Question

An element ‘A’ reacts with oxygen to form a protective layer of compound ‘B’. The component ‘B’ is also obtained by the reaction of ‘A’ with rust. The compound ‘B’ is known to react both with acids and bases. What is the element ‘A’?

Answer 1

Al?

Explanation:

I really wish know what is element A, because the ones that react with acid and basic solutions are the hydroxide (very less the oxides) of anfoteric metals like Zn, Cr, Sn, Pb, Sb, Al; All of them can form protective layers with oxigen while with rust (oxide and hydroxide of iron) teorically could react only the more reducent metals like Zn , Cr and Al, but they are kinetically inerts, expecially the first two. Perhaps "A" may be Al

Answer 2

Element `bb"A"` is aluminium.

Explanation:

Aluminium reacts with oxygen to form a protective layer of aluminium oxide `"Al"_2"O"_3` on its surface.

`4underbrace("Al")_color(red)(bb"A") + "3O"_2 → 2underbrace("Al"_2"O"_3)_color(red)(bb"B")`

Aluminium is above iron in the activity series, so `"Al"` will displace `"Fe"` from its compounds.

`2underbrace("Al")_color(red)(bb"A") + underbrace("Fe"_2"O"_3)_color(red)("rust") → "Al"_2"O"_3 + 2"Fe"`

`"Al"_2"O"_3` reacts with acids.

`underbrace("Al"_2"O"_3)_color(red)(bb"B") + "6HCl" → "2AlCl"_3 + "3H"_2"O"`

`"Al"_2"O"_3` also reacts with bases.

`underbrace("Al"_2"O"_3)_color(red)(bb"B") + "2NaOH" + "3H"_2"O" → "2NaAl(OH)"_4`