chemistry questionsheets a2 level · a) complete the following table to show the acid-base...

INORGANIC CHEMISTRYA2 TOPIC 21

REACTIONS OF PERIOD 3 ELEMENTS WITH WATER

REACTIONS OF PERIOD 3 ELEMENTS WITH OXYGEN

STRUCTURE AND BONDING OF PERIOD 3 OXIDES

PERIOD 3 OXIDES WITH WATER

ACID - BASE CHARACTER OF PERIOD 3 OXIDES

STABILITY OF GROUP 4 OXIDATION STATES

HYDROLYSIS OF GROUP 4 CHLORIDES

DEFINITIONS AND ELECTRONIC CONFIGURATIONS

BONDING IN COMPLEX IONS

COLOUR OF COMPLEX IONS

ISOMERISM

LIGAND EXCHANGE REACTIONS

DEPROTONATION THEORY

REACTIONS OF CATIONS WITH OH- AND NH3

OXIDATION STATES

COLORIMETRY

LIGAND EXCHANGE AND STABILITY CONSTANTS

d-ORBITAL SPLITTING AND LIGHT ABSORPTION

VANADIUM CHEMISTRY I

VANADIUM CHEMISTRY II

CHROMIUM CHEMISTRY I

CHROMIUM CHEMISTRY II

COBALT CHEMISTRY I

Questionsheet 1

Questionsheet 2

Questionsheet 3

Questionsheet 4

Questionsheet 5

Questionsheet 6

Questionsheet 7

Questionsheet 8

Questionsheet 9

Questionsheet 10

Questionsheet 11

Questionsheet 12

Questionsheet 13

Questionsheet 14

Questionsheet 15

Questionsheet 16

Questionsheet 17

Questionsheet 18

Questionsheet 19

Questionsheet 20

Questionsheet 21

Questionsheet 22

Questionsheet 23

QUESTIONSHEETS A2 LevelCHEMISTRY

10 marks

12 marks

16 marks

17 marks

14 marks

18 marks

14 marks

19 marks

17 marks

12 marks

19 marks

13 marks

18 marks

18 marks

8 marks

5 marks

20 marks

10 marks

15 marks

14 marks

15 marks

15 marks

21 marks

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10

REACTIONS OF PERIOD 3 ELEMENTS WITH WATERTOPIC 21 Questionsheet 1

a) (i) Describe what is observed when sodium is added to a beaker of cold water.

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Quality of language [1]

(ii) Write a balanced chemical equation for the reaction.

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(iii) Estimate the pH of the resulting solution.

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(iv) What type of chemical reaction occurs?

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b) (i) Why will magnesium and aluminium not react with cold water?

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(ii) Suggest how the conditions could be changed so that magnesium or aluminium would react in a similarway.

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12

REACTIONS OF PERIOD 3 ELEMENTS WITH OXYGENTOPIC 21 Questionsheet 2

a) Complete the following table for the elements of Period 3.

b) Write the fully balanced equation for the reaction of the elements with oxygen.

(i) Na .......................................................................................................................................................... [1]

(ii) Mg ......................................................................................................................................................... [1]

(iii) Al ........................................................................................................................................................... [1]

(iv) Si ............................................................................................................................................................ [1]

(v) P ............................................................................................................................................................ [1]

(vi) S............................................................................................................................................................. [1]

Reaction conditions

Formula of oxide(or lower oxide)

Na Mg Al Si P S Cl

[6]


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16

STRUCTURE AND BONDING OF PERIOD 3 OXIDESTOPIC 21 Questionsheet 3

a) State the nature of the bonding in the oxides of Period 3 elements and the type of structure by completing thefollowing table.

b) On the basis of your answers to a), describe and explain how the melting points of these oxides vary across theperiod.

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(c) Why is magnesium oxide used in the manufacture of firebricks for lining high temperature furnaces, ratherthan calcium oxide?

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....................................................................................................................................................................... [3]

Structure

Bonding

Na2O MgO Al

2O

3SiO

2P

4O

10SO

2Cl

2O

[5]


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17

PERIOD 3 OXIDES WITH WATERTOPIC 21 Questionsheet 4

a) On progressing from left to right across a period of the Periodic Table, what outstanding changes are observedin the behaviour of oxides with water? You should refer to three oxides of elements in either Period 2 (Li – F)or Period 3 (Na – Cl), and illustrate your answer by chemical equations.

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b) When a non-metallic element forms more than one oxide, how do these oxides compare in their acidic character?Refer in your answer to the oxides of carbon and phosphorus, write chemical equations for their reactions (ifany) with water, and give the approximate pH values of the resulting solutions.

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ACID - BASE CHARACTER OF PERIOD 3 OXIDESTOPIC 21 Questionsheet 5

a) Complete the following table to show the acid-base character of the oxides of elements in Period 3 of thePeriodic Table.

[4]

b) For the oxides of magnesium and aluminium, and one oxide of sulfur, write balanced chemical equations toillustrate the acid-base character you have described in a).

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c) Write ionic equations, and apply the Bronsted-lowry theory or G.N.Lewis theory (or both), to explain thedifference in acid-base behaviour between magnesium oxide and the oxide of sulfur you have selected in b).

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Acid - base character

Oxide Na2O MgO Al

2O

3SiO

2P

4O

6

P4O

10

SO2

SO3

Cl2O

ClO2

Cl2O

7


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18

STABILITY OF GROUP 4 OXIDATION STATES

a) (i) State the oxidation states which are exhibited by the elements of Group 4.

....................................................................................................................................................................... [2]

(ii) Tin occurs naturally as cassiterite, SnO2. Lead occurs as galena, PbS, and cerussite, PbCO

3. What does

this information suggest is:

the more stable oxidation state of tin? .................................................................................................. [1]

the more stable oxidation state of lead? ................................................................................................ [1]

b) (i) Predict whether each of the following compounds could be expected to behave as an oxidising agent,reducing agent or neither.

SnCl2...................................................................................................................................................... [1]

PbCl2...................................................................................................................................................... [1]

SnO2

...................................................................................................................................................... [1]

PbO2

...................................................................................................................................................... [1]

(ii) For each compound which you have described as an ‘oxidising agent’ or ‘reducing agent’, give oneexample of the compound behaving as such. (Balanced equations are not required, but you must indicateboth reactants and products.)

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c) Explain clearly why, on descending Group 4, one of the oxidation states mentioned in a) (i) increases instability, while the other decreases.

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TOPIC 21 Questionsheet 6


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14

HYDROLYSIS OF GROUP 4 CHLORIDES

a) (i) Write an equation for the reaction of silicon(IV) chloride with water at room temperature and outline themechanism of the reaction.

Equation ................................................................................................................................................ [1]

Mechanism

[4]

(ii) Explain why CCl4 does not react in this way.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

b) (i) Lead(II) chloride is largely unaffected by cold water, but tin(II) chloride behaves very differently. Describewhat is observed when tin(II) chloride is dissolved in water, write an equation for the reaction thatoccurs, and explain how this reaction can be prevented.

Observation ........................................................................................................................................... [1]

Equation ................................................................................................................................................ [1]

Prevention .................................................................................................................................................

............................................................................................................................................................... [2]

(ii) How do you account for the difference in behaviour of lead(II) chloride and tin(II) chloride with water?

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DEFINITIONS AND ELECTRONIC CONFIGURATIONS

19

a) Explain the difference between the terms d-block element and transition element.

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b) State, giving a reason in each case, whether or not scandium is:(i) a d-block element.

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....................................................................................................................................................................... [2]

(ii) a transition element.

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c) (i) Give the electron configuration of the following:

(ii) In what way is the electron configuration of both copper and chromium unusual compared with the otherfirst row of transition elements? Suggest why this occurs.

Unusual feature .......................................................................................................................................

............................................................................................................................................................... [2]

Reason for copper ...................................................................................................................................

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Reason for chromium ..............................................................................................................................

............................................................................................................................................................... [2]

d) (i) Name two stable cations having the following electronic configuration:

....................................................................................................................................................................... [2]

(ii) What feature makes this electronic configuration stable?

....................................................................................................................................................................... [1]

[4]

[Ar]

4s3d 4p

[Ar]

[Ar]

[Ar]

Cu

Cu2+

Cr

Cr3+

[Ar]

4s3d 4p



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17

BONDING IN COMPLEX IONS

a) (i) What is meant by the term ligand ?

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....................................................................................................................................................................... [2]

(ii) Explain what is meant by the terms complex cation and complex anion and give an example of each.

Complex cation ........................................................................................................................................

............................................................................................................................................................... [2]

Example ................................................................................................................................................ [1]

Complex anion .........................................................................................................................................

............................................................................................................................................................... [2]

Example ................................................................................................................................................ [1]

b) The hydrated chromium(III) ion, Cr3+(aq), is a cationic complex.

(i) State the shape of this ion and draw its structure

[3]

(ii) What type of bonding exists between the ligands and the chromium(III) ion?

....................................................................................................................................................................... [1]

(iii) Which structural feature of a water molecule and which structural feature of a chromium cation permitthis bonding to occur?

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....................................................................................................................................................................... [2]

(iv) Draw appropriate arrows in the following ‘boxes’ to represent orbital occupation in the hydratedchromium(III) ion. Label the diagram so as to distinguish between electrons possessed by the simple Cr3+

ion and those originating from the ligands.

[3]

Cr3+ [Ar]

4s3d 4p



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12

COLOUR OF COMPLEX IONS

a) Complete the following table:

ION Cr3+(aq) Mn2+(aq) Fe2+(aq) Fe3+(aq) Cu2+(aq)

COLOUR

[5]

b) (i) Give an example to show how, for a given metal in a and a given oxidation state, colour changes as theligands are changed.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

c) (i) Draw the following electron configurations:

Ti4+ [Ar]

Cu+ [Ar]

4s3d 4p

Zn2+[Ar]

Ti2+ [Ar]

[4]

(ii) Which of the above ions is/are coloured?

....................................................................................................................................................................... [1]

(iii) Explain the choice you made in c) (ii).

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ISOMERISM

a) [Co(NH3)

5Br]SO

4 (compound A) and [Co(NH

3)

5SO

4]Br (compound B) are isomeric compounds. Suggest two

simple tests which could be carried out in test tubes to distinguish between them.

Test 1Reagent ........................................................................................................................................................ [1]

Observation with compound A .................................................................................................................. [1]

Observation with compound B .................................................................................................................. [1]

Test 2Reagent ........................................................................................................................................................ [1]

Observation with compound A .................................................................................................................. [1]

Observation with compound B .................................................................................................................. [1]

b) There are five compounds of platinum(IV) chloride and ammonia, each containing a different octahedralcomplex ion. Details are given below.

(i) Draw the complex ions in compounds A, B, C and D.

[4]

(ii) Outline a simple experimental method to distinguish between compounds A, B, C and D.

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Compound Molecular formula No. of chloride ions per mole

A PtCl4.6NH

34

B PtCl4.5NH

33

C PtCl4.4NH

32

D PtCl4.3NH

31

E PtCl4.2NH

30


(Continued....)


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ISOMERISMTOPIC 21 Questionsheet 11 Continued

c) (i) The square planar compound [NiCl2(NH

3)

2] can occur as two geometric isomers. Draw their structures

and label each as cis or trans.

[3]

(ii) The octahedral complex cation [CoCl2(NH

3)

4]+ can also occur as two geometric isomers. Again, draw

their structures and label each as cis or trans.

[3]

19


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13

LIGAND EXCHANGE REACTIONSTOPIC 21 Questionsheet 12

a) Define the term ligand exchange reaction, as applied to the hydrated cations of transition elements, and givetwo reasons why such reactions may occur.

Definition ..........................................................................................................................................................

....................................................................................................................................................................... [2]

Reason 1 ....................................................................................................................................................... [1]

Reason 2 ...................................................................................................................................................... [1]


b) Starting from [Cu(H2O)

6]2+, give examples of the following types of reaction. In each case write an ionic

equation, describe the colour change that would be observed, and state the shape of the resulting complex ion.

(i) Ligand exchange reaction with no change in coordination number

Ionic equation ...................................................................................................................................... [1]

Colour change ..................................................................................................................................... [1]

Shape of resulting complex ion .......................................................................................................... [1]

(ii) Ligand exchange reaction accompanied by a change in coordination number

Ionic equation ...................................................................................................................................... [1]

Colour change ..................................................................................................................................... [1]

Shape of resulting complex ion .......................................................................................................... [1]

c) Suggest a reason why there is a change in coordination number in some ligand exchange reactions but not inothers.

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DEPROTONATION THEORYTOPIC 21 Questionsheet 13

a) (i) When iron(III) chloride is dissolved in pure water, how does the pH change?

....................................................................................................................................................................... [1]

(ii) Give reasons for any pH change, and support your answer with a balanced ionic equation.

Reasons .....................................................................................................................................................

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............................................................................................................................................................... [3]

Equation ............................................................................................................................................... [1]

(iii) State the type of reaction occurring in a) (ii) and give the chemical functions of both the hydrated metalions and the water molecules.

Type of reaction ................................................................................................................................... [1]

Function of hydrated metal ions ........................................................................................................ [1]

Function of water molecules .............................................................................................................. [1]

b) On standing for several weeks, a solution of iron(III) chloride may deposit a small amount of iron(III) hydroxide.

(i) Write ionic equations (following on from that in a) (ii) ) to represent the formation of iron(III) hydroxide.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

(ii) If OH- ions (e.g. from NaOH(aq)) are introduced into iron(III) chloride solution, iron(III) hydroxide isprecipitated copiously and immediately. How do you account for the difference?

....................................................................................................................................................................... [1]

c) The pH value of a solution formed by dissolving copper(II) sulfate in water differs from the pH of a solution ofiron(III) chloride, even when the molar concentrations of the hydrated cations are equal.

(i) Predict whether the copper(II) sulfate solution is acidic, neutral or basic, giving your reasoning.

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(ii) Also suggest, giving reasons, which solution has a pH value further from neutrality.

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18

REACTIONS OF CATIONS WITH OH- AND NH3


a) Both NaOH(aq) and NH3(aq), when used in limited amounts, behave in the same way when added to aqueous

solutions of transition element salts.

(i) Why is this?

....................................................................................................................................................................... [1]

(ii) Quote three examples from the first row of d-block elements to illustrate this statement, giving yourexpected observation and formula of the compound produced in each case.

Example 1 .................................................................................................................................................

Example 2 .................................................................................................................................................

Example 3 ............................................................................................................................................. [3]

b) NaOH(aq) and NH3(aq) behave very differently from each other when they are added to aqueous solutions of

transition element salts until they are eventually present in excess. Excess NaOH(aq) will dissolve some of thecompounds produced at first, while excess NH

3(aq) will dissolve others. Illustrate the differences in observations

and underlying chemistry by completing the following table.

Example of a compound which will dissolve

Reason for dissolving

Type of reaction occurring

Observation

Formula of the ion produced

[10]

c) (i) Name two compounds of p-block elements, produced by the action of NaOH(aq) on salt solutions, whichalso dissolve when the reagent is present in excess.

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(ii) Give the formulae of the ions produced in these reactions.

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Excess NH3(aq) Excess dilute NaOH(aq)


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OXIDATION STATESTOPIC 21 Questionsheet 15

a) Give the oxidation number of the transition element in each of the following chemical species:

(i) CrO4

2- .....................................................................................................................................................

(ii) MnO4

2- .....................................................................................................................................................

(iii) Fe2Cl

6.....................................................................................................................................................

(iv) VO2

+ .....................................................................................................................................................

(v) VO3

- .....................................................................................................................................................

(vi) [CrCl(H2O)

5]2+ .........................................................................................................................................

(vii) [PtCl(NH3)

5]3+ .........................................................................................................................................

(viii) [Co(NH3)

4Cl

2]2+ ........................................................................................................................................

(ix) Na2FeO

4.................................................................................................................................................

(x) K2CuF

4.....................................................................................................................................................

[5]

b) Why do transition elements show a variety of oxidation states in their chemistry?

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8


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COLORIMETRYTOPIC 21 Questionsheet 16

The above graph shows the results obtained when aqueous copper(II) sulfate and aqueous ammonia are mixedtogether in different proportions in the presence of ammonium sulfate. A complex is formed between ammoniaand the copper(II) ion, which has a different and much more intense colour than [Cu(H

2O)

6]2+.

(i) What volumes of 0.1 mol dm-3 CuSO4(aq) and 0.1 mol dm-3 NH

3(aq), when mixed together, give the highest

concentration of the complex?

Volume of 0.1 mol dm-3 CuSO4(aq) .........................................................................................................

Volume of 0.1 mol dm-3 NH3(aq) ......................................................................................................... [1]

a)

0 cm3 100 cm3

100 cm3 0 cm3

volume of 0.1 M CuSO4(aq)

volume of 0.1 M NH3(aq)

met

er r

eadi

ng

(ii) Calculate the mole ratio of Cu2+ : NH3 in the complex.

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(iii) Write down the formula of the complex.

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5


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A2 Level TOPIC 21 Questionsheet 17


(a) Aqueous nickel(II) sulfate contains the [Ni(H2O)

6]2+ ion.

(i) The green nickel(II) sulfate turned blue when treated with aqueous ammonia. This blue solution whentreated with aqueous sodium cyanide turns yellow, but this yellow colour is unaffected by the addition ofexcess aqueous ammonia. Explain these observations, stating what is formed and why, but formulae ofany complex ions formed is not required.

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(ii) When aqueous ethane-1,2-diamine was added to the blue solution described in part (i) (ie aqueous nickelsulfate and aqueous ammonia), it turned mauve. However, aqueous ethane-1,2-diamine had no effect onthe yellow solution described in part (i). Explain these observations, stating what is formed and why, butformulae of any complex ions formed is not required.

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(Continued....)


TOTAL /

A2 Level TOPIC 21 Questionsheet 17 Continued


20

(a) Using Stability Constants Data (Note: en = ethane-1, 2-diamine)

Complex ion Stability Complex ion Stabilityconstant (lgK) constant (lgK)

[Cu(NH3)

2]+ 11 [Co(NH

3)

6]2+ 5

[Cu(CN)4]3- 27 [Co(NH

3)

6]3+ 34

[Cu(NH3)

4(H

2O)

2]2+ 13 [Co(CN)

6]3+ 64

[Cu(en)2(H

2O)

2]2+ 20 [Co(EDTA)]2+ 16

[Cu(EDTA)]2- 19 [Co(EDTA)- 36

(i) The complex ion [Cu(NH2CH

2CH

2NH

2)

2(H

2O)

2]2+ contains the ethane-1,2-diamine ligand, would you

expect it to be displaced by EDTA? Use the data to explain your answer.

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(ii) The ion [Cu(H2O)

6]2+ reacts with cyanide ions to give the complex ion [Cu(CN)

4]3-. Would you expect

the cyanide ions to be replaced by ammonia? Use the data to explain your answer.

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(iii) 0.02 moles of [Co(H2O)

6]3+ was treated with 0.12 moles of potassium cyanide and 0.12 moles of ammonia.

What would be the formula of the complex ion? Show how you get the answer.

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(iv) 0.02 moles of [Co(H2O)

6]3+and 0.02 moles of [Co(H

2O)

6]2+were mixed with 0.12 moles of ammonia.

What would be the formula of the complex ion?

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A2 Level TOPIC 21 Questionsheet 18

d-ORBITAL SPLITTING AND LIGHT ABSORPTION

a) Complete the diagrams below(i) Write down the electronic structure of Cu2+ in an octahedral complex and hence complete the diagram

(ii) Write down the electronic structure of Fe3+ in an octahedral complex and hence complete the diagram

Adding ligands Absorbing light

dx2y2 dx2 dx2y2 dx2

dxy dxz dyz dxy dxz dyz

Ground state Excited state

EnergyCu2+ uncomplexed


dx2y2 dx2 dx2y2 dx2



EnergyFe3+ uncomplexed

(iii) Write down the electronic structure of V3+ in an octahedral complex and hence complete the diagram


dx2y2 dx2 dx2y2 dx2



EnergyV3+ uncomplexed

[6]

b) Explain why the following ions form white compounds

(i) Sc3+ ..........................................................................................................................................................

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............................................................................................................................................................... [2]

(ii) Zn2+ ..........................................................................................................................................................

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10


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15

VANADIUM CHEMISTRY I

a) Complete the following table to give the electronic structure of V and V3+.

[2]

V [Ar]

V3+ [Ar]

4s3d 4p

b) Complete the following table by giving the colours and names of the aqueous cations of vanadium.

[8]

c) What colour changes would you expect to see when a sample of ammonium vanadate(V) is dissolved in warmaqueous sulfuric acid and zinc is added?

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Oxidation Number Formula Colour Name

+2 Violet Vanadium(II)

+3 [V(H2O)

6]3+ Vanadium(III)

+4

+5



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14

VANADIUM CHEMISTRY II

a) The complex ion [V(H2O)

6]3+ is present in aqueous solutions of vanadium(III). State its shape and describe

the types of bonding in this ion.

Shape ............................................................................................................................................................ [1]

Types of bonding..............................................................................................................................................

....................................................................................................................................................................... [2]

b) (i) Predict whether a solution containing [V(H2O)

6]3+ would be acidic, basic or neutral. Write an ionic

equation to support your prediction.

Prediction ............................................................................................................................................. [1]

Equation ............................................................................................................................................... [1]

(ii) When a solution containing [V(H2O)

6]

3+ is treated with NaOH(aq) a green precipitate is obtained. Suggest

the identity of this precipitate and write an ionic equation for its formation.

Identity .................................................................................................................................................. [1]

Equation ............................................................................................................................................... [1]

c) VO2

+(aq) can be reduced using an acidic aqueous solution containing sulfite ions.

(i) Write an ionic half-equation for the reduction of VO2

+(aq) in acidic solution to VO2+(aq).

............................................................................................................................................................... [2]

(ii) Write an ionic half-equation for the oxidation of sulfite ions in aqueous acidic solution to form sulfateions.

....................................................................................................................................................................... [2]

(iii) Using your answers from parts (i) and (ii), deduce an equation for the reduction of VO2

+(aq) in acidicsolution to VO2+(aq) by sulfite ions.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

(iv) Suggest a reagent which could be expected to convert a solution of VO2+(aq) ions to VO2+(aq) ions.

....................................................................................................................................................................... [1]



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15

CHROMIUM CHEMISTRY I

a) When the purple salt, chromium(III) nitrate-9-water, is dissolved in water, a blue-green solution A is obtained.With the help of an ionic equation, explain the colour change which occurs on dissolving.

Equation ...........................................................................................................................................................[1]

Explanation ......................................................................................................................................................

....................................................................................................................................................................... [2]

b) Aqueous sodium hydroxide was added dropwise to a sample of A, followed by an excess of aqueous sodiumhydroxide to form solution B. What observations were made? Write ionic equations to describe the reactionsoccurring.

Observations ....................................................................................................................................................

....................................................................................................................................................................... [3]

Equations ..........................................................................................................................................................

....................................................................................................................................................................... [2]

c) Zinc metal and aqueous hydrochloric acid were added to a sample of A. What colour change would be seento occur? Write an ionic half-equation to describe the reaction occurring to A.

Observations ................................................................................................................................................ [2]

Half-equation ............................................................................................................................................... [1]

d) To B was added aqueous sodium hydroxide and aqueous hydrogen peroxide. The solution was boiled. Thecolour of the solution became yellow. Excess hydrogen peroxide was then removed and the solution wasacidified. Finally, an orange colour formed.

(i) Name the chemical species responsible for the yellow colour.

....................................................................................................................................................................... [1]

(ii) Name the chemical species responsible for the orange colour and write a balanced ionic equation for itsformation from the yellow species.

Name ..................................................................................................................................................... [1]

Equation ...................................................................................................................................................

............................................................................................................................................................... [2]



TOTAL /

A2 Level

15

CHROMIUM CHEMISTRY IIWhen an aqueous solution of chromium(III) chloride is evaporated at room temperature, violet crystals areformed (compound X). When a hot aqueous solution of chromium(III) chloride crystallises, pale green crystals(compound Y) are formed. When an excess of silver nitrate is added to 1 mole of either of these salts a whiteprecipitate of silver chloride is formed. Compound X forms 3 moles of silver chloride and compound Y formsonly 1 mole of silver chloride. Both compounds have the same composition by mass: 19.5% chromium, 40.1%chlorine and 40.4% water.

a) Calculate the empirical formula of both these salts.

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [3]

b) Assuming that the empirical formulae are identical with the molecular formulae, what are the formulae andnames of the complex cations present?

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [4]

c) Why do these compounds have different colours?

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

d) One of these complex ions can exhibit geometric isomerism. Using sketches, explain how such isomerism canoccur.

[4]

e) (i) Give the formula of a third compound Z which is isomeric with compounds X and Y.

....................................................................................................................................................................... [1]

(ii) How many moles of silver chloride would you expect to be precipitated from 1 mole of compound Z ontreatment with excess silver nitrate solution?

...................................................................................................................................................................... [1]



TOTAL /

A2 Level

21

COBALT CHEMISTRY I

a) Explain the meaning of the terms transition element, cationic complex and anionic complex, and illustrateyour answers with examples taken from the chemistry of cobalt.

Transition element ...........................................................................................................................................

....................................................................................................................................................................... [2]

Example ........................................................................................................................................................ [1]

Cationic complex .......................................................................................................................................... [2]

Example ........................................................................................................................................................ [1]

Anionic complex ...............................................................................................................................................

....................................................................................................................................................................... [2]

Example ........................................................................................................................................................ [1]

b) Sketch the structures of two complex ions of cobalt(II), one of which has an octahedral shape and the otherone a tetrahedral shape.

[2]

c) State the type of bonding occurring between the central metal cation and a ligand. What structural featuremust a ligand possess for this type of bonding to occur?

Type of bonding ........................................................................................................................................... [1]

Feature .......................................................................................................................................................... [1]

d) (i) Describe what you would observe if concentrated aqueous ammonia were added dropwise (until inexcess) to an aqueous solution of cobalt(II) nitrate.

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....................................................................................................................................................................... [3]

(ii) Using your answer to d) (i), explain the meaning of the term ligand exchange reaction. Include in yourexplanation the chemical equation for the reaction involved.

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....................................................................................................................................................................... [3]

e) What would you observe if the solution resulting from d) (i) were allowed to stand in air, and how do youaccount for the change?

Observation .................................................................................................................................................. [1]

Explanation .................................................................................................................................................. [1]


chemistry questionsheets a2 level · a) complete the following table to show the acid-base...

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