Using mass percent

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Rachel Tat 3E
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Joined: Fri Sep 25, 2015 3:00 am

Using mass percent

Postby Rachel Tat 3E » Wed Oct 14, 2015 5:59 pm

What is the empirical formula of a hydrocarbon which produces 2.703 g CO2 and 1.108 g H2O when combusted?


Part of finding empirical formulas involve finding the mass percent of a compound's individual elements, but for a question like the one quoted above, why is it unnecessary to find the mass percent after converting the grams of CO2 and H2O into grams of C and H?

Vanessa A 3F
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

Re: Using mass percent

Postby Vanessa A 3F » Wed Oct 14, 2015 9:44 pm

"why is it unnecessary to find the mass percent after converting the grams of CO2 and H2O into grams of C and H?"

In a question like this, you do use mass percents, in the beginning when you are converting the grams of CO2 and H2O to grams of C and H.

The steps to solve are
-Find mass percentage of carbon in CO2, multiply this by the given grams of CO2 to get how many grams of carbon are present.
-Find the mass percentage of hydrogen in H20, multiply this by the given grams of H20 to get how many grams of hydrogen are present.
-Convert the grams of carbon to moles.
-Convert the grams of hydrogen to moles.
-Divide each moles value by your smaller answer.
-You will get a ratio of C to H, telling you the empirical formula for the hydrocarbon, which is the objective of the question and your answer.


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