Properties and uses of some metals
2 marks · EasyExplain why steel is an alloy and why it is harder than pure iron.
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Steel is a mixture of iron with carbon (and sometimes other elements), which is an alloy. The different sized atoms disrupt the layers, so they cannot slide easily, making steel harder than pure iron.
Also accept: Steel is an alloy because it is made of iron mixed with other elements. The structure is disrupted so layers cannot slide over each other.
Common mistakes: Steel is just pure iron that is harder.
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Marking points
B1 · 1 mark · States that steel is an alloy or a mixture of iron with other elements (or carbon).
B2 · 1 mark · Explains that different sized atoms mean layers cannot slide easily, making it harder than pure iron.
Worked solution
Steel is an alloy because it is made by mixing iron with carbon (and other elements). The carbon atoms are a different size, which disrupts the regular arrangement of iron atoms and prevents the layers from sliding, making steel harder than pure iron.