A nail left outside in the rain develops a flaky, reddish-brown coating. What happened?
ADirt from the rain stained the nail
BThe iron in the nail reacted with oxygen and water to form rust — a new substance
CThe nail melted slightly in the rain and changed color
DThe paint on the nail wore off, revealing the red metal underneath
The nail rusted. Iron reacted chemically with oxygen from the air and water from the rain to create iron oxide, commonly called rust. Rust is a completely different substance from iron — it is flaky, reddish-brown, and weaker. This is a chemical change, not just a surface stain.
Question 2 True / False
Rust can be turned back into iron by simply washing it off with water.
TTrue
FFalse
Answer: False
False. Rust is a new chemical substance (iron oxide) formed by a chemical change. You cannot reverse a chemical change by washing it. The iron atoms have combined with oxygen atoms to form something entirely different. Once iron has rusted, that portion of the iron is gone — it has become rust.
Question 3 Short Answer
Why does painting a metal fence help prevent rusting?
Think about your answer, then reveal below.
Model answer: Paint creates a barrier that keeps oxygen and water from touching the iron surface. Since rust requires both oxygen and water to react with iron, blocking them prevents the chemical change from happening.
Rusting needs three things: iron, oxygen, and water. Remove any one of these and rusting stops. Paint acts as a shield over the iron, stopping oxygen and moisture in the air from reaching the metal. This is why scratches in paint often lead to rust spots — the exposed metal can now react.