Steel is a mixture of iron and carbon. Why do builders use steel instead of pure iron for buildings and bridges?
ASteel is shinier than iron
BSteel is lighter than air, so it floats into place
CSteel is stronger and more resistant to bending than pure iron
DSteel is a pure substance and pure substances are always better
Adding a small amount of carbon to iron creates steel, which is significantly stronger and harder than pure iron. It resists bending and breaking better, which is exactly what you need for structures that hold heavy loads. Steel is not a pure substance — it is a mixture (alloy) — but that mixture is more useful than either ingredient alone.
Question 2 True / False
An alloy is a pure substance because it is a single solid piece of metal.
TTrue
FFalse
Answer: False
False. An alloy is a mixture, not a pure substance. It contains two or more different materials that were melted and combined. Even though an alloy looks like one uniform piece of metal, it is made of different types of particles mixed together. Bronze, for example, contains both copper and tin particles.
Question 3 Short Answer
What is an alloy?
Think about your answer, then reveal below.
Model answer: An alloy is a mixture of two or more metals (or a metal with a small amount of another material) that are melted together and cooled to form a solid with improved properties.
Alloys are made by melting metals together so they blend completely, then letting the blend cool into a solid. The result usually has better properties than either metal alone — stronger, harder, more resistant to rust, or a better color for coins and jewelry.