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? (Atomic mass of gold is 197).

• A. $0.9$ atoms
• B. $6.022\times {10}^{23}$ atoms,
• C. $0.45\times {10}^{23}$ atoms,
• D. $2.77\times {10}^{21}$

Answer 1

Answer: (D)

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

As sample is 90% pure wrt to Gold,
So one gram of sample will have $90/100=0.9gm$ gold.
Number of moles of gold $=\frac{Massofgold}{Atomicmassofgold}$
$=\frac{0.9}{197}=0.0046$
According to mole concept,
One mole of gold contains $N_A$ atoms $=6.022\times {10}^{23}$ atoms,
$\therefore 0.0046$ mole of gold will contain $=0.0046\times 6.022\times {10}^{23}$
$=2.77\times {10}^{21}$