Question

What is the number of Au atoms in 300 mili gram of gold of 20 carat gold where pure gold is 24 carat.

Answer 1

∵ 300mgof a gold ring is 20 of 20 Carat . It means in 300 mg ring , 20 part is pure gold and 4 part is other metal.
∴ weight of pure gold in 300mg =300 × (20/24) × 100 = 250mg

Now, weight of pure gold = 250mg = 0.25g
molecular weight of pure gold = 197g/mol
∴ mole = weight of gold/molecular weight of gold
= 0.25/197

Now, number of gold atoms = number of mole of gold × 6.023 × 10²³
= 0.25/197 × 6.023 × 10²³
= 7.64 × 10²⁰