Aluminium reacts with hydrochloric acid to form aluminium chloride, ${\mathrm{AlCl}}_3$, and hydrogen. This is a redox reaction. Construct a balanced ionic equation for the reaction between aluminium atoms and hydrogen ions.

When a salt containing iodide ions is warmed with concentrated sulphuric acid and ${\mathrm{MnO}}_2$, iodine is evolved:

$2{\mathrm{I}}^{-}+{\mathrm{MnO}}_2+6{\mathrm{H}}^{+}+2{{\mathrm{SO}}_4}^{2-}\stackrel{ }{\to }{\mathrm{I}}_2+{\mathrm{Mn}}^{2+}+2{{\mathrm{HSO}}_4}^{-}+2{\mathrm{H}}_2\mathrm{O}$

State the systematic name for ${\mathrm{MnO}}_2$.

When a salt containing iodide ions is warmed with concentrated sulphuric acid and ${\mathrm{MnO}}_2$, iodine is evolved:

$2{\mathrm{I}}^{-}+{\mathrm{MnO}}_2+6{\mathrm{H}}^{+}+2{{\mathrm{SO}}_4}^{2-}\stackrel{ }{\to }{\mathrm{I}}_2+{\mathrm{Mn}}^{2+}+2{{\mathrm{HSO}}_4}^{-}+2{\mathrm{H}}_2\mathrm{O}$

Deduce the oxidation number of $\mathrm{S}$ in the ${{\mathrm{SO}}_4}^{2-}$ ion.

When a salt containing iodide ions is warmed with concentrated sulphuric acid and ${\mathrm{MnO}}_2$, iodine is evolved:

$2{\mathrm{I}}^{-}+{\mathrm{MnO}}_2+6{\mathrm{H}}^{+}+2{{\mathrm{SO}}_4}^{2-}\stackrel{ }{\to }{\mathrm{I}}_2+{\mathrm{Mn}}^{2+}+2{{\mathrm{HSO}}_4}^{-}+2{\mathrm{H}}_2\mathrm{O}$

State which reactant gets oxidised in this reaction? Explain your answer by using oxidation numbers.

When a salt containing iodide ions is warmed with concentrated sulphuric acid and ${\mathrm{MnO}}_2$, iodine is evolved:

$2{\mathrm{I}}^{-}+{\mathrm{MnO}}_2+6{\mathrm{H}}^{+}+2{{\mathrm{SO}}_4}^{2-}\stackrel{ }{\to }{\mathrm{I}}_2+{\mathrm{Mn}}^{2+}+2{{\mathrm{HSO}}_4}^{-}+2{\mathrm{H}}_2\mathrm{O}$

State which substance is the oxidising agent? Explain your answer.

The compound ${\mathrm{KBrO}}_3$ decomposes when heated:

$2{\mathrm{KBrO}}_3\stackrel{ }{\to }2\mathrm{KBr}+3{\mathrm{O}}_2$

State the oxidation number of bromine in ${\mathrm{KBrO}}_3$.