stpm trials 2009 chemistry answer scheme (smi ipoh)

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S.M.K. ST. MICHAEL IPOH STPM TRIALS 2009 CHEMISTRY PAPER 1 (ANSWERS) 1 B 26 A 2 A 27 C 3 C 28 D 4 A 29 B 5 D 30 B 6 B 31 C 7 B 32 C 8 C 33 C 9 B 34 D 10 A 35 B 11 C 36 B 12 B 37 B 13 D 38 C 14 D 39 B 15 B 40 A 16 C 41 D 17 C 42 D 18 A/C 43 B 19 C 44 A 20 C 45 B 21 A 46 B 22 C 47 D 23 D 48 D 24 B 49 A 25 C 50 A SMK St. Mich:l el, IpOh Name: 2009 Trilll ex:lIl1inatiun : pg I 19 Class: ST. MICHAEL'S INSTITUTION, IPOH 2009 TRIAL EXAMINATION CHEMISTRY PAPER 2 TIME: 2 y, HOURS Instructions to candidates : Answer ALL the questions in Section A in the spaces provided. All work ing MUST be shown. For numerical answers, units MUST be quoted where they are appropriate. Answer any FOUR questions from Section B. For this section, wr it e your answers on test pad papers provided. Begin each answer on a fresh sheet of paper and arrange your answers in numeri cal order. Tie your answer sheets to this booklet. A Data Booklet is provided. Section A [40 marks] Answer ALL the questions in this section. I. (a) Arrange the elements (i) in the Third Peri od of the Periodic Table in the order of decreas ing atomic radius, Na , Mg , AI Si , P , S CI , Ar ./ ( ii) of chlorine, bromine and iodine in Group 17 of the Periodic Table in the order of increasing fi rst ionisat ion energy. I Be . CI,( NOT I, Be, CI, [2J (b) Draw the Lewis structure and state the l?eomet -v for the SF, molecule and the 13 - ion. SF6 molecule 13 - ion Lewis stnlcture Lewi s structure F F ., ., [ .. " .. r : I : I , I : F S F , , .. xx xx .. .. .. . , , . ,( F F MUST show with different dot for the e -.. .. received ,( GeometrY: octahedral ./ Geometry: linear -/ (c) State why (i) SF, is used as an insulati ng gas in high voltage electric appliances, SF, is chemically inert-/ (ii) SI6 do not exist, Due 10 the steri c hindrance./ and because the $- 1 bond is weak. hence making SI6 unstable ./ (iii) h - and Br3 - ions exist but.F3 - ion does not exist under normal conditions. TIle repUlsion between the lone pair of electrons on adjacent fluorine atoms makes [4J the F 3 - unstable ./ [4] SMt< St. Michael. Ipoh 2009 Trial examination: pg 219 2. (a) p and Q ions are isoelectroni c with Ihe X isotope. (i) Identify P and Q ions. P has 19 e, P = K, p . = K ( ii ) Elements P and Q form an ionic compound PQ. The enthalpy changes involved in the formation of thi s compound under standard conditi ons are as follows. P (s) --> P (g) y, Q, (g) --> Q (g) P(g)--> p ' (g) + e Q (g) + e -->Q- (g) p (s) + y, Q, (g) --> PQ (s) b. HO::: + 77 kJ ,,11' = + 121 kJ "H' =+ 4 19kJ "He = _ 349 kJ ,,11' = - 436 kJ Write equation whi ch represents the lattice energy of compound PQ and calculate the value of the lattice energy. - 436 P (s) + y, Q, (g) --> PQ (s) l+77 l+121 P (g) Q (g) Ll H laC! 1+419 1-349 P , (g) + Q - (g),- ----" Equation , P ' (g) + Q - (g) --> PQ(s)./ - 436 = + 77 + 4 19 + ! 21 - 349 + b.H lall ./ b. H lall = - 704 kJ ./ (with unit and negative sign) (b) Carboxylic acids are organic acids obtained from plants and animals. The structural formu lae of four carboxylic acids are given below. CH,COOH , @-eOOH , O,[email protected] [email protected] (i) [2] [3] Arrange the acids in the order of increasing acidity, CH,COOH < @-eOOH < O,[email protected] < [email protected] ./ Oi) Which of the above acids has the strongest conjugate base? CH)COOH ./ (iii) State the effect group on the acidity of Presence of the -NOz group will increase the acid strength ofthi s compound ./ -NO} , an electron- withdrawing group ./ helps to withdrav .. ' electrons from the O-H bond in thc-COOH group making the O---H bond easier to break./, OR -N02 an electron- withdrawing group./ will disperse the negat ive charge on the carboxylate ion, -COO ./ thus stabilises the carboxylate ion [5] SMK St. Mi chael. Ill oh 2009 Tri:. 1 exa rnin ali on : Ilg 3 / 9 3. (a) The tetrachl orides of Group 14 elements, example CCI.1, SiCI4 GeCI4 SnCI4 and PbCI4 are liquids at room temperature. All the tetrachl orides, wit h the exception of CCI-, , are hydrolysed in aqueous solution to form acidic solut ions. ( i) State the molecul ar shape of all the Group 14 tetrachlorides. Tetmhedral ./ (ii) Wri te a balanced equation for the hydrolys is of SiCI4. S;CI, (I) + 2 H,O (I) -----> S;O, (s) + 4 He l (g) ./ (iii) Explain why C C I ~ does not undergo hydrolysis. has the electronic configuration of I s22s22p2 ./ does not have empty d orbital s, cannot expand its valence ./ OR cannot fonn the inrermediate coordinate bond wit h the water molecule (b) Aqueous aluminium sulphate contains [AI(H20)6]1'. Aqueous ammonia is added to aqueous alumi nium sulphate unti l in excess. The reaction that occurs in limited aqueous ammonia is as foll ows. [AI(H,O).)' (aq) + 3 OH - (aq) ) AI(H,O)J(OH), (s) + 3 H,O (I) (i) Descri be one observation in the above reaction. A white precipitate is formed ./ (ii) What chemical nature of the aluminium ion is shown in (a) (i) ? Acidic in nature ./ (ii i) What happens when excess aqueous ammonia is added to the solution ? Write an equati on for the reaction invol ved. The white precipitate is soluble in excess aqlleous ammoni a ./ and form a colourless solut ion ./ ) [AI(H,Oh(OH),1 - (aq) + H,O (I)'" (tv) What chemical nature of the aluminium iOIl is shown in (a) (iii) ? Acidic in nature ./ 4. (a) Ethylamine, C1HsNHl is a foul smelling liquid that reacts with dilute hydrochloric acid at room temperature. ( i) Write a balanced equation for the reaction between ethylamine and dilute hydrochl ori c acid. C21"I,NH2 + HC1-- C2HsNH) .. CI - ./ (ii) Name the type of reaction taking place between ethylami ne and dilute hydrochloric acid. Neutrali sati on reaction . ./ (iii) State two observable changes for the reaction between elhylamine and dilute hydrochl ori c acid. The fi shy smell of ethylamine disappears . ./ Temperature of mi xture rises ./ as heat of neutrali sation is li berated [41 (6) (4) SMK St. Michel, Ipoh 2009 Trial examination : pg 4 / 9 (b) State Ihe reagents and wrile balanced equJli ons ror the preparation of ethylamine from the foll owing compounds. (c) ethanol cone. in excess ./ ethanol (ii) CH,CN CHlCN + 2 H! ----- ./ CHjCH2NH2 ./ 180 C Aspirin has the foll owing structure. o I I :(O-- H,O (ag) 2 H,O (I) + 2. ---> H, (g) + 2 OH - (ag) Cu" (ag) + 2. ---> Cu (s) - (I) - (2) - (3) At anode, NO]- can't react as reducing agent./ E' = + 1. 23 V E' =- 0.83 V EO = + 0.34 V H20 reacts as reducing agent and is oxidised to O2 ./ O2 gas is liberated H,O (ag) ---> y, 0, (g) + 2 H (ag) + 2e ./ At cathode, E O ofCu2+ I Cu is more positive than that of H20 I OH - ./ :;:::) Cu2" is a stronger oxidising agent than H20 Cu2" is chosen to be reduced to reddish brown copper METAL ./ Cu2 (aq) + 2e Cu (s) ./ ./ [4] [6J SMK St. Michael, Ipoh (e) CI CI x X AI X X CI CI CI X AI X CI 2009 Trial elimination : pg 6 / 9 AI : 2.8.3, Is2 2S2 2p6 3s2 3pt C1 : 2.8. 7, Is2 2S2 2p6 3s2 3ps AbCI6 forms di mer with sharing electrons with CI atoms ./ AI has empty p orbitals to receive the lone pair of electrons from CI atom ./ 2 coordinate bonds are formed ./ Each atom achieved the stable noble gas max diagram ./ configurat ion./ [4} 7. (a) ( i) ( ii ) The graph shows a minimum boil ing point .:::::> a maximum vapour pressure PT > P A + Ps calcul ated from Raoult's ./ Positive deviat ion from Raoult' s law ./ 100 "' __ T, Boi ling point I C 78.1 o 12 C, 96 100 Composition of ethanol Whet! the mixture wit h the composition of 12 % of ethanol is di slilled, the mixture will boi l at Tt ./ The vapour produced with the composition of C2 is richer in ethanol . ./ When this vapour is condensed, the composition of the liquid obtained is the same as the compos ition of its vapour, C2 . ./ If t he vaporisation and the condensation processes are repeated, the disti llate produced at 78. 1 C is an azeotrope I azeotropic mi xture . ./ The res idual liquid in the distillation flask is pure water and evenlUally distilled over at 12J 100 C . ./ No ethanol will be obtained. [5] (b) (i) White fumes of He l arc given off and white precipitate of 8e(OH)1 ./ is formed BeCl, (s) + 2 H, O (I) ---> Se(OH), (s) + 2 HCI (S) -' Be(OHh dissolves in excess NaOH to produce a colourless solution ./ Be(OH), (s) + 2 01-1 . (aq) ---> [Be(OH), J' (aq) -' : .. JJ:k (i i) Yell ow precipitate of silver R-itmte./ is formed, does not dissolve in ammonia aqueous ./ AS' (aq) + I . (aq) ---> AgI (5) -' (c) CO2 s imple covalent molecules./ Weak Van der Waal's forces between molecules ./ 8. (a) (i) All Group 2 elements react with water to form their respective hydroxides with the liberation of hydrogen ./. M (5) + 2 H,O (I) --+ M(OHh (aq) + H, (S) -' The reactivity increases due to the increase in the reducing strength of the metals ./ (ii) Nitrates of the Group 2 elements dissociate to respective metal oxide when heated 2 M(NO,), (s) ---+ 2 MO (5) + 4 NO, (g) + 0 , (g) -' " Down the Group The cationic size of M2+ 't, the cationi c charge density J.. ./ The polarising power of the cation J.. ./ The thennal stability ofthe nitrates 't ./ max 13J (3) (2) [3J [4) ,sMK.st. Michael, Ipoh 2009 Trial uamination : pg 7 / 9 9. (5J (2J (2J (2J [2J