Question

State true or false with calculations

Chlorophyll contains 2.68% of magnesium by mass.The number of Mg atoms in 3g of chlorophyll is 2.01 × 10²¹ atoms.

Answer 1

We are given that chlorophyll contains 2.68 % of magnesium. Therefore mass of magnesium that is present in 3g of chlorophyll is

(2.68 / 100) X 3 = 0.0804g

Thus 3g of chlorophyll contains 0.0804g of Mg. Now the molar mass of magnesium is 24.312g. This means that there are 6.023 X 10^23 atoms of magnesium present in 24.312g of Mg. So

24.312 g of Mg = 6.023 X 10^23 atoms of Mg

or 1 g of Mg = (6.023 X 10^23/ 24.312) atoms of Mg

Hence 0.0804 g of Mg = (6.023 X 10^23 X 0.0804) / 24.312 atoms of Mg

= 1.992 X 10^21 atoms of Magnesium

So, false. It approximately equal to 2.01×10^21, but its not the exact value.