Question

Why does zinc increase in weight after being placed in NaOH?

Answer 1

Of course the mass of zinc does not increase........

Explanation:

However, zinc, as an active metal, can be OXIDIZED in basic solution as well as acidic solution........to give the `"zincate salt"`, `Na_2[Zn(OH)_4]`

`"Oxidation:"`

`Zn(s) +4HO^(-) rarr Zn(OH)_4^(2-)+2e^(-)` `(i)`

`"Reduction:"`

`H_2O(l) +e^(-) rarr 1/2H_2(g) + HO^-` `(ii)`

And we take `(i)+2xx(ii)`:

`Zn(s)+2H_2O(l) +2HO^(-) rarr Zn(OH)_4^(2-)+ H_2(g)uarr`

You could presumably isolate the zincate ion as its sodium salt, `Na_2[Zn(OH)_4]`, which complex has clearly a greater mass than the metal equivalent.