Question

Rust is formed by the interaction of iron and oxygen. When rust formed on an iron nail with a mass of 100 g, the mass of the rusted nail was 143g. What mass of oxygen gas most likely reacted with the iron nail? A) 43g B) 50g C) 100g D) 243g

Answer 1

Answer: The correct option is A.

Explanation: Moles of Iron nail can be calculated by using the formula:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$       ...(1)

Given mass of iron nail = 100 g

Molar mass of iron = 56 g/mol

$\text{Number of moles}=\frac{100g}{56g/mol}$

Number of moles of iron nail = 1.79 moles

The chemical equation for the formation of rust if given by:

$4Fe(s)+3O_2(g)\rightarrow 2Fe_2O_3(s)$

By Stoichiometry of the reaction,

4 moles of iron reacts with 3 moles of oxygen gas to produce 2 moles of rust.

So, 1.79 moles of iron will react with = $\frac{3}{4}\times 1.79$ = 1.3425 moles of oxygen gas.

For oxygen gas,

Molar mass = 32 g/mol

Mass of oxygen can be calculated by using equation 1, we get

$1.3425mol=\frac{\text{Given mass}}{32g/mol}$

Mass of oxygen gas = 43 grams

Hence, the correct option is a.