How To Find The Number Of Representative Particles In Each Substance

Many chemistry students have to calculate the number of representative particles in a substance. A substance has a definite chemical composition with a corresponding chemical formula. Representative particles can be atoms, molecules, formula units or ions, depending on the nature of the substance. The standard unit used to represent the amount of a substance is the mole, where 1 mole contains 6.02 x 10^23 particles. This quantity is referred to as Avogadro's number.

1. Measure Mass

Measure the mass of the substance in grams. For example, you weigh a sample of water and its mass is 36.0 grams.

2. Calculate Molar Mass

Calculate the molar mass of the substance. Add the average atomic masses of the individual atoms in the chemical formula, as per the periodic table. For example, the molar mass for water is 18.0 grams per mole. Water is made of two hydrogen atoms, each weighing 1.0 gram, and one oxygen atom, weighing 16.0 grams.

3. Divide Mass by Molar Mass

Divide the mass measured in Step 1 by the molar mass determined in Step 2. This will change the unit of the substance to moles. Following the example, 36.0 grams ÷ 18.0 grams/mole = 2 moles of water.

4. Multiply by Avogadro's Number

Multiply the value obtained in Step 3 by Avogadro's number, which represents the number of representative particles in a mole. Avogadro's number has a value of 6.02 x 10^23. Continuing the example, 2 moles of water x 6.02 x 10^23 particles per mole = 1.20 x 10^24 particles.