# 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’?

Oct 16, 2016

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

Oct 31, 2016

Element $\boldsymbol{\text{A}}$ is aluminium.

#### Explanation:

Aluminium reacts with oxygen to form a protective layer of aluminium oxide ${\text{Al"_2"O}}_{3}$ on its surface.

$4 \underbrace{\text{Al")_color(red)(bb"A") + "3O"_2 → 2underbrace("Al"_2"O"_3)_color(red)(bb"B}}$

Aluminium is above iron in the activity series, so $\text{Al}$ will displace $\text{Fe}$ from its compounds.

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

${\text{Al"_2"O}}_{3}$ reacts with acids.

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

${\text{Al"_2"O}}_{3}$ also reacts with bases.

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