A blacksmith heats a ball of iron wool in a Bunsen burner flame in the open air. The iron reacts with oxygen gas to form iron(III) oxide, a reddish-brown solid. (a) Construct the balanced symbol equation, including state symbols, for this reaction. [2] (b) Calculate the relative…

Answer: ((a)) 4Fe(s) + 3O2(g) → 2Fe2O3(s) ((b)) 160 ((c)) 0.1 mol. Part (a): Balanced symbol equation Iron reacts with oxygen from the air. Iron(III) oxide has the formula Fe2O3 (each iron ion is Fe^3+ and each oxide ion is O^2-, so two iron ions balance three oxide ions). Starting from Fe + O2 → Fe2O3, b…

IGCSE Chemistry 0620: Equation, Mr and Moles for Iron(III) Oxide Formation

Part (a): Balanced symbol equation

Iron reacts with oxygen from the air. Iron(III) oxide has the formula $\text{Fe}_2\text{O}_3$ (each iron ion is $\text{Fe}^{3+}$ and each oxide ion is $\text{O}^{2-}$ , so two iron ions balance three oxide ions).

Starting from $\text{Fe} + \text{O}_2 \rightarrow \text{Fe}_2\text{O}_3$ , balance the oxygen atoms first (a multiple of $2$ on the left must match a multiple of $3$ on the right, so use $6$ oxygen atoms), then balance the iron atoms:

$4\text{Fe(s)} + 3\text{O}_2\text{(g)} \rightarrow 2\text{Fe}_2\text{O}_3\text{(s)}$

Check: Fe $=4$ on each side; O $=3\times2=6$ on the left, $2\times3=6$ on the right. Balanced.

Part (b): Relative formula mass of iron(III) oxide

$M_r(\text{Fe}_2\text{O}_3) = (2\times A_r(\text{Fe})) + (3\times A_r(\text{O}))$

$M_r(\text{Fe}_2\text{O}_3) = (2\times56) + (3\times16) = 112+48=160$

Part (c): Moles of iron atoms

Use $\text{moles} = \dfrac{\text{mass}}{\text{molar mass}}$ , with the molar mass of iron atoms equal to $A_r(\text{Fe})=56\ \text{g/mol}$ :

$\text{moles of Fe} = \frac{5.6}{56} = 0.1\ \text{mol}$

Final answers

(a) $4\text{Fe(s)} + 3\text{O}_2\text{(g)} \rightarrow 2\text{Fe}_2\text{O}_3\text{(s)}$
(b) $M_r(\text{Fe}_2\text{O}_3) = \boxed{160}$
(c) Moles of Fe $= \boxed{0.1}\ \text{mol}$