Question

A sample of gold (Au) has a mass of 35.12 g..
a. Calculate the number of moles of gold (Au) in the sample. .. .
b. Calculate the number of atoms of gold (Au) in the sample

Answer 1

a) Molar mass gold ( Au) = 196.96 g/mol

1 mole Au ----------- 196.96 g
? moles Au ---------- 35.12 g

35.12 x 1 / 196.96

= 0.178 moles of Au
_____________________________

b) 196.96 g --------------- 6.02x10²³ atoms
    35.12 g ---------------- ( atoms ? )

35.12 x ( 6.02x10²³) / 196.96

2.114x10²⁵ / 196.96

= 1.07x10²³ atoms
_____________________________________________

Answer 2

Answer:

a) 0.1783 moles of gold.

b) $1.074\times 10^{23}$ atoms of gold.

Explanation:

Mass of gold sample = 35.12 g

Atomic mass of gold = 197 g/mol

Moles of compound = $\frac{\text{mass of the compound}}{\text{molar mass of compound}}$

a) Moles of gold :'$\frac{35.12 g}{197 g/mol}=0.1783 mol$

1 mole = $6.022\times 10^{23}$ atoms. molecule

b) Number of gold atoms in 0.1783 moles:

$=0.1783\times 6.022\times 10^{23}=1.074\times 10^{23} atoms$