Hydocarbons, obtained from coal and coal tar and from oil and gas wells, are organic compounds composed entirely of `C` and H. A `0.1647 g` sample of a pure hydrocarbon was burned in a `C - H` combustion train to produce `0.4931 g` of `CO_(2)` and `0.2691 g` of `H_(2)O`. Determine the masses of `C` and `H` in the sample and the percentages of these elem ents in the hydrocarbon.
Strategy:
Step `1`. Use the observed mass of `CO_(2)` to determine the mass of `C` in the original sample using the information that there is `1 mol` of `C` atoms in each mole of `CO_(2)`.
Step `2`. Use the observed mass of `H_(2)O` to calculate the mass of `H` in the original sample using the fact that there are `2 mol` of `H` atoms in each mole of `H_(2)O`. (We can also calculate the mass of `H` by subtracting the mass of `C` from the mass of sample. However, it is good experimental practice, when possible, to base both on experimental measurements as this would help to check for errors in the anlysis of calculation.)
step `3`. Calculate the percentages by mass of each element in turn, using the relationship
`%` Element `= ("Gram of element")/("Gram of sample") xx 100 %`

Explanation

Step 1. ? `gC = 0.4931 g CO_(2) xx (12.01 gC)/(44.01 g CO_(2))`
`= 0.1346 g C`
Step 2. ? `g H = 0.2691 gH_(2)O xx (2.016 gH)/(18.02 g H_(2)O)`
`= 0.03010 gH`
Step3. `%C = (0.1346 gC)/(0.1647 g "sample") xx 100% = 81.72% C`
`%H = (0.03010 g H)/(0.1647 g "sample") xx 100% = 18.28% H`
Sum total of percentages is `100%`.