A few days ago
Anonymous

FORmula question..PLZ help!?

A sample of an unknown biochemical compound is found to have a percent composition of 71.34 percent carbon, 8.43 percent hydrogen, 6.16 percent nitrogen and the balance oxygen. What is the simplest formula for this compound ?

If the percentage composition is given, assume a 100g sample make sure you have whole number coefficients

I tried this n received the final formula numbers to be 13.56, 19.16, 1 , 1.9575 for C, H, N, O respectively…is tht correct? hw do I round up the numbers though????

Top 3 Answers
A few days ago
TurtleFromQuebec

Favorite Answer

first divide the percentages by the atomic weights to get the proportions of the numbers of atoms. (x is a constant that will magically make the numbers come out to whole numbers)

C: 71.34/12.01 = 5.94x

H: 8.43/1.008 = 8.36x

N: 6.16/14.01 = 0.440x

O: 14.07/16.00 = 0.879x

The number for N is smallest, and there has to be at least 1 atom of nitrogen, so guess that x = 1/0.440 and multiply everything by that:

C: 13.5 (roughly)

H: 19

N: 1

O: 2

These are very near whole numbers, except for C the result is very near a whole number plus1/2. So multiply everything by 2 to get

C: 27 atoms

H: 38

N: 2

O: 4

This is probably the simplest formula. To check, multiply the numbers by the atomic weights and take percentages to see if you get the original composition.

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A few days ago
greenwhitecollege
Approximately that is correct. Because you can not muliply them by a number where the C and the H would be very close to a whole number. If you can get a whole number for one, you will not get a whole number for the other. So just round them to the nearest number to get

C14H19NO2

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A few days ago
shuaib
C14 H19 N1 O2
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