Problem 30 - Chemistry: The Central Science

Question

The first stage in corrosion of iron upon exposure to air is oxidation to \(\mathrm{Fe}^{2+}\), (a) Write a balanced chemical equation to show the reaction of iron with oxygen and protons from acid rain. (b) Would you expect the same sort of reaction to occur with a silver surface? Fxplain.

Step-by-Step Solution

Answer

(a) The balanced chemical equation for the reaction of iron with oxygen and protons from acid rain is: \[4 \, \mathrm{Fe} + 3 O_2 + 4 \, \mathrm{H}^{+} \to 2 \, \mathrm{Fe}_2 \mathrm{O}_3 + 4 \, \mathrm{H}^{+}\] (b) No, a similar reaction would not occur with a silver surface because silver is less reactive than iron and forms a thin oxide layer on its surface that protects it from further corrosion.

Step 1: Write a balanced chemical equation for the reaction of iron with oxygen and protons from acid rain.

Iron reacts with oxygen and protons from acid rain to form iron(II) ions (\(\mathrm{Fe}^{2+}\)) and water. Furthermore, we'll balance the chemical equation. The balanced chemical equation is as follows: \[4 \, \mathrm{Fe} + 3 O_2 + 4 \, \mathrm{H}^{+} \to 2 \, \mathrm{Fe}_2 \mathrm{O}_3 + 4 \, \mathrm{H}^{+}\]

Step 2: Determine whether the same reaction would occur with a silver surface.

Silver is a less reactive metal compared to iron. In the activity series of metals, silver is found below hydrogen, which means that it doesn't react with acids under normal conditions to produce hydrogen gas. Therefore, we wouldn't expect silver to react with protons from acid rain and oxygen in the same manner as iron. Silver tends to form a thin oxide layer on its surface that protects it from further corrosion, whereas iron oxide (rust) doesn't provide that level of protection. In conclusion, the balanced chemical equation for the reaction of iron with oxygen and protons from acid rain is: \[4 \, \mathrm{Fe} + 3 O_2 + 4 \, \mathrm{H}^{+} \to 2 \, \mathrm{Fe}_2 \mathrm{O}_3 + 4 \, \mathrm{H}^{+}\] And a similar reaction would not occur with a silver surface due to its lower reactivity and better protection from the oxide layer that forms on it.

Key Concepts

Oxidation Reactions

Understanding oxidation reactions is crucial when studying the corrosion of metals like iron. Oxidation is a type of chemical reaction where a substance loses electrons, and in the context of metals, it often refers to the combining of a metal with oxygen. This is particularly common with metals exposed to air or water. In the case of iron, when it reacts with oxygen from the air, particularly in the presence of moisture (which can come from acid rain), iron loses electrons and forms iron(II) ions, denoted as defined as In this reaction, iron ( that gets accepted by the oxygen; hence, oxygen is being reduced and iron is being oxidized. Since this reaction occurs in an aqueous environment where protons (As for the exercise improvement advice, it's beneficial to explain the concept of oxidation states and how the transfer of electrons during a reaction can determine the outcome. Therefore, simply put, in our exercise, iron increases its oxidation state from 0 in separating electrons from the iron, leading to its oxidation.

Chemical Equation Balancing

Balancing chemical equations is akin to solving a puzzle where we ensure that the number of atoms for each element is equal on both sides of the reaction. The law of conservation of mass dictates that matter is not created or destroyed in a chemical reaction, which is why it's essential to balance chemical equations. For students, balancing equations can be a challenging skill, but it's fundamental in accurately depicting chemical reactions.

Having this balanced equation tells us the stoichiometry of the reaction – the ratio in which reactants combine and products form. It is critical to have a properly balanced equation for any chemical calculation, such as determining the amount of reactants needed or predicting the yield of a product. Educators suggest practicing by first balancing the most complex molecule, which usually gives a strong foundation for the rest of the balancing process. The balanced equation from the original exercise is a perfect example of respecting the conservation of mass and charge.

Activity Series of Metals

The activity series of metals is a chart that organizes metals according to their reactivity. A highly reactive metal, such as magnesium, will be placed above a less reactive metal, like gold. This series is particularly valuable when predicting the outcome of replacement reactions and corrosion behavior. Metals higher up in the series will generally displace ions of metals below them from a solution.

When examining the reactivity of silver in comparison to iron, as asked in the exercise, it's observed that silver is much less reactive. Silver is located below iron in the activity series and below hydrogen as well, which indicates that it generally does not corrode or react with acids to release hydrogen gas. Consequently, the reaction seen with iron and acid rain is not expected with silver, which is less prone to oxidation and corrosion. Understanding the reactivity of metals through the activity series can significantly enhance a student's ability to predict chemical behavior and is an integral part of chemistry education.