Question

calculate the number of moles present in :
(i) 3.011 × 10²³ number of oxygen atoms
(ii) 60g of calcium
[Give that atomic mass of Ca = 40u, Avogadro no. = 6.022 × 10²³ ]

Answer 1

Answer:

(i) 1 mole of oxygen contains 6.022 × 10²³ atoms

∴ 6.022 × 10²³ atoms of oxygen = 1 mole

$\bf 1\:\: atoms \:\:of \:\:oxygen\:\: \frac{1}{6.022 \times 10^{23}}\: mol$

$\bf \therefore \: 3.011 \times 10^{23} \:\: atoms \:\: of \:\: oxygen =\frac{1 \times 3.011 \times 10^{23}}{6.022 \times 10^{23}}\: mol\\\\=0.5\:\: mol$

(ii) Atomic mass of Ca = 40 u

40 g of calcium = 1 mol

$\bf 60g \:\:of \:\: calcium=\frac{60}{40}\: mol = 1.5\: mol$