Question

How many grams of sodium contain the same number of atoms as 12.4 g of potassium? Using correct significant figures.

Answer 1

Molar mass of Na = 22.99 g/mol

Molar mass of K = 39.10 g/mol

First calculate number of K atoms in 12.4 g of potassium sample as:

Number of K atom in 39.10 g of potassium is 6.022 × 10 ²³ (Avogadro's number)

Hence, number of atom of K in 12.4 g of potassium = 6.022 × 10 ²³ x 12.4 / 39.10

= 74.67 x 10²³ / 39.10

= 1.909 x 10²³ atomsof K

Now,

Since, 6.022 × 10 ²³ atoms of Na are present in 22.99 g (1mole) of sample of sodium

then mass of sodium which contain 1.909 x 10²³ atomsof Na = 1.909 x 10²³ x 22.99 /  6.022 × 10 ²³

= 43.887 x 1023 / 6.022 × 10 ²³

= 7.28 g of sodium sample.