Does it say percentage by mass or percentage of atoms or what?
I will assume percentage of mass.
Now O atoms have a mass of about 16 grams per about 6*10^23 of them (Avagadro's number, sort of like 12 is a dozen, 6*10^23 is a mole)
So in a mole of this stuff we have 32 grams of O
H atoms have a mass of about 1 gram per 6^10^23 of them so in a mole of this stuff we have 2 grams of H
Mg has a mass of about 24.3 grams per mole so we have about 24.3 grams of MG
so in total we have
O = 32 grams
H = 2 grams
Mg = 24.3 grams
so the total mass of a mole or 6*10^23 molecules = 58.3 grams
so
percent O = (32/58.3) 100 = 54.9 %
Now I was not careful about significant figures or arithmetic here so use your periodic table and do all that more carefully.
What is the percentage of oxygen in____?
Mg(OH)2
1 answer
2 answers