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) (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 manufac... 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

Relative Strength: Kevlar® has a higher relative strength compared to steel. This means that for the same weight, Kevlar® can provide more protective strength, making it better suited for lightweight body armour.
Flexibility: Kevlar® is more flexible than steel, which allows it to contour better to the body, enhancing comfort and limiting mobility restrictions. This flexibility increases the wearability of body armour, making it easier for the user to move.

Step 2

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

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Answer

To calculate the surface area to volume ratio of a cube:

Calculate the surface area (SA) of the cube:

The formula for the surface area of a cube is: $SA = 6a^2$ where a is the length of one side of the cube. For a = 2 cm, $SA = 6(2)^2 = 6(4) = 24 ext{ cm}^2$
Calculate the volume (V) of the cube:

The formula for the volume of a cube is: $V = a^3$ For a = 2 cm, $V = (2)^3 = 8 ext{ cm}^3$
Calculate the surface area to volume ratio:

The formula for surface area to volume ratio is: $ext{SA:V ratio} = \frac{SA}{V} = \frac{24}{8} = 3 ext{ cm}^{-1}$ .

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 as nanoparticles, its high surface area increases the number of active sites available for reaction. As a result:

Higher Reactivity: The larger surface area allows for more collisions between the catalyst and reactants, which enhances the rate of reaction.
Lower Concentration of Particles: With nanoparticles, there are fewer particles to react, reducing the chance of blocking active sites. This leads to more efficient catalytic activity, as fewer particles means there is less crowding or competition for reaction sites.

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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