Bukit View Prelim Ans

Bukit View Secondary School PRELIM 2024 – Chemistry 4 E Pure Chemistry Mark Scheme 1 P1 Qns 1 2 3 4 5 6 7 8 9 10 Ans B D B A B C B A A C Qns 11 12 13 14 15 16 17 18 19 20 Ans B C A B C D D C B D Qns 21 22 23 24 25 26 27 28 29 30 Ans C A D B C D C C C C Qns 31 32 33 34 35 36 37 38 39 40 Ans C A A B D C C B B B MCQ analysis: 1 Qn did not mention speed of reaction or loss of mass to record volume of gas 2 Liquids – no need mp, 3 A, C and D wrong from graph 4 Solid sodium chloride is soluble, filtration is for insoluble solid 5 Bp of water 100 deg, anything above cannot be boiled to vapour 6 Mr NH 3:17, Mr N2:28, 7 1 X: 19 p 18 e 21 n 2 Y: 19 p 19 e 20 n 3 Z: 16 p 18 e 18 n 8 Since only part of the substance reacts with acid, it must be a mixture. Iron would completely react with acid, given enough time. Since the entire substance conducts electricity, it must be a mixture of metals. Brass is the best answer. 9 R+ : Q- 8 : 4 2 : 1 10 Graphite – only 3 bonds occupied, Graphene – all bonds occupied – no delocalised e, Graphene – layered structure similar to graphite – soft than diamond 11 Y from group 16 – proton numbers in group 16 12 Co: NH 3 36.6/59 : 63.4/17 1 : 6 13 Convert to mol  multiply 6.02 x 10^23 H2: 1 mol, Ne: 0.2 mol, O2:0.25 mol, CO2:0.5 mol 14 20 dm 3 H2 needs only 20 dm3 Cl2, hence 10 dm3 Cl2 excess + 40 dm3 HCl 15 Mol water = 27/18 = 1/5 mol Mol pure NH4NO3 = 0.75 mol , mass NH4NO3 = 0.75 X 80 = 60.0 g 16 80% - 60 100% -75 g calculated mass Mol urea – 75/60 = 1.25 mol, mol NH3 = 2.5 mol , mass NH3 = 42.5 g

Bukit View Secondary School PRELIM 2024 – Chemistry 4 E Pure Chemistry Mark Scheme 2 17 Max temp reached is where acid has been neutralised. Take volumes from this temp. Mol H2SO4 = 0.03 mol, mol NaOH reacted = 2 x 0.03 = 0.06 mol, conc NaOH = 3mol/dm3 18 Strong acid, completely ionise – A,B wrong, D- depends on amount of water 19 Sulfur dioxide formed dissolves in water for form acidic solution. 20 Acidic and amphoteric oxides react with bases 21 Conductance depends on mobile ions, K has high conductance, temperature change same – both neutralise sodium hydroxide, K reacts rapidly with Mg 22 Zn + Cu(NO3)2  Zn(NO3)2 + Cu [displacement], B,C & D no reactions 23 White ppt with aq ammonia soluble – Zinc Blue ppt forming dark blue sol with aq ammonia – Cu 2+ 24 Cl (0) in Cl 2 to Cl (-1) in NaCl and Cl (+1) in NaOCl 25 A: H + and Cl- discharged, NaOH – more alkaline B: Cu2+ and OH- discharged , H2SO4 – more acidic C: Cu2+ discharged and released from electrode – no change D : H+ and OH- discharged, becomes more conc NaCl 26 Need mobile ions/ electrons/ more & less reactive metals connected 27 Zn 2+ + 2e  Zn (s) 1 mol 0.5 mol Crx+ + xe  Cr (s) 1mol 0.2 mol 1/0.2 = 5 28 Most reactive: U, V, Fe, W Least reactive 29 P>Q 30 Charge from group no., acidic / basic from LHS/RHS of PT 31 Excess bromine, KBr, I2, unreacted KCl 32 Pb> D, D > Cu, Pb> Cu 33 More energy released in forming bonds than breaking bonds 34 Hydrogen as fuel, oxygen as oxidiser, pure water is the product, oxygen is reduced 35 Endothermic  energy from surr 36 Increase speed and amount of reactants 37 M: C 3H8 + F2  C3H7F 38 20.32 g Iodine  20.32/ 254 =0.08 mol I2 0.08/0.02 = 4 mol C=C 39 CH 3 and Cl on diff C atom 40 propanoic acid-C3H7CO2C2H5 – ETHANOL

Bukit View Secondary School PRELIM 2024 – Chemistry 4 E Pure Chemistry Mark Scheme 3 P2 Section A A1 (a) Any two from: Glycine/ alanine/ serine 1 (b) (8400/42) x 3= 600 1 (c) 1 correct amide linkage 1 correct sequence 2 (d) Calculate Rf value of current substance and compare with known value 1 A2 (a) pentene 1 (b) Compound 2 and 3 have the same molecular formula of C5H10 but different structural formula. 1 (c) Or 2 (d) divide by relative atomic mass / calculated mole ratio C : H : O 5.175. : 10.3 : 1.725 divide by smallest number to get ratio C3H6O 1 1

Bukit View Secondary School PRELIM 2024 – Chemistry 4 E Pure Chemistry Mark Scheme 4 A3 (a) experiment 1: positive electrode : 2Cl- (aq)  Cl2 (g) + 2e- negative electrode: Na+ (aq) + e-  Na (l) experiment 2: positive electrode: 4OH- (aq)  2H2O(l) + O2 (g) + 4e- negative electrode: Cu2+ (aq) + 2e-  Cu (s) 1 1 1 1 (b) hydrochloric acid As the copper and hydroxide ions are preferentially discharged, the remaining ions are hydrogen and chloride ions. 1 1 (c) The electrode at positive terminal dissolves and decreases in mass/ colour of solution remains unchanged/ blue. Copper being reactive oxidises to form copper(II) ions. 1 1 A4 (a) To reuse the unused reactants to minimise cost of production To increase the rate of reaction to produce ammonia/ increase yield of ammonia 1 1 (b) Nitrogen / hydrogen can oxidise to form oxides of nitrogen/ water 1 (c) As pressure increases, rate of reaction increases, increasing the amount of ammonia produced At higher pressure, there are more nitrogen and hydrogen molecules per unit volume/ molecules are closer together increasing the frequency of effective collisions. 1 1 1 A5 (a) C6H12O6  2 C2H5OH + 2CO2 1 1 (b) Yeast, 37°C , Absence of oxygen 1(ALL) (c) Ethene obtained from crude oil/ fossil fuel is a finite resource/ run out/ non-renewable Glucose obtained from plants so continuous supply/ renewable/ will not run out 1 1 (di) Ethanoic acid 1

Bukit View Secondary School PRELIM 2024 – Chemistry 4 E Pure Chemistry Mark Scheme 5 (dii) 1 A6 (a) 2NaClO3 + (COOH)2 + H2SO4  2ClO2 + Na2SO4 + 2CO2 + 2H2O 1 (b) Mol NaOH = 14/1000 x 0.100 =0.00140 mol Mol (COOH)2 = In 25.0 cm3 : 0.000700 mol In 1 dm3. : 0.028 mol Mass of hydrated oxalic acid = 0.028 x (90+36) =3.528 g % purity= 3.528/5.00 x 100% =70.6 % 1 1 (1 dm3) 1 (c) Repeat experiment without indicator Using same volume of acid to neutralise the alkali. 1 1 A7 (a) Mass of iron decreases as reaction proceeds Solid iron reacts with bromine to form aqueous iron(II) bromide 1 1 (mention change in solid to aq) (b) Increases the frequency of collision between particles Hence increases rate of reaction 1 1 (c) Mol Fe = 8.4/ 56 =0.15 mol Mol Br = 4/1000 x 0.05 = 0.0002 mol Fe : Br 1 : 1 For 0.0002 mol of Br, only 0.0002 mol of Fe is required. Enthalpy change per mol = - 250 kJ Enthalpy change 0.0002 mol = - 0.05kJ 1 – calc mol 1 – limiting 1 - enthalpy A8 (a) Lithium loses 1 electron to form positively charged lithium ion & Chlorine gains 1 electron form negatively charged chloride ion To obtain noble gas configuration 1 1 (b) Radius of lithium atom decreases when it forms ion Lithium loses 1 electron shell when it forms an ion 1 1 (c) No visible reaction/ Solution remains red-brown/ reddish brown. Bromine is less reactive than chlorine. 1 1

Bukit View Secondary School PRELIM 2024 – Chemistry 4 E Pure Chemistry Mark Scheme 6 A9 (a) More energy is given out when bonds are formed in NO and H2O in stage 1 compared to energy given out for bond formation of HNO3 in stage 2 OR More energy taken in to break bonds in stage 2 for NO, H2O, O2 than energy taken in when bonds are broken in stage 1 for NH3 and O2. 1 (b) Nitric acid gas molecules diffuse from a higher concentration to a lower concentration where the blue litmus is located turning the damp blue litmus red 1 1 (ci) When air/petrol ratio increases, concentration of CO decreases as More complete combustion takes place when more oxygen is available 1 1 (cii) 2NO + 2CO  N2 + 2CO2 1 (d) 2 ozone molecules can be destroyed when one NO reacts in eqn 1 through formation of NO2 which regenerates NO and repeats the dep