EduNinja
[Maximum number: 1]

Iron is a transition element in the fourth period. Iron forms compounds containing the ions Fe2+\mathrm{Fe}^{2+} and Fe3+\mathrm{Fe}^{3+}.

(a)
(i)

Define the term transition element.

[ 1 ]
[Maximum number: 1]

Transition elements are important metals because of their characteristic properties.

(a)

Define what is meant by a transition element.

[ 1 ]
(a)

Many commercial copper and brass polishes contain ammonia. The tarnish that forms on the surface of copper is often copper sulfide, CuS . In the presence of O2\mathrm{O}_{2} from the air, NH3\mathrm{NH}_{3} can combine with this copper sulfide to produce the soluble cuprammonium sulfate, [Cu(NH3)4]SO4\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}.

[ 1 ]
(i)

State the colour of cuprammonium sulfate solution.

[ 1 ]
(a)

When aqueous solutions of KI and K2 S2O8\mathrm{K}_{2} \mathrm{~S}_{2} \mathrm{O}_{8} are mixed almost no reaction occurs, but when a few drops of Fe2+(aq)\mathrm{Fe}^{2+}(\mathrm{aq}) or Fe3+(aq)\mathrm{Fe}^{3+}(\mathrm{aq}) are added, iodine, I2(aq)\mathrm{I}_{2}(\mathrm{aq}), is produced at a steady rate.

[ 3 ]
(i)

State the precise role of the iron ions during this reaction.

(ii)

By means of equations or otherwise, explain why the presence of either Fe2+\mathrm{Fe}^{2+} or Fe3+\mathrm{Fe}^{3+} is able to speed up the reaction.

[ 3 ]
[Maximum number: 1]

Iodine is found naturally in compounds in many different oxidation states.

(a)

The concentration of Cu2+(aq)\mathrm{Cu}^{2+}(\mathrm{aq}) in a solution can be determined by the reaction of Cu2+\mathrm{Cu}^{2+} ions with I−\mathrm{I}^{-}ions.

reaction 12Cu2++4I−→2CuI+I212 \mathrm{Cu}^{2+}+4 \mathrm{I}^{-} \rightarrow 2 \mathrm{CuI}+\mathrm{I}_{2}

The I2\mathrm{I}_{2} produced in reaction 1 is titrated against a solution containing thiosulfate ions, S2O32−\mathrm{S}_{2} \mathrm{O}_{3}{ }^{2-}, using a suitable indicator.

 reaction 22 S2O32−+I2→ S4O62−+2I−\text { reaction } 2 \quad 2 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-}+\mathrm{I}_{2} \rightarrow \mathrm{~S}_{4} \mathrm{O}_{6}^{2-}+2 \mathrm{I}^{-}
[ 1 ]
(i)

Copper(I) and copper(II) both contain electrons in all five 3d orbitals.

Sketch the shape of a 3 dxy3 \mathrm{~d}_{\mathrm{xy}} orbital on the axes provided.

Question image
[ 1 ]
(a)
(i)

State how the melting point and density of iron compare to those of calcium.
melting point of iron:
density of iron:

(ii)

Explain why these differences occur.
melting point:
density:

[ 4 ]
(a)
(i)

Explain why transition elements can form complex ions.

[ 1 ]
(a)

Describe three characteristic chemical properties of transition elements that are not shown by Group II elements.

[ 3 ]
(a)

Cobalt is a transition element and forms compounds with oxidation numbers +2 and +3 .
Complete the electronic structures for
a cobalt atom,
1s22s22p61 s^{2} 2 s^{2} 2 p^{6}
cobalt in the +3 oxidation state.
1s22s22p61 s^{2} 2 s^{2} 2 p^{6}

[ 2 ]
(b)
(i)

State two chemical properties of cobalt, other than the formation of complexes, that are not shown by a typical s-block element.

[ 2 ]

In the Haber process, the reaction between the two gaseous reactants requires the use of a catalyst that contains a transition element.

What is the metal and in which mole ratio do the gases react?

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