Question

Chlorophyll, the green colouring matter of plants contains $2.68\%$ of magnesium by weight. Calculate the number of magnesium atoms in $2.00g$ of chlorophyll?

(Atomic mass of $Mg=24$)

• A. $1.3\times {10}^{20}$
• B. $1.3\times {10}^{21}$
• C. $1.3\times {10}^{22}$
• D. $1.2\times {10}^{23}$

Answer 1

The correct option is B $1.3\times {10}^{21}$

Given amount of chlorophyll $=2.0gm$

given amount of magnesium $=2.68$

Mass of $Mg$ in $2.0gm$ of chlorophyll $=\frac{2.68\times 2}{100}=0.054gm$.

$6\times {10}^{23}$ atoms of magnesium $=24gm$

$24gm$ of $Mg$ contains $6.022\times {10}^{23}$

$0.054g$ of $Mg$ contains $=\frac{6.022\times {10}^{23}\times 24}{0.054}=1.3\times {10}^{21}$