Question 6 (6 marks) Brass is an alloy of copper and zinc: To determine the percentage of copper in a particular sample of brass, an analyst prepared a number of standard solutions of copper(II) ions and measured their absorbance using an atomic absorption spectrometer (AAS) - VCE - SSCE Chemistry - Question 6 - 2016 - Paper 1

To find the mass of copper in the 100 mL solution, we use the formula:

$m(Cu) = c(Cu^{2+}) \times V$

Where:

• $c(Cu^{2+}) = 0.11 g \, L^{-1}$
• $V = 0.100 \, L$ (100 mL)

So,

$m(Cu) = 0.11 \, g \, L^{-1} \times 0.100 \, L = 0.011 \, g$

The percentage by mass of copper in the brass sample can be calculated as follows:

$\% \text{Cu} = \left( \frac{m(Cu)}{m_{sample}} \right) \times 100$

Here, $m_{sample} = 0.198 \, g$.

Substituting values: $\% \text{Cu} = \left( \frac{0.011}{0.198} \right) \times 100 \approx 5.56\%$