Describe the delocalization of pi (\(\pi \)) electrons and explain how this can account for the structure and stability of the carbonate ion, \({\text{CO}}_3^{2 - }\).

Explain the meaning of the term hybridization. State the type of hybridization shown by the carbon atoms in carbon dioxide, diamond, graphite and the carbonate ion.

Explain the electrical conductivity of molten sodium oxide and liquid sulfur trioxide.

Samples of sodium oxide and solid sulfur trioxide are added to separate beakers of water. Deduce the equation for each reaction and predict the electrical conductivity of each of the solutions formed.

\(^{{\text{60}}}{\text{Co}}\)/Co-60/cobalt-60 and radiotherapy/sterilization of medical supplies/radiation treatment of food sterilizations/industrial radiography/density measurements in industry/(medical/radioactive) tracer;

Allow treatment of cancer.

Do not allow “just used in medicine”.

OR

\(^{{\text{57}}}{\text{Co}}\)/Co-57/cobalt-57 and medical tests/label for vitamin B12 uptake;

Do not allow “just used in medicine”.

mixing/combining/merging of (atomic) orbitals to form new orbitals (for bonding);

Allow molecular or hybrid instead of new.

Do not allow answers such as changing shape/symmetries of atomic orbitals.

Carbon dioxide: sp;

Diamond: \({\text{s}}{{\text{p}}^{\text{3}}}\);

Graphite: \({\text{s}}{{\text{p}}^{\text{2}}}\);

Carbonate ion: \({\text{s}}{{\text{p}}^{\text{2}}}\);

Molten sodium oxide: conducts because of free moving/mobile ions in molten state;

Sulfur trioxide: doesn’t conduct because no free moving/mobile charged particles/it has neutral molecules;

Award [1 max] for stating molten sodium oxide conducts but sulfur trioxide doesn’t.

Do not award M2 for “just sulfur trioxide does not conduct because it is molecular.”

\({\text{N}}{{\text{a}}_2}{\text{O(s)}} + {{\text{H}}_2}{\text{O(l)}} \to {\text{2NaOH(aq)}}\);

\({\text{S}}{{\text{O}}_3}{\text{(l)}} + {{\text{H}}_2}{\text{O(l)}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_4}{\text{(aq)}}\);

both solutions conduct;

Ignore state symbols.

(d) was poorly answered since candidates were unable to logically structure their response often a description of pi bonding alone was given.

(e) usually was well done, although the precise meaning of hybridization was rarely given. Sometimes an incorrect hybridization of \({\text{s}}{{\text{p}}^{\text{4}}}\) was given for diamond.

In (f), most candidates were unable to state that molten sodium oxide is able to conduct electricity because the current is carried by mobile ions (not delocalized electrons). Most did not realise that molten sulfur trioxide consists of neutral molecules and therefore does not conduct an electric current.

Most were able to write the balanced chemical equations but then were not able to state that both solutions conduct. Many often gave the incorrect formula for sodium oxide.