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Alloys of gold are often used to make jewellery - Edexcel - GCSE Chemistry - Question 1 - 2020 - Paper 1
Question 1
Alloys of gold are often used to make jewellery. The purity of gold is measured in carats. Different alloys of gold have different carats. (a) Figure 1 shows ... show full transcript
Worked Solution & Example Answer:Alloys of gold are often used to make jewellery - Edexcel - GCSE Chemistry - Question 1 - 2020 - Paper 1
Step 1
Explain why 18 carat gold is stronger than 24 carat gold.
Answer
18 carat gold contains 75% gold and 25% other metals (silver and copper), while 24 carat gold consists of 100% gold. The presence of other metals in 18 carat gold introduces a mix of atoms of different sizes. This disrupts the structure of the metal, preventing layers of atoms from slipping over one another, which enhances its strength compared to pure gold.
Step 2
Determine the purity of the gold necklace in carats.
Answer
To find the purity in carats, we first determine the percentage of gold in the necklace.
The mass of the gold in the necklace is 2.9g. Total mass of the necklace = 5.0g.
Purity in percentage = ( \frac{2.9g}{5.0g} \times 100 = 58% )
To express this in carats, we use the formula:
( \text{purity in carats} = \text{percentage} \div 4 = \frac{58}{4} = 14.5 \text{ carats}. )
Step 3
Calculate the number of gold atoms in the ring.
Answer
The mass of gold in the ring is 3.94g. To find the number of atoms, we first convert the mass of gold into moles using the formula:
( \text{number of moles} = \frac{\text{mass}}{\text{molar mass}} = \frac{3.94g}{197g/mol} = 0.020 \text{ moles}. )
Then, we multiply by Avogadro's constant to find the number of gold atoms:
( \text{number of gold atoms} = 0.020 \text{ moles} \times 6.02 \times 10^{23} = 1.204 \times 10^{22} \text{ atoms}. )