Question

How many atoms are in
$1.00 \times {10}^{ - 9}$
grams of lead?

Answer 1

Molar mass of Pb is 207.2g

1 mole of Lead (207.2g) contains 6.022x10²³ atoms

1x10⁻⁹ g of lead contains --------?

=1x10⁻⁹x6.022x10⁻²³/207.2

=10¹⁴x0.029

=2.9x10¹²

∴ 2.9 x 10¹² atoms are present in 1x 10⁻⁹g lead

Answer 2

given weight of lead , w = 10^-9 gram

atomic mass of lead {e.g. Pb } , M = 207.2 g/mol

number of mole of lead = weight of lead/atomic mass of lead

= 10^-9/207.2

number of atoms = number of mole of lead × Avogadro's number

= 10^-9/207.2 × 6.023 × 10²³

= 0.029068 × 10¹⁴

= 2.9 × 10¹²

hence, number of atoms in 10^-9 gram of lead = 2.9 × 10¹²