Question

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

Answer 1

Solution :

Step 1: Given data:

One gram of gold sample will contain

=$90/100=0.9\mathrm{g}$of gold

Step 2: Calculation of the number of moles of gold

Number of moles of gold =$\frac{\mathrm{mass}\mathrm{of}\mathrm{gold}}{\mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{gold}}$

Number of moles of gold = $\frac{0.9}{19.7}$

= $0.0046$

Step 3: Calculating the number of atoms of gold

We know one mole of gold contains N_A atoms = $6.022\times {10}^{23}$

∴ $0.0046$ mole s of gold = $0.0046\times 6.022\times {10}^{23}$

= $2.77\times {10}^{21}$

Hence, the number of atoms of gold are present in one gram of this sample of gold = $2.77\times {10}^{21}$ atoms.