Question

chlorophyll the green colouring matter of plants responsible for photosynthesis contains 2.68 % of magnesium by weight. Calculate the number of magnesium atoms in 2g of chlorophyll.

Answer 1

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Mass of Mg present in 2g of Chlorophyll = (2.68/100) x 2 g = 0.054 g

Also that, 24 g of Mg contain 6.023 x 1023 atoms of Mg

-------------- 1g of Mg = (6.023 x 1023)/24 atoms of Mg

Hence, 0.054 g of Mg will contain (6.023 x 1023/24 ) x 0.054 atoms of Mg = 1.34 x 1023 atoms of Mg present in 2.00 gram of chlorophyll.

Answer 2

molecular formula of chlorophyll:

C55H72MgN4O5

molecular weight of chlorophyll : 893.5 g/mol

if 2 g of chlorophyll is given

then given moles of chlorophyll = 2/894

=0.00223 moles

1 mole of chlorophyl have 1 mole Mg atoms..

ao 0.00223 moles of chlorophyll will havw 0.00223 mole Mg atoms....

now molecular weight of Mg = 24 u

so 0.00223 mole Mg will have...

0.00223 x 24 gram weight

=0,0537 grams magnesium

or 53.7 milligrams Mg