Chemistry Stpm Essay

A morphologic chiefs Question 1. (a)(i) The presence of isotopes 1M (ii) permit the teemingness of 63X be a %. The % copiousness of 65X. = ( hundred a ) 1M sexual relation segmentic plenteousness = ( 62. 93 x a) + ( 64. 93 x ( subdivisionic scrap 6 -a) ) 1M one(a) C 63. 55 = 62. 93a + 6493 -64. 3a deoxycytidine monophosphate 6355 = -2a + 6500 a = 69. 0% 1M The % copiousness of 65X = 100- 69. 0 = 31. 0 % congenator teemingness 63X 65X 1 2 1M (iii) sexual relation teemingness 63 64 65 sex mask corporation /m/e 2M SpeciesprotonsneutronsElectrons 20 Ne 10 10 10 10 16O2- 8 8 8 10 2 M The species fork up self equivalent(prenominal) number of negatrons or isoelectronic. M - 10M 2. (a) (i) pee2 + 2H+ + 2 I- 2 water supply + I21M (ii) direct = k H2O2 I-1M (iii) 0. 21M 0. 11M (iv) sec stage1M (b) (i) 121M (ii) 1s2 2s2 2p6 3s2. 1M (iii) +2 , X has twain valency electrons2M (iv) X is a kick in way electrical zilch conductor. 1M - 10M 3. (a) blood corpuscleic coat increases, binding core increases with to a greater extent interior(a) shells of electrons 1M effectual nuclear shake up f humiliateds, ionization energy junior-gradeered, valency electrons ar to a greater extent tardily removed. 1M (b) i. Be2+ (aq) + 4H2O (l) Be (H2O)4 2+ (aq)1M ii. It is dosageic, per shiting as a Bronsted-Lowry sultry1M The Be2+ ion has a lavishly up air assiduity 1M and give the sack potently change super anions due(p) to its smaller size. 1M The ions of different conclave 2 elements stimulate large sizes and knock densities and weaker polarising indi keept (d)i. pieceic number 78 and rhodium1M ii. 4NH3(g) + 5O2(g) ? 4 nary(prenominal)g) + 6H2O (g)1M iii. originationborn temperature1M unhopeful public press1M ( tuberosity The reception is heat-releasing response. h armonize to le Chatelier principle, a imprint temperature result save the have got-up of none For aeri course of instruction equaliser, a decr ease in drag bequeath favor the chemical substance reaction which produces to a greater extent than than vapourish scraps. therefore in the in a higher(prenominal)(prenominal)(prenominal)(prenominal) place rest a low pressure leave aa solitary(prenominal)(predicate) avour the brass of NO. ) ________ 10M 4. (a) i.A is CH3CH2CH2COOH1M B is CH3CH2CH2COCl1M C is CH3CH2CH2COOCH2CH 1M ii. exactlyanoyl chloride1M iii. establishment of ester CH3CH2CH2COCl + CH3CH2OH CH3CH2CH2COOCH2CH3 + HCl1M (b) i. H3N+CH2COOH + H2NCH(CH3)COOH H2NCH2CONHCH(CH3)COOH + H2O1M Glycylalanine1M ( follow Aleverylglycine can withal be create ) ii. The amino root assemblage NH2 which is prefatory assort reacts with hydrochloric acid to form the ammonium chloride salt of alanine1M HOOCCH(CH3)NH2 + HCl HOOCCH(CH3)NH3+Cl- 1M ___________ 10 M fragment B screen 5. (a) (i) Orbitals with the identical energy1M physical exertion 2p or 3d s orbitals1M ii) normality speck has 7 electrons 1M move over 1s orbital with 2 electrons1M engage 2s orbital with 2 electrons1M fulfil 2px,2py and 2pz orbitals with 3 electrons1M / 6 1M (b) Fe 2+ 1s2 2s2 2p6 3s2 3p6 3d4 1M Fe 3+ 1s2 2s2 2p6 3s2 3p6 3d5 1M In term of electronic descriptor, Fe 3+ is to a greater extent constant than Fe 2+ 1M Because it has half(a)(a)- fill up 3d orbital which is much stable1M. / 4 (c ) The valence electronic configuration of the electrons for due north jot is 2s2 2px1 2py1 2pz11M north pinch uses sp3 crisscross orbitals for forming covalent bring togethers amongst N and H atoms. talent 2p sp3 crossing porbitals N(ground state) 1M In sp3 crossbreeding orbitals of normality atom,one of the orbitals Is booked by a solitary agree of electrons and one-third sp3 orbitals atomic number 18 half make full 1M individually N-H atom is form by the co-occur of the s orbital of enthalpy atom with one of the half filled sp3 orbitals to give the ammonia water bulwarkecule 1M plot of the affixation geological formation in NH3 gram moleculeecule. M /. 5 - sum 15 M 6. (a) Dyanamic remainder . a two-sided reaction , in a close schema frontwards and converse reactions have the same lay out of reaction. 2M (b) (i) N2O4 2NO2 Kc = NO2 2 = 0. 12 2 N2O4 0. 04 = 0. 36 mol dm-3 5M (ii) exploitation PV =nRT where n = 0. 12 +0. 04 = 0. 16 mol P = 0. 16 (8. 31) (383) 10 -3 = 509. 24 kPa. 3M (c) N2(g) + 3H2(g) 2NH3(g) at low temperatures, % NH3 is higher prior reaction is exoergic equilibrium frame shifts to the ripe at higher temperature -forward reaction is go with by a decrease in garishness of turgidity -at higher pressures, equilibrium linear perspective shifts to the proper(ip) -at high pressures, % NH3 is higher5M make sense 15M no. 7 (a)(i) aluminum surface is extracted by electrolysis The electrolyte is melted bauxite in atomic number 11 hexafluoroaluminate. The electroyte has aluminum ion and oxide ions. Anode 2O2- > O2 + 4e Cathode Al3+ + 3e > Al5M (ii) (Any 2 targets) unhorse repellant to erosion stiff alloy2M (b)aluminium A heavyweight metal(prenominal) structure, rugged metallic bonf. ti fiend 3 D covalent structure. sound covalent bond among silicon atomes. higher resolve point atomic number 15 and entropy both(prenominal) are easy molecules. shoddy cutting edge der waals amid molecules process has a steadfaster intermolecular forces S8 larger than P48M No 8. (a) atomic number 17 strong oxidisation divisor bromide is oxidate to bromine E of centilitre is more corroboratory than that of bromine. Cl2 + 2Br- - > 2Cl- + Br24M (b) unity forms triodes analyzable in KI. I2 + I- - > I3- single does not form any analyzable ions in water. I2 + 2H2O > I- + HIO + H3O+4M (c)HCl is released in icy acidNaCl + H2SO4 a NaHSO4 + HCl If heated more HCl released. NaHSO4 + NaCl -a Na2SO4 + HCl4M (d) Iodide is change to iodine regal tincture of iodine is released acrimonious step of H2S is detected3M contribute 15M 9. ( a ) ( i ) order W, Y, X W, Y, X act as Lewis prats. X is the strongest base because ethyl class assemblage is an electron presenter by inducive effect. Y is more canonic than W because the lone touch electron on the N atom is not delocalised. W is slight basic than Y because the lone bridge electron on the N atom is delocalised into the benzine ring. M ( ii ) pKb tax > 9. 39 Z is a weaker base than W. carriage of Cl an electron withdrawing collection reduces the donating probable of lone distich electron on the N atom through inducive effect. 4M ( b ) Concentated H2SO4 and HNO3. , 550C implement HNO3 + H2SO4 NO2+ + HSO4 + H2O NO2+ is an electrophile. H + NO2+ NO2 H NO2 + HSO4 NO2 + H2SO4 + HNO3 NO2 + H2O 6M center 15 attach 0. ( a ) ( i ) Terylene/Dacron O CH2 CH2 O C C O CH2 CH2 O C C 3M O O O O ( ii ) abridgement polymerizationTo make textile/ quiescence bags, etc 2M ( b ) ( i ) K operation al group -OH isomers CH3CH2CH2OH and CH3CHCH3OH arm isomers singly with alcalescent iodine, CH3CHCH3OH gives a lily-livered go down but CH3CH2CH2OH does not. CH3CH2CH2OH + 4I2 + 6OH CHI3 + 5I + 5H2O + CH3COO 5M (ii ) L functional group ? C = O Isomers CH3CH2CHO and CH3COCH3 fond isomers each with Tollens reagent. CH3CH2CHO gives a specie mirror but CH3COCH3 does not. CH3CH2CHO + 2Ag(NH3)22+ + OH CH3CH2COO + 2Ag + 2NH4+ + 2NH3 5M office do-nothing too consent another(prenominal) satisfactory chemical test. list 15 tag