Question

Name the product formed when $Zn$ reacts with $NaOH$.
A.$Zn{\left( {OH} \right)_2}$
B.$N{a_2}Zn{O_2}$
C.${H_2}$
D.${H_2}O$

Answer 1

We need to know the behaviour of the reactants and accordingly predict the product formed as a result of the chemical reaction. We know that Zinc is an amphoteric metal. An amphoteric metal is one which can react with both acids and bases. To be precise, the oxide of zinc is amphoteric in nature in contrast to other oxides which react with acids only due to their basic character. The other reactant NaOH is a base hence we evaluate the reaction of Zinc with a base.

Complete step by step answer:
We have to remember that when $NaOH$ reacts with a metal like $Zn$ , a metal salt is produced with the evolution of ${H_2}$ gas. We can write the chemical equation for this chemical reaction is as follows:
$Zn + 2NaOH \to N{a_2}Zn{O_2} + {H_2}$
This reaction is balanced where 1 mole of zinc reacts with 2 moles of sodium hydroxide to produce 1 mole of $N{a_2}Zn{O_2}$ and 1 mole of hydrogen gas.
We need to know that the product $N{a_2}Zn{O_2}$ is a metal salt called sodium zincate. The metal is a part of the anion as a zincate ion. It is also known as disodium tetrahydroxyzincate or sodium zinc hydroxide when it exists in its molecular form as $N{a_2}Zn{(OH)_4}$ . This molecular sodium zincate is formed by reacting zinc with sodium hydroxide in the presence of water. The salt formed is a colourless salt and hydrogen gas is evolved as a byproduct.
Therefore, the option B is correct.

Note:
We must be noted that the presence of hydrogen gas and the success of this reaction can be detected with the help of a simple test. The mouth of the tube in which the reaction has taken place should be kept open and a burning matchstick is brought near the mouth of the test tube. A pop sound is heard with the burning of the hydrogen gas confirming the evolution of the hydrogen gas as a success of the reaction.