chemistry: Fundamentals and Principals

Question

Consider a sample containing 0.320 mol of a substance. How many atoms are in the sample if the substance is lead?

How many atoms are in the sample if the substance is gold?

How many molecules are present in the sample if the substance is benzene, C6H6?

Answer 1

Regardless of the substance, be it atoms, molecules, formula units, ions, or even people, the number of particles in 1 mole is always the same (just as the number of 'things' in 1 dozen is always the same: 12). namely 6.022 x 10²³.

So, if you have 0.320 mol of a substance you will have (0.320 mol) x (6.022 x 10²³ things/mol) of that substance.

Answer 2

The key to this question is understanding what the word "mole" (here abbreviated "mol") means in chemistry.

The word "mole" refers to a specific number of atoms or molecules: a tiny bit more than 6.022*10²³ of them.

So one mole of gold contains 6.022*10²³ atoms of gold.

One mole of benzene contains 6.022*10²³ molecules of benzine.

0.320 mol of gold (or lead, or uranium for that matter) will therefore contain 0.320 times 6.022*10²³ atoms, which is 1.93 * 10²³.

Similarly, 0.320 mol of benzene will contain 1.93 * 10²³ molecules, for the same reason - a mole is just a specific number of atoms or molecules.

But this is not the most amazing fact about the mole, or why chemists use it as a unit of measure so much...

- that fascinating property will have to wait for another question, ...or another lesson.