Question

Calculate the number of magnesium atoms in 3.2 gram of chlorophyll if it contains 0.024 % of magnesium

Answer 1

We are given that chlorophyll contains 2.68 % of chlorophyll. 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 1023 atoms of magnesium present in 24.312g of Mg. So

 24.312 g of Mg = 6.023 X 1023 atoms of Mg

 or 1 g of Mg = (6.023 X 1023/ 24.312) atoms of Mg

 Hence 0.0804 g of Mg = (6.023 X 1023 X 0.0804) / 24.312 atoms of Mg

 = 1.992 X 1021 atoms of Magnesium. 

The option that is closest to the answer is a) 1.98 X 1021 atoms

Answer 2

Answer: = The number of magnesium atoms in 3.2 grams of chlorophyll if it contains 0.024 % of magnesium is  0.000192704x$10^{23}$ atoms

Explanation:

The atomic mass of Mg = 24g

Mass of chlorophyll = 3.2g

Percentage of magnesium =0.024%

Mass of Mg in 3.2g of chlorophyll =  3.2 x (0.024/100) = 0.000768g

Number of atoms = number of moles X Na (Avogadro number)

Implies number of Mg atoms = (0.000768/24) x (6.022x)

= 0.000192704x