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Aluminium alloys are used instead of pure aluminium in aircraft manufacture - Edexcel - GCSE Chemistry - Question 4 - 2021 - Paper 1
Question 4
Aluminium alloys are used instead of pure aluminium in aircraft manufacture. (a) Explain, in terms of the arrangement of metal particles, why aluminium alloys are s... show full transcript
Worked Solution & Example Answer:Aluminium alloys are used instead of pure aluminium in aircraft manufacture - Edexcel - GCSE Chemistry - Question 4 - 2021 - Paper 1
Step 1
Explain, in terms of the arrangement of metal particles, why aluminium alloys are stronger than pure aluminium.
Answer
Aluminium alloys exhibit greater strength than pure aluminium due to the differences in atomic size and arrangement. In pure aluminium, all atoms are the same size; however, in aluminium alloys, the atoms are of different sizes. This size variation causes the alloy atoms to disrupt the layer arrangement of the pure aluminium. As a result, these different-sized atoms can impede the movement of dislocations within the crystal lattice.
Additionally, in an alloy, the layers or rows of atoms are not uniform; they cannot slide over each other easily. The presence of different-sized atoms creates a more complex structure that resists deformation.
Step 2
Calculate the mass of aluminium in this sample.
Answer
To find the mass of aluminium in the alloy:
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Calculate the mass of magnesium in the sample:
- Mass of magnesium = 2.00% of 695.0 g
- Mass of magnesium = 0.02 × 695.0 g = 13.9 g
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Subtract the mass of magnesium from the total mass to find the mass of aluminium:
- Mass of aluminium = 695.0 g - 13.9 g = 681.1 g
Step 3
Figure 5 shows a graph of the relative strength of aluminium-magnesium alloys when the percentage by mass of magnesium in the alloy is changed.
Answer
From the graph, it is observed that as the percentage of magnesium increases, the strength of the aluminium-magnesium alloy also increases up to a certain point. Specifically, the strength starts to decrease after reaching a magnesium content of about 3.5%. This indicates that while magnesium can enhance the strength of the alloy up to that threshold, an excess may weaken it, likely due to altered phase structures and brittleness.