How do you calculate the mass of a compound from its formula?

To calculate the mass of a compound from its formula, you add up the relative atomic masses of its constituent elements.

The mass of a compound, also known as the molar mass, is calculated by adding up the relative atomic masses of all the atoms present in the compound. This is done by referring to the periodic table, where the relative atomic mass of each element is listed.

For example, let's consider water (H2O). The formula tells us that there are two hydrogen atoms and one oxygen atom in each molecule of water. The relative atomic mass of hydrogen is approximately 1, and that of oxygen is approximately 16. Therefore, the molar mass of water is (2*1) + 16 = 18 grams per mole.

For a more complex compound like glucose (C6H12O6), you would calculate the molar mass by adding up the relative atomic masses of carbon (C), hydrogen (H), and oxygen (O) in the proportions indicated by the formula. That is, (6*12) for carbon, (12*1) for hydrogen, and (6*16) for oxygen, which gives a total of 180 grams per mole.

Remember, the relative atomic masses you use should be the most accurate ones available, usually to one or two decimal places. Also, the molar mass is usually expressed in grams per mole (g/mol), which is a measure of the mass of one mole of that substance.

This method of calculating the mass of a compound from its formula is a fundamental concept in chemistry, and is used in many calculations, including stoichiometry, gas laws, and solution concentration. It's a crucial skill to master for anyone studying IGCSE Chemistry.