Teaching Students About Units for Avogadro’s Number


Chemistry is an essential science that involves a deep understanding of the composition, structure, and properties of matter. One of the fundamental concepts in chemistry is Avogadro’s number, which is crucial in understanding the relationships at the molecular level. This article aims to guide teachers on how to effectively teach students about units for Avogadro’s number.

Understanding Avogadro’s Number

Named after the Italian scientist Amedeo Avogadro, Avogadro’s number (N_A) is a constant value used to relate the amount of substance to the total number of particles such as atoms, ions, or molecules in that substance. The constant is defined as 6.022 x 10^23 particles per one mole of substance. The value helps accurately determine different properties and ratios in chemical reactions.

Introducing Units for Avogadro’s Number

Mole: The first step in teaching students about units for Avogadro’s number is to introduce them to the concept of the mole. Inform students that one mole (abbreviated as mol) refers to a specific number of particles in a substance, precisely similar to how a dozen represents 12 items.

Dimensional Analysis: Once students are familiar with the concept of a mole, teach them how to use dimensional analysis to convert between moles and particles (atoms, ions, or molecules). Provide examples that cover both converting moles to particles and particles back to moles using conversion factors.

Example Problem:

Considering chlorine has two isotopes (Cl-35 and Cl-37), calculate how many individual Chlorine atoms are present in 2 moles of Cl-37?


(2 mol Cl-37)(6.022 x 10^23 atoms/mol) = 1.2044 x 10^24 atoms Cl-37

Molar Mass: Another essential concept related to Avogadro’s number is molar mass, which is the mass of one mole of a substance expressed in grams per mole (g/mol). Teachers should explain to students the importance of the periodic table as it helps determine the molar mass of an element using its atomic weight.

Example Problem:

Determine the amount of moles present in 20 grams sample of sulfur?


Using the periodic table, we find that sulfur has a molar mass of 32.06 g/mol.

Amount of moles = (20 grams) / (32.06g/mol) = 0.624 mol

Mole Ratios: Finally, teach students how to use stoichiometry – a method that involves calculating different quantities involved in chemical reactions – and mole ratios, specifically. Provide examples showing how to use coefficients in a balanced chemical equation to determine the mole ratio between two reacting substances.

Example Problem:

For the synthesis of ammonia, there is a balanced equation as follows:

N2(g) + 3H2(g) → 2NH3(g)

Determine the number of moles of hydrogen required to react completely with 1 mole of nitrogen?


Using the mole ratio from balanced equation:

1 mol N2 / 3 mol H2 = 1 mol N2 / x

x = 3 mol H2


Teaching students about units for Avogadro’s number is crucial in ensuring they grasp vital chemistry concepts. By introducing the idea of a mole, dimensional analysis, molar mass, and stoichiometry sequentially, teachers can help provide students with a strong foundation and enhance their comprehension of these essential aspects.

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