Question

Consider an iron bar on a balance as shown.

As the iron bar rusts, which of the following is true? Explain your answer.
a. The balance will read less than 75.0 g.
b. The balance will read 75.0 g.
c. The balance will read greater than 75.0 g.
d. The balance will read greater than 75.0 g, but if the bar is removed, the rust scraped off, andthe bar replaced, the balance will read 75.0 g.

Short answer

The correct statement is an option (c). when the iron bar gets rust.

Step-by-step solution

Formation of rust

The formation of rust involves a chemical change.

When iron reacts with moisture and atmospheric oxygen then rust is formed.

The balanced chemical equation can be denoted as,

$\mathbf{\text{4Fe(s)}}\mathbf{\text{+}}{\mathbf{\text{3O}}}_{\mathbf{2}}\mathbf{\left(}\mathbf{s}\mathbf{\right)} \mathbf{+}\mathbf{x}\mathbf{.}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\to \mathbf{2}{\mathbf{Fe}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}\mathbf{.}{\mathbf{xH}}_{\mathbf{2}}\mathbf{O}\mathbf{\left(}\mathbf{s}\mathbf{\right)}$

Hence, rust is heavier than iron.

Explanation

The mass of the iron bar is given as75.0 g.

The formation of rust makes it heavier. Hence, the correct choice is an option (c).