Extraction and Uses of Metals
6 marks · NormalMetals above carbon in the reactivity series cannot be extracted by carbon reduction. Some, like titanium, are extracted using a more reactive metal, such as magnesium.
Explain, in terms of reactivity, why magnesium can be used to extract titanium from its oxide, but carbon cannot.
Steel is an alloy made from iron and carbon.
Define the term alloy.
Describe why alloys such as steel are usually harder than pure iron. You may draw a labelled diagram to support your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Magnesium is more reactive than titanium so it can displace titanium from titanium oxide. Carbon is less reactive than titanium and cannot do this.
(b(i)) An alloy is a mixture of a metal with other elements (usually metals or carbon).
(b(ii)) Alloys are harder than pure metals because the different sized atoms from the added element(s) distort the regular lattice, making it more difficult for the layers of ions to slide over each other. A labelled diagram should show layers in pure iron and distorted layers in steel due to different atom sizes. · must show layers in pure metal slide, distorted arrangement in alloy, layers cannot slide in alloy
Common mistakes: Saying carbon can extract titanium; not referring to relative reactivity; 'alloy' definition as just 'mixture' with no mention of metals; no reference to lattice distortion or atomic size differences in part b(ii)
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Marking points
M1 (a) · 1 mark · States magnesium is more reactive than titanium/can displace titanium from its oxide
A1 (a) · 1 mark · States carbon is less reactive than titanium/therefore cannot reduce titanium oxide
B1 (b(i)) · 1 mark · States a correct definition of alloy as a mixture of a metal with other elements/metals/carbon
M2 (b(ii)) · 1 mark · Mentions (or diagrams) that atoms in alloy are of different sizes, distorting the lattice
M3 (b(ii)) · 1 mark · Explains/how that prevents/slows the sliding of layers of ions/atoms over each other
A2 (b(ii)) · 1 mark · Diagram: shows regular layers for pure metal, distorted for alloy, with accurate or labelled atom sizes/types and clearly indicates inability to slide
Worked solution
a) Magnesium can be used to extract titanium because magnesium is more reactive than titanium. It can displace titanium from titanium oxide in a reduction process. Carbon cannot be used because it is less reactive than titanium and therefore unable to take oxygen away from titanium oxide.
b)(i) An alloy is a mixture of a metal with one or more other elements (often metals or carbon).
b)(ii) In pure metals, atoms are all the same size and form regular layers that can slide over each other, which makes the metal soft.
In alloys, different atoms have slightly different sizes. This breaks up the regular arrangement, distorting the lattice. As a result, the layers cannot slide over each other as easily, making alloys harder than pure metals.
(Left: regular layers in pure metal can slide. Right: larger 'atom' represents a different sized atom, distorting layers in an alloy so they cannot slide easily.)