(a) (i) State three characteristic properties of transition metals. (ii) What is the oxidation state of manganese In each of the following species? (1) \(\m...

(a)(i) Three characteristic properties of transition metals are:

1. They exhibit variable oxidation states.
2. They form coloured ions or compounds.
3. They form complex ions.

(ii)

• In \(\mathrm{MnCl_2}\): \(x+2(-1)=0\), hence \(x=+2\).
• In \(\mathrm{MnO_2}\): \(x+2(-2)=0\), hence \(x=+4\).
• In \(\mathrm{MnO_4^-}\): \(x+4(-2)=-1\), hence \(x=+7\).

(iii) Manganese is metallic and contains mobile, delocalised electrons which carry electric current in the solid state. Manganese(II) chloride is ionic. In the solid state its ions are fixed in a lattice, but when molten or dissolved in water, the ions are free to move and conduct electricity.

(b)(i) A collision produces products only when:

1. the colliding particles possess energy equal to or greater than the activation energy; and
2. the particles collide with the correct orientation.

(ii) The energy profile below is for an exothermic reaction. \(E_A\) is the energy difference between the reactants and the activated complex, while \(\Delta H\) is the energy difference between products and reactants.

For this exothermic reaction, the products are at a lower energy than the reactants; therefore, \(\Delta H\) is negative.

(c)(i) Addition of \(\mathrm{KSCN(aq)}\) increases the concentration of \(\mathrm{SCN^-}\) ions. The equilibrium shifts to the right to use up some of the added \(\mathrm{SCN^-}\):

\[\mathrm{Fe^{3+}(aq)+3SCN^-(aq)\rightleftharpoons Fe(SCN)_3(aq)}\]

More deep-red \(\mathrm{Fe(SCN)_3}\) is formed, so the pale red solution becomes deeper red.

(ii) The ion that forms an insoluble hydroxide is \(\mathrm{Fe^{3+}}\).

\[\mathrm{Fe^{3+}(aq)+3OH^-(aq)\rightarrow Fe(OH)_3(s)}\]

(iii) On adding \(\mathrm{NaOH(aq)}\):

1. a reddish-brown precipitate of \(\mathrm{Fe(OH)_3}\) is formed; and
2. the red colour fades or disappears, leaving a colourless solution above the precipitate.