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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: chemguy on April 30, 2005, 06:47:25 PM

Title: how to work out percentage composition
Post by: chemguy on April 30, 2005, 06:47:25 PM

I'm having difficulties with how to work out the percentage composition of a compound. How exactly do you work it out?

Title: Re:how to work out percentage composition
Post by: Mitch on April 30, 2005, 06:48:27 PM

need to give an example  ::)

Title: Re:how to work out percentage composition
Post by: chemguy on April 30, 2005, 06:51:48 PM

ok take for example calcium nitrate or aluminium chloride

Title: Re:how to work out percentage composition
Post by: Donaldson Tan on April 30, 2005, 07:13:12 PM

one method is to obtain the percentage composition from the chemical formula. Examing Ca(NO3)2, we can deduce that one mole of calcium nitrate contains 1 mole of calcium, 2 mole of nitrogen atoms and 6 moles of oxygen atoms.

taking a basis of one mole,
total mass = 1 x Mr = 104g
mass of Ca = 1mol x 40g/mol = 40g
percentage composition of Ca = 40/104 x 100%

Title: Re:how to work out percentage composition
Post by: omicrondraconis on April 30, 2005, 08:17:48 PM

Percent Composition of, say, an element in a compound, equals to the molar mass of the element / the molar mass of the compound.