# Chemistry Materials Question - Weight % Fraction

1. Sep 24, 2007

### ][nstigator

Heres a question Im stuck with

Crosslinked polymers consisting of 62 wt% ethylene and 38 wt% propylene may have elastic properties similar those for natural rubber. For a copolymer of this composition, determine the fraction of the ethylene mer.

Express your answer with three decimal points.

I honestly am lost with how to do this question...

What I did was....

Found the weight of ethylene (28.052) and the weight of propylene (42.078)...then multipled by the percentages and got...

28.052*0.62 = 17.39
42.078*0.38 = 15.98

then..

fraction = 17.39/(15.98+17.39)

I doubt this is right...any help would be much appreciated.

Thanks in advance!

2. Sep 26, 2007

### chemisttree

This problem is done the same way in which you have done similar problems using the results from an elemental analysis.

ie. What is the empirical formula of a compound composed of carbon, hydrogen and oxygen given the following elemental analysis:

C - 53.2%
H -17.4%

The answer would be given in the form of $$C_xH_yO_z$$.

Do this the same way, substituting ethylene or propylene for one of the elements. The answer will be in the form $$CH_3-[CH_2-CH_2]_m-[CH_2(CH_3)CH_2]_n-CH_3.$$

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