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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: jaydee on August 28, 2011, 06:50:31 pm

Title: gravimetric analysis help
Post by: jaydee on August 28, 2011, 06:50:31 pm

can someone please help me with this question - i keep getting the answer wrong  :-[

An impure sample of iron(II)sulphate, weighing 1.545g,was treated to produce a precipitate Fe₂O₃. If the mass of the dried precipitate was 0.315g calculate the percentage of iron in the sample

Title: Re: gravimetric analysis help
Post by: b^3 on August 28, 2011, 06:55:25 pm

n(Fe₂O₃)=0.315/(2*55.85+48)
=0.001972mol
so n(Fe)=2*0.001972
=0.003944mol
so m(Fe)=0.003944*55.85
=0.2203g
% by mass of Fe in sample = 0.2203/1.545 *100
=14.26 (w/w)
just double check the answer is right

WOOOHOO 500^th Post

Title: Re: gravimetric analysis help
Post by: jaydee on August 28, 2011, 06:59:26 pm

omg thankyou! i just realised i kept multiplying the number of moles of iron by molar mass of iron sulphate instead of just iron D: thanks!