Question

A sample of crushed rock is found to have 4. 81 x 10^21 atoms of gold, how many moles of gold are present in this sample?

A. 7. 99 x 10^-3 moles

B. 1. 57 x 10^-1 moles

C. 1. 25 x 10^3 moles

D. 2. 47 x 10^5 moles

Answer 1

A

Step-by-step explanation:

Recall that a mole of any substance contains 6.02 × 10²³ amounts of that substance.

In other words, a mole of gold atoms contains 6.02 × 10²³ gold atoms.

Hence, by dimensional analysis, we have that:

`\displaystyle 4.81* 10^(21) \text{ Au} \cdot \frac{1\text{ mol Au}}{6.02* 10^(23) \text{ Au}} = 7.99* 10^(-3) \text{ mol Au}`

Therefore, there is about 7.99 × 10⁻³ moles of gold present in the sample.

In conclusion, the answer is A.