Question

Question 39
A gold sample contains $90\%$ of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

Answer 1

Let the mass of the sample is 100g.
Mass of gold = 90g
Mass of copper = (100-90) = 10g
One gram of gold sample will contain $\frac{90}{100}=0.9gofgold$
Number of moles of gold $=\frac{Massofgold}{Atomicmassofgold}$
$=\frac{0.9}{197}=0.0046$
One mole of gold contains $N_A$ atoms $=6.022\times {10}^{23}$
$\therefore$ 0.0046 mole of gold will contain $=0.0046\times 6.022\times {10}^{23}$
$=2.77\times {10}^{21}$