[fatima]

  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?

[Borek]

Please read forum rules.

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

[AWK]

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

[n4k]

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