Question

A sample of 18K gold contains the following by mass: 18.0 grams gold. 3.0 grams silver, and 3.0 grams copper. What is the percentage of gold?

Answer 1

A sample of 18K gold contains the following by mass: 18.0 grams gold. 3.0 grams silver, and 3.0 grams copper. What is the percentage of gold?

**Solution**

Total mass of the sample:

$$m_{\text{sample}} = m_{\text{gold}} + m_{\text{silver}} + m_{\text{copper}}$$

Calculating:

$$m_{\text{sample}} = 18.0 + 3.0 + 3.0 = 24.0\,g$$

Mass percentage of gold in sample can be calculated as:

$$\omega_m(\text{gold}) = \frac{m_{\text{gold}}}{m_{\text{sample}}} * 100\%$$

Calculating:

$$\omega_m(\text{gold}) = 18.0 / 24.0 * 100\% = 75\%$$

**Answer:** mass percentage of gold in sample is 75%