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States of Matter and Diffusion: Question 1

Syllabus 1.1

Multiple choice Core 1 mark

An electronics repair technician heats a small blob of solder (a metal alloy) with a hot soldering iron until it turns into a liquid. The technician then removes the iron and watches the liquid solder cool down until it turns solid again on the circuit board.

Which change of state occurs as the liquid solder cools and turns solid?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Identify the states involved

The solder starts as a liquid (just melted by the soldering iron) and ends as a solid (cooled on the circuit board). The change described is therefore liquid →\rightarrow solid.

Step 2: Match the change to its correct name

The five named changes of state each describe a specific direction between states:

  • melting: solid →\rightarrow liquid
  • freezing: liquid →\rightarrow solid
  • boiling and evaporating: liquid →\rightarrow gas
  • condensing: gas →\rightarrow liquid

The solder is changing from liquid to solid, which matches freezing.

Why the other options are wrong

  • A (evaporating): this describes a liquid turning into a gas, not into a solid.
  • C (condensing): this describes a gas turning into a liquid, but the solder was never a gas.
  • D (boiling): this also describes a liquid turning into a gas, the opposite direction to what happens to the solder.

Final answer

  • The liquid solder cooling and turning solid is freezing\boxed{\text{freezing}}, option B.