mol dm,3,' )

1 0,060 0,020 1,0 x 10"2 0,060 0,040 2,Ox 10"3 0,120 0,020 2,Ox 10'

I} Write a chemical equation for the reaction .

ii ) Deduce the rate equationRate : k [e,H.Br] ' (eN ' ]' wu -[Q...Q2!! )'-xpt 3 - 0,120 - 2,0 x 10": (l!.Qlll ' : 1,Ox l0"Expt 2 0,040 ) 2,0 x 10" y : 1

So,x=l Rat. : k (C,H.Br] (eN ' ]

ii) Suggest a possible reaction mechanism for the reaction .1) c - f ~ C N c - ~ ~ : : : ][ ,B. Jast2J C c - ~ :'CN . . Transition states"'activated compounds"HIH,C-C-CN + fk -IH

2 b. l actic acid, C3H60 3, is a weak organic acid present in both sour milk andbuttermilk. It is also a product of carbohydrate metabolism and is found inthe blood after vigorous muscular activity. Solution 5 is prepared bydissolving 1.00 mol of lactic acid, Hl, and 1.00 mol of sodium lactate, Nal,in enough water to form 550 em3of solut ion. The pH of solution 5 is 3.85.

i) What unique property does solution 5 has?Resist pH change when a small amount of acid or base is added to it,

2009 STPM CHEMISTRY TRIAL

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il) Calculate the H' concentrat ion of solution S.pH - - lg(Hl

3_85 =-lg(Hl(H ' ) =1.41 x 104 mol dm-'

iii) Determine the Ka of lactic acid,pH =pKa -lg(acld)/(sall)since (acid) = sail)pH = Ka = Ig Ka3.85 = Ig KaKa =1.41 x 10" mol dm ,l

Class:

Iv) If a few drops of 0,1 moldm ') hydrochloric acid is added, the pH change insolution 5 is very small. Give exp lanat ion to th is observation ,The conjugate base of lactic acid, L, combines with the added H6 ,and removes pract lcally"all of them

3 a. Refer to the data below for questions 3a(i) - (ii)(I) H,O, +2H ' + 2 . = 2H ,O ~ " , = 1 . 7 7 6 V (II) H,O, + 2. = 2 OH ' " ,= 0.88 V(III) MnO. + 8 H- + 5 =Mn" + 4 H,O '" =1.491 V(IV) MnO' + 2 H,O + 3 e' = Mno, + 4 OH - .. . =O.S88 V

Ii) Identify the strongest oxidizing agen t and the strongest reducing agent.Write an equation for the reaction between the two of them .Strongest oxid ising agent: H10 l in acidStrongest reducing agent: MnOlln alkali


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(II) You wish to build an electrochemical cell that will produce the highestpossible electromotive fore (e.m.f.', tn the space provided, draw a fullylabelled diagram to show the cell that you will set up, Calculate the e.m.f, ofth is cell .

b.

PlatinumH,O, lM

H,SO. O.5M

Predict T.Around 300 c

PlatinumMn04 1MOH ' lM...... MnO '

ii) Exp lain the trend in decomposition by heat for Group 2 carbonates.Go ing down the group, as the size of the cation increases,charge density and polarising power decreases

[4]

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4. p-ionone occurs in oil of violets and is used as a fragrance . Its structure is:CH, CH,

" /C CH,/ " ICH , C-CH: CH -C : 0I ICH, C" / '\.CH, CH,

a. State the type of isomer ism you expect p-ionone to exh ibit?Geometric/cis- trans-

b. Write the structural formula(e,-ofthe product(s) formed when ~ - o n o n e reacts withI} Brom ine in eCI"CH, CH ,

CH,// C " er/C- CHBr -CHBr C:OICH ,I ICHZ / c , er

CH , CH ,

if) 2,4-dinitrophenylhydrazine

CH,ICH , C-CH : CH - C:I ICH, C" / '\.CH , CH ,


NH

~ ( " )

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iii) li thium aluminum hydride (lIA IH ,, ) in etherCH, CH," /C CH,/ "- ICH , C-CH = CH - CHOHI I

CH, C"- / "-CH, CH,

c. Name the type of reaction ini) 4b( i)

Electrophilic add itionii) 4b(ii)

Condensation

d. Triodome thane (iodoform) test is carried out on fH onone.I) Describe how you would perform the test .Add Iodine solut ion In aqueoussodium hydroxideWarm/heat

ii) You expect to see positive resu lt in this test. Give a reason .Presence of R structure

ICH , - C = 0

2009 STPM CHEM iSTRY TRiAL

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SECTION B [ANSWER]S a C, H,O could be CH,CH ,CH ,OH / CH)CH(OH)CH,f HsC,- 0 - CH,

Mass spectrum m/e 17 is characteristic of presence of group/alcoholNegative iodoform test means absence of CH1CH(OH) st ructureP is CH,CH , CH ,OH/l-propanolIdeal gas:pV = RT ie" p = (RT/M,)pIp = onstantCO z:At moderately high pressure, attract ion between molecules ex istsGas volume Is smaller than expectedp is higher than ideal caseAt high pressure, repulsion between molecules occurs and volume of gasparticles not negligible.Gas volume Is bigger than expectedand p Is lower than ideal case

c Planar and 120 C bond angles indicate both Cand N atoms undergo spzhybridisationC(ground state): 152 2s22p/ 2p, / 2pzOC(excited state}: 1$2 2S12Px! 2Pyl 2p/

p'O(ground state) : 152 2S22P..z 2p/ 2p/ and H(ground state): 151C, N, 0 and H atoms combine and delocalization of 2pzelectrons of neigbouringatoms happens as shown

2pz 2pz ora 2 a q ) + 20H"(aq )7 Mg(OHh(s)

NH , (aq) + H,O = NH.' (aq) +OH "(aq)NH 40 solution causes Increase In [NH41Equilibrium sh ift s LEFT and {OH '1 decreases[Mg'J[ OH "]'


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b The entha lpy change when 1.m.2l.t of octane is formed fromhydrogen elements under standard conditions.

IAI C(s) + O, (g) CO , (g) -393 kJ mar'11 H, (g) + ) \ O, (g) H,O (I) -285.63 kJ mar'IQ C, HII(I) + 25/2 O,(g) 8CO ,(g) + 9 H, O (I) -5512 kJ mar'

8(A) + 9(8) - (C) :8C(s) + 9H , (g) C, HII(I) 6H ' ,

6H' , =8(-393) + 9( -285.6) - (-5512)= - 202.4 kJ mor l

c Energy / kJ mor lBb IF) C! (gl I 3491 b ' (s) + cr (s)i 122Rb' (g) + )\ CI , (g)r+403I Rb (g) + )\ CI, (g)+81Rb (s) + ].I CI , (g)

1-35RbO(s)6H ' " = -435 - 81-403 -122 + 349

= - 692 kJ mor l

u smaller sizeStronger attraction/bonding

a i) Ionisation energy IncreasesData from data bookletatomic size decreasesEffective nuclear charge increases /

ILabeled y-axis andEnergy levels = 1All 6 steps correct =Some steps (u(,a t = 1

nuclear charge increases but screening effect remains almost constant.II) From bas ic to amphoteric to acidic

Nal O and MID are Ionic oxidesAhDJ Ionic with covalent characterSiOz, P.010 510 1 and SIDJ are covalent oxidesEquations (each type at least one)



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b i) Let x be solubilitiy In mol dmoBaF, (5) Ba ' (aq) 2. (aq)x x 2xKsp ' [sa'1[ . ) '

x(2)


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Co N CI : H= : Zl!.l!!L : 2.2258.9 14.0 35 .5 1.0= 0.3993 : 2.0 : 1.1980 : 5.95

: 5 : 3 : 15Formula of H: Co CI , (NH,) . / x=3 and V=5

Ag (aq) + CI ' (aq) AgCl (.)CI ' " AgCI12.52 g H - -- 14.35/143.5 mole AgCl

Class:

250.4 g H(1 mole) ---- (250.4/12.52)(14.35/143.5) =2 mole1 mole H has 2 moles free chloride ionsstructural formula of HI. (Co CI (NH,).]'. 2 c,/ (Co CI (NH,) . ]C,H Is coloured.Co' : (Ar]3d'3d orbital. are ~ f i l 1 e d Under the influence of lipnds, the 3d orbitals are split into 2 groupsd-d transition happens

a W: 2-chloropropan-l-olIICH, - f-CH ,OHCIX:ItCH,- C-COOHb

V:

Z: fOOHCOOHItCH, - f - COO -+ 41, + 60H' CHI, + -OOC-(OO-+ 51' + 5H,0OHY

-OOC-COO ' + 2H" ~ O O H 2009 5TPM CHEMI5TRV TRIAL Page 15


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COOHZ

~ ~

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CH,- f - COOH + ZOW 7 CH,- F coo + C' + H,OC OH

YIiCH,- f-CH,OH+Z[O) 7 CH,- F-COOH + H,Oa aw xI) Mechanism

1) CHJ CHzBr+AIBrJ 7 AIBr4 +CH1CHz

Z) + CH, CH,' 7 :H ' CH'3) AIBr4+ H 7 AIBrJ + HBr

rAr ' CH, CH,7 g +H '

b ii)Temperature! c

1,1

labeled alCes =labeled curves =

100 60 0% Ethylbenzene1. The liquid mixture of composition C1 The vapour given off ascendsthe column and condenses Into liqyl d with composit ion ez.2.liquld of composition Czboils at Tl' The vapour given off ascends the columnand condenses into liquid with composition C .3. The process repeats and the mole fraction (" ) of benzene Increases going upthe column. Eventually, pure benzene distills over it S the first dlstlilate.4. As more and more benzene distills over the liquid remaining in the flask getsricher In ethyl benzene.S. Eventually, only pure ethylbenzene is left In it and will be distilled over at itsboiling point

10 a i) Add a few drops of water to each sample.2009 STPM CHEMISTRY TRIAL Page 16


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Only ethanoyl chloride produces white fumes .CH,COa + H,O 7 CH,COOH + HCI (White fumes)

dass:

ii) Add NalC03(or NaHC03) to sample and deliver gas produced into lime wa ter.Only f 3H1 has effervescence and gas produced turns lime water milky.C O

C O + Na ,CO , 7b i) CH ,COCI

anhydrous Aiel , Conc . HNO, andConc. H1S0 4@lQ\o

ii) a CH '0 CH ' MBCIiii)o

Room temperature

SnCone . HO

a,sunlight

1. CH,CHO2. Dilute Hd

Cone . KMn04Warm

Nylon-4,S


NH ,

Scheme = 1Reagents = 1COndit ions = 1

o CH ' CI _ _M.:g.i_"_e_t_h_e ..HOOqCH, hcOOH

Scheme =Reagents =1COnditions =

Scheme = 1Reagents = 1Cond itions = 1

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STPM Trials 2009 Chemistry Answer Scheme (SMJK Sam Tet Ipoh)