An alloy consists of 30 wt% Zn and 70 wt% Cu. What is the composition of the alloy in atom percent Zn?

• A. 44% Zn
• B. 70% Zn
• C. 56% Zn
• D. 30% Zn

Answer: (A)

Verified step by step guidance

1. Identify the given data: the alloy contains 30 wt% Zn and 70 wt% Cu. We want to find the atomic percent of Zn in the alloy.
2. Recall that atomic percent is based on the number of moles of each element, not their masses. So, convert the weight percentages to moles using the molar masses: Zn has a molar mass of approximately 65.38 g/mol, and Cu has a molar mass of approximately 63.55 g/mol.
3. Calculate the number of moles of Zn and Cu in a hypothetical 100 g sample of the alloy: moles of Zn = \( \frac{30\,g}{65.38\,g/mol} \), moles of Cu = \( \frac{70\,g}{63.55\,g/mol} \).
4. Find the total moles by adding the moles of Zn and Cu together: \( n_{total} = n_{Zn} + n_{Cu} \).
5. Calculate the atomic percent of Zn using the formula: \( \text{atom \% Zn} = \frac{n_{Zn}}{n_{total}} \times 100\% \).