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Raffles Institution (JC)

JC2 H2 Chemistry 2010/11

Tutorial 24-A: An Introduction To The Chemistry Of Transition Elements

1 (a)  Arrange the following species in order of increasing number of unpaired electrons:

(i)  V, Cr, Fe, Ni and Cu (ii)  V2+

, Ti2+

, Mn2+

, Co3+

, Zn2+

 

(b) Identify all the metal atoms, doubly charged cations and triply charged cations with threeunpaired 3d electrons and write down their electronic configurations.

(c)  (i)  An ion X2+

 contains 22 electrons. What is the electronic configuration of X?

(ii)  An ion Y2+

 contains 40 protons. What is the electronic configuration of Y2+

?

(d)  For each of the species given below, state the oxidation state and electronicconfiguration of the central metal ion/atom.

TiCl 2, [V(H2O)6]3+

, [Cr(NH3)6]Cl 3, [Fe(SCN)(H2O)5]2+

, [CoCl 4]2 – 

, [Fe(CN)6]4 –

, [Ni(CO)4]

2 Explain the following:

(a) The atomic radii  of the transition elements Cr to Cu are similar.

(b)  The atomic radius  of vanadium is smaller than that of calcium despite the vanadiumatom having more electrons than the calcium atom.

(c)  The fourth ionisation energy  of cobalt is lower than that of iron.

(d) The melting point  of vanadium is significantly higher than that of calcium.

(e)  The transition metals have a tendency to vary in their oxidation states, whereas s-blockelements such as calcium do not. 

(f)  NH3, but not BH3, can act as a ligand .

(g)  An aqueous solution of chromium(III) chloride has a pH value of less than 7.

(h)  An aqueous solution of Al Cl 3 is colourless but that of CrCl 3 is coloured.

(i)  Both Cu2SO4(s) and anhydrous CuSO4(s) are white but CuSO4.5H2O(s) is blue.

3 Self-check question

Define the following terms: (a) transition element , (b )  complex ion, (c) ligand , (d) co-ordination

number , (e) homogeneous catalysis, and (f) heterogeneous catalysis.

4  The rate of the reaction between iodide and peroxodisulfate(VI) ions is increased by the

presence of small concentrations of Fe3+(aq) or Cu2+(aq) ions.

(a)  What type of catalysis does this illustrate?

(b) Write an equation for the reaction between iodide and peroxodisulfate(VI) ions.

(c)  Suggest how copper(II) ions are able to participate in this reaction.

(d)  The deterioration in the air of some organic substances, such as cosmetics, is a similar

process to that described in (c)  above. Suggest why the deterioration can be sloweddown by the addition of small quantity of edta.

(e)  By considering relevant E values from the Data Booklet, choose two other examples oftransition metal ions that would be predicted to act as catalysts for the above reaction.What other factors might prevent the ions of your choice from behaving as catalysts?

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5  (a)  Explain the meaning of the term heterogeneous catalysis.

(b) Transition metals are often used as heterogeneous catalysts for industrial processesinvolving hydrogen. Give two examples of metals used in this way and write equations forthe reactions they catalyse.

(c)  Using one of the two examples in (b), explain clearly how the transition metal catalyses

the reaction with the help of suitable diagrams.

6  Describe and explain what is seen  for each of the following, using relevant data from the

Data Booklet wherever appropriate to support your answer.

(a)  Anhydrous copper(II) sulfate is stirred with water, followed by the addition of aqueousammonia until in excess.

(b) Dilute sulfuric acid is added to a solution of Cu2+

 ions in aqueous ammonia.

(c)  An acidified solution of Fe2+

(aq) is left open to the air.

(d)  Aqueous sodium hydroxide is added to an aqueous solution containing Fe2+

  ions, andthe resulting moist precipitate is left open to the air. 

(e)  Dilute aqueous sodium hydroxide is added to aqueous potassium dichromate(VI) anddilute hydrochloric acid is added to aqueous potassium chromate(VI).

7  Using relevant data from the Data Booklet  wherever appropriate, explain  each of thefollowing observations.

(a)  Copper(I) sulfate is a white powder which reacts with water to give a blue solution and apink-coloured solid.

(b)  When aqueous iron(III) chloride is added to aqueous potassium iodide, a brown solution

is formed, but aqueous potassium hexacyanoferrate(III) does not react with aqueouspotassium iodide.

(c)  When aqueous sodium hydroxide is added to aqueous iron(II) sulphate a greenprecipitate is obtained, but when aqueous sodium hydroxide is added to aqueoussodium hexacyanoferrate(II), no precipitate is obtained.

(d) When KSCN(aq) is added to K3[Fe(C2O4)3](aq), a red colour is observed. By contrast,when KSCN(aq) is added to K3[Fe(CN)6](aq), no such red complex is formed.

(e)  Although acidic solutions of iron(II) salts are only slowly oxidised in air, the precipitatethat is obtained on adding NaOH(aq) to a solution of iron( II) salt rapidly turns brown on

the surface.

8  (a) Suggest the function of haemoglobin in the body, and how it carries out this function.

(b)  What change of oxidation number of the iron(II), if any, occurs when haemoglobin isconverted into oxyhaemoglobin? Explain your answer.

(c)  Carbon monoxide acts as a poison through its interaction with haemoglobin. Describe thisinteraction and discuss why carbon monoxide is so much more poisonous than carbondioxide.

(d)  A patient suffering from carbon monoxide poisoning can be treated by being given pure

oxygen to breathe. Suggest a reason why this treatment is effective.

(e)  Name another poison that can affect haemoglobin, and describe how it reacts.