Opal is a hydrated form of silica. If a laboratory analysis of a sample of opal reveals it to contain29.2% Si, 33.3%O, and 37.5% H 22 O, what is its empirical formula?

Let us assume that there is a 100g sample of Opal. The masses of each element will be:

29.2g Si

33.3g O

37.5g H2O

Now we divide each constituent's mass by its Mr to get the moles present

Si: (29.2 / 28) = 1.04

O: (33.3 / 16) = 2.08

H2O: (37.5 / 18) = 2.08

Now we divide by the smallest number and obtain:

Si: 1

O: 2

H2O: 2

Thus, the empirical formula of Opal is:

SiO2. 2H2O