If `10^(21)` molecules are removed from 200 mg of `CO_(2)`, the number of moles of `CO_(2)` left will be ?

Options

A. `2.85 xx 10^(-3)`
B. `2.88 xx 10^(-3)`
C. `0.288 xx 10^(-3)`
D. `1.68 xx 10^(-2)`

Answer

A

Explanation

200 mg of `CO_(2) = 200 xx 10^(-3) = 0.2g`
44g of `CO_(2) ~~ 6 xx 10^(23)` molecules (approx)
0.2 g of `CO_(2) = (6 xx 10^(23)/(44)) xx 0.2 = 0.0272 xx 10^(23)` molecules
` = 2.72 xx 10^(21) ` molecules
Now `10^(21)` molecule are removed.
So remaining molecules `= 2.72 xx 10^(21) - 10^(21) = 10^(21) (2.72 - 1) = 1.72 xx 10^(21)` molecules
Now, `6.023 xx 10^(23)` molecules = 1 mol
`1.72 xx 10^(21) ` molecules `= (1 xx 1.72 xx 10^(21))/(6.022 xx 10^(23)) = 0.285 xx 10^(-2)`
` = 2.85 xx 10^(-3)` moles.