Question

Calculate the number of gold atom

Answer 1

The number of gold atom : 1.204 x 10²¹

Further explanation

Given

0.6 g of 18 carat gold

mass number of gold = 197

24 carat as 100% gold

Required

The number of gold atom

Solution

Percentage of gold in 18 carat :

$\tt \dfrac{18}{24}\times 100\%=75\%$

Mass of gold in 0.6 g of 18 carat :

$\tt 75\%\times 0.6~g=0.45~g$

mol :

$\tt mol=\dfrac{mass}{MW}=\dfrac{0.45}{197}=0.0023$

A mole is a number of particles(atoms, molecules, ions)  in a substance

1 mole = 6.02.10²³ particles  

So the number of gold atom :

$\tt 0.0023\times 6.02\times 10^{23}=1.204\times 10^{21}$