Question

\[Al\] dissolves in molten $NaOH$ with the formation of:
A.Sodium aluminate ($N{a_3}Al{O_3}$)
B.Sodium meta aluminate ($NaAl{O_2}$)
C.Aluminium hydroxide
D.Alumina

Answer 1

Hint: At first think about the reaction between aluminium and sodium hydroxide without any conditions. Crystalline $A{l_2}{O_3}$ at room temperature is hardly soluble in any solvent, even concentrated acid or alkali. Amorphous aluminium oxide may be soluble in any solvent.

Complete step by step answer:
Sodium meta aluminate is formed by the action of sodium hydroxide on elemental aluminium which is an amphoteric metal. Sodium meta aluminate is the hydrated form of sodium aluminate. The term meta refers to the least hydrated form of sodium aluminate. The reaction is highly exothermic and is accompanied by the rapid evolution of hydrogen gas. The overall reaction is as follows,
$2Al + 2NaOH + 2{H_2}O \to 2NaAl{O_2} + 3{H_2}$
So the answer is B.
Additional Information:- Sodium meta aluminate is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium meta aluminate is a white crystalline solid. Sodium meta aluminate mainly occurs in the form of hydroxide. Sodium aluminate is manufactured by the dissolution of aluminium hydroxide in a caustic soda solution. In water treatment, it is used as an adjunct to water softening systems as a coagulant aid to improve flocculation and for removing dissolved silica and phosphates. It is also used in the paper industry and for fire brick production. Sodium aluminate solutions are intermediates in the production of zeolites. Sodium hydroxide commonly promotes faster reactions and higher yields than potassium hydroxide. The kinetics of the reaction of spectrally pure aluminium in an aqueous solution of sodium hydroxide is governed in the investigated reaction regime.

Note:
Anhydrous sodium aluminate, $NaAl{O_2}$, contains a three-dimensional framework of corner linked $Al{O_4}$ tetrahedral. In aqueous reaction conditions, sodium aluminate will be accompanied by two water molecules, $NaAl{O_2}.2{H_2}O$.