# Beryl is a mineral which contains 5.03% Be, 10.4% Al, 35.5% Si and 53.58% O. What is the simplest formula for beryl?

So I tried to follow a 3 step rule to solving this equation:

1. Divide each % by it's own atomic mass
2. Dived each of those by whichever is smallest
3. Find the lowest whole #

Be = 5.03% / 9 = .558 moles
Al = 10.04 / 26.98 = .372 moles (smallest number)
Si = 31.35% / 32 = .979 moles
O = 54.58% / 16 = 3.3 moles

Be = .558 / .372 = 1.5
Al = .372 / .372 = 1
Si = .979 / .372 = 2.63
O = 53.58 / 16 = 3.3

From here I don't know what I have done wrong, but these numbers are all whack silly and I can't see to get a number that leads me to the answer.

The correct answer is $\ce{Be4Al(SiO3)8}$

• You have the wrong atomic mass for Si. I'd use 4 significant figures for all of the atomic masses also. – MaxW Sep 28 '16 at 4:07
• Good catch! I didn't even spot that. 32 is sulfur, not silicon. – orthocresol Sep 28 '16 at 5:41

Firstly the "correct" answer seems to be wrong, which is not an uncommon occurrence, so please do not always take answers at the back of books to be correct. Wikipedia lists the formula of beryl as $\ce{Be3Al2(SiO3)6}$ which is much more in accordance with what you have done.