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Name: ……………………………………………………………………………………….Class: ………… Adm.No. ……………School: ………………………………………………………………………………………Index No. ………………………………..Date: ……………………………………… Sign:………………………………………..233/2CHEMISTRYPaper 2JULY 2019Time: 2 hoursM O K A S A II J O I N T E X A M I N A T I O N Kenya Certificate to Secondary EducationCHEMISTRY PAPER 2TIME: 2 HOURSINSTRUCTIONS TO CANDIDATESWrite your name, admission number, date and school in the spaces provided. Answer all the questions in the spaces provided.All working must be clearly shown where necessary.Scientific calculators may be used. FOR EXAMINERS’ USE ONLYQuestionMaximum ScoreStudent’s Score11221031041151069778111.Study the table below and answer the questions that follow.ElementAtomic numberRelative atomic massMelting point (0C)Aluminium1337.0Calcium2040.0850Carbon12.03730Hydrogen1.0-259Magnesium1224.3650Neon10-249Phosphorus1531.044.2 (white)Phosphorus1531590 (red)Sodium23Complete the table by filling in the missing atomic numbers and atomic mass.(2 marks)(b)Write the electron arrangement for the following ions.(2 marks)Ca+………………………………………………………………………………………………………P3………………………………………………………………………………………………………(c)What is the melting point of hydrogen in Kelvin?(1 mark)…………………………………………………………………………………………………………………(d)Which of the allotropes of phosphorous has a higher density? Explain.(2 marks)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………(e)The mass numbers of three isotopes of magnesium are 24, 25 and 26. What is the mass number of the abundant isotope of magnesium? Explain.(2 marks)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………(f)Give the formula of the compound formed between calcium and carbon.(1 mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………(g)Explain the difference in the melting points of magnesium and sodium.(2 marks)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………2.Hydrogen gas can be obtained by reacting carbon (II) oxide and steam as shown below.17672545573314945941436081494692143657148590090903CO(g)+H2O(g) CO2(g)+H2(g) ?H=+VeThe curve below was obtained during the process.153352518224501531620154940234315012827040481257620I I 154305069850590550104775Concentration moles/litreConcentration moles/litre40005008890II0II219075022860X Time (seconds)0X Time (seconds)154304932385Which curve represents the change in the concentration of hydrogen, give a reason.(2 marks)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………Give a reason for the shapes of curve at point X.(1 mark)…………………………………………………………………………………………………………………State and explain the effect on equilibrium when concentrated potassium hydroxide solution is added on equilibrium above.(2 marks)………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………Explain the effects of increasing temperature of the system above on the yields of hydrogen.(2 marks)………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………The table below shows the volume of oxygen produced with increase in time during a reaction of 2g Manganese (IV) oxide and 50cm3 hydrogen peroxide at 250C.Time sec.01020304050607080Volume (O2 ) cm306090105112116120120120Calculate the rate of reaction between 20th and 40th second.(1 mark)Explain why volume of O2 produced does not exceed 120cm3.(1 mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………(iii)Explain the effect of using 4g of manganese (IV) oxide on total volume of oxygen produced. (1 mark)………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………3.Use the table below to answer the questions that follow.SubstanceFormulaACH3CH22OHBC2H5COOHCCH3CHCH2DCH3CH2CH3ECH3CCH(a)Explain how one would differentiate between substance D and E in the laboratory.(2 marks)…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………(b)Write an equation to show the reaction that will take place when substance A is heated in presence of concentrated sulphuric VI acid at temperature of 1700C. (1 mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………(c)What is the name of the process involved when substance D reacts with chlorine? Give the condition required for the process. Process - ………………………………………………………………………..(1 mark)Condition -……………………………………………………………………………………………(1 mark)(d)Select two substances from the table that could be reacted to form a pleasant smelling substance.Substances - ……………………………………………………………………………………. (1 mark)Conditions - ……………………………………………………………………………………..………………………………………………………………………………………………………...(1 mark)(e)Substance C is subjected to high temperatures and pressure to form a solid substance.Name the solid substance formed.(1 mark)……………………………………………………………………………………………………….Explain the effect of using the substance formed above for a long time.(2 marks)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………4.The standard electrode potentials of metals J, K, L and M are as shown below. Use it to answer the questions. (The letters are not the actual chemical symbols). 1343025117475J2+(aq)+2e J(s) -0.13V136207597155K2+aq+2e Ks -0.77V1314450111125L3+aq+3e L -1.66V1409700115570M2+(aq)+2e M -2.37V(i)Select two metals whose half cells will yield the highest e.m.f. when connected.(1 mark)…………………………………………………………………………………………………………………(ii)Write the cell diagram for the cell formed in (i) above. (1 mark)…………………………………………………………………………………………………………………(iii)Calculate the initial e.m.f of the cell formed.(1 mark)(iv)State one use of salt bridge in electrochemical cells.(1 mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………4305300287655Gas YGas Y1666875335280(v)The set-up below shows electrolysis of dilute solution of magnesium sulphate.140017516891095250027305Gas XGas X3495675641351752600546100328485517843533147008890002181225163830004448175173355Dilute magnesium sulphateDilute magnesium sulphate367157124003025488902590801762125259079001771650259080002160905154305-41376602603500-3009265203200024669753530603307080362585003619500391160388619911493500131445014484353476625962660023145759810750023240991029335002266950219710340995017208517526006197600028860751838960Dry cellsDry cells144780010960101304925109220Identify the gases X and Y.(1 mark)X-……………………………………………………………………….Y-……………………………………………………………………….(ii)On the diagram, label the electrode that is the anode.( ? mark)(iii)A current of 1.5A was passed through the solution for 50 minutes. Calculate the volume of the gas produced at the cathode. (M.G.V. r.t.p. = 24000cm3, IF = 96500c).(3 marks)(iv)State the effect of electrolysis of magnesium sulphate on the concentration of the electrolyte. (? mark)…………………………………………………………………………………………………………………………Give any one application of electrolysis.(1 mark)……………………………………………………………………………………………………..5.(a)The following set-up was used by a Form 3 student to prepare and collect dry hydrogen sulphide gas. (3 marks)125730046990Dilute HCl00Dilute HCl66421018986500833120189865004552950314325006953251143000656590314960008407405715000760095196215008045457048500676275285750077152517081500776605218440004591050220980002743200325755002781301325755002800350297180002762250287656097155032575500311467519850100065659065405004543425299720004562475351790006381751809115009391653041650025812753073400010439403327400026079452051050009531351370965004552950114300045243752095545720001143028289251143026098493257550027813001143000254317510514260985078105009715501143000971550685800426720087630004057650781054229100876290203835020955002400300781050061912578105001133476201930006191251543052476503251200091948031623010191759715550958752965455334000153670Gas jar0Gas jar449580030607099060010795002756535279400021050252584452943225239395002238375172720002686050172720002133600225425003457575170180Conc. H2SO400Conc. H2SO4-104775334645-571500248920ZnS(s)ZnS(s)52387520129510953752393955810252012958858252298705238752870209715503060707239002870202476505842029718001727202857508699566675067945060864751250955114925393704181475393704181475134620533400144145209550163195At the end of the experiment, the student realized that no gas was collected. Give a reason. (1 mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………Write an equation for the reaction when excess hydrogen sulphide gas is passed through sodium hydroxide solution.(1 mark)…………………………………………………………………………………………………………………Study the flow chart below to answer the questions that follow.415290010795 Excess Air0 Excess Air971550172720 Fe0 Fe4581525133351752600146685179070032004053149509201155581650748665Solid DSolid D3486150147256537719001263015Step IIStep II42481503486152333624329565695325920115Step III H2SO4(l)0Step III H2SO4(l)8858251291590Gas C + Water0Gas C + Water47910751301115 SO3(g) SO3(g)26003251291590 H2SO4(l) H2SO4(l)4324350329565HeatHeat866775453390 Solid A Solid A1333500805815229552591440Heat Step I0Heat Step I3295650196215Black solid EBlack solid E4953000177165 B + Gas C B + Gas C528637528575529590066675Air0AirName;(3 marks)Solid A ………………………………………………………………Solid D………………………………………………………………Substance B………………………………………………………………Write equations for the two consecutive reactions that must take place in step II before sulphuric (VI) acid is formed. (2 marks)………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………State the property of solid A that enables it to react with H2SO4 in step III.(1 mark)………………………………………………………………………………………………………………………….State any two uses of sulphuric (VI) acid.(2 marks)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………39719251028700204787510287002057400102870035909251343025ResidueResidue17335501323975Solution0Solution2933700504825center247650 Ore T Ore T2381250733425Step I0Step I6.I.Study the flow chart below and answer questions that follow.2905125248920Add excess hot NaOH(aq)0Add excess hot NaOH(aq)20669251409702076450217170Step II0Step II1447800264160Aluminium hydroxide0Aluminium hydroxide20955004445152400051435Solid Aluminium oxide00Solid Aluminium oxide21621751644652190750106680Step III0Step III638175106680Solid Na2AlF600Solid Na2AlF617240252400303762375102870Molten Aluminium0Molten Aluminium280035084455Step (IV)Electrolysis0Step (IV)Electrolysis154305025400Molten mixtureMolten mixture271462523495Name ore T.(1 mark)………………………………………………………………………………………………………………..(b)Explain why the ore is dissolved in excess NaOH(aq).(1 mark)………………………………………………………………………………………………………………..………………………………………………………………………………………………………………..(c)Name compound present in:- (1 mark)(i)Solution ……………………………………………………………………………….(ii)Residue……………………………………………………………………………….(d)Name the process that takes place in step II.(? mark)……………………………………………………………………………………………………………….(e)Why are sodium and fluoride ions not discharged in step IV?(? mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………Write the equation for reaction in step IV.(1 mark)……………………………………………………………………………………………………………….…………………………………………………………………………………………………………………….Why should the anode be replaced from time to time?(1 mark)……………………………………………………………………………………………………………….…………………………………………………………………………………………………………………….State any two uses of aluminium.(1 mark)……………………………………………………………………………………………………………….…………………………………………………………………………………………………………………….II.The figure below shows the behavior of emissions by radioactive isotope X. Use it to answer questions that follow. 276225012065+ Ve00+ Ve9429758064500274320069215274320088265PP952500178435084772510223500952500168275X0X1047750207010340995034290Q00Q95250157160095249917716500103822412255600952500654060269557547942500center298450RR2524125441325-ve-ve(a)Explain why isotope X emits radiation.(? mark)…………………………………………………………………………………………………………………..(b)Name radiations P, Q and R.(1 ? marks)P…………………………………………………………………………Q…………………………………………………………………………R…………………………………………………………………………7.(a)State Hess’s law.(1 mark)……………………………………………………………………………………………………………….……………………………………………………………………………………………………………….…………………………(b)Calculate the enthalpy of formation of ethane given that the molar enthalpies of combustion of carbon, hydrogen and ethane are -394kJ, -286kJ and -1560kJ respectively.(3 marks)(c)Calculate the enthalpy change for the relation.2000250103505C2H4(g)+ H2(g) C2H6(g), Given;(3 marks)C-C =347 kJ/moleC=C =612 kJ/moleC-H =413 kJ/moleH-H =436 kJ/mole8.The experiment below was used to investigate the effect of dry hydrogen gas on hot Lead (II) oxide. Use it to answer the questions that follow. -36661113970Dry hydrogen gas0Dry hydrogen gas39052564135center13336Combustion tube00Combustion tube41910173659003419474143809Lead (II) oxideLead (II) oxide238124911430005524499969512104351689440017352147697702200275635017820438156500424815043814Anhydrous copper (II) sulphate0Anhydrous copper (II) sulphate1306846985981838325184151724025411133295649125730206692511811019145251333528956009207529762451671570558165022225Excess hydrogen burningExcess hydrogen burning172402566040Heat Heat 3086100279405143500142240494347575565491490054190396143810649046767759921146672507048539909759906039751184427900467677524765(i)What was observed in the combustion tube at the end of the experiment? (1 mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………(ii)Why should the tube be slanting?(1 mark)……………………………………………………………………………………………………………………………………………………………………………………………………………………………………State any two precautions to be observed when doing this experiment.(2 marks)…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………(i)If 2.07g of lead (II) oxide was reduced by certain amount of hydrogen gas during experiment. Calculate the mass of hydrogen gas that reduced 2.07g of lead (II) oxide. (Pb = 207, O = 32, H = 1)(3 marks)Calculate the mass of the residue in the combustion tube.(2 marks)Calculate the volume of hydrogen gas used at r.t.p. (MGV = 24L)(2 marks) ................
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