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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: fatima on September 07, 2008, 08:16:42 AM

Title: determining a chemical formulae
Post by: fatima on September 07, 2008, 08:16:42 AM

 ::) 1. can you determine the molecular formula of a substance from its percentage composition?how?why?
 :( 2. given that zinc chloride has a formula weight of 136. 28, what is its formula?
 :-[ 3. how many grams of zinc chloride could be formed from the reaction of 9.76 g of zinc wiht excess HCL? ???

Title: Re: determining a chemical formulae
Post by: Borek on September 07, 2008, 09:45:05 AM

Please read forum rules (http://www.chemicalforums.com/index.php?page=forumrules).

Surely you know something, you just don't know how to use it. Tell us what you know and where you get stuck.

Title: Re: determining a chemical formulae
Post by: AWK on September 08, 2008, 01:36:44 AM

Quote from: fatima on September 07, 2008, 08:16:42 AM

::) 1. can you determine the molecular formula of a substance from its percentage composition?how?why?
 :( 2. given that zinc chloride has a formula weight of 136. 28, what is its formula?
 :-[ 3. how many grams of zinc chloride could be formed from the reaction of 9.76 g of zinc wiht excess HCL? ???

1. sometimes - usually you can obtain a n empirical formula
How? Why? - see any general chemistry texbook. See also Borek stoichiometry lectures
2. Combine mass of zinc and chlorine atoms to obtain mass very close to 136.28
3. start from a balanced reaction. Assume all Zn form  a salt

Title: Re: determining a chemical formulae
Post by: n4k on September 17, 2008, 09:04:54 AM

Zn+2HCl=ZnCl2+H2
v(Zn)=0.15 mol
v(ZnCl2)=v(Zn)=0.15 mol
m(ZnCl2)=20.4 g