Calculation of relative molecular mass: Add the relative atomic mass of all atoms in the chemical formula to get the sum.

So sodium carbonate (Na? CO？ ) has a molecular weight of 23 * 2+12+16 * 3 =106.

General chemistry relative atomic mass

Hydrogen h (1); c( 12)； Nitrogen n (14); Oxygen o (16); Sodium sodium (23).

Magnesium mg (24); Al (27); Silicon si (28); Phosphorus P(3 1).

Sulfur s _ (32); Chlorine cl (35.5); Potassium k _ (39); Ca _ (40).

Manganese Mn (55); Iron Fe (56); Copper Cu (63.5); Zinc Zn(65).