Question

How many atoms are there in a 20 g sample of gold?

Answer 1

We know that there are 20g of gold and we must calculate how many atoms there are in the sample.

First, we must use the molecular mass of the gold,

$M(Au)=196.97\frac{g}{mol}$

Then, we must use the next formula

$n(Au)=\frac{m(Au)}{M(Au)}$

Where,

- n represents the number of molecules

- m is the given mass (20 g)

- M is the molecular mass

Now, replacing the values in the formula

$n(Au)=\frac{20g}{196.97\frac{g}{mol}}=0.1015\text{mol}$

Finally, we must use that there are 6.022 * 10^23 molecules per mole

$N(Au)=n(Au)\cdot N_a=0.1015mol\cdot6.022\cdot10^{23}=6.1\cdot10^{22}$

ANSWER:

6.1 * 10^22 atoms are in 20g sample of gold.