S4.7.3 For the adult
The mole
How can a chemist count atoms when they are far too small to see?
What this chapter teaches
The relative formula mass is the sum of the relative atomic masses in a formula. One mole holds 6.02 × 10²³ particles and has a mass of Mr grams, so moles = mass ÷ Mr. Concentration in mol/dm³ is moles divided by the volume in dm³.
Three questions to ask
There is no one right wording. Listen for the idea.
- How do you find the relative formula mass of Ca(OH)₂?
- How many moles are in 36 g of water, and how did you work it out?
- Why must a volume in cm³ be changed to dm³ before finding a concentration?
After the chapter, the learner can
- Calculate relative formula mass
- Convert between mass and moles
- Calculate concentration in moles per cubic decimetre
What they copy into their notebook
Mr is the sum of the relative atomic masses. One mole is Mr grams and 6.02 × 10²³ particles. moles = mass ÷ Mr. concentration = moles ÷ volume in dm³.