This question is about properties of materials. (a) Figure 6 shows some properties of steel and Kevlar®. Body armour, such as a bullet-proof vest, could be manufactured using either of these materials. Explain two reasons why Kevlar® is preferred to steel as the material for body armour. (4) (b) The use of nanoparticles has increased in recent years. (i) The length of one side of a cube of silver is 2 cm as shown in Figure 7. Calculate the surface area to volume ratio of this cube of silver. (3) surface area to volume ratio = (ii) Suggest an explanation of why a given mass of silver is more effective as a catalyst when used as nanoparticles rather than in a powder form. (3)

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This question is about properties of materials - Edexcel - GCSE Chemistry - Question 7 - 2016 - Paper 1

Question 7

This question is about properties of materials. (a) Figure 6 shows some properties of steel and Kevlar®. Body armour, such as a bullet-proof vest, could be manuf... show full transcript

Worked Solution & Example Answer:This question is about properties of materials - Edexcel - GCSE Chemistry - Question 7 - 2016 - Paper 1

Step 1

Explain two reasons why Kevlar® is preferred to steel as the material for body armour.

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Answer

Higher Relative Strength: Kevlar® has a relative strength of 5 compared to steel’s relative strength of 1. This means that, for the same weight, Kevlar® can withstand greater forces, making it more effective for body armour, which needs to absorb energy from impacts such as bullets.
Greater Flexibility: Kevlar® is characterized by high flexibility, allowing for better mobility when worn. This is essential in body armour, as it enables the wearer to move more freely while still being protected, whereas steel can be rigid and restrict movement.

Step 2

Calculate the surface area to volume ratio of this cube of silver.

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Answer

To find the surface area to volume ratio of a cube, we first calculate the surface area (SA) and volume (V).

Surface Area Calculation:
- Formula for surface area of a cube: $SA = 6s^2$
- For a side length, $s = 2 ext{ cm}$ : $SA = 6(2 ext{ cm})^2 = 6 imes 4 ext{ cm}^2 = 24 ext{ cm}^2$
Volume Calculation:
- Formula for volume of a cube: $V = s^3$
- For $s = 2 ext{ cm}$ : $V = (2 ext{ cm})^3 = 8 ext{ cm}^3$
Surface Area to Volume Ratio:
- Ratio = $\frac{SA}{V} = \frac{24 ext{ cm}^2}{8 ext{ cm}^3} = 3 ext{ cm}^{-1}$

Thus, the surface area to volume ratio is 3 cm⁻¹.

Step 3

Suggest an explanation of why a given mass of silver is more effective as a catalyst when used as nanoparticles rather than in a powder form.

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Answer

When silver is used in nanoparticle form, the increased surface area relative to the volume allows for more active sites for chemical reactions. This means that:

Higher Surface Area: Nanoparticles have a much larger surface area per unit mass compared to powder forms, providing more sites for reactants to collide and undergo reaction.
Enhanced Reactivity: The unique properties of nanoparticles, such as quantum effects and increased reactivity due to size, lead to a higher catalytic efficiency, making them significantly more effective than larger powder forms.

This question is about properties of materials - Edexcel - GCSE Chemistry - Question 7 - 2016 - Paper 1

Worked Solution & Example Answer:This question is about properties of materials - Edexcel - GCSE Chemistry - Question 7 - 2016 - Paper 1

Explain two reasons why Kevlar® is preferred to steel as the material for body armour.

Calculate the surface area to volume ratio of this cube of silver.

Suggest an explanation of why a given mass of silver is more effective as a catalyst when used as nanoparticles rather than in a powder form.

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