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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: monorail on March 24, 2009, 07:44:44 AM

Title: determine formula of compound from mass of elements
Post by: monorail on March 24, 2009, 07:44:44 AM

Four samples of a compound containing only iron and chlorein were prepared in different ways. A chemist analysed the samples and measured the mass of the 2 elements in each. the results are:

Mass of iron (g)                      Mass of chlorine (g)
5.59                                     10.64
1.68                                     3.20
1.40                                     2.67
1.96                                     3.73


Use any pair of results to calculate the formula of the compund


Really stuck on this question. I know I will have to use the atomic mass or moles or something, but i have no idea where to start.

Title: Re: determine formula of compound from mass of elements
Post by: Las on March 24, 2009, 08:02:12 AM

Try using RAM of iron and chlorine to find the molar ratio. I'm not entirely sure but I have a feeling that's how you're supposed to approach the question:)

Title: Re: determine formula of compound from mass of elements
Post by: monorail on March 24, 2009, 08:22:12 AM

ok i think I got it
Fe - 5.59/55.847 = 0.1
Cl - 10.64/35.453 = 0.3
0.3/0.1 = 3

Fe:Cl
1:3

Therefore the formula is FeCl3
Does this look right?

Title: Re: determine formula of compound from mass of elements
Post by: Las on March 24, 2009, 08:30:09 AM

that looks fine to me:) and why dont you check with the other sets of masses and see if you get the same answer??

Title: Re: determine formula of compound from mass of elements
Post by: monorail on March 24, 2009, 08:34:36 AM

Ok i did it with the 2nd pair of values and it all worked out. Thanks for the help, i really didn't know where to start.

Title: Re: determine formula of compound from mass of elements
Post by: Las on March 24, 2009, 09:25:57 AM

anytime:)