WAEC Chemistry 2012 Paper

Concept:Aluminium reacts with aqueous sodium hydroxide to form a soluble complex salt called sodium tetrahydroxoaluminate.Explanation:When aluminium dissolves in aqueous sodium hydroxide, it displaces hydrogen and forms a coordination complex.The balanced reaction is:$$2\mathrm{Al} + 2\mathrm{NaOH} + 6\mathrm{H_2O} \rightarrow 2\mathrm{NaAl(OH)_4} + 3\mathrm{H_2}$$In this complex, the aluminate ion is $\mathrm{[Al(OH)_4]^-}$.The sodium salt of this ion is $\mathrm{NaAl(OH)_4}$.Thus, the complex compound formed is sodium tetrahydroxoaluminate, $\mathrm{NaAl(OH)_4}$.Answer:B. $\mathrm{NaAl(OH)_4}$