need help with % mass of an element

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here's the question;

Calculate the % mass of EACH element:

C3H7OH

Posted: 01-12-12 17:59 by simran

love this stuff.. 

first u write the relative atomic mass of each element..

so C3 is ... 12 * 3 = 36 (percentage mass)

(carbon proton number is 12 but because there is three carbon u multipy it by 3)

so H7 is ... 1 * 7 = (percentage mass)

(hydrogen proton number is 1 but because there is seven carbon u multipy it by 7)

so OH is ... 16 * 1 = 16 (percentage mass)

(oxygen proton number is 16 so you multiply this with the hydrogen proton number which is 1 )

That should be it.. hope it helps..

Posted: 01-12-12 18:28 by ? Secret - Team GR

thanks but isn't the formula for % mass: total masss of the element in the compound divide by relative folrula mass of compound

the thing you have done is the molar mass of each element  isn't it.

Posted: 01-12-12 18:32 by simran

woops..

yh then u would add the total mass up.. so its 

C3H7OH = 36 + 7 + 16

                 = 59

Then to find the mass of the C3 u would do

( 36 divide 59 ) *100 = 61%

that is the percentage mass of the carbon

any helpful ???

Posted: 01-12-12 18:40 by ? Secret - Team GR

to find the mass of the H7 u would simply do..

(7 divide by 59) * 100 =12% of Hydrogen

to find the mass of the OH u would simply do..

(16 divide by 59) * 100 =27% of Hydrogen

As you can see if you add up the percentages of each element it makes up 100 so u know uve done it right.. sorry for the mistake :)

Posted: 01-12-12 18:43 by ? Secret - Team GR

thanks a lot and its okak don't worry

THANKS AGAIN :)

Posted: 01-12-12 18:47 by simran

aww... ur welcome :)

Posted: 01-12-12 18:49 by ? Secret - Team GR