Percent Composition Problems

Question

I need a brief example on how to solve Percent Composition probs please. Oh and btw how I can I tell when a compound is ionic or covalent ?

 

Answer 1

for an excellent description of ionic versus covalent bonds, please open

http://chemwiki.ucdavis.edu/Theoretical_Chemistry/Chemical_Bonding/Covalent_Bonds_vs_Ionic_Bonds

 

regarding percent composition, the term simply means the amount of a given element in a compound, and the calculation is based on the atomic weight of an element divided by the atomic weight of the compound. the resultant decimal will then be multiplied by 100% to yield the answer.

 

let us look at ordinary salt, NaCl; the atomic weight of sodium ≅ 23; the atomic weight of Cl ≅ 35; the atomic weight of the compound ≅ 58

 

the percentage of Na will be (23/58) x 100% ≅ 39.7; the percentage of Cl will be (35/58) x 100% ≅ 60.3

 

in the case of carbon dioxide, CO₂, we have one atom of carbon (aw =12), and two atoms of oxygen (aw = 2 x 16), so the percentage of carbon = (12/44) x 100% = 27.2%; the percentage of oxygen = (32/44) x 100% = 72.7%

 

as you can see, if more than one atom is present, its atomic weight must be multiplied by the number of atoms present, but the basic concept will apply