Questions: Separating Mixtures: Magnets and Sieves

Question 1

You have a mixture of iron filings and sand. What is the fastest way to separate them?

• A. Pour water on the mixture and filter it
• B. Use a magnet — the iron filings will stick to it and the sand will stay behind
• C. Heat the mixture until the sand melts
• D. Use a sieve — the iron filings are larger than the sand grains

Answer: (B)

Iron is magnetic and sand is not. Running a magnet through the mixture pulls out the iron filings while the sand stays put. This is the fastest and simplest method because it takes advantage of a clear property difference — magnetism.

Question 2

A sieve separates materials based on their weight.

• T. True
• F. False

Answer: False

False. A sieve separates materials based on their size, not their weight. Small pieces fall through the holes regardless of how heavy they are, and large pieces stay on top regardless of how light they are. A heavy pebble stays on the sieve while a lighter but smaller grain of sand falls through.

Question 3

Name a property besides size that you could use to separate a mixture of two solids.

Model answer: Magnetism — if one solid is magnetic (like iron) and the other is not (like sand or plastic), you can use a magnet to pull out the magnetic material.

Separation methods rely on finding a property that differs between the materials in a mixture. Magnetism is one of the easiest differences to exploit. Other properties that can help include color (hand-sorting), density (one floats and one sinks), and whether one dissolves in water and the other does not.