Question

Zinc reacts with aqueous sodium hydroxide to form dihydrogen and _____.
A. Zinc oxide
B. Sodium zincate
C. Zinc hydroxide
D. Sodium precipitate

Answer 1

Hint: The reaction of zinc with sodium hydroxide is an example of single displacement reaction. The products formed are hydrogen gas and a compound of zinc and sodium.

Complete step by step answer:
Bases react with some metals like zinc or aluminium to produce hydrogen gas. In the reactivity list, the reactivity of zinc is lower than that of sodium. So, when zinc is reacted with aqueous sodium hydroxide, it reacts according to the following reaction:
$$Zn+2NaOH\to 2N{a}_{2}Zn{O}_2+H_2$$
Zinc reacts with aqueous sodium hydroxide to form sodium zincate and hydrogen gas. The reaction takes place at a temperature of ${550}^{\circ }$C. This compound is possible because Zn is capable of displacing Hydrogen from both acids and bases and therefore is called an Amphoteric metal and its oxide is an Amphoteric oxide. Sodium zincate is found in two forms. Sodium zincate in water is $$N{a}_2[Zn(OH{)}_4]$$, and sodium zincate when dry is $$N{a}_{2}Zn{O}_2$$. The molecular mass of aqueous sodium zincate ($$N{a}_{2}Zn{O}_2$$) is 179.41 g/mol. It can also be prepared by dissolving zinc hydroxide or zinc oxide in an aqueous solution of sodium hydroxide.

Hence, the correct answer is (B) Sodium zincate.

Note: A student can confuse the product of the reaction to be sodium hydroxide, which looks a much likely product. But remember the product is sodium zincate due to the amphoteric nature of zinc.