Problem 31 - Chemistry: The Central Science in SI Units, Global Edition

Question

(a) It has been reported, that acid rain with a pH of 3.5 could corrode mild steel. Write a chemical equation that describes the attack of acid rain on an iron (Fe) material. (b) If the iron material were covered with a surface layer of copper, would this help to stop the effects of acid rain? Explain.

Step-by-Step Solution

Answer

(a) The balanced chemical equation for the reaction between iron (Fe) and sulfuric acid (H2SO4) in acid rain is: Fe(s) + H2SO4(aq) -> FeSO4(aq) + H2(g). (b) Covering the iron material with copper may help reduce the corrosion of the iron by acid rain since copper is less reactive and corrodes slower. However, defects in the copper layer and the formation of a galvanic cell can still result in the iron corroding. Proper coverage and alternative protective methods should be considered for more effective corrosion prevention.

Step 1: (a) Writing the chemical equation for the reaction between acid rain and iron

Acid rain is formed when sulfur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere and react with water, oxygen, and other chemicals to form sulfuric and nitric acids. The pH of the acid rain given in the problem is 3.5. We will focus on the reaction between iron and sulfuric acid for this exercise. Here is the chemical equation representing the reaction between iron (Fe) and sulfuric acid (H2SO4): Fe(s) + H2SO4(aq) -> FeSO4(aq) + H2(g) To balance this equation, we can see that there is already 1 Fe atom, 1 H2SO4 molecule, 1 FeSO4 molecule, and 1 H2 molecule on each side of the equation, so the equation is balanced.

Step 2: (b) Will covering the iron material with copper help to stop the effects of acid rain?

To answer this question, we need to consider the electrochemical series. Metals such as copper and iron possess varying tendencies to you lose or gain electrons. Metals that are more likely to lose electrons (and hence corrode more easily) have a lower position in the electrochemical table compared to metals that have a higher position. Copper is less reactive than iron and has a higher position in the electrochemical series. This means that copper is slower to corrode and would require stronger acids to initiate the corrosion process. Furthermore, copper can serve as a barrier between the acid rain and the iron, slowing down the rate of corrosion of the iron material. However, if there are defects or cracks in the copper layer, the acid rain can still come into contact with the iron material, leading to its corrosion. Additionally, if there is a galvanic cell formed between the copper and iron material, it may result in promoting the corrosion of the iron. In conclusion, covering iron material with copper may help reduce the corrosion of the iron by acid rain. However, the protection is not absolute, as defects in the copper layer and the formation of a galvanic cell can still result in the iron corroding. It is important to ensure proper coverage, and other methods like protective coatings or galvanizing may be more effective in preventing corrosion.

Key Concepts

Acid Rain

Acid rain is a type of precipitation made acidic by atmospheric pollution that it contains higher than normal levels of hydrogen ions (low pH). This is primarily caused by the release of sulfur dioxide (SO extsubscript{2}) and nitrogen oxides (NO extsubscript{x}) into the atmosphere by burning fossil fuels. When they react with water vapor, they form sulfuric and nitric acids, which are harmful to the environment.
The damage caused by acid rain is seen not just in natural ecosystems but also in man-made structures. This includes the corrosion of metals like iron, which react with these acids, leading to damage and deterioration. Monitoring and controlling emissions can significantly reduce acid rain formation.

Chemical Reactions

Chemical reactions involve the breaking and forming of bonds between atoms, resulting in the transformation of substances. In the case of acid rain and iron, sulfuric acid reacts with iron in a process called oxidation-reduction.

• The reaction between iron (Fe) and sulfuric acid (H extsubscript{2}SO extsubscript{4}) can be shown as: Fe(s) + H extsubscript{2}SO extsubscript{4}(aq) → FeSO extsubscript{4}(aq) + H extsubscript{2}(g).
• This equation describes iron being oxidized to iron sulfate, while sulfuric acid is reduced to hydrogen gas.

This reaction occurs because iron tends to lose electrons, facilitating the corrosion process. Understanding these reactions helps in assessing how different materials might degrade under acidic conditions.

Electrochemical Series

The electrochemical series is a list of elements arranged according to their standard electrode potentials. It reflects an element's ability to lose or gain electrons, affecting how it reacts in electrochemical cells.

• Metals higher in the series, like copper, are less reactive than those lower, like iron.
• Copper having a higher position means it corrodes slowly and is often used as a protective covering over metals like iron to slow the corrosion process.

The comparison between metals in the electrochemical series is crucial in determining their suitability for contact with corrosive substances. It's a valuable tool for predicting and preventing corrosion.

Metal Reactivity

Metal reactivity refers to how readily a metal will react with other substances, such as acids. In the context of acid rain, understanding metal reactivity helps in determining which materials are more likely to corrode.

• Metals like iron are more reactive with acids found in acid rain, making them susceptible to corrosion.
• Conversely, metals like copper have a lower reactivity compared to iron, which is why they are used for coating to provide protection.

Choosing the right materials based on their reactivity can mitigate the effects of corrosive environments. It involves selecting metals with suitable reactivity to ensure longevity and durability of structures exposed to potential acid rain damage.