Question

Chlorophyll, the green coloured pigment in plants
contains 2.5% of magnesium by mass. The number
of magnesium atoms in 4.5 g of chlorophyll is
(1) 4.7 * 10-
(2) 4.7 * 109 NA
(3) 27 × 10-3 N. (4) 9.4 × 10-N.​

Answer 1

2.5g Mg in 100 g chlorophyll

moles of Mg = Given mass/molar mass = 2.5/24 = 0.1 mol

No. of Mg atoms in 100g chlorophyll = 0.1 x 6.02 x 10^23 = 6.02 x 10^22

1g chlorophyll = 6.02 x 10^22/100 = 6.02 x 10^20

4.5g chlorophyll = 4.5 x 6.02 x 10^20 = 2.7 x 10^21 atoms of Mg