>;ame Sewon DalO- - -. --------~- - . --------- - . - - -16ij- Cllemicd llUaatities .

• I ..••..•. E;t;~!';~C;i::!';~:':': .VPercent CompositionChemists often have to detennine the percent composition of a compound. PercentcOmposition refers to the number of grams of each element in a compound presentin 100 g of that compound. Knowing a compound's percent composition is the firststep in determining the fonnula of that compound. Percent Composition isdetermined in the laboratory by analyzing a sample of the compound to see whatmass of each element is present in the compound. Then for each element

mass of elementPercent of element ptesent ~ al f d X 100%tOt mass 0 compoun

ElampJe A

A compound analyzed in a chemistry laboratory consists of 5.34 g of carbon. 0.42 gof hydrogen. and 47.08 g of chlorine. What is the percent composition of thiscompound? 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 X 100%rotal mass of compound

5.34 g CPercent C ~ d x 100% ~ 10.1%C52.84 g cp

percent H ~ ~842 g Hd

x 100% ~ 0.79%H5 . 4 g cp

percent CI ~ 47.08 g C~ X 100% ~ 891 % CI52.84 g cp

You Try It

I. Find the percent composition of a compound containing [in and chlorine if18.35 g of the compound contains 5.74 g of tin. 6.9

Your SOlution

ChapleT 6 Chemical nlJm .•,;,;"...

.., .,.:J

Example B ••• ...Determine the percent composition of ammonia from its formula. NH3•

solution In this problem, you can determine the percent composition from thegram atomic masses of the elements and the gram molecular mass of thecompound.

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 - 17.0g NH

3x lOa:"c- 82.4%N

_ 3.0gH _percent H - 17.0g NH

3x 100%- 17.6%H

You Try It ,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 ofcarbon and 0.874 g of hydrogen.

4. From the formula for calcium acetate. Ca(CZH30Z),' calculate the mass of carbonthat can be obtained from 65.3 g of the compound.

.-

6.9

.C, .

6.9

(

69,...~-...

• 1

. _,I.

-~ ..•. ",(;"".'':,,1'• ...# ••• - . -

6.9

," .',~,',~ -