What is the percentage of carbon by mass in citric acid?

1 Answer
Sep 25, 2016

Answer:

#%C# #=# #(6xx12.011*g)/(192.12*g*mol^-1)xx100%# #=# #37.5%#.

Explanation:

I think you have intuitively realized the correct approach.

#%"element"# #=# #"mass of element in the compound"/"mass of all elements in the compound"xx100%#

The #"mass of all elements in the compound"# is simply equal to the sum of the atomic masses: #(6xx12.011(C)+8xx1.00794(H)+7xx15.999(O))*g*mol^-1# #=# #192.12*g*mol^-1# (the which of course is the molecular mass of the compound).

And thus #%C# #=# #(6xx12.011*g)/(192.12*g*mol^-1)xx100%# #=# #37.5%#.

And #%H# #=# #??#

And #%O# #=# #??#

Of course all the individual percentages must sum to 100%. Why?

Alternatively see here.