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
