A researcher performed a combustion analysis on a 5.00 g sample of ethanol, the alcohol in wine. The data showed that the sample contained 261 g of carbon and 0.66 g of hydrogen.

Question

The researcher assumed that the remaining mass was oxygen. Calculate the percentage composition of ethanol.

Answer 1

Hello, Ranheem,

My answer assumes you meant 2.61 g of carbon, not 261. Find the percentage of each element by dividing its mass by the total mass of 5.00 g (and multiplying by 100 to get % in column 3).

As a bonus, we can also determine the empirical formula of ethanol. Divide the percent of each element by it's atomic mass to get a weighted average of the elements. Carbon's value divided by 12 is 0.044. Do the analogous step for the other elements (5th column). Divide all the values by the lowest (0.022) to normalize so that we get the smallest number to 1 (last column). We need whole numbers for each element. The others are close enough to round, and provide an empirical formula: C₂H₆O. Ethanol is, in fact, exactly that. It is more commonly written as C2H5OH, to better reflect the alcohol (-OH) group.

Bob