Question

Dissolving metallic tin in excess of $NaOH$ produces
(A). $Sn{(OH)_2}$
(B). $N{a_2}Sn{O_2}$
(C). $N{a_2}Sn{O_3}$
(D). ${H_2}$ and $Sn{(OH)_2}$

Answer 1

Hint: Alkali metal stannate compounds are prepared by dissolving elemental tin in a suitable metal hydroxide. In this electrochemical process tin is made as anode and is dissolved in suitable alkali metal hydroxide in the anode compartment of an electrochemical cell.

Complete step by step answer:
Tin reacts with excess of sodium hydroxide to form sodium stannite $(N{a_2}Sn{O_2})$ and sodium stannate $(N{a_2}Sn{O_3})$ and hydrogen. The reaction is given as follows:
$Sn + 2NaOH \to N{a_2}Sn{O_2} + {H_2} \\
Sn + 2NaOH + {H_2}O \to N{a_2}Sn{O_3} + 2{H_2} $
In the above equation we can see that the tin, on reaction with two molecules of sodium hydroxide forms on molecules of sodium stannite along with one molecule of hydrogen gas. In a similar way, in the next reaction we see that, one molecule of tin reacts with two molecules of sodium hydroxide along one molecule of water, so we can say that the tin is reacting with aqueous solution of sodium hydroxide, in order to give one molecule of sodium stannate along with one molecule of gaseous hydrogen.
Sodium stannate is an inorganic compound which is formed upon dissolving metallic tin in excess of sodium hydroxide. The compound is sometimes also represented as hydrate with three water crystallisations. Now if we consider the question, it is clearly mentioned that sodium hydroxide is present in excess, and we can see that the concentration of sodium hydroxide in the first reaction is more than that of the second reaction, so the former would be appropriate.

So, the correct answer is Option B.

Note: Sodium stannate is used as a stabiliser for hydrogen peroxide. It is important to note that sodium hydroxide dissolves amphoteric metals and compounds to release hydrogen gas. Sodium stannate is slightly soluble in water and stable in nature but it is air sensitive. Important point to be noted is that the tin which is present in sodium stannate is present in four oxidation states.