Brainlag PlusThe pH scale, neutralisation, naming salts and writing their formulae, and the required practical for making crystals of a soluble salt.
The pH scale
Acids make hydrogen ions, H⁺, in water.
Alkalis make hydroxide ions, OH⁻. The pH scale runs from 0 to 14:
- 0 to 2: strongly acidic (car battery acid, stomach acid)
- 3 to 6: weakly acidic (clean rainwater)
- 7: neutral (pure water)
- 8 to 10: weakly alkaline (sea water, baking soda)
- 11 to 14: strongly alkaline (oven cleaner)
Measure pH with universal indicator (compare the colour with a chart) or, more precisely, with a pH probe.
A base is any substance that neutralises an acid: metal oxides, hydroxides and carbonates. An alkali is a base that dissolves in water. In every neutralisation in water the same thing happens:
H⁺(aq) + OH⁻(aq) → H₂O(l)
The rest of this lesson and its 14 practice questions are in Plus.
Screen 1 of 4, free to read.
- 14 exam-style questions, marked as you go, each with a worked solution
- The Periodic Table beside every question
- Anything you get wrong is saved to your flashcards