Avogadro's Constant
Physics: Cambridge International A Level, topic 1.1.4
Moles
The amount of a substance is measured using a unit called a mole (mol).
What is a mole?
- A mole is simply a massive number of particles.
- You can have a mole of anything: laptops, sunglasses and, of course, atoms (this is what we care about!).
- A mole of things contains 6.02 ×1023 things.
Carbon-12
- The value of the mole is set so that a mole of carbon-12 atoms weighs 12 grams.
- This is important because the mass of one carbon-12 atom is 12 amu.
- So the mole converts between amu and grams:
- 1 g = 1 mol × 1 amu
Convenience
- Atoms are really tiny and so it's very difficult to measure a single atom.
- By using the mole, we can do calculations about the amount of stuff we have in any reaction.
Avogadro's constant
- The value of Avogadro's constant is 6.02 ×1023.
- So one mole contains Avogadro's constant of things.
- Number of particles = number of moles × Avogadro's constant
Test yourself on Avogadro's Constant
What is a mole?
Which of the following is true of moles?
What is the value of Avogadro's constant?