16ij>;ame
-
-
-.
--------~
- -
.
---------
Sewon
DalO
Cllemicd llUaatities
-
.
- -
-
.
•V I ..••..•. E;t;~!';~C;i::
!';~:':':
.
Percent Composition
Chemists often have to detennine the percent composition of a compound. Percent
cOmposition refers to the number of grams of each element in a compound present
in 100 g of that compound. Knowing a compound's percent composition is the first
step in determining the fonnula of that compound. Percent Composition is
determined in the laboratory by analyzing a sample of the compound to see what
mass of each element is present in the compound. Then for each element
Percent of element ptesent ~
almass of felement d
tOt
mass 0 compoun
X
100%
ElampJe A
A compound analyzed in a chemistry laboratory consists of 5.34 g of carbon. 0.42 g
of hydrogen. and 47.08 g of chlorine. What is the percent composition of this
compound?
6.9
Solution The total mass of rhe compound is equal to the sum of (he masses of
[he three elements that make it up.
-.
Mass of compound ~ mass of C + mass of H + mass of CI
~ 5.34 g + 0.42 g + 47.08 g
~ 52.84 g
"--/
Then the percent of each element in the compound is calcuJated as follows.
Mass of the element
rotal mass of compound
Percent C ~
X
100%
5.34 g C
d x 100% ~ 10.1%C
52.84 g cp
percent H ~ ~842 g H x 100% ~ 0.79% H
5 . 4 g cp d
percent CI ~ 47.08 g C~
52.84 g cp
You
I.
X
100% ~ 891 % CI
Try It
Find the percent composition of a compound containing [in and chlorine if
18.35 g of the compound contains 5.74 g of tin.
6.9
Your SOlution
ChapleT 6
Chemical
nlJm .•,;,;"...
.., .,.:J
...
•••
Example B
6.9
Determine the percent composition of ammonia from its formula. NH3•
solution
In this problem, you can determine the percent composition from the
gram atomic masses of the elements and the gram molecular mass of the
compound.
.C
,.
.-
Molecular mass of NH3 = gam of N + (3 x gam of Ii]
= 14.0g+ (3 x l.0g)
,..
=14.0g+3.0g=17.0g
Then the percent of each elemen~ in ammonia is calculated below.
Percent of element = total atomic mass of element in compound x 100%
molecular mass of compound
_ 14.0gN
_
percent N - 17.0 g NH x lOa:"c- 82.4% N
3
_ 3.0gH
_
percent H - 17.0 g NH x 100%- 17.6%H
3
You Try It
,
6.9
2. Calculate the percent of each element present in potassium phosphate from its
formula. K3PO..
••
•
Your Solution
(
problems For YOU To Try
~I
3. Determine the percent composition of a compound that consists of 3.907 g of
carbon and 0.874 g of hydrogen.
.
69
, ..~-...
•1
. _,I.
-~...#..•.
",(;"".'':,,1'
••• .
-
•
4. From the formula for calcium acetate. Ca(CZH30Z),' calculate the mass of carbon
that can be obtained from 65.3 g of the compound.
6.9
,~, .'
,"
',~
-