Question

A 7.36 g sample of copper is contaminated with a additional 0.51 g sample of zinc. suppose an atomic mass measurement was performed on this sample. What would be the measured atomic mass?

64.46
63.67
63.94
65.38

Answer 1

The correct answer is 63.67.

Explanation:

The atomic mass of copper is 63.546 amu

The atomic mass of zinc is 65.38 amu

The weight of total sample is 7.36 grams

Weight of zinc is 0.51 gram

Therefore, weight of copper is 7.36 - 0.51 = 6.85 grams.

By calculating the percent composition we get:

% of copper = 6.85 * 100 / 7.36 = 93.07 %

% of zinc = 100 - 93.07 = 6.93 %

Average atomic mass of sample = (atomic mass of copper * % copper) + (atomic mass of zinc * % of zinc) / 100

= (63.546 * 93.07) + (65.38 * 6.93) / 100

(5914.22 + 453.08) / 100

= 6367.3 / 100 = 63.67

Hence, the measured atomic mass of the sample is 63.67.

Answer 2

For the answer to the question above, the molar mass of the sample is equal to the summation of the molar mass of the elements multiplied by the abundance of the elements by mole. In this case, copper has an abundance of 93.69 percent while zinc has 6.31 percent. In this case, the average molecular weight is 63.67 g/mol. So the answer is the second one.