Question

how many atoms of Cl are there in 6.3 grams of Cl? (show your work.)

Answer 1

Solution:

1) Find the amount of substance from the following equation:

$$n = \frac{m}{M}$$

$n$ — Amount of substance

$m$ — mass of the substance

$M$ — the molar mass of the substance

$$n(Cl) = \frac{m(Cl)}{M(Cl)}$$ $$n(Cl) = \frac{6.3\,g}{35.45\,g/mole} = 0.178\,mole$$

2) Obtain the amount of atoms:

$$N_A = 6.022 \times 10^{23} \, \text{mol}^{-1}$$ $$N = n \times N_A$$ $$N(Cl) = n(Cl) \times N_A$$

So,

$$N(Cl) = 0.178\,mole \times 6.02 \times 10^{23} = 1.072 \times 10^{23}$$

Answer: $1.072 \times 10^{23}$ atoms of Cl