Chemical Reactions and Equations · Lesson 8 of 9
Have You Observed The Effects Of Oxidation Reactions In Everyday Life?
“Rusty metal and stale chips turn out to share one quiet villain: oxidation.”
• Define corrosion and identify examples involving iron, silver and copper. • Explain why corrosion damages metallic objects. • Define rancidity as oxidation of fats and oils. • Explain methods used to slow rancidity. • Distinguish corrosion from rancidity as two effects of oxidation.
Oxidation does not occur only in laboratory reactions. Two familiar effects appear slowly in everyday life: metals corrode, and foods containing fats and oils can become rancid. Both involve chemical change caused by reaction with the surroundings.
Corrosion
Corrosion is the gradual attack of a metal by substances in its surroundings such as moisture or acids.
Fresh iron objects can be shiny, but after exposure they may become coated with a reddish-brown material. This is rusting of iron. Silver can develop a black coating, while copper can develop a green coating. These different appearances are examples of corrosion on different metals.
Corrosion damages car bodies, bridges, iron railings, ships and other metallic objects. The problem is especially serious for iron because structures and equipment may need repair or replacement.
Rancidity
Rancidity is the change in smell and taste that occurs when fats and oils are oxidised.
Foods rich in fats and oils may develop an unpleasant smell and taste after being kept for a long time because oxidation changes the substances present in the food.
Slowing Rancidity
Rancidity can be slowed by reducing contact with oxygen or by using substances that slow oxidation. Antioxidants are added to some foods. Airtight containers reduce exposure to air. Packets of chips are commonly flushed with nitrogen so that much less oxygen remains around the food.
| Method | How It Helps |
|---|---|
| Antioxidants | Slow oxidation reactions in fats and oils |
| Airtight containers | Reduce contact between food and air |
| Nitrogen flushing | Replaces much of the oxygen around the food |
Corrosion And Rancidity Compared
| Feature | Corrosion | Rancidity |
|---|---|---|
| Material affected | Metals | Fats and oils in food |
| Typical observation | Metal surface develops a coating or is damaged | Smell and taste change |
| Connection | Oxidation of metal in surroundings | Oxidation of fats and oils |
A protective coating separates iron from surrounding air and moisture, reducing the contact needed for corrosion to proceed.
Quiz
What is the reddish-brown coating associated with iron?
Which metal is described as developing a black coating during corrosion?
What is rancidity?
Why are chip packets flushed with nitrogen?
Which method can slow rancidity?
Practice Problems
- Define corrosion and give the examples of iron, silver and copper described in the lesson.
- Explain why corrosion is an important practical problem for bridges, ships and car bodies.
- Define rancidity and describe the changes it causes in fat- or oil-containing food.
- Explain how antioxidants and airtight containers help slow rancidity.
- Explain why nitrogen is used in packets of chips.
- Compare corrosion and rancidity in terms of the materials affected and the observable effects.
Key Takeaways
• Corrosion is the attack of metals by substances in their surroundings such as moisture and acids. • Rusting of iron, blackening of silver and green coating on copper are examples of corrosion. • Corrosion can seriously damage metallic objects and structures. • Rancidity results from oxidation of fats and oils and changes their smell and taste. • Antioxidants, airtight storage and nitrogen flushing help slow rancidity.