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Chapter 19: Problem 42

How does the tendency of iron to rust depend on the \(\mathrm{pH}\) of solution?

Short Answer

Expert verified
The tendency of iron to rust increases in acidic conditions (lower pH) and decreases in basic or neutral conditions (higher pH). This is because acidic conditions facilitate the removal of electrons from iron (oxidation), promoting rust formation, whereas basic conditions slow down the rust formation by creating a protective layer on iron's surface and the low concentration of hydrogen ions slows down the oxidation process.

Step by step solution

01

Understanding pH

pH is a measure of how acidic or basic water is. It ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic. Acidic solutions have high concentration of hydrogen ions (H+), while basic solutions have high concentration of hydroxide ions (OH鈭�).
02

Effect of pH on rusting process

When iron reacts with oxygen and water, it forms hydrated iron(III) oxide, commonly known as rust. This reaction (corrosion process) be expressed as: \(4Fe(s) + 3O2(g) + 6H_2O(l) \rightarrow 4Fe(OH)_3(s)\), where \(Fe(s)\) is iron, \(O2(g)\) is oxygen, \(H2O(l)\) is water, and \(Fe(OH)_3(s)\) is hydrated iron(III) oxide or rust. This process is faster in acidic conditions (lower pH) because in acidic conditions, the concentration of hydrogen ions (which are positively charged) is increased and these ions promote the removal of electrons from iron (oxidation process), hence helping to form rust.
03

pH Levels and Corrosion Rate

Research studies have found out that the corrosion rate of iron is slower in neutral or basic conditions (higher pH). There are two reasons for this. Firstly, at higher pH, the concentration of hydrogen ions is lower, so the removal of electrons from iron is slower. Secondly, basic conditions often produce a protective layer on the iron's surface that inhibit further corrosion.

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Most popular questions from this chapter

Predict whether \(\mathrm{Fe}^{3+}\) can oxidize \(\mathrm{I}^{-}\) to \(\mathrm{I}_{2}\) under standard-state conditions.

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