Question

When elemental iron corrodes it combines with oxygen in the air to ultimately form red brown iron (III) oxide which we call rust. (a) If a shiny ironnail with an initial mass of 23.2 g is weighed after being coated in a layer of rust, would you expect the mass to have increased, decreased, or remained the same? Explain. (b) If the mass of the iron nall increases to 24.1 g what mass of oxygen combined with the iron?

Answer 1

Answer:

a) Increase

b) Mass of oxygen = 0.9 g

Explanation:

The chemical reaction depicting the formation of rust is:

$4Fe(s) + 3O_{2}(g)\rightarrow 2Fe_{2}O_{3}(s)$

where rust is Fe2O3 i.e. iron(II) oxide or ferric oxide

a) When a piece of Fe is exposed to air or oxygen the surface gets coated with Fe2O3. This will increase the amount of matter and hence the mass.

b) Initial mass of iron , Fe= 23.2 g

Mass of iron coated with oxide, Fe2O3 = 24.1 g

Therefore mass of oxygen combined= $24.1 - 23.2 = 0.9 \ g$