Question

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

One gram of gold sample will contain 90/100 =0.9g of gold   

Number of moles of gold = Mass of gold/ Atomicmass of gold 

                                    = 0.9/ 197 = 0.0046   

One mole of gold contains NA atoms = 6.022 ×10²³ 

∴ 0.0046 mole of gold will contain = 0.0046 × 6.022 ×10²³ 

                                                      = 2.77×10²¹