VS 2022 O Level Pure Chemistry P1+P2 Answer Scheme

2022 Answer1 Victoria School2022 Chemistry O Levels / 6092Suggested Answer Key PAPER 1Q1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Q15Q16Q17Q18Q19Q20AACBBDDDCCCBDDADABCCQ21Q22Q23Q24Q25Q26Q27Q28Q29Q30Q31Q32Q33Q34Q35Q36Q37Q38Q39Q40ADBAADDDABCCCDBBBBAAPAPER 2 (SECTION A)QuestionAnswerMarkA1aM 1bR 1cMQ3 1dT 1eQ and Z1fRQ4 1A2aThe perfume molecules/particles are always in random motion and will diffuse from a region of higher concentration to a region of lower concentration.1bThe particles must be packed closely together and in disorderly arrangement.The label “a few seconds later” should be changed to a few minutes/hours later.11cThe distance moved by the ions in beaker B will be larger than that in beaker A.Since the water in beaker B is at a higher temperature of 30 C, the ions will gain more heat from it and hence possess higher kinetic energy resulting in higher rate of diffusion.11

2022 Answer2 The distance moved by V2+ ions in beaker C will be larger than Cu2+ ions in beaker A.V has an Ar of 51 while Cu has an Ar of 64. V2+ ions will diffuse faster due to their lower mass and cover a larger distance in the same amount of time.11A3acarboxylic acidalkenealcohol1biAdd aqueous brominechanges reddish-brown bromine to colourless11biiB is a weak acid which dissociate partially when dissolved in water to produce a low concentration of H+ ions.1biiiD will be oxidisedto form ethanoic acid.11cielementCHOmass per 100 g / g40.06.753.3amount / molmole ratio3.33 ÷ 3.33 = 16.7 ÷ 3.33 = 23.33 ÷ 3.33 = 1empirical formulaCH2O 111ciiCompound BCompound B has molecular formula C2H4O2/the ratio of C:H:O is 1:2:1.1A4ahalogencolour and state at room temperature and pressurechlorineyellow green colour and gaseous statebrominereddish brown colour and liquid stateiodinepurple black colour and solid state colour [1]state [1]biThe reactivity of the halogens decreases down the Group. (must state but no mark)Chlorine, being placed on top of bromine and iodine, is the most reactive as it can displace both bromine and iodine from their respective halide solutions.Bromine, being placed below chlorine but above iodine, is less reactive than chlorine and hence unable to displace chlorine from the chloride solution, but more reactive than iodine and hence can displace iodine from the iodide 11

2022 Answer3 solution.Iodine, being placed below chlorine and bromine, is the most unreactive as it neither displace chlorine nor bromine from their respective halide solutions.biiIn A, aqueous bromine has displace iodine from aqueous iodide forming the brown aqueous iodine.In B, aqueous iodine is present and did not undergo any reaction.1cThe fluorine molecule gains two electrons readily during chemical reactions and is reduced to two fluoride ions.1diAlthough the Cl atom reacted with the O3 molecule to form ClO, the ClO reacts with another ozone molecule to form back Cl atom. Hence, the Cl atom remains chemically unchanged at the end of the reaction.1diiCl atoms will react and break down O3 molecules repeatedly in the presence of UV light, causing ozone depletion.This will allow more harmful UV radiation from the sun to enter the atmosphere and cause skin cancer or eye damage.11A5a2H2 + O2  2H2O 1bSince 2H2  O2, volume of O2 needed = 500 ÷ 2 = 250 cm3volume of air needed = 11cAqueous potassium hydroxide contains free mobile ions but not water which consists of neutral covalent molecules.1d Ea(1)energyhydrogen and oxygenEa(2)Hwaterprogress of reactionproduct [1]Ea(1) [1]Ea(2) [1]H [1]A6aHeat the solution in a beaker.This will remove the water in the solution thereby causing the solution to become concentrated.11bi(NH4)2SO4 + O2  N2 + 4H2O + SO2 formula [1]balancing [1]biinitrogen: -3 to 0sulfur: +6 to +411cmanufacture of detergents/fertilisers1

2022 Answer4 dBecause large amount of energy is required for heating in process 2, the processes do not follow the principle of using minimum amounts of energy.Both processes 1 and 2 use ammonium sulfate waste. Process 2 uses oxygen from air which is renewable. Hence both processes follow the principle of using raw materials which are renewable or use waste from other processes.Process 1 produces only water while process 2 produces water and nitrogen, which are all harmless.111PAPER 2 (SECTION B)QuestionAnswerMarkB7aBoth LDPE and LLDPE contain side chains that are made up of only carbon and hydrogen atoms.However, LDPE contains side chains that have more than one carbon atom while LLDPE contains side chains with only one carbon atom. 11bEmpirical formula for LDPE is CH2.For LDPE with 4000 carbon atoms:Total molecular mass = 4000 x 14 = 56 000Total mass of 1 mol of LDPE = 56 000 x 1 = 56 000 gTotal mass of 1 molecule of LDPE = 56 000 ÷ (6 x 1023) = 9.33 x 10-20 gFor LDPE with 40 000 carbon atoms:Total molecular mass = 40 000 x 14 = 560 000Total mass of 1 mol of LDPE = 560 000 x 1 = 560 000 gTotal mass of 1 molecule of LDPE = 560 000 ÷ (6 x 1023) = 9.33 x 10-19 gRange between 9.33 x 10-20 and 9.33 x 10-19 g 111ciLDPE and LLDPE have side chains to push the polymer chains away from each other while HDPE has no side chains. Hence, HDPE polymer chains can be arranged closer together with more molecules per unit volume, making it more dense. 11ciiLDPE has more side chains than LLDPE and HDPE, hence LDPE has a lower softening temperature and is weaker than the other two polymers.Thus, it is less suitable to be used as building materials, packaging or hot drinks containers. 11

2022 Answer5 diCCHCH3CCHCHHCCH2HHHHHHH 1diiCH3 CHHCCH2HCH2CH2CH3CHHCCH2H 2B8aLithium and beryllium tend to lose electrons to form positive ions and ionic compounds, hence the elements show metallic properties. From boron to fluorine, the elements tend to share electrons with other non-metal elements to form molecules and covalent compounds, hence the elements show non-metallic properties.Neon does not react with other elements to form compounds as it is stable and has a completely filled valence shell of electrons. 111bLithium has a giant metallic structure with metallic bonds between valence electrons and positive ions. A moderate amount of energy is needed to overcome the metallic bonds.Graphite has a giant molecular structure with strong covalent bonds between atoms. A large amount of energy is needed to overcome the strong covalent bonds.Oxygen has a simple molecular structure with weak intermolecular forces of attraction. Little energy is needed to overcome the intermolecular forces of attraction.As more energy is needed to overcome covalent bonds in graphite than metallic bonds in lithium, which in turn requires more energy to overcome compared to intermolecular forces of attraction in oxygen. 111

2022 Answer6 Hence, graphite has a very high melting point, lithium has a low melting point and oxygen has a very low melting point.The mobile valence electrons in lithium and graphite allows them to conduct electricity.Oxygen is unable to conduct electricity as it does not contain any mobile charged particles. 11EITHERB9aAnode: 4OH-  O2 + 2H2O + 4e-Cathode: 2H+ + 2e-  H2In both experiments, reactions at both electrodes are the same.In both experiments, hydrogen ions are preferentially discharged over sodium ions as hydrogen ions gain electrons more easily than sodium ions to form hydrogen gas.In experiment 2, hydroxide ions are preferentially discharged over chloride ions as hydroxide ions lose electrons more easily than chloride ions to form oxygen gas.In experiment 1, only hydroxide anions are present and hydroxide ions are discharged to form oxygen gas.Therefore, the ratio of the volume of gases collected is the same in both experiments.As the same number of moles electrons are involved in the reaction at both electrodes, double the number of moles of hydrogen gas is formed compared to oxygen gas. Hence, double the volume of hydrogen gas is formed compared to oxygen gas.111111bIn experiment 3, chlorine gas is produced at the anode instead of oxygen gas.In both experiments, hyd