KCSE Past Papers Chemistry 2011

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2.3 CHEMISTRY (233)

2.3.1 Chemistry Paper 1 (233/1)

1 (a) What name is given to the process by which alcohol is formed from a carbohydrate? (1 mark)

(b) Explain why the solubility of ethane in water is lower than that of ethanol. (2 marks)

2 Complete the nuclear equation below:

131 131

(a) I ~—~ Xe + ____ (1 mark) 53 54 l3l

(b) The half-life of I is 8 days. ~ 53 131

Determine the mass of I remaining if 50 grammes decayed for 40 days. (I mark) 53

(c) Give one harmful effect of radioisotopes. (1 mark) 3 A mixture contains ammonium chloride, copper (II) oxide and sodium chloride.

Describe how each of the substances can be obtained from the mixture. (3 marks)

4 The set-up below shows how nitrogen gas is prepared in the laboratory.

,Nitmgen / gas h..t_i__u I '3:5:i I§3§i:'. $51? ‘@215 233353 ~"“'*"@' '-:;:;:;;;:;:;:;: :I:I:I:I:I?§-‘-::3;I-I- :5? -:-:»:-:-.- l\ M-M ' 'l-- \\\Mixture of sodium nitrite t T T and nmmoniumehloride Heat —

(a) Describe how nitrogen gas is formed in the flask. (2 marks)

(b) Nitrogen is inert. State one use of the gas based on this property. (1 mark) 5 The diagram below represents part of the periodic table. Use it to answer the questions that follow:

—i Z < 2 /O

(a) Write the electronic arrangement for the stable ion formed by W. (1 mark)

(b) Write an equation for the reaction between V and Q. (1 mark)

(c) How do the ionisation energies of the elements M and T compare? Explain. (1 mark)

6 A certain mass of gas occupies 0.15dm3 at 293K and 98,648 .5Pa. Calculate its volume at l0l325Pa and 273K. (2 marks)

7 When lead(ii) nitrate is heated. one of the products is a brown gas. (a) Write the equation of the reaction that occurs. (1 mark)

(b) If O.290dm3 of the brown gas was produced, calculate the mass of the lead(ii) nitrate that was heated. (R.F.M of lead (II) nitrate = 331; Molar gas volume = 24dm3). (2 marks)

8 (a) What is meant by a strong acid? (1 mark)

(b) In an experiment, 4()cm3 of 0.5M hydrochloric acid was reacted with excess sodium carbonate and the volume of carbon (IV) oxide produced recorded with time.

In another experiment, the same volume and concentration of ethanoic acid was also reacted with excess sodium carbonate and the volume of carbon(lV) oxide produced recorded with time.

On the grid below, sketch and label the curves if the volumes of carbon (IV) oxide were plotted against time. (2 marks)

Volume of C02 cm3 v P Time (min)

9 State two reasons why hydrogen is not commonly used as a fuel. (2 marks)

10 During a class experiment, chlorine gas was bubbled into a solution of potassium iodide. (a) State the observations made. (1 mark)

(b) Using an ionic equation, explain why the reaction is redox. (2 marks)

11 Exhaust fumes of some cars contain carbon (II) oxide and other gases. (a) Explain how carbon (II) oxide is formed in the internal combustion engines. (1 mark)

(b) Name two gases other than carbon (II) oxide that are contained in exhaust fumes and are pollutants. (2 marks)

12 Sodium hydroxide can be prepared by the following methods; I and II.

I, Sodium metal , Sodium hydroxide + Hydrogen d Process A H‘ Ca_nCemmtE"""*""'_*’ Sodium hydroxide+ Chlorine + Hydrogen Sodium chloride

(a) Name one precaution that needs to be taken in method I. (1 mark)

(b) Give the name of process A. (1 mark)

(c) Give one use of sodium hydroxide. ( 1 mark)

13 Distinguish between the terms deliquescent and effiorescent as used in chemistry. (2 marks)

14 Two organic compounds P and Q clecolourise acidified potassium manganate (VII) solution; but only P reacts with sodium metal to give a colourless gas. Which homologous series does compound P belong? Give a reason. (2 marks)

15 Soap dissolves in water according to the equation below;

NaSt(aq'j*> Nam‘ + St“ where St_ is the stearate ion.

(a) Write the formula of the scum formed when soap is used in hard water. (1 mark)

(b) Write the ionic equation for the reaction that occurs when sodium carbonate is used to remove hardness in water. (1 mark)

16 Ethanoic acid and ethanol react as shown in the equation below:

crncooum + C21-I501-{(1) ;._-> CH3COOC2H5”) + H20”)

Other than warming, how would the state of equilibrium be established within a short time? (1 mark)

The set up below was used to prepare a gas and study some of its properties. Study it and answer the questions that follow:

Dilute F'8‘“° \. A hydrochloric I 5 / acid * 5» \- ? ..|. m &\‘\\\\‘§' &\\\\\‘ “QT ’/lsead (ll) . h Imnm) et anoate sulphide _- -_-_-_-_ ___-__ U , gal . . . . . . . - - . - _ _ . _ ~,~,~?;; I :-:-:-:-:-:-:-* ““"' »~ 331$:3:3:3:3:3:3:3:3:3:3:3' " '-:-:-:-:-:-:--‘ indiwwr '-:~:~:~:-:-:-:~:-:-:-:-:-:-:3 ‘ A B

(a) State and explain the observations made in the:

(i) tube labelled A; (1 mark)

(ii) beaker labelled B. (1 mark)

(b) State one precaution that should be taken when carrying out this experiment. (1 mark)

18 Under certain conditions, chlorine gas reacts with sodium hydroxide to form sodium hypochloxite.

(a) Name the conditions under which sodium hydroxide reacts with chlorine to form sodium hypochlorite. (1 mark)

(b) State two uses of sodium hypochlorite. (2 marks) 19 50kg of ammonium sulphate (NH 4 )2 S0, and 30kg of urea :CO(NH1)1 fertilizers were applied in two equal sizes of plots A and B to enrich their nitrogen content. Show by working, which plot was more enriched with nitrogen. (N = 14; S = 32; O = 16; C = 12; H = l) (3 marks)

20 Describe how the P" of anti-acid (Actal) powder can be determined in the laboratory. , (2 marks)

91 Em §n€g»:;;rm= figmeses g wwwv-Innnynlinlh-QI\cl11Io-con:In 21 Graphite is one of the allotropes of carbon. (a) Name one other element which exhibits allotropy. (1 mark) 22 The table below gives some properties of three elements in group (VII) of the periodic table. Study it and answer the questions that follow: Element Atomic Melting Point Boiling Point No. (°C) (“(3) Chlorine 17 -101 -34.7 53 Bromine 35 -7 58.8 Iodine 114 184 (a) Which element is in liquid fonn at room temperature? Give a reason. (1 mark) (b) Explain why the boiling point of iodine is much higher than that of chlorine. (2 marks) 23 The thermalchernical reaction between carbon and sulphur is as shown by the equation below: Cw + 2Sm ih CS2“) AH = " 117.0 kJmol". On the grid below, sketch and label the energy level diagram for the reaction. (2 marks) Energy P Reaction co-ordinate 92 Em §,n?L’1_1.$>‘a’ "xv Q 2: i. E >-*' = i WU fie g §;“:2e§.“23.§f;.ZE.%251?;-_ 29 27 The flow chart below shows some processes involved in the industri v Ail‘ Ore W Ofi e \I hich zinc is extracted. (b) Write the equation of the (a) Name one ore from w reaction taking place in unit ll. (c) Name two uses of zinc metal. 28 The diagram below shows the bondin be g tween aluminium chloride and ammonia. H Cl ' i H-----N ----->Al -----Cl H Cl (a) Name the types of bonds that exist in the molecule. (b) How many electrons are used for bonding in the molecule? Explain why the following substances conduct an electric current. (a) Magnesium metal. (b) Molten magnesium chloride. 30 A sample of river water is su ted spec to contain zinc and sulphate ions. Describe how the presence of zinc ions and sulphate ions can be e 94 stablished. al extraction of Zinc metal (l mark) (1 mark) (l mark) (1 mark) (1 mark) (l mark) (1 mark) (3 marks) Em §r’11?2$>v_7@; g wwwv-Innnynnllh-QnchlIo-con:In / / / /. // (b) The data in the table below was recorded when one mole of ethene was reacted // with excess steam. The amount of ethanol in the equilibrium mixture was recorded under different conditions of temperature and pressure. Use the data to answer the questions that follow. Temperature Pressure Amount of ethanol (DC) (Atm) at equilibrium (Moles) 300 50 0.40 300 60 0.46 300 70 0.55 250 50 0.42 350 50 0.38 (i) State whether the reaction between ethene and steam is exothermic or endothermic. Explain your answer. (3 marks) . (ii) State and explain one advantage and one disadvantage of using extremely high pressure in this reaction. I. Advantage (2 marks) II. Disadvantage (2 marks) 97 :E- z vs’ Q 2: a cl. tr 3-" = i [W memegwmfimfleaéfi g (c) In an experiment to determine the rate of reaction between calcium carbonate and dilute hydrochloric acid, 2g of calcium carbonate were reacted with excess 2 M hydrochloric acid. The volume of carbon (IV) oxide evolved was recorded at regular intervals of one minute for six minutes. The results are shown in the table below. Time (minutes) 1 2 3 4 5 6 Volume of carbon (IV) oxide (cm3) 170 296 405 465 480 480 (i) Plot a graph of time in minutes on the horizontal axis against volume of carbon (IV) oxide on the vertical axis. 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T I " " QTY ;'Q._§l'I ffti II" i ; ' J1? ;;§. ‘i, ti“ ‘*i“= "“i Il::|:I *3" »1.:....ia“ ' " ““"* Maw M»; -..L W, w; 1 1. » » > "' 1~% iv; .r{*:: 75 ' 1,;,;i.u:';:;f , , .*:: “ ' ;;_:p.V:V m_;5:,:§ij'.€:;> ; . *:r'?""""";; 9 .. . ‘ii~L """"“ “' 1 inn : W _+f1t.15;,;"tr ‘ . i IIIII “" " ‘ 1”?" *" i“ ". ’ Q ii" V ‘- llnnnn ' ‘i *' » ‘ III ::::_- "II ~ ~ "‘ “=E::i ' apt: mi|::i!5:. :.a:: ::::5:5ii::::::. ‘m: ':i:n:nu:::::=:%: ‘III: an H-n u--u-nnnnnn inn (ii) Determine the rate of reaction at 4 minutes. (2 marks) -'~\ mmii= aw“ take tatamaifii at §fifi%= Efififia‘ _- rwmmrr Q '.§=.:gn:§-~ .-.3 :§::§§5§r2%Ei‘ itséififililli : $£3; E mfi@£ zaaiitairtlar fififii gfiwm c 4 (a) When excess calcium metal was added to 50 cm3 of 2 M aqueous copper (II) nitrate in a beaker, a brown solid and bubbles of gas were observed. (i) Write two equations for the reactions which occurred in the beaker. (2 marks) (ii) Explain why it is not advisable to use sodium metal for this reaction. (2 marks) 98 ®@§aa§5r3aa§%§E; YT???-1Z>Ilyll1kZ.IlGh1_Q-¢()‘i / (b) (0) (<1) (H) (b) Calculate the mass of calcium metal which reacted with copper (Il) nitrate solution. (Relative atomic mass of Ca = 40) (2 marks) The resulting mixture in (a) above was filtered and aqueous sodium hydroxide added to the filtrate dropwise until in excess. What observations were made? (i) Starting with calcium oxide, describe how a solid sample of calcium ( 1 mark) carbonate can be prepared. (3 marks) (ii) Name one use of calcium carbonate. (l mark) Other than their location in the atom, name two other differences between an electron and a proton. (2 marks) The table below gives the number of electrons, protons and neutrons in particles A, B,C,D, E,F and G. 6 6 6 B lO 10 12 Q"=1B1UO 12 l0 12 6 6 8 13 I 10 ] 14 17 17 ] 18 10 | 8 8 Particle Protons Electrons Neutrons A (i) Which particle is likely to be a halogen? (ii) What is the mass number of E? (m) Write the formula of the compound fonned when E combines with G. (iv) Name the type of bond formed in (m) above. (v) How does the radii of C and E compare? Give a reason. (1 mark) ( l mark) (1 mark) (l mark) (2 marks) (vi) Draw a dot (.) and cross (X) diagram for the compound formed between A and F. (vii) Why would particle B not react with particle D? 99 (1 mark) ( 1 mark) IE’ z ‘aw z Ir 5 i. ts;-Y‘ : WU m fie g :?l“.E‘.%%’.§‘..,.:.T.“Zt£;‘*E=‘$EE-_. 6 (a) Study the flow chart below and answer the questions that follow. O > Step (I) Acidified potasium manganate (VII) Ethyl Sodium metal E methanoate Step thanol Step (VII) I ydmgcn gas (VI) Step _ _ (ll) Concentrated sulphuric (VI) acid Ethane Step (IV) Step (V) H Polymerisation SW? (HI) Bromine gas (i) I What observation will be made in Step I? II Describe a chemical test that can be carried out to show the identity of compound C. (ii) Give the names of the following: IE ................................................................................................... .. (1 mark) (2 marks) (2 marks) II Substance D ........................................................................................ .. (m) Give the formula of substance B. (iv) Name the type of reaction that occurs in: I Step (I1) .................................................................................... .. u Step (IV) .................................. .. (v) Give the reagent and conditions necessary for Step (VI). (1 mark) (1 mark) (2 marks) Reagent: .................................... .. Conditions .................. .. 100 Em znepwame 31%~§m?§@; Q wwwv-Innlny-.1111!-1I\cl1lIo-con:In (b) (i) Name the following structure. _C-II _CE _I _I _I ‘-5: ' H— — — - ~ — -OH 7 (a) What is meant by molar heat of combustion? (1 mark) ’II""O CE‘“('} E""fi I""O I‘t') I*O (1 mark) (ii) Draw the structure of an isomer of pentene. (1 mark) (b) State the Hess’s Law. (1 mark) (c) Use the following standard enthalpies of combustion of graphite, hydrogen and enthalpy of formation of propane. Mg (Graphite) = -393w mar‘ A112 (H2(g)) = ~286kJ mar‘ AHg¢(C3H8(g)) = —104kJ marl (i) Write the equation for the formation of propane. (1 mark) (ii) Draw an energy cycle diagram that links the heat of formation of propane with its heat of combustion and the heats of combustion of graphite and hydrogen. (3 marks) (m) Calculate the standard heat of combustion of propane. (2 marks) (d) Other than the enthalpy of combustion, state one factor which should be considered when choosing a fuel. (1 mark) (e) The molar enthalpies of neutralization for dilute hydrochloric acid and dilute nitric (V) acid are -57.2k.l/mol while that of ethanoic acid is —55.2kJ/mol. Explain this observation. (2 marks) 101 Efifil znzrpwsme 3i%~$1-Jrfig Q WVWVTV-iZ>IlyZ.i1i'1Il¢lllQQ-G@‘IIIl 3.3.3 Chemistry Paper 3 (233/3) 1 You are provided with: ~ l.6Og of solid A. a dibasic acid. ' Solution B containing 4.75g per litre of salt B. ~ Aqueous sodium hydroxide. solution C. ~ Phenolphthalein indicator. You are required to prepare a solution of solid A and use it to determine the:- ' Concentration of sodium hydroxide. solution C - React salt B with excess sodium hydroxide and then determine the relative molecular mass of salt B. Procedure I (a) Using a burette, place 25 .Ocrn3 of solution B in each of two 250ml conical flasks. Using a pipette md pipette filler, add 25 .0cm3 of solution C to each of the two conical flasks. (The sodium hydroxide added is in excess). Label the conical flasks l and 2. (b) Heat the contents of the first conical flask to boiling and then let the mixture boil for 5 minutes. Allow the mixture to cool. (c) Repeat procedure (b) with the second conical flask. While the mixtures are cooling, proceed with procedure II. Procedure II (a) Place all of solid A in 21 250 ml volumetric flask. Add about l50cm3 of distilled water, shake well to dissolve the solid and then add water to make up to the mark. Label this as solution A. (b) Place solution A in a clean burette. Using a pipette and pipette filler, place 25 .0cm3 of solution C in a 250ml conical flask. Add 2 drops of phenolphthalein indicator and titrate with solution A. Record your results in Table 1. Repeat the titration two more times and complete the table. 102 ' ?<>\=\7£;fzi E23": \ WU fie g $‘5J3“3.%“:’.§.‘§.“3.;.:.‘3Ztf;“¢‘H£?.@-_. I .'/ 1 . i Table 1 Final burette reading Initial burette reading | 3 / 1 II I III I l Volume of solution A used (cm ) (4 marks) Calculate the:- (i) average volume of solution A used: (}§ mark) (ii) concentration in moles per litre of the dibasic acid in solution A; (2 marks) (Relative molecular mass of A is 126). (m) moles of the dibasic acid used; (1 mark) (iv) moles of sodium hydroxide in 25 .0cm3 of solution C. (l mark) (v) concentration of sodium hydroxide in moles per litre. (2 marks) Procedure III Add 2 drops of phenolpthalein indicator to the contents of the first conical flask prepared in procedure l and titrate with solution A. Record your results in Table 2. Repeat the procedure with the contents of the second conical flask and complete the table. Table 2 1st conical flask 2nd conical flask Final burette reading initial burette reading Volume of solution A used (01113) (3 marks) Calculate the:- (i) average volume of solution A used; (l/§ mark) (ii) moles of the dibasic acid used; (l mark) (m) moles of sodium hydroxide that reacted with the dibasic acid. (1 mark) 103 ? 2 ‘aw 5 If 5 i ‘I-:2 3*‘ = \ WU t.%?§222m-fl¥‘.m&s@§§ g (iv) moles of sodium hydroxide that reacted with 25 .0cm3 of salt B in solution B; (2 marks) (v) Given that l mole of salt B reacts with 2 moles of sodium hydroxide, calculate the: l. number of moles of salt B in 25.0cm3 of solution B; (1 mark) ll. concentration in moles per litre of salt B in solution B; (1 mark) lll. relative molecular mass of salt B; (2 marks) 2 (a) You are provided with solid D. Carry out the following tests and write your observations and inferences in the spaces provided. (i) Place about one half of solid D in a test-tube and heat it strongly. Test any gases produced with both red and blue litmus papers. Observations I lnferences (2 marks) I (1 mark) (ii) Place the rest of solid D in a boiling tube. Add about 10cm3 of distilled Water. Shake well. To a 2cm3 portion of the solution, add about lcm3 of hydrogen peroxide and shake well. To the resulting mixture, add aqueous sodium hydroxide dropwise until in excess. Observations I Inferences ( I mark) l (1 mark) (b) You are provided with solution E. Carry out the following tests and write your observations and inferences in the spaces provided. Divide solution E into two portions. (i) To one portion of solution E in a test-tube, add 3 drops of barium nitrate. Retain the mixture for use in test (ii) below. 104 ? 2 \=\7 l If 1 i ‘I-:2 3*‘ = \ [W wmemegmem-fimfisaéfi g /" ’ Observfiiiflils 1 inferences M (l mark) | (2 marks) (ii) To the mixture obtained in (i) above, add about 5 cm3 of 2M nitric (V) acid. Observations l [nfemmes (l mark) ' (1 mark) (m) To portion two of solution E in a test-tube, add 2 drops of acidified potassium dichromate (VI) and warm the mixture. ‘v 3 You are provided with liquid F. Carry out the following tests and record your observations and inferences in the spaces provided. (a) Place five drops of liquid F on a clean dry watch glass and ignite it‘ ObS€l'Vflfi0llS I Infgrgngeg (1 mark) ‘ (1 mark) (b) Place about 2em3 of liquid F in a clean dry testatube, add all the sodium hydrogen carbonate provided. Observations I Inference; (1 mark) \ (1 mark) (0) Place about 2cm3 of liquid F in a test-tube, add about lcm3 of acidified potassium dichromate (VI) and warm the mixture. Qbservafiflns I Inferences (1 mark) I (1 mark) 105 Eqfu gseywms fizmmfi g wwvwv-Irnnlnynlinflh--.Ilcl11-o-co‘1:n

1 > 11.0 CHEMISTRY (233) 11.1 Chemistry Paper 1 (233/ 1) Fermentation. ' l . (a) 2- (3) fie (b) 50g >25g )12.5g >625 )3.125 >1.5625g. (c) Instant death, or gene mutation, induce cancer. V 3. ~ Heat the mixture to sublime the ammonium chloride. \/ > l 1 WU gergfatme %i;1'1'ruEi‘aJ>1i’-§f g 4. (a) ' Oxygen is used up. %‘ 5. (a) - 2.8 (b) 3v + Q2——--9 vaoz on 3Mg + N2‘-"'9 Mg3N2 (c) T has a lower ionisation energy than M. ~/% ( l mark) (b) Ethane remains in molecular form while ethanol forms hydrogen bonds with water. (2 marks (1 mark) (1 mark) (1 mark) (1 mark) ' Add Water to dissolve the sodium chloride 1/ %; copper (ii) oxide does not dissolve (1 mark) ' Filter x/% and evaporate the filtrate to obtain sodium chloride. x/Z (1 mark] (1 markj (l markj T has an extra energy level and hence electrons is less attracted by the positive nuc P,v.=P.v. y 6‘ T1 T1 ‘/1 V2=£,_v_.X;l: 98,658.5xl50x273 1/1 T. P2 293 X 101,325 v,= 0.136 am; t/% 7. (a) 2Pb(NO3")2--> 2PbO + 4NO2 + 02 (S) (S) (2) (2) 348 (l mark (2 mark (1 mark WWVWV igllynllnlh-ggggjgj--_¢°-;.‘ i % (11) Moles of bronm gas (No.) = -‘l§= 0.012 M Q Moles of lead (n) nitrate = -5- >< % = 0,006./' 1 (2 marks) = Mass of lead (11) nitrate = 0.006 X 33w % = 1.9992 2 J % (a) Strong acid ionises fully. (1 mark) .°° (b) Hcl ' CO2 Ethanoic acid cmi . (2 marks) Time 9. (a) Hydrogen is expensive. Hydrogen is explosive. (2 marks) 5 10. (a) ' Green colour of chlorine disappears. ‘ ' Brown gas is produced or black solid is deposited. (1 mark) C11 + I'i)2 Cl“ + I (8) (aq) (aq) (5) Explanation: Iodine oxidation state changes from ~1 to O hence oxidation while chlorine oxidation state changes from 0 to -l hence reduction. (1 mark) 11. (a) Carbon (II) oxide is formed in the internal combustion engines when fuel burns under limited oxygen. (1 mark) (b) Pollutant gas - Carbon (IV) oxide, Nitrogen (IV) oxide and Sulphur (IV) oxide. (Any two) (2 marks) I2. (a) ~ Small piece of sodium metal (pea size) with alot of water. O Perform the experiment wearing goggles. (I mark) (b) Electrolysis. (1 mark) (c) Manufacture of soap. (1 mark) 13. Deliquescent substance absorbs water from the atmosphere to form a solution. while a fluorescent substance loses water of crystallisation to the atmosphere. (2 marks) 14. P is in alkanol R - OH.‘ The alkanol reacts with sodium metal to produce the colourless gas. (2 marks) 349 _-i . . .. ._ r ._ . i a j E’ z \>I\r £1 & : -I ' [Fm] mmpmnn? m<§1nucelZ_[33>1i’§§ wwwv-In-.lny-1:11!-1Ilel11I--co_nIn 15. (a) Ca (st); or Mg (st)2 Ca“ + C0,?“ i) Cacoz (aq) (aq) (S) OR Mg“ CO3‘ —-—-—> Mg CO3 (S) 16‘ By adding Conc. H2504 as a catalyst. 17. (a) (i) Black solid is depositedl (ii) The indicator turns red. (b) The experiment should be done in fume chamber or in open air. is. (ii) Cold % and dilute sodium hydroxide. % (b) ' Used in sterilising of water. (1) ' Used as a bleaching agent. (1) 19. Plot A Percentage of Nitrogen in (NH )2 S04 = -1-2?,1?x1OO = 212% Amount Nitrogen in 50 kg (NFL); SO» = LAX 50 100 = 10.6 kgw/% P10tB Percentage of Nitrogen in urea = %%x 100 = 46.7%% The amount of Nitrogen in 30 kg = L x 30 100 I ' = 14.01 kg)/A Plot B w/% is more enriched with nitrgen since if has higher amount of nitrogen than plot Ax/Y % 20. ' Add water to dissolve the anti-ziéid powder. 350 (1 mark) (1 mark) (1 mark) (1 mark) (1 mark) (1 mark) (1 mark) (2 marks) ( 3 marks) ‘ ~ V \/V ~ Add univerxga/I indicator and match the colour of solution with pl-l chag zind read the value ~/% (2 marks) WU gnepwmar zzieazmfises Q wwwv-II:-lay-1:111-1Ilel11I--co:l1 21. (a) Sulphur or phosphorus. (1 mark) ~/% (b) Carbon atoms in graphite are arranged in layers of hexagons which are held by weak van der 7 V . V waal forces. The layers slide/oi/er each other when some force is applied 0% them; hence suitable in making pencil leads. (3 marks) 22. (a) ~ Bromine v/K ' At room temperature (25“C), Bromine is liquid since its MP and bP is between -7 and 59.4% ~/1 (b) - Atomic mass of iodine is higher than that of chlorine. v'i - Van der waal’s forces are stronger in iodine than chlorine hence iodine’s bl’ is higher than that of chlorine. (3 marks) (1) 23. ¢s....<%> Energy cm+2s®(%) (2 k) H131’ S > Reaction oath 24. (a) Y ~/1 (b) Y and z \/1 They have the same number of protons (8) but different atomic masses. w/l (3 marks) 25. (a) When gases combine together at constant \/'l temperature and pressure they do so in volumes which bear a simple ratio to each other, and to the volumes of the products if gaseous. (b) CZHX + 302 —--) 2CO2 + ZHZO % (g) _ Vol. 10 : 30 20 20 ‘/A I Mole ratio l : 3 2 2 ‘/A X = 4 ‘/% (3 marks) 26. (a) (i) Mass of oxygen = 10.400 - 10.352 = 0.048 g% (ii) Mass ofM powder = 10.352 - 10.24 = 0.118 g% 351 1A» , - - ~ _ ~ - __.. i T‘ i \>I\r 3 2- cI- i=I 3"‘ : W aettnngvsznnu ;UJJ?Tral1'n1r:1;l:1 11% . WVTYW-1lIly_»ill'Q.IVl¢.lI1DQ-¢()_i 27. (a) (ll) (C) 2s. (3) (b) 29‘ (a) (b) M O - 0. 1 12 Mole 1‘8I10 56 0.0020 Simplest ratio 2 Empirical formula M203 ( Zinc blende or calamite \/I ZnO + c—--->2" + cor/1 (S) (S) (S) (g) Use of Zinc metal: - dry cells; x/% ' galvanising iron sheet‘ \/% - as electrodes. - Single covalent bonding 1/% .0-_4§. l6 0.0030 (1) 3 1) I Dative (coordinate) bonding x/% 7 bonds x 2 = 14 electrons.1/ l Mg metals have mobile delocalised electrons which carry the current \/ l Molten magnesium chloride has Mg“ and Cl‘ ions which are free to move \/1 30. Add aqueous ammonia to fill \/% in excess. A formation of white precipitate which dissolves in excess shows presence of zinc ions. i/1 ~/1 Add aqeous actified Barium Nitrate Formation of a white precipitate shows Presence of sulphate ions 31. Alkaline earth metals. 352 (3 marks) (3 marks) (2 marks) (2 marks) (3 marks) (1 mark) zs-¢\>\r@;_— ca. t=>.w-= armgvalnnu ;[I1fiZt?<5ZLII‘l'I£Bll’13 11% wwvwv In.-lay-malt-Qllelnlio con: 11.2 Chemistry Paper 2 (233/2) 1 . (1) (b) (C) (d) (e) (1) 2. (a) (b) _L~ Purify to remove (1/1) dust, bubble in NaOH or KOH to remove (1/1) CO2, reduce tem perature to remove water as (1/1) ice, compress to liquify the remaining air then fraction ally (1/1) distill to obtain Oxygen at —l83°C. (1) (3 marks) (i) 98% concentrated sulphuric (VI) acid (1) (1 mark) (ii) SO3(g) + H2504 (1 ) H2520. (1) (1 mark) (i) Platinum or platinised asbestos (1 mark) (ii) It is cheap and not easily poisoned. (2 marks) They turn from blue to (1/1) white and form a powder (1/1). (1 mark) The sulphuric (VI) acid dehydrates the copper (H) (1) sulphate crystals forming copper (II) sulphate powder. (1 mark) HZSOA is less- volatile (1) (1 mark) ~ Manufacture fertilizers eg. Super phosphate ' Production of rayon fibres ~ Car batteries as electrolyte ' Sulphur detergents any four ~ Cleaning of metals (Pickling) (1/1) mark each ~ Paints etc. (2 marks) (i) Cu2*(aq) + 2e Cu(s) (1) (1 mark) (ii) It decreases (1). The anode is not inert so it dissolves.(l) (2 marks) (m) Chlorine gas (1). Use moist blue litmus paper (1). It will change from blue to pink then to white or is bleached. (1) (3 marks) Quantity of electricity = 0.45 x 72 x 60 (1/1) ' = 1944 coulombs (1/1). 0.6 g require 1944 1951-i)L52 59 require ? 0.6 (1) Q 191116 Q 1 Faraday = 96,500 Q 7 = 191160 Q Number of Faradays/Charge = lfllfifl Q 1.98 Q 2 (1/1) 96500 :. B“ 1 3 k ( ) 353 ( mar S) §..r;1»%s:;;.§ %§m§1rr§ ' _L v\rww-I:Innlny-.1111!-..I\cl11Io-co_nIn (0) From the electrode potentials, zinc is more reactive than cadmium .(l) Therefore zinc will displace cadmium ions from solution hence the metal container will dissolve. (1) (2 marks) 3. (a) Increase or change in amount of reagent either reactants or products. (Concentration). (1 mark) (b) (i) Exothermic (1) increase in temperature from 250 - 350 (1/1) at constant pressure (‘/1) the amount of ethanol formed at equilibrium decreases. (1) (3 marks (ii) I Advantage - it would increase the yield of ethanol (‘/2); since increase in pressure will favour side with less moles i.e. the products. (l) (1 (1/1) marks) H Disadvantage - it would mean investment in equipment to withstand the high pressure(l) and would be expensive . (1 (‘/2) marks) 354 ; WU gnsszaaar %§m€§r:§r Q wwvwv In-.lny-malt-lllelnlio con: (c) (i) See graph drawn. 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J; : ‘ > > : _ _ 1 ‘ i < _ _ z = - 5 = ~ 1..-.; -.1 - .= » ' .5 .§.g.. 44 +.+.4..-.;..%....}..;.;..;..,.¢,.ST? ; .i.....§..;.,....§...%.%..;,.¢,.§..§,i...§.,.. 0 J 'fir\4e@»u»\.~¥¢-.5) 355 f i ‘ar 2 2- <:fl- % 3r : ‘ . [W mmgvslnm jfirmmmb is v\rwwv-I:Innny-.1111!-..§\cl11Io-co_nIn (ii) Drawing tangent ('/1) Rate = §25 - 414 (1/1) = Q = 30 cm3/min (1/2) (2 marks) 6 - 2.3 (1/1) 3.7 (a) (i) ' Ca (s) + Cu(NO3)2 (aq) Ca(NO1)2(aq) + Cu(s) (1) (2 marks) ' Ca (s) + H20 (1) Ca(OH)2 (aq) + H2 (g) (ii) Sodium metal is more reactive than calcium (1/2). Reaction between sodium and copper nitrate will be explosive (1/2) as it reacts with water evolving hydrogen gas. (1) (2 marks) (b) Ca (s) + Cu(NO3)2 (aq) Ca(NO3)Z (aq) + Cu(s) 1 : 1 moles of copper nitrate Q x 2 = 0.1 moles (l) 1000 Ratio 1:1 » Moles of Ca = 0.1 Mass ofCa =O.1x4O=4g (l) (2 marks) (c) A white precipitate is formed which is insoluble in excessr (1) (l mark) (d) (i) Add dilute nitric (V) acid to calcium oxide to form the soluble salt (1/2) calcium nitrate. Add sodium (1/2) carbonate (another soluble salt) to form insoluable. Calcium Carbonate and sodium nitrate (1/2). Filter out (1/2) the calcium carbonate, wash it (1/2) with distilled water to remove traces of sodium nitrate and dry between filter papers (1/1) ' (3 marks] (ii) Manufacture of cement Manufacture of sodium carbonate. (1 mark) (a) - electron has 1 mass while proton has mass of one mass unit. - proton is pdslm?/ely charged while electron is negatively charged. (2 marks: (b) (i) F (1 mark) (ii) 27 (1 mark) (m) E2G3 (1) (1 mark] (iv) Ionic bond (l) or electrostatic (l mark] (v) E has a smaller atomic radius than C (1) E has more protons than C :. nucleur attraction stronger. (1) (2 marks 356 WU getawme E-emzmaes Q wwwv-nanny-malt-QIlel11I--con1 (vi) wit: (vii) Particle B is inert with a stable electronic configuration :. will not react. (1) 6. (a) (i) I The potasium permanganate is decolurised or changes from purple to colourless. (1) II C is a ethanoic acid (carboxylic acid) (1 mark) (1 mark) Add sodium carbonate, you will see effervescence, test gas evolved with lime water, it will form a white precipitate. (2) (ii) I Polyethene ( 1) II Substance D - sodium ethoxide (1) (m) Substance B - CH2BrCH2Br. (1) or C2H4Br2. (iv) I Step II - dehydration (1) II Step IV - hydrogenation. (1) (v) Reagent: Methanoic acid (1) Conditions: Concentrated sulphuric (VI)acid & (1) Warm. (b) (i) Hexan - 1 - ()1 357 (2 marks) (2 marks) (1 mark) (1 mark) (2 marks) (1 mark) . Em gnepwamr %i1,1'ntr.£kti:l,lJJ>1i,;£§ Q 1 wwwv-all-any-.1111!--.Ilcl11I--co_n:1 7 (a) (b) (C) (<1) 6) <1» @=@ié-1é.£ I I I I I I I I - c- c- e e -c I I I I H I I I -c-c= -c- —(\-—F\ (1 marl The amount of heat liberated when one mole of a substance is burnt in excess oxygen. (1 marl The heat evolved ar absorbed in a chemical change is the same whether the change occurs in one step or through many steps. (1 marl (1) scm + 4HZ® c3n8(g) (1 marl 3C(§) + 4H2l2> C3HXlgI <1) <1) A“@‘°=H=9 <1) scom + 4 HZOU) (3 mark (m) -104 = 3 X -393 + 4 >< -286 -AHC (C3H8)‘" AHC (CSHS) = 104 + (-1179) + -1144) (1/1) = — 2219 kJ mol‘1 (‘/1) (2 mark - cost - effect on environment - availability - storage (1 marl Ethanoic acid is a weak acid therefore heat is used to ionise it before neutralization occurs (1). It value is therefore lower than that of hydrochloric acid which is fully i0nised(1). (2 mark 358 F W ? \>I\r .1’ cl i : aln?gr>< 2) = 0.001145 moles moles of NaOH that reacted with 25.0cm3 of salt B in solution B; = 0.0029314 - 0.001145 = 0.0017864 moles I. moles of salt B in 25.0cm3 of solution B; 0.0017884 >< ‘/1 6 = 0.00089 moles (1 mark marks (1 mark II. concentration in moles per litre of salt B in solution B; (1 mark _ 1000 - 0.0008 9 X 25 = 0.0357 M (1 mark II]. relative molecular mass of salt B; 4.73 = 0.0357 = 133.0 (1 mark) (i) Observations Inferences - Gas which turns red litmus paper blue NH 4* present - Brown solid formed (2 marks) (l mark) (ii) Observations Inferences - Yellow / brown solution Fe“ fonned - Brown ppt (1 mark) (1 mark) 360 (3 marks F an ?i§>I\?}Z' ¢§- %§": armgvalnnu ;1]fi§_3r
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