What is the mass % composition of iron (III) chloride?
FeCl3
Molar Mass of FeCl3= 162.2g/mol
Fe/FeCl3=
55.85amu/162.2amu= .34432 rounded to the 4th SF .3443 x 100 = 34.43%
Cl3/FeCl3=
106.35amu/162.2amu= .65567 rounded to the 4th SF .6557 x 100 = 65.57%

Question

What is the mass % composition of iron (III) chloride?
FeCl3
Molar Mass of FeCl3= 162.2g/mol 
Fe/FeCl3=
55.85amu/162.2amu= .34432 rounded to the 4th SF .3443 x 100 = 34.43%
Cl3/FeCl3=
106.35amu/162.2amu= .65567 rounded to the 4th SF .6557 x 100 = 65.57%

photon336 · Answer

calculate the total mass of the entire compound. then the mass of the atom you're interested in. 

$$\frac{ mass~of~atom }{ total~mass }*100 %$$

photon336 · Answer

this looks right

matt6288 · Answer

thanks again lol

photon336 · Answer

Yeah, usually they would ask for like the % of one atom in the compound, but for % composition it's usually the % for all atoms in that compound.

matt6288 · Answer

yeah I was doing problems with finding the % of just one but this question wanted both