How To Calculate Silicon From Silica

Silicon makes up 25.7 percent of the Earth's crust, by weight, and is exceeded in abundance only by oxygen. Silicon occurs principally in a family of silicate minerals and in sand. Silica is a common name for silicon dioxide, the principal material in sand. Silica is a chemical compound of silicon that contains the element oxygen. The weight percentage of silicon in silica can be calculated if you know the relative masses of silicon and oxygen.

Step 1

Find the atomic masses of silicon (symbol Si) and oxygen (symbol O). You can find them in the Periodic Table Of The Elements (See Resources.) Si appears near the top of the table on the right half of row 3. O appears above Si in row 2.

Step 2

Determine the molecular mass of silica by adding together the atomic masses of all the elements in a molecule of silica. Silica has the formula SiO2, which in chemical terms means that each molecule is composed of one silicon atom bonded to two oxygen atoms. Your calculation should then be: 28.0855 (Si) + (15.9994 (O) x 2) = 60.084.

Step 3

Calculate the weight-percentage of silicon in silica by dividing the atomic mass of silicon by the molecular mass of silica: Your calculation should be: 28.055/60.084 = 0.4669. Multiply this number by 100 to convert it to percent. Your final answer is: silica contains 46.69 percent silicon by weight.