Quantitative Chemistry›3a. Amounts of Substances›The Mole
Lesson 02 of 06
The Mole
Key Concepts
- The mole as a number
- Avogadro's constant (6.022 × 10²³)
- Relative atomic mass (Ar)
- Relative formula mass (Mr)
- Moles = mass ÷ Mr
- Mass = Mr × moles
- Reacting masses from balanced equations
- History: Avogadro, Ostwald, Perrin
- Quantitative chemistry
- Mole calculations
- Mass to moles conversion
- Moles to mass conversion
- Stoichiometry
Checking the Basics
If you're watching this video as part of your chemistry course, then you might find it helpful to be able to answer these questions before continuing.
What is the relative atomic mass of magnesium?+
24
How many carbon atoms are present in this molecule: C₄H₉OH+
4
What is the relative formula mass of Ca(OH)₂? a) 58 b) 74 c) 57+
b) 74
Video 1
Lesson notes
The mole is one of those ideas that sounds mysterious until someone explains it simply — and this video does exactly that. You'll discover where the concept came from, what Avogadro's constant actually means, and how the core equation (moles = mass ÷ Mr) connects the invisible world of atoms to the masses you weigh in a laboratory. By the end you'll have both the conceptual understanding and the calculation skill you need to go further in quantitative chemistry.
What You Will Learn
00:27Why chemists need a counting unit for atoms and molecules and why individuals cannot be directly counted or weighed.
01:25What a mole is and how it compares in size to everyday quantities like grains of sand.
03:05Who Avogadro, Ostwald, and Perrin were and what each contributed to the mole concept.
05:03What Avogadro's constant is and what it means for any substance.
05:20How to use moles = mass ÷ Mr and its rearrangement mass = Mr × moles.
05:51How to calculate relative formula mass (Mr) from atomic masses.
09:40How to use a balanced equation and the mole to calculate reacting masses.
10:54Why the mole is described as a bridge between the atomic world and laboratory measurements.
Video 2
Lesson notes
If moles calculations feel like a mystery, this is the video to watch. You'll work through the core equation (moles = mass ÷ Mr) with a series of exam-style examples, building from simple mass-to-moles conversions up to two-step reacting mass calculations using balanced equations. By the end you'll have a reliable method you can apply to any quantitative chemistry question.
What You Will Learn
00:37What the mole represents in chemistry and why it is used to count particles in reactions.
03:38How to convert mass into moles using the equation moles = mass ÷ Mr.
04:02How to calculate relative formula mass (Mr) for a compound.
06:45How to convert moles into mass using the equation mass = Mr × moles.
07:39Why all masses must be converted into grams before calculating moles.
08:22How to avoid the most common exam mistake of using kilograms instead of grams.
08:51How to apply mole calculations to reacting mass questions using a balanced equation.