A-Level H2 Chemistry 01 Redox Stoichiometry

MULTIPLE CHOICE QUESTIONS

SECTION A

1 The term "mole" is attributed to Wilhelm Ostwald who introduced the concept.

Which of the following best defines the term "a mole"?

A The mass of an element which is the same as 12 grams of 12C.B The mass of 6.02 x 1023 atoms of an element relative to the mass of 12 grams of 12C.C The number of atoms of an element which Is the same as that in 12 grams of 12C.

D The number of atoms of an element which Is equal to 1 the number of atoms in 1212

grams of 12C.

2 Which of the following quantities Is equal to the Avogadro constant?

A The number of atoms in 24 dm3 of nitrogen gas at r.t.p. conditions. B The number of molecules In 1 dm3 of oxygen at 273 K and 1 atm. C The number of zirconium atoms In 962 g of tranquillityite, Fe3Zr2Ti3Si3O24, of molar mass

961.8 g moi-1 D The number of Ions In 83.5 g of [Co(NH3)5CC/2.

3 Which of the following has the greatest mass?

A 6 x 1 023 molecules of hydrogen gasB 3 moles of nitrogen molecules

C 1.2 x 102" atoms of IronD 3 x 1023 Ions of copper( I I)

AJ

5 The greatest amount of particles Is found In

A 5.0 dm3 of H2S gas at r.t.p.B

c 0

1.8 x 1023 molecules of C11H1205.

280 cm3 of 2.5 mol dm-3 HC/04(aq) 50 g of Fe203(s)

6 Which of the following statements is not true?

A One mole of methane contains four moles of hydrogen atoms.

B One mole of 12C has a mass of 12.00 g .

C One mole of hydrogen gas contains 6.02 x 1023 atoms of hydrogen. D One mole of methane contains 75% of carbon by mass.

AC.JC. I Preli'nl JOOb

LJC. I Preln>l J0-01

7 The main Ingredient in chocolate bars Is sugars, typlcally about 47% of milk chocolate bars. If these sugars are represented by sucrose, C12H22011 (M, = 342), how many sugar molecules ar there In 1000 kg of chocolate brs?

A

c

9.67 x 1025

8.27 x 1026

B

0

2.82 x 1026

3.57 x 1027

Y JC. I J>relml JOOb

8 Bluret reagent, H2NCONHCONH2 Is a chemical test for proteins and It can be formed by heating urea (NH2)2CO above Its melting point.

How many hydrogen atoms are present In bluret If 15.0 g of urea Is used?

A

c

3.76 x 1023

7.53 x 1022B 0

3.01 x 1023

1.51x1023

lJC. I Pte\n\3 J006

9 Iron Is an essential nutrient for pregnant women. Doctors usually prescribed 350 mg FeS04tablets as dietary supplement for the pregnant women. However, It was found that Iron tabletsmay cause poisoning deaths In children since as little as 590 mg of Fe2 can be fatal to a 12.5 kgchild.

How many 350 mg FeS04 tablets would It take to constitute a lethal dose to a 12.5 kg child?

A 2 B 3 c 4 D 5 MJC. I Preli"n3 J0-07

2

Redox and Stoichiometry

10 9 cm3 of hydrogen sulphide is Q_ubbled through 50 cm3 of 0.01 mol dm-3 aqueous hydrogen peroxide under r.t.p. according to the equation shown below:

What is the volume of hydrogen produced at r.t.p.?

A 9 cm3 B 12 cm3 c 18 cm3 0 24 cm3

11 Calcium nitrate decomposes on strong heating according to the following equation:

What is the loss in mass when 1 0.0 g of Ca(N03)2 Is heated stro9gly until no further change inmass?

A B

1 .50 g

6.59 g

c D

7.50 g

8.41 9 f PJC. I Pre\m) J007

12 When a refrigerator comes to the end of its useful life, It is desirable to recover and destroy any chlorofluoroalkanes (CFCs) used as a refrigerant.

A process was devised In 1996 to pass CC/2F2 through a packed bed of sodium ethandioate at 270 C; this efficiently converts this CFC into solid and gaseous products.

CC/2F2(9) + 2Na2C204(s) -+ 2NaC/ (s) + 2NaF(s) +. X(s) + yC02(9)

What is the Identity of the product X and the number y?

A B

c

D

c c 2C

2C

'i. 2

4

2

4 Ml I Pre!m JOOll

13 What is the volume of water needed todllute 30.0 cm3 of 0.01 mol dm-3 aqueous hydrochloric acid Into 0.00230 mol dm-3?.

A

B

50.0 cm3

100.0 cm3

,c D

3

130.0 cm3

180.0 cm3


14 During water treatment, cations in water are exchanged with hydrogen ions from an ion exchange resin. For example, a sodium ion Is replaced by one hydrogen Ion, while a magnesium ion Is replaced by two hydrogen ions.

H'- 500 cm3 of a solution of calcium Ions was passed through the Ion exchange resin. The product solution after treatment required 20 cm3 of .00 x 10-2 mol dm3 sodium hydroxide forneutralization.

What Is the concentration (In mol dm 3) of calcium Ions in the original solution?

A

B

o.o4 x 10-3

0.20 x 10-3

c D

15 Group I and Group II Ionic hydrides react with water.

0.40 x 10-3

0.80 x 103

In an experiment, 1 .g of a sample of an ionic hydride Is dissolved In excess H20. The resulting solution required 24.0 cm3or a 2.0 mol dm-3 HCt solution for complete neutralization.

What Is the formula of the hydride?

A B UH c D NaHHCt I Prelrn$ .:lOO

16 Magnesium nitride Is a yellow.green powder and It reacts with water according to the following equation:

If 20 g of water are mixed with an excess of powder and any solids are filtered away, what is the approximate volume of 0.82 mol dm-3 of HCl that ls required to neutralize the ammonia produced?

A B

150 cm3

300 cm3

c D

450 cm3

900 cm3 CJC. I Pre1Tn$ :1001

17 25.0 cm3 of an aqueous mixture of sodium carbonate and sodium hydroxide was titrated against 0.100 mol dm-3 hydrochloric acid using the double Indicator method.

1 5.00 cm3 of the acid was required to change the colour of phenolphthalein (first indicator) and another 10.00 cm3 of It was added before methyl orange (second Indicator) changes colour.

What was the molar concentration of sodium hydroxide In the original aqueous mixture?

A 1.00 x 1 0-2 8 2.00 x 1 0-2 c 4.00 x 10-2 D 6.00 x 10-2

4


18 A sodium salt, X was dissolved ih 40.0 cm3 of water. A 20 .0 cm3 sample of this solution required 24.60 cm3 of 0 . 1 00 mol dm-3 NaOH for neutralization. Another 20.0 cm3 sample of the solution required 49.20 cm3 of 0 . 1 00 mol dm-3 AgN03 for complete reaction.

What is the formula of the anion present In X?

A B c . .

D

19 A sample containing ammonium sulphate (M, = 1 32) was warmed with 1 50 cm3 of0.500 mo! dm-3 sodium hydroxide solution. When the evolution of ammonia ceased, the excess sodium hydroxide solution was neutralized with 45.50 cm3 of 0 . 1 00 mol dm-3 hydrochloric acid. What was the mass (in grams) of ammonium sulphate in the sample?

A 4.65 B 9.30 c 1 8.60 D 21 .80 RJC I JCI 811 I J006

20 1 .5 g of an impure sample of calcium carbonate was heated strongly until there was no changein mass and 100 cm3 of carbon dioxide was collected. What Is the percentage purity of calcium carbonate? Assume that the measurements were made under room temperature and pressure.

A 27.8% B 29.8% c 30.4% D 35.8% ACX. I Prelml J007

21 An impure sample of 3.50 g of sodium hydrogencarbonate (M, = 84.0) was heated. Given thatthe loss In mass was 0.85 g and sodium hydrogencarbonate decomposed completely intosodium carbonate, carbon dioxide and water vapour on heating, calculate the percentage purity by mass of sodium hydrogencarbonate in the sample.

A 32.9% B 65.8% c 88.4% D 98.6% RJC. I JC.I an I JOOI>

22 The process of fermentation produces ethanol. Brandy contains a significant proportion ofethanol. Three 10.00 g samples of brandy were acidified and then titrated with 2.50 mol dm-3 potassium dichromate solution In order to determine the amount of ethanol that the brandy contained. The average titre determines the amount of ethanol that the brandy contained. The average titre obtained was 20.25 cm3. The equation for the reaction that occurs Is

The percentage by mass of ethanol In this sample of brandy based on these results is

A 1 5.5 % B 16.5 % c 23.3 % D 34.9 % ACX. I Pre Im JOO(,

5


23 Solutions of 45 cm3 of 0.8 mol dm-3 of potassium Iodide and 30 cm3 of 0.5 mol dm-3 of lead(ll)nitrate were mixed together according to the equation below:

2Kl(aq) + Pb(N03}2(aq) ...., Pb12(s) + 2KN03(aq)

What will be the approximate concentration of te Iodide Ions In the solution after the reactionhas completed? .

A c

0.006 mol dm-3 0.0023 mol dm-3

B D

0.0036 mol dm-3 0.080 mol dm-3

CJC. I Preli'Tll :loo6

24 The foul smell that skunks spray is due to a number of thlols, one of which Is methanethlol, CH3SH. A 10 cm3 sample of methanethlol was exploded with 60 cm3 of oxygen. What would bethe final volume of the resultant mixture of gases when cooled to room temperature?

A 20 cm3 B 30 cm3 c 50 cm3 0 70 cm3 ACJC. I Preli'Tll .J006

25 On heating, 0.02 mole of element M reacts with 600 cm3 of oxygen gas at room temperature andpressure. What Is the empirical formula of the oxide of M?

A B c DllJC. / Promol .J006

26 20 cm3 of hydrogen was mixed with 60 cm3 of air. The air contains only oxygen and nitrogen in unknown proportions. The hydrogen and air mixture Is sparked so that combustion of hydrogen Is possible. The resulting mixture contains 1 O cm3 of oxygen.

What is the volume of oxygen in the Initial air sample?

A 60 cm3 B 40 cm3 c 20 cm3 0 1 0 cm3 VJC / Preli'Tll :iooo

27 12 cm3 of AxBy decompose's on heating to form 12 cm3 of A2 and 1 8 cm3 of 82 All volumes aremeasured under thesame temperature and pressure. The formula of AxBy should be

A B c D

28 Calcium hydride, CaH2, reacts with water to produce an alkaline solution and hydrogen gas. What is fhe volume of hydrogen gas, measured under standard temperature and pressure that can be produced when 1 g of calcium hydride reacts with water? (M, of CaH2 = 42.1}

A 1.14 dm3 B 1.07 dm3 c 0.53 dm3 D 0.27 dm3 NJC I JC.I Bfl I :2007

6


29 0.0337 g of a volatile liquid when vapourized completely at 100 kPa and 300 K occupied avolume of 20 cm3. When this volume of vapour was completely burnt in an excess of oxygen, 40 cm3 of carbon dioxide and 20 cm3 of water vapour were formed. All volumes being measured at the same temperature and pressure.

What is the formula of the compound?

A B c

30 The use of Data Booklet is relevant to this question.

D MJC. I Prelhls JOO\I

Oxides of nitrogen are pollutant gases which are emitted from car exhausts. In urban traffic, when a car travels one kilometer, it releases 0.23 g of an oxide of nitrogen N,Oy. which occupies 120 cm3.

What are the values of x and y? (Assume 1 mol of gas molecules occupies 24.0 dm3)

Y. A 1 B 1 2 c 2 1 D 2 4

MJC. I Prelhll J007

31 Two volumes of hydrogen are mixed with five volumes of dry air at 100 c and atmospheric pressure. The mixture Is sparked so that the combustion of hydrogen goes to completion. If air contains oxygen and nitrogen In the molar ratio of 1 : 4, what it the mole fraction of water vapour In the resulting mixture at 100 C?

A 2 3

B 1 3

c 1 5 D 4 NX. I Pre'ins JOO

32 0.1 g of dry hydrogen gas was placed in a closed 2 m3 vessel with 3.2 g of oxygen gas. Thegases were exploded and the system.was allowed to cool to 25 c.

What will be the pressure, in Pa, of the gas left In the vessel after the reaction? (The volume and vapour pre.ssure of water may be neglected.)

A 8

56.7

61.9 c 0

7

92.9

123.8


33 Carbon disulphide, CS2, is a volatile flammable liquid which can be oxidised on combustion to give carbon dioxide and sulphur trioxide. A 20 cm3 sample of CS2 vapour Is Ignited with 100 cm3 of oxygen. The final volume of gas after burning Is passed Into an excess of aqueous alkali. What percentage of this final volume dissolved In the alkali?

A 25% B 50% c 60% D 75% fPJC. / Pre\l>n$ J006

34 Carbon disulphide, CS2, Is a volatile flammable llquld used In the manufacture of cellophane. On combustion, CS2 is oxidised as follows:

CS2(9) + 302(g) C02(g) + 2S02(9)

A 20.0 cm3 sample of CS2 vapour is Ignited with 120 cm3 of oxygen. The final volume of gas after burning is treated with an excess of aqueous alkali. What percentage of this final volume dissolves In the alkali?

A 40% 8 50% c 60% D 70% :'.>A.IC. I JC.I 61'1 I Joo.I

35 A gaseous organic compound, X, was burnt In an excess of oxygen. A 0.112 dm3 sample of X, measured at s.t .p. produced 0.88 gof carbon dioxide.

How many carbon atoms are there In 1 mole of X?

A L B 2L c 3L D 4L

36 4 dm3 of ethane were burnt In 16 dm3 of oxygen gas and the resulting mixture cooled to room temperature. The residual gas would contain

A equal volume of carbon dioxide and oxygen. B twice the volume of carbon dioxide as oxygen.

C twice the volume of oxygen as carbon dioxide. I

D only carbon dioxide. YJC. / Prelrn$ J006

37 A mixture of 50 cm of oxygen and 1 0 cm3 of hydrogen ls ignited continuously. What is themaximum theoretical decrease In volume? (All gas volumes are recorded at 293 K and standard atmospheric pressure.)

A 10 cm3 B 15 cm3 c 20 cm3 D 30 cm3

8


38 Complete combustion of a sample of a hydrocarbon. X, gave 0.66 g of carbon dioxide and 0.36 gof water. The empirical formula of X Is

A B c D AJC. I Promo) JOOJ

39 What volume of C02 will be formed when y cm3 of a 50:50 mixture by volume of methane andpropane are completely burnt?

A 2y cm3 B 5y cm32

c 4y cm3 D 5y cm3 Y JC I Pre lTn$ J005

40 A mixture of 20 cm3 of methane and 1 O cm3 of ethane was mixed with an excess of oxygen andthe mixture was sparked. After cooling to room temperature, the residual gas was passed through a solution of potassium hydroxide.

What was the volume of the gas absorbed by the alkali?

A 10 cm3 B 20 cm3 c 30 cm3 D 40 cm3 HCJC. I Promo$ .JOO\!

41 0.1 mol of an organic compound X gives 0.3 mol of carbon dioxide and 0.4 mol of water on complete combustion. 3 g of X when vapourized was found to occupy 1 .2 dm3 at s .t.p. X could be

A

B CH3CH2CH20H

CH3CH2CH3

c D

PJC. I PrelTn) JOO'n$ J007

43 1 0 cm3 of a pure hydrocarbon was completely burned in 80 cm3 of oxygen (an excess) at 425 K. After cooling to room temperature, the gaseous mixture volume decreased from 105 cm3 to 55 cm3 A further reduction of 40 cm3 was observed when the residual gas was passed through barium hydroxide. All gas volumes were measured at the same temperature and pressure.

What is the formula of the hydrocarbon?

A B' c 0

AJC. I Pre!Tn$ J005

9


44 Carbon disulphide vapour was burnt In oxygen according to the equation:

..- 10 cm3 of carbon disulphide was burnt In 50 cm3 of oxygen. After measuring the volume of gasremaining, the mixture of gases was treated wit an excess of aqueous sodium hydroxide and the volume of gas was again measured. All meaurements were made at the same temperature and pressure.

What were the measured volumes?

Volume of gas after burning I cm3 Volume of gas after treatment with NaQH(ag) I cm3 A 30 0 B 30 20 c 50 20 D 50 40

MJC. t PrelrM :l

4 7 1 5 cm3 of a mixture of carbon -monoxide and methane was mixed with excess oxygen andexploded. There was a contraction in volume of 21 cm3 at room temperature and pressure. Whatis the percentage by volume of methane in the mixture?

A 20 B 33 c 60 D 75 HCJC. I JC.I 8fl I JOOJ

48 Methane was burned In an Incorrectly adjusted burner. The methane was converted into a mixture of carbon dioxide and carbon monoxide In the ratio of 98:2, together with water vapour.

What will be the volume of oxygen consumed when y dm3 of methane is burned?

A (2 0.01 ) d 3y--y m 2

B (2y-0.01y) dm3

49 Which of the following Is a redox reaction?

A A/H3(9) + W(g) - A/H -(g)B A/3.(g) + 30W -+ Al(OHh(s)

C 2A/(s) + 3Cl2(g) - 2AIC/3(S)

c

D

D A/02(aq) + H(aq) + H20(/) - A/(OH)J(s)

(y-0.01y) drn3

RJC. I Pre\Tn) J006

HCJC. I JC.I 8ft I JOOJ

50 Iron In lron( l l l ) oxide can be reduced by the reaction with carbon monoxide to give iron metal andcarbon dioxide. What volume of carbon dioxide will be produced atr.t.p. by the reduction of 16 g of lron(lll) oxide? (1 mole of gas occupies 24.0 dm3 at 25 C and one atmosphere.]

A B

2.4 dm3

4.8 dm3c

D

7 .2 dm3

9.6 dm3 CJC. I Pre\Tn) J007

51 In an experiment, 50 cm3 of a 0. 1 mol dm-3 solution of a metallic salt reacted exactly with 25 cm3of 0.1 mol dm-3 sodium s ulphite solution: The half-equation for oxidation of sulphite ion is

S032-(aq) + H20(1) - so.2-(aq) + 2H.(aq) + 20-

If the original oxidation number of the metal 1n the salt was +3, what would be the new oxidationnumber of the metal?

A 0 B +1 .c +2 D +4 I

PJC. I Pre\Tn) ;)006

11


52 25.0 cm3 of 0.05 mol dm-3 KC/04(aq) required 50.0 cm3 of 0.20 mol dm-3 TiC'3(aq) to reach endpoint. Given that Tl(lll) Ion Is oxidised to Tl(IV) In this reaction, which one of the following formulae correctly represents the reduction product of the C/04 - Ion?

A ocr B c er D

53 1.978 g of an oxide of an element X, represented by X20n (Mr: 197.8), Is found to react with 0.008 mol of acidified potassium manganate(Vl l ) solution. In the reaction, aqueous HXO/- Ion Is formed. By considering the reduction of manganate(Vll) Ion to manganese(ll) Ion, deduce the oxidation number of X In X20n.

54

A +1 B +2

Consider the following half equations: Fe2

C20/- ;:::::

c +3 D +4

In an experiment, 20 cm3 of an acidified solution of 0.02 mol dm-3 FeC204 Is oxidised by 15 cm3 of 0.02 mol dm-3 KMn04. What is the final oxidation state of manganate(Vl l )?

A +1 B +2 c +3 D +4

55 An element Z form an oxide which Is a powerful oxidizing agent.

In a redox experiment, 1 o.o cm3 of 0.5 mol dm-3 of the oxide of z was used to oxidize 15.0 cm3 of0.40 mol dm-3 of acidified. manganate( l l ) Ions to manganate(Vll ) ions. If the oxide of Z wasreduced to the element Z, what Is the formula of the Z oxide?

A zo B c D lJC. f Pre\rn .J006

56 In an experiment, 100 cm of 0.020 mol dm-3 acidified lron( l l ) sulphate is quantitatively oxidised by 50 cm3 of a solution containing 0.020 mol dm-3 of an oxidizing agent, X03-. What is the finaloxidation state of X?

A -1 B -2 c +2 D +3

57 Nitrogen dioxide reacts with Iodide Ions under acidic conditions according to the equation shown.

N02 + 21- + 2H -+ NO + 12 + H20

. How many moles of electrons are gained by one mole of nitrogen dioxide?

A B 2 c 3 D 4 VJC. I Pre\rn .2006

12


58 In an experiment, 1 0.0 cm3 of a. solution containing a known concentration of iodate(V) ions,103-. was run into an acidified solution containing an excess of Iodide ions. Both lodate(V) ionsand iodide ions reacted to form iodine. The iodine liberated was found, on titration, to reactexactly with 30.00 cm3 of 0.100 mol dm-3 sodium thiosulphate solution.

What was the concentration (in mol dm-3) of the iodate(V) ions?

A 0.05 B 0. 1 0 c 0.20 D 0.25 He.I I PrelTTll J006

59 The metallic Ion, xn, Is oxidised to X03- by K2Cr207 in an acidic solution. H 25.0 cm3 of 0.088mol dm-3 aqueous xn require 22.45 cm3 of 0.065 mol dm-3 aqueous K2Cr201 for completereaction, what Is the value of n?

A 1 B 2 c 3 , D 4 He.I I JCI 111'1 /JOO!>

60 A sample of 0.025 moles of the chloride of an element Z was dissolved in distilled water and thesolution made up to 500 cm3 1 2.5 cm3 of this solution was required to react completely with 25cm3 of 0. 1 mol dm-3 sliver nitrate solution. What Is the most likely formula of the chloride?

A B

B D

ZCI zc1.

He.I I JCJ 81'J I J006

61 1 0 cm3 of 0.2 mol dm-3 K2X04 will react with 40 cm3 of 0.1 mol dm-3 iron{ll} sulphate solution. IfFe2 is oxidized to Fe3 by K2xo . what Is the final oxidation state of X?

A +2 B +3 c +4 D +5 He.I I JCJ lll'J I J006

62 25.0 cm3 of a 0.100 mol dm-3 solution of Y205 is reduced by sulphur dioxide. To re-oxidize Y toits original oxidation state, 50.0 cm3 of 0.0200 mol dm-3 of acidified potassium manganate(Vll)solution is required.

What is the oxidation state of Y after Y 205 Is reduced by sulphur dioxide?

A +3 B +4 c +5 D +6 He.I I Promol JOO!>

63 A solution of an oxidizing agent contains 5.80 g of XO/- per dm3 of solution. 10.0 cm3 of thissolution, acidified with dilute sulphuric acid, r,equlred 15.00 cm3 of 0.1 mol dm-3 Fe2(aq) Ions forreaction. Given that the final oxidation state of X Is +3 after the reaction, what is the relative atomic mass of element X?

A 50.9 B 52 .0 54.9 D 63.5 II/JC I XI llfl I J007

13

64 In an experiment, 25.o cm3 of 0.0200 mol dm-3 KMn04(aq) were found to absorb and react with 12.0 cm3 or nitrogen monoxide, NO at room temperature and pressure. A colourless solution contatnlng a brown precipitate of manganese(IV) oxide was produced. Which one of the following is a possible nitrogen-containing product of this reaction?

A B Ct I

D .V,JC. I J

69 In a redox experiment, an oxo-anlon of a metal, Mox-. was used to oxidize 22.0 cm3 of a 0.2 moldm-3 sodium sulphate(IV). For complete reaction, 1 1 .0 cm3 of 0.16 mol dm-3 of Mox- solution was required. If MO; was reduced to M2.(aq), determine the value of x.

A B 2 c 3 D 4 1' JC I Pre li'nl JOO

70 An ion of metal X can be oxidised by potassium manganate(V l l ) In acid solution to form X03-. Inan experiment, 1 .25 x 1 03 mol of the ion of X required 37.5 cm3 of 0.0200 mol dm-3 potassiummanganate(Vll) for complete reaction.

What is the initial oxidation state of the ion of X?

A +1 B +2 c +3 D +4 - y JC I Pre li'nl JOO

71 An element Y can exist In a few oxidation states. 1 2 . 50 cm3 of an aqueous solution of v2 ofconcentration 0.800 mol dm-3 needed 40.00 cm3 of 0 . 1 00 mol dm-3 acidified KMnO.(aq) forcomplete reaction.

What is the final oxid

74 2.0 g of copper metal Is added to react completely with 25.0 cm3 of a 0.315 mol dm-3 of nitrogencontalnlng. solutlon. Cu2(aq) and NH4 (aq) are formed. By calculatlng final oxidation state of nitrogen In NH4 (aq), deduce the lnltlal oxldatlonstate of nitrogen In the solution.

+1 B +3 c +4 0 +5 f P JC. I Preli'n Joo.I

75 Hydroxylammonlum Ion, HONH3, reduces Fe3 to Fe2 In acid solution. If 4 mol of Fe3 isreduced by 1 mol of HONH3 Ion, which of the following nitrogen-containing species Is formed inthe reaction?

A NH/ B c 0

76 The percentage of copper in a copper(ll) salt can be determined by using a thlosulphate titration. 0.401 g of a copper(ll) salt was dissolved In water and added to an excess of potassium Iodide solution, liberatlng Iodine according to the following equation:

2Cu2(aq) + 4r{aq) -+ 2Cul(s) + h(aq)

The Iodine liberated required 38.00 cm3 of a 0.100 mol dm-3 solutlon of sodium thlosulphate. The. percentage of copper, by mass, In the copper(ll) salt Is

A 60 .2 B 57.1 c 30.1 0 28.6 JJC I Preli'n J

17 Manganate(Vll) Ions, Mn04 -, are reduced In acidic conditions to manganese(ll) Ions, Mn2,whereas they are reduced In neutrat conditions to manganese( IV) oxide, Mn02

The oxidation of 25 cm3 of a solution X containing lron(ll} Ions required, In acidic conditions, 20 cm3 of a solution Y containing manganate(Vll) Ions. What volume of solution Y would berequired to oxidize 25 cm3 of solution X In neutral conditions?

A 4 20x- cm37

c 5 20 x- cm33

B 20x cm35

D 20 x ?_ cm34

VJC /JC.I !lfl I J001

78 Nitrogen oxide, NxOy. undergoes reaction with hydrogen In the presence of a catalyst to give ammonia and steam as the only products. 2400 cm3 of the nitrogen oxide, measured at roomtemperature and pressure (r.t.p) produced 7.20 g of water. The ammonia produced was neutralized by 200 cm3 of 1.0 mol dm"3 of HC/.

What is the-oxidation number of the nitrogen In the nitrogen oxide?

A +2 B +3 c +4 0 +5 VJC /JC.I !lfl I J007

16


79 25.0 cm3 of a solution of hydrogen peroxide, H202, was oxidized by excess potassiummanganate(Vll) solution under acidic condition. Effervescence of oxygen gas was observed. The volume of oxygen gas produced at room temperature and pressure was 26 cm3. What Is the concentration (in mol dm-3) of hydrogen peroxide In the solution?

A B

2 .89 x 10-2

4 .33 x 10-2 c D

8.66 x 10-2

1 .30 x 1 0-

RJC. I l'rorno JOOb

. 80 In an experimental Investigation of the reduction of chlorate(VII) ions, C/O -, in aqueous solution,It was found that 25.0 cm3 of 0.0500 mol dm-3 aqueous potassium chlorate(Vfl) required 50.0 cm3 of 0.200 mol dm-3 aqueous titanlum(IJI) chloride to reach the end-point. The titanlum{lll)Ions are oxidized to titanium(IV) Ions In this reaction.

Which of the following formulae could correctly represent .th'e reduction product of the chlorate(VII) Ions?

A B er c D HCJC. I JC.I 8fl I JOOJ

17


SECTION 8

The responses A to D should be selected on the basis of

A B c 0 1, 2 and 3 are 1 and 2 only are \2 and 3 only are 1 only Is correct

correct correct correct

No other combination of statements is used as a correct response.

1 Which of the following quantities are equal to the Avogadro constant?

1 The number of ions in 41 g of CH3COONa.2 The number of electrons In 1 g of hydrogen gas. 3 The number of molecules In 24 dm3 of nitrogen at 273 K and 1 atm.

2 Which of the following statements about one mole of a metal are always correct?

1 It contains the same number of atoms as 12 g of 12C.2 It contains the same number of atoms as 1 mol of hydrogen atoms.

NX. I X.1 llfl I J001

3 It contains the same number of atoms as the number of electrons In 1 g of hydrogen gas. HC.X. I X.1 llfl I JOOJ

3 Which statement about a 12.0 g sample of 12C Is correct?

1 The number of atoms In the sample Is 6.02 x 10232 The number of atoms In the sample Is the same as the number of atoms In 4.0 g of 4He.3 The number of atoms In the sample Is the same as the number of atoms In 2 g of 1H2

f x. I PreU,,,$ JOO!>

4 Which statement about relative atomic mass of X Is correct?

1

2

3

.

It is the ratio of the mass of one atom of X relative to -1 the mass of one atom of 12C. 12 1 It Is the ratio of the average mass of one atom of X relative to - the mass of one atom

12 or 12C.

It Is the ratio of the mass of one mole of X relative to J... the mass of one mole of 12C.12

NX. I Pr\Tn$ J007

18


5 At r.t.p., 2.8 dm3 of hydrogen sulphide was mixed witt1 1.6 drn1 or sulphur dioxide when thefollowing reaction occurred.

Which of the following statements are true?

1 Final volume of gases was 0.2 dm3.

2 The llmitlng reactant was S02.

3 The volume of water produced was 2.8 dm3.HCl / J(.1 &f1 I JOO'.>

6 In an experiment, 20 cm3 of an organic compound was sparked with excess oxygen. 80 cm) of carbon dioxide and 80 cm3 of water vapour were obtained. All gases were measured at the sametemperature and pressure. Which of the following molecular formula fit the data?

1 CH3CH2CH2CH3 2 CH3CH2CH2CHO

3 CH3CH2CH2C02H

7 In an experiment, 10 cm3 of a gaseous organic compound were sparked with an excess ofoxygen. 40 cm3 of carbon dioxide and 5 cm3 of nitrogen were obtained among the products. All the gas volumes were measured at the same temperature and pressure.

Which of the following molecular formulae fit these data?

1 2

8 Which of the following equations represent redox reactions?

1 N02 + 21- + 2H+ -. NO + Ii + H202 2Na0H + 2Al + 6H20 --. 2NaA/(OH)4 + 3H2 3 NH4N03 -. N20 + 2H20

3 HC.J(. I JC.I IHI I JOO

HC.JC I JC.I 8 fl I JOOl

12 Which of the following statements concerning the reaction between chlorine and aqueous sodium hydroxide are true?

3C/2 + 6Na0H -. 5NaC/ + NaC/03 + 3H20

1 Chlorine undergoes disproportionation in the reaction. 2 Chlorine is reduced to the +5 oxidation state. 3 NaOH Is acting as a reducing agent .

19

PJ(. I Pro.'no :>OO.l


9 Which of the following statements about the following reaction are correct?

The hydrogensulphite ion is a reducing agent.

2 The iodine liberated can be determined using standard sodium thiosulphate solution. 3 20 cm 3 of 0.1 mol dm-3 ioda te(V) solution produces 0 .001 mole of iodine.

1 O Below is a list of chemical reactions {I) to {Ill)

{I) Cu{OH)i(s) + 2HN03(aq) -. Cu(N03)2(aq) + 2H20(/)(lJ) Fe203(s) + 3CO(g) -. 2Fe{s) + 3C02{g) {JrI) Sr(N03)2{aq) + H2$Q4(aq) -. SrSO,(s) + 2HN03(aq)

Which of the following statements are true?

1 Reaction {I) is a redox reaction.2 CO(g) is the reducing agent in reaction (II). 3 Reaction {Ill) is a precipitation reaction.

llJ

STRUCTURED AND FREE RESPONSE QUESTIONS

1 0.50 g of Impure ammonium chloride Is warmed with an excess of potassium hydroxide solution.The ammonia liberated Is absorbed in 25.0 cm3 of 0.200 mol dm-3 sulphuric acid. The excess ofsulphuric acid requires 5.64 cm3 of 0.200 mol dm-3 sodium hydroxide solution for titration.

(I) Calculate the number of moles of excess sulphuric acid. [ 1 I (II) Calculate the number of moles of ammonia liberated from the reaction between

ammonium chloride and potassium hydroxide. [2] (Ill) Calculate the percentage purity of ammonium ct1loride in the 0.50 g impure sample. [3]

:,Ax. / l'rorr>0) :ioo!:>

2 Gold can be dissolved from gold-bearing rock by treating the rock with sodium cyanide in thepresence of oxygen In air.

3

(a) (I)

4Au(s) + 8NaCN(aq) + 02(g) + 2H20(/) _, 4NaAu(CN)2(aq) + 4Na0H(aq)

Calculate the number of moles of gold present in 10001

4 A supply of soclium metal was contaminated with sodium oxide and sodium chloride. A sample ofthis metal weighing 1 .00 g was reacted with water, producing 4 70 cm3 of hydrogen gas underroom conditions. The resulting solution was made up to a volume of 250 cm3 with water and a 25.0 cm3 portion of the final solution was exactly neutralized by 37.20 cm3 of 0.056 mol dm-3 sulphuric acid.

5

(i) Calculate the number of moles of hydrogen gas released. [1]

(ii) Calculate the number of moles of sodium hydroxide produced by the reaction between water and the sample. [2]

(iii) Use your answers to parts (i) and (ii), together with the equations below, to calculate the number of moles of sodium and sodium oxide in the sample.

Given: 2Na + 2H20 _, 2NaOH + H2Na20 + H20 __. 2Na0H [2]

(iv) Hence, deduce the % by mass of sodium and sodium oxide in the sample. [2)

(a)

1' JC I JCI 81'1 / JOJ

Al r.t.p, 10.0 dm3 of polluted air is passed through limewater so that all the C02 isprecipitated as CaC03. The mass of CaC03 formed Is 0.050 g. What is the percentage byvolume of C02 in the air sample? [Molar volume of a gas at r.t.p = 24 dm3] [2]

(b) 40.0 cm3 of a HC/ solution was diluted with water and made up to a 250 cm3 solution. 25.0 cm3 of this diluted solution required 20.90 cm3 of 0.01 mol dm-3 NaOH solution for complete neutralization. Whal is the concentration of the original HC/ solution in mol dm-3? [2)

(c) Balance the following equations:

(I)

(ii)

S02 + 103.. __. so/- + 12 (acidic medium)Cr20/- + C20/- + W _. Cr3' + C02 + H20

(d) The following is a method by which the reaction between iron(lll) Ions and hydroxylammonium chloride, NH30Hcr. may be Investigated.

25.0 cm3 of a solution containing 3.60 g dm-3 of hydroxylammonlum chloride was added to a solution containing an excess of Fe3 Ions and about . 25 cm3 of a 1 mol dm-3 sulphuric acid and the mixture boiled. It was then diluted with water and allowed to cool. The Fe2' ions formed was then titrated with 0.020 mol dm-3 potassiummanganate(Vll) of which 25.90 cm3 were required.

(I)

(ii)

Calculate the molar ratio Fe3' I NH30H' In the reaction.Determine the oxidation number of nitrogen In the product.

22

HCJC I JCI en I JOOJ

[2)

[2] (2)


6' 30 cm3 of colourless 0.04 mol dm"3 aqueous ammonium vanadate, N H4VO) was reduced undersuitable conditions to give a violet solution containing positively charged vanadium ions , V" ' . On titration, this solution was found to require 48 crh of 0.01 mol dm-3 aqueous potassiummanganate(V l l ) solution to oxidize the vn back to the original vanadate ions.

(a) What Is the oxidation number of vanadium in ammonium vanadate, NH4V03? 1 1 1

(b) Calculate the number of moles of manganale(V l l ) ions required to oxidize 1 .0 mol of V"' ion. (1 mol of vn -+ 1 mol of V03-) [3]

(c) Hence, determine the value of n in the formula of the violet vanadium ion, V"'. [2] jAJC I Prornol JOOJ

7 The compound Na3Cr04 Is a green solid. When mixed with dilute H2S04, it disproportionates toyield CrJ.(aq) and Cr2o/-(aq). The mixture produced was mixed with excess Kl and the 12liberated required 40.0 cm3 of 0.25 mol dm-3 Na2S203(aq) for reaction.

8

Write equations for the following changes: (I) Cro/- to Cr3 and (II) crol- to Cr20/-(Ill)

(Iv)

(a)

hence, write the overall equation for the disproportionation of Cr04 3- in acid. Calculate the mass of Na3Cr04 used In this reaction.

AC.JC I Preltnl ;)OO\

When a 1 0 .65 g sample of NaC/03 is heated at its melting point, it disproportionate toNaC/04 and NaCl.

(I) Explain the term 'disproportionate' with reference to NaC/03.

(II} Determine the oxidation number of Cl in NaC/03 and NaC/04.

(Il l) Write a balanced equation for the described reaction. (Iv) Calculate the mass of NaC/04 that can be obtained from the reaction.

(b) The oxidation number of an element M In a compound was determined as follows.

0.01 3 mol of the compound was d issolved in water and the solution was made up to1 00 cm3 1 0.0 cm3 of this solution required 21 .65 cm3 of 0.02 mol drn-3 K2Cr20, to oxidizeM in the compound to the +5 oxidation state. Given

Calculate the original oxidation number of M In the compound.AJC I JC\ flfl I :JOOI

23

[6]

[5]

[5]


9 (a) Sodium sulphate( IY) , Na2S03, is somet imes added to sausage meat to act as a preservative. The amount of sodium sulphate(IV) present can be determined by boiling a samp le of the meat with acid and then determining the quantity of sulphur dioxide produced by titration against iodine.

1 00 g of sausage meat was boiled with 500 cm3 of 1 mo l dm"3 hydrochloric acid. Thesulphur dioxide evolved was dissolved In water and found to require 24.00 cm3 of0.0 1 25 mol dm-3 iodine solution for complete reaction. The iodine was reduced to iodideions in the reaction. In order to check the results of the titration, excess barium chloride is added to the final solution after titration and the resultlng precipitate of barium sulphate(V I ) is collected and weighed .

\. ( i ) Write a balanced equation to represent the reaction betwebn sulphur dioxide and

iodine. (ii) S ta te clearly the colour change that occurs at the end-point of the above

mentioned titration. (iii) Government scientists often expre,ss the amount of sodium sulphate(IV) in meat

in p.p .m (parts per m i llion ) where 1 p.p.m. = 1 g In 106 g of meat.Determine the amount of sodium sulphate(IV) (in p.p.m.) in the sausage meat.

(iv) Calculate the mass of barium sulphate{VI) formed when excess barium chloridesolution is added to the solution at the end of the titration.

(b) Alloys of aluminium and magnesium are often used in aircraft manufacture because of their strength and low density.

When aqueous sodium hydroxide Is added to a sample of one such alloy, the alumlnium present reduces water in the basic solution to produce hydrogen gas while Itself Is ox id ized to aluminate, (A/(OH)4r.

For the above reaction, write down the following:

(i) Oxidation hal f-equat ion, (ii) Reduction half-equation,

(i Ii) Overall balanced equationAJC. / JC.I llfl I JOOl

1 0 Ch lorine reacts with iodine to form a compound T, IC/1. When dissolved in an excess of aqueouspotassium iodide, T liberates iod ine , 1 2 , wh ich Is the only Iodine-containing product In the reaction.

( i ) Write the equation for the reaction between T and potassium Iodide.

( i i ) Calcu la te the number of moles of iodine liberated when 1.00 g of T reacts with an excessof aqueous potassium iodide.

(ill) What volume of 1 .00 mol dm-3 sodium thiosulphate would be required to react with all theiodine liberated in (I I)?

A JC. I Pre\>-n) JOOb I Poper J

24

(8)

[2]

[3]


1 1 Hydroxylamlne (NH20H) may be oxidized under different conditions eitt)er to nitrogen (N2) or todinitrogen oxide (N20).

(a) The half equation for the oxidation of hydroxylarnine to nitrogen is

(b)

Constrct a similar half equation for the oxidation of hydroxylamine to N20.

It was found experimentally that solution A (80 cm3 of 0.05 mol dm-3 hydroxylarnine) wasquantitatively oxidized by solution B (20 cm3 of 0 .40 mol dm-3 Fe3' ions).

Calculate the number of moles of (I} NH20H in solution A, (II) (Ill)

Fe3 in solution B Fe3 that reacted with 1 mole of NH20 H .

[ 1 J

[3]

(c} From your answers to (b), deduce whether the hydroxylamine has been oxidized to nitrogen or dinltrogen oxide and hence write an equation for the redox reaction between N H20H and Fe3. [2 )

AC.JC. I Promo JOOJ

1 2 Chlorine was bubbled through 250 cm3 of aqueous sodium thiosulphale, Na2S203 A redox reaction occurs between chlorine and thlosulphate Ions, forming chloride ions and sulphate ions .Excess chlorine was then removed by some suitable means.

(a) Explain what is meant by a "redox reaction", making reference to the reaction betweenchlorine and thlosulphate Ions . { 1 ]

(b) (I)

( I I)

Construct the half equations and the overall balanced equation for the reaction occurred. A 25.0 cm3 sample of the resu ltant solution was found to give 0.583 g of bariumsulphate precipitate when treated with an excess of aqueous barium nitrate. Calculate the concentration of Na2S203 in the 250 crn3 solution used.

(c) Another halogen., iodine, reacts with thiosulphate ions In a diHerent manner:

By comparing the changes In oxidation state of sulphur in this reaction and the reaction in

[3)

(b)(I), suggest which halogen, iodine or chlorine, is the stronger oxidizing agent. (2) HU / JC.I !lfl I JOO!>

25


1 3 Iodine and chlorine react together to form compound X ( IC/n). When 0.0.010 mol of X was reactedwith an excess of K l (aq). all of its iodine was converted into '2. The iodine liberated required 40.0 cm3 of 0. 1 0 mol dm - J sodium thiosulphate. Na2S203 for complete reaction.

( i ) Calculate the amount ( in moles) of iodine produced.

12 + 2S10/ - -. 21- + $4062-( i i ) Hence calculate the value of n in IC/n.

( i i i ) Write a balanced equation for the reaction between C/2 and ( i .

HC JC I JC I 8 1'1 I JOO

1 6 Sheep are most prone to chronic copper poisoning (CCP), common ly caused by consumingcontaminated liquld feed. Any excess absorbed copper is stored in the cells or tile liver,eventually reaching toxic levels. Levels in the liver 500 p.p.m. (using the mass or the liver as a reference) are usually considered toxic.

The concentration of copper( l l ) Ions in the l iquid reed can be quantified by first reac ting thesample with excess potassium iodide (to produce copper( ! ) iodide and iod ine) followed by titration of the liberated Iodine against standard aqueous sodium thiosulphate.

(a) Write down the balanced equations, with sta te symbols, ror the two reactions men t ioned above. [2]

(b) If a 25.0 cm3 sample of the liquid reed was reacted as described above, the volume or 1 .00 x 1 0-5 mol dm-3 standard aqueous sodium thiosulphate needed for completereactlon was 20.05 cm3. Calculate the concentration of Cu2' in the sample. [2]

(c) Consider a sheep candidate with a 1 kg l iver and which needs 0.004 g of copper(A, = 63.5) and can eliminate 0.001 g of excess copper via the kidneys daily. If it is fed 1 0 dm3 of the above feed dally and the average sheep can live up to 20 years in age,show whether the feed Is safe for cons umption . [3]

(d) Suggest another method to determine the amount of copper( l l ) ions in a sample solutionof the feed. [ 1 ] .

f!J(. I JC.I en I .JO

1 8 Ch rom ium oxide, CrO, is a n unusual oxide of chromium. I t is normally found on the magnetic layer of c;:issette tapes. This compound is both highly conductive and ferromagnetic, whichprovidAs a good audio response.

When the oxide from a particular length of tape is dissolved in dilute sulphuric acid, disproportionation occurs, forming Cr3' and Cr20/-. The resulting solution required 30.0 cm3 of 0 . 1 0 mo l dm "3 Fe2' (aq) to completely reduce Cr2o/- to Cr3'.

( i ) Suggest a n equat ion for the disproportionation or Cr02 in acid solution.

( i i ) Wri te an equation for the reaction of Cr2072- with Fe2' in acid solution.

(i i i ) Calculate the mass of Cr02 in the length of cassette tape.

( iv} If 1 2 .5% of the or igina l length of tape was used for the experiment, calculate the original length of the tape. (Width of the tap :: 0.5 cm; thickness = 0 . 1 mm; coating density of Cr02 :: 2.24 g cm-3).

C.JC I Prelrnl J006 I Poper J

1 9 The Winkler method can be used to determine the amount of dissolved oxygen in a water sample. In an experiment, manganese ( I I ) sulphate solution Is first added to a 1 00 cm3 watersample in a conical fiask, followed by alkaline saturated potassium Iodide solution In excess. Abrown precipitate of manganese( ! r I ) hydroxide is formed. Concentrated sulphuric acid Is thenadded and the solution is carefully mixed unti l the precipitate disappears, leaving a dark brownsolution. Th is solut ion requ ires 7 .50 cm3 of 0.0 1 25 mol dm-3 sodium thlosulphate for titration.

(a) Write a balanced ionic equation for the reaction of manganese(ll) sulphate and oxygen in

[7]

the water sample under alkaline condition. [ 1 ]

(b) Write an equation for the disappearance of the brown precipitate on adding concentrated sulphuric acid. [ 1 ]

(c) Write an equation for the titration reaction and hence calculate the concentration of the dissolved oxygen in the water sample in mg dm-3. [4]

PJC I Prelrnl J()()j I Poper J

2 0 Acidified potassium manganate(Y l l ) . KMnQ4, oxidizes ethanediolc acid, H2C204, to form acolourless gas. 1 .27 g of iron ( l l ) ethanedioate were made up to 250 cm3 of acidified aqueoussolution. 25.0 cm3 or this solution reacted completely with 26.50 cm3 of 0.0200 mol dm-3 KMnO

. solut ion .

( i ) Calculate the mole ratio of KMnQ4 to FeC204 taking part in this reaction.

( i i ) Hence, write an ionic equation for the reaction between KMnO. and FeC20. In the presence of H2S04.

NJC I Prelml J006 I Pope J

28

[4]


21 (a) (I)

(Ii)

A hydride of nitrogen , Q, contains 1 2 .5% or hydrogen by mass .Calculate the empirical formula or Q .

When Q was heated very strongly, it decomposes into its elements. 1 0 cm'J or Q gave 30 cm 3 of products (volumes are measured under the same conditions) .

[ 1 I

Whal Is the molecular formula of Q and the oxidation state of ni trogen in Q? [2]

( I l l ) Q Is an unstable compound which will disproportionate to give two nitrogencontaining products when heated gently . The oxidation numbers of n itrogen in the two products are O and -3 respectively.

Write a balanced equation for the reaction and explain what is meant by disproportionation In this reaction. 12]

(b) 25.0 cm3 of an aqueous solution containing 0 .050 mol dm-3 of an ion M3'(aq) wasreduced using excess zinc, and the unreacted zinc removed. The resulting solution required 5.0 cm3 of an acidified solution of potassium manganate (V l l ) of 0 .050 mol dm-3to restore M to I ts original +3 oxidation state. To what oxidation state was M:i' reduced byzinc? [2)

22 (a)

:C,AJC I Preln> :JOOI I Poper :J

Although xenon Is a noble gas, it forms many different compounds with fluorine and oxygen. Xenon trioxide, Xe03, dissolves In water to form an acidic solution of xenic acid,H2Xe04.

Xenlc acid Is a very powerful oxidizing agent that can oxidize manganese( l l ) to maoganate(Vll) Ions.

What Is the oxidation state of Xe In xenic acid?

(b) 1 6.75 g of Xe03 was dissolved in water to give a solution of xenic acid . The solution wasmade up to 1 00 cm3 using deionised water. 10.0 cm3 of the solution was then titratedagainst a 0.500 mol dm-3 aqueous solution of Mn2' . 22.45 crn3 of aqueous Mn2' wasrequired for complete reaction.

(i) Write the half-equation showing the conversion of manganese ( l l ) to manganate(V l l ) ions under acidic conditions.

( I I ) Determine the a mount of xenic acid formed.

( I l l ) Hence, calculate the mole ratio of H2Xe04 to Mn2' .

(Iv) Deduce the final oxidation state and suggest a possible identity for the xenoncontaining product.

(v) Hence, write a balanced equation for the reaction between HXe04 and Mn .

k.K. I JCI llfl I :lOOb

[ 1 J

[7]


23 (a) A rusted iron nail was analysed to determine the amount of iron that had been oxidised to rust. The iron nail was dissolved in excess dilute sulphuric acid to give 1 dm3 of solutionwhich now contains both Fe2' ions from the unrusted Iron and Fe3 ions from the rusted iron.

(I) 25.0 cm3 of this solution required 33.80 cm3 of 0 . 1 0 mol dm-3 KMnO for completeoxidation of the Fe2' ions. Calculate the amount of Fe2 Ions In the 1 dm3 of theoriginal sample.

( I i ) To a second 25.0 cm1 sample of solution, an oxidising agent was added toconvert al l the Fe2' ions present to Fe3 ions. The Fe3 Ions were then titrated witha solution of EDTA ions and 1 7.60 cm3 of 1 .00 mol dm-3 EDTA were required.Calculate the amount of Fe3 Ions from the rust In 1 dm3 of the original sample.

[ 1 mole of EDT A reacts with 1 mole of Fe3' ions]

(b) When hydrated iodic acid is heated to 240 C, the acid dehydrates to form anhydrous white crystals .

24 (a)

A sample of these anhydrous crystals, H103, reacted completely with 1 00 cm3 of agaseous mixture of carbon monoxide and carbon dioxide. The carbon monoxide gas in the mixture was oxidised to carbon dioxide. The iodine liberated in this reaction required1 4 .60 cm3 of 0.050 mol dm-3 Na2S203 for complete reaction.

( I ) Write a balanced equ ation for the reaction between lodlc acid and carbon monoxide.

( 1 1 )

(I I I )

Calculate the amount of iodine liberated in the reaction.

Hence determine the percentage of carbon monoxide In the gaseous mixture. [All gas volumes were measured at s.t.p.)

HCI f Promol J006

FA 1 is a mixture of sodium bromide and sodium sulphate. 6.000 g of FA 1 was dissolvedin water to make up FA 2. The FA 2 solution was divided Into two portions of equalvolume. Barium ch loride solution was added in excess to a portion of FA 2 and 3.776 g ofa white precipitate was formed.

( I ) Identify the white precipitate and hence calculate the mass of sodium sulphate in

[2]

(2)

( 1 ]

(2]

( 1 )

6 .000 g of FA 1 . (3)

( i i ) Calculate the percentage by mass of sodium In FA 1. (4)

(b) 0 . 1 50 mol dm-3 of acidified K2Cr201(aq) was added to the other portion of FA 2. TheCr20/-(aq) Ions are reduced to Cr'(aq) ions.

By writing a relevant equation. calculate the volume of K2Cr201(aq) required to bring about complete reaction. (3]

AJC. f JC. 1 111'1 / J007

30


25 (a) A given chromate compound, Na3Cr0. is an unstable dark green solid. On addition ofdilute sodium hydroxide, It may undergo disproportionation to produce a solution containing chromium(l l l ) ions, Cr3' and chromate(V I ) ions . Cro/.

When a 2.00 g sample of the impure green solid was treated in ltiis way, ti lechromate(VI) Ions in the resulting basic solution reacts wit11 an excess or tiqueous potassium bromide to liberate 5.00 x 1 0 3 moles of bromine and a green solutioncontaining chromlum(l l l ) ions, Cr1 .

(I) Calculate the oxidation number of chromium in Na3Cr04.

(II) Define the term "disproportionation".

(Ill) Write balanced half-equations for each of the following processes:

1 reduction of the given chromate ion to chromium( 1 1 l ) ion 2 oxidation of the given chromate ion to chromate( V I ) ion

(Iv) Construct a balanced ionic equation for the reaction between chromate(Y l ) andbromide, Br - ions.

(v) With the aid of the two overall equations in (a)(iii) and (a)(lv), calculate thenumber of moles of Na3Cr04 in the 2.00 g sample and hence calculate itspercentage purity.

(b) A solution containing ammonium polytriovanadate(V), NHN03, in dilute sulphuric acidcan be reduced by zinc to give a lilac-coloured solution . A 25 .0 cm3 portion or a solutioncontaining 0.0500 mol dm-3 ammonium polytriovanadate(V ) was reduced by zinc and subsequently re-oxidized to the original state using 37 .5 crn3 of 0.0200 mol dm 3 potassium manganate(V l l ) solution.

Calculate the oxidation state of vanadium in the lilac-coloured solution. RJ( I JC.I Bfl I :!OOJ

26 A solution of uranium Ions, uo/(aq) is yellow. The uo/(aq) are reduced by zinc powder in thepresence of acid to green u1(aq) Ions.

The u2(aq) can be oxidized quantitatively back to UO/'(aq) by acidified Mno4-(aq). It was found experimentally that 20.0 cm3 of 0.100 mol dm-3 U2'(aq) reacted with 1 6.00 cm3 Mn04-(aq) ofconcentration 0.050 mol dm-3.

(a) What Is the oxidtlon state of U in Uo/(aq)?

(b) Calculate the number of moles of uz that reacted wltt1 mole of acidified Mn Odaq ) .

(7]

[3]

[ 1 ]

Hence determine the value of z . [4] (c) Using the value in (b), write a balanced equation ror the reaction between UL' and

acidified Mn04 -(aq). [ 1 ] AJC. I />totnol JOOb

31


27 A complex ethanedioate salt W , K,Mn(C204)y. zH20 was prepared. On heating , 1 .00 g of W gave 0 . 1 1 g o f water. On ignition with phosphoric(V ) acid, 1 .00 g of the salt W gave a residue of 0.29 g Mn2P201. On dissolving with sulphuric acid. 0 . 1 0 g of W required 1 2.25 cm3 of 0.020 mol dm"3aqueous potassium ma ngana te(V I I ) to reach the end-point on titration.

( i ) Balance the following ionic equation for the redox titration between . the sal t W andpotassium manganate(V l l ) in acidic condition.

C20/- + Mn04 - ..... C02 + Mn2 (1 )

( i i ) Find the mass of Mn in 1 .00 g of W. [ 1 ] ( i i i ) Find the mass of ethandioate, c20/ i n 1 .00 g of W. ( 1 ) (iv) Find the mass of potassium from 1 .00 g of W. ( 1 ] (v) Find x, y and z. [2]

28 (a) Balance the following redox equations :

(i)

(Ii)

As203(S) + N03 "(aq) -+ H3AS04(aq) + NO(g)

MnOdaq) + N02-(aq) - Mn02(s) + N03"(aq)

(acidic)

(basic)

He.JG I Jc.I 81'1 I JOO)

(b) The mineral hydromagnesite is a hydrated carbonate of magnesium, with the formulaMgx(C03)y.(0 H )z.nH20 and a molar mass of 466 g mof-1 . Hydromagnesite decomposes to

give magnesium oxide as the only solid product, together with carbon dioxide and steam.

Mgx(C03)y(0H)z.nH20(s) xMgO(s ) + yC02(g) + (f + n) H20(g)When 1 . 1 0 g of a pure sample of hydromagnesite is heated to constant mass, 0.415 g of carbon dioxide was given off.

( i ) Calculate the amount of hydromagnesite heated and carbon dioxide given off, and

[2]'

hence determine the value of y. [2]

The magnesium oxide obtained from the above decomposition was completely dissolved in 50 cm3 o f a 0.500 mol dm-3 solution of sulphuric acid. The resultant solution was transferred into a volumetric nask and diluted lo 250 cm3 with deionized water. A 25.0 cm3 aliquot of this diluted solution required 26.40 cm3 of a 0 . 100 mol dm "3 solution of potassium hydroxide for complete neutralisation.

( 1 1 ) Fine the amount of sulphuric acid that reacted with magnesium oxide.

( I i i ) Using the equation given below, determine the value of x In the formula of hydromagnesite.

(iv) Hence or otherwise, deduce the values of z and 11.

HCl I J

ANSWERS

MULTIPLE CHOICE QUESTIONS

Section A 1 c 2 D 3 c 4 c 5 D 6 c 7 c 8 -A-9 -0 -10 B

1 1 B 12 B 1 3 B 1 4 c 1 5 c 1 6 c 1 7 B 1 8 B 1 9 B 20 A 21 A 22 D 23 D 24 c 25 c 26 c 27 c 28 B 29 c 30 8 3 1 B 32 c 33 D 34 B 35 D 36 8 37 B 38 c 39 A 40 D 41 A 42 D 43 c 44 c 45 c 46 D 47 c 48 B 49 c 50 c 51 c 52 c 53 c 54 c 55 c 56 D 57 B 58 A 59 A 60 D 61 c 62 B 63 B 64 B 65 B 66 A 67 B 68 c 69 D 70 B 7 1 A 72 c 73 c 74 0 75 c 76 1A 77 c 78 c 79 B 80 B

Section B 1-I _1 _._I -1-I _1 _...._, -1-I _1 ;_..._1 :-1--4_..._I c_,__s_l._o_,__6__.l_c___._7_.l_s___.._8_.l_A__.Ol_9__._o__._1_0_.l_A___,

STRUCTURED ANO FREE REPONSE QUESTIONS

1 (I) I 5.64 >< 1 04 mol (II) I 8.87 x 10- mol

2 (a)(I) 9 .64 >< 102 mol I (a)(ll) I 2 .57 x 1 03 cm3(b)(ll) 9 .46 g

3 (a) 1 1 a.o cm3 (b) I 30. 73 kg

4 I (I) I (111)1 .96 >< 1 0"2mol I (II) l 4 . 1 7 x 10- mol 3.92 >< 102 mol, 1 .25 >< 103 mol

(a) 0.12% I (b) I 0.0523 mol dm 35 (c)(I) 5502 + 2103- + 4H20 -- 5so/ + 1 + SH'

(c)(li) Cr20/- + 3C20/- + 14H ....... 2Cr3 + 6C02 + 7H20( d)(I) 1 : 2 I (d)(ii) I +1

6 (a) I +s (b) I 0 .4 mol

(I) cro/- + aH + 2e ... Cr3' + 4H207 (II) 2Cr04 + 2H --+ Cr20,2 + 2e- + HiO

( I l l) 3Cr04 + 1 0H ....... er + Cr20/- + 5H20

(i l l) I 94.9%

I (b){i} I 3 . 1 5 g- .

I (iv} I 90. 1 % , 1.74%

(c) j 3

I (iv) I o .925 g

(a)(I) NaC/03 Is simultaneously reduced and oxidized to form two different products.8 (a)(ll) +5, +7 (a)(i l l) 4NaC/03 ... 3NaC/04 + NaCl

(a)(lv) 9 . 1 9 g (b} +3

(a)(I) so2 + ii + 2H20 ....... 2r + so/ + 4H' I (u)(li} I Brown to colourless9

(a)(lll} 378.3 p.p.m. I (a)(lv) I 0. 070 g (b)(I) Al + 40H" -+ (Al(OH).r + 3e- j (b)(ll} I 2 H ' + 2e . ... H

(b)(lll) 2Al + 20H" + 6H20 ........ 3H2 + 2[Al(OH)4r

33

I


i 1 0 I ( I ) j 1c1, + K 1 4 1 2 + 7KC/ ( i i ) j 1 .07 x 1 0 2 mol (Ill) j 2 1 .3 cm3

(a} 2NH 20H N20 + 4 H ' + H20 + 4e- I (b)(I} I 0.004 mol 1 1 (b)( i i) 0.008 mol I (b)(i i il I 2

(c) N10: 4Fe3' + 2NH20H -+ 4Fe2' + N20 + 4H' + H20

(a) f l is a type of chemical reaction whereby atoms (chlorine and sulphur in this case) have theiroxidation number changed.

1 2 Ct2 + 2e _, 2cr

(b){i ) S20/- + 5H20 - 2so/ + Be- + 1 O H '4Ct2 + s20/ + 5H20 ..... 2so,2- + 1 0H ' + acr

(b )(i i) 0.05 mol dm-3 I (c) I chlorine

I 1 3 I ( I) j 0.002 mol en) I 3

1 4 (a)(i) 2Mn0, - + 6r + 4H20 -.... 3 12 + 2M n02 + BOW(a)(li) 0.408 mol dm 3 I (b) 1 3

(i) 2103- + 1 2H' + 1 oe- -- 12 + 6H20 I (II) I 2.51 5 I I 5S02 + 2 103- + 4H20 - sso/- + 12 + 8H( i i i) +6 (iv)

(a) 2Cu2'(aq ) + 41-(aq) . .... 2Cul(s) + l 2 (s)

1 6 12(s) + 2S20/-(aq) ---+ S,Of;2-(aq) + 2i-(aq) (b) 8.02 x 1 oI; mol dm-3 I (c) I Not safe I (d) I Precipitation

(a) 1 . 30 g I (b)(I) I N02- + H20 - N03- + 2H' + 2e-1 7 (b)(il) 2Mno,- + SN02- + 6H' ..... 2Mn2' + 5N03 - + 3H20 (c)(i) 0.922 g I

23 (a)(I)(b )(I)

1 24 (a)(I)(b)

(a)(I)

25 (a)(lll) (a)(iv) (b)

26 (a) (c)

27 (I) (Ill)

(a)(I) 28 (a)(ll)

(b)(ll)

0.676 mol I (a )(l i) I 0.028 mol (b)(ii) 3.65 )( 1 o- mol2Hl03 + 5CO ...... 12 + 5C02 + H,O (b)(ill) 40.9%

Baso.: 4.604 g I (a)(llJ I 30.0%Cr2012- + 6Br - + 1 4H. _, 2Cr3' + 3Br2 + 71-i,O; 1 5. 1 0 cmJ

+5 I ( )( i ' ) I a reaction in.

which a substance is simultaneouslya 1 oxidized and reduced, giving two different productsReduction: CrO/- + 4H10 + 2e- ...... C(l + 80W Oxidation: CrO,;)... ...... cro/- + e-2Cro, 2- + 6Br - + 8H20 ...... 2Cr3' + 3Br + 1 60H. I (a)(v) I 0.005 mol; 46.25%+2

+6 I (b) 1 4 2Mno,- su 2Mn2 2 . 4H' + -+ + suo, +

I 5C20.2- + 2Mno,- + 1 6H. -+ 10C02 + 2Mn'' + 8H20 (ii) I o.539 g I (Iv) I 0.239 9 (v)

3As203 + 4N03- + 4H' + ?H20 -- 6H;iAs04 + 4NO 2Mn0, - + 3N02- + H20 _, 2Mn02 + 3N03- + 20H- (b)(i) 0.0 1 1 8 mol I (b)(ill) I s (b)(iv)

TABLES OF CHEMICAL DATA

Import.ant valuea, constants and standards

molar gee constant n c 8 3 1 J K-' mo1'the Faraday constant F = 9.65 x 10' c mor'

the Avogadro constant L = 6 .02 x 10n moi-' the Planck constant h ::: 6.63 x 1 0-1< J s

speed of light In a vacuum c = 3.00 x 10 m s '

rest mass of proton, : H mp = 1 .67 x 1021 kg

rest mass of neutron, n mn : 1.67 X 10"11 kg

rest mass of electron, .e me = 9. 1 1 x 1 o-l' kg electronic charge e = -1 .60 x 1 0- c

molar volume of gas Vm = 22.4 am3 moi-' at s t p

0.1 1 2 g x = 3 , y = 3, z = 3

4 l. : 2, II : 4

Vm = 24 om3 mol"1 undt11 room conditions (wtiere s.t.p. is expressed as 101 kPa, approximately, and 273 K (0 C)) tonic product or water

specific heal capacity of water

35

= 1 .00 x 1 0" tnol dm-' (al 298 K [25 CJ) = 4.1 8 kJ ko ' K1 (= 4. 1 8 J g 1 K1)

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I

I I


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A-Level H2 Chemistry 01 Redox Stoichiometry