Question
$$0.2\,g$$ of an organic compound contains $$C, H$$ and $$O.$$ On combustion, it yields $$0.15\,g\,C{O_2}$$ and $$0.12\,g$$ $${H_2}O.$$ The percentage of $$C, H$$ and $$O$$ respectively is
A.
$$C = 15\% ,H = 20\% ,O = 65\% $$
B.
$$C = 10\% ,H = 8.2\% ,O = 81.8\% $$
C.
$$C = 12.2\% ,H = 8.8\% ,O = 79\% $$
D.
$$C = 20\% ,H = 6.66\% ,O = 73.34\% $$
Answer :
$$C = 20\% ,H = 6.66\% ,O = 73.34\% $$
Solution :
$$\eqalign{
& \% \,{\text{of}}\,C = \frac{{12}}{{44}} \times \frac{{0.15}}{{0.2}} \times 100 = 20\% \cr
& \% \,\,{\text{of}}\,\,H = \frac{2}{{18}} \times \frac{{0.12}}{{0.2}} \times 100 = 6.66\% \cr
& \% \,\,{\text{of}}\,\,O = 100 - \left( {20 + 6.66} \right) = 73.34\% \cr} $$