Today is rung 4 of 5 on this topic
Moles, concentration and acids and bases
Can do: Uses the mole as a counting unit, calculates concentration, and explains the pH scale.
Why it matters
The mole is chemistry's hardest abstraction and its most necessary one — it's how a countable idea gets attached to a weighable amount.
What it looks like when it's wobbly
Treats the mole as a mass unit, and thinks pH 5 is only slightly more acidic than pH 6.
⏱️ Two-minute check
"How many moles in 36 g of water? How many times more acidic is pH 3 than pH 6?"
Solid looks like: 2 moles, and 1,000 times — knowing the scale is logarithmic.
The full activity for this topic · 30 minutes
Count by Weighing
- 1Weigh 100 grains of rice, then use the mass to count a bag without counting — that's exactly the mole idea.
- 2Apply it: molar mass lets you count atoms by weighing.
- 3Calculate moles for three real substances from the kitchen.
- 4Make a red cabbage indicator and test household liquids, ranking them by colour.
- 5Dilute one tenfold, retest, and see the pH move by one — the logarithmic scale, demonstrated.
If it's too hard
Mole calculations from given molar masses.
If it's too easy
Stoichiometry: predict the mass of product from a given mass of reactant.
Say this
"You counted the rice by weighing it. That's the whole idea of the mole — nothing more mysterious than that."