Chapter 2 · Chemistry
Acids, Bases and Salts
Acids give H⁺(aq), bases give OH⁻(aq), and salts are what remains when they neutralise each other. This chapter is built around a working pH engine that computes real hydrogen-ion concentrations.
pH Lab — Universal Indicator & Indicator Colours
Drag the pH or pick a real sample. Colours, ion concentrations and indicator responses are computed from the pH value.
- pH
- 7.0
- Nature
- Neutral
- [H⁺]
- 1.00e-7 mol/L
- [OH⁻]
- 1.00e-7 mol/L
- Blue litmus
- stays blue
- Red litmus
- stays red
- Phenolphthalein
- colourless
- Methyl orange
- yellow
Formula sheet
pH definition
pH = −log₁₀[H⁺]
The lower the pH, the higher the hydrogen ion concentration.
pOH & relation
pOH = −log₁₀[OH⁻] ; pH + pOH = 14
At 25 °C the two always add to 14.
Ionic product of water
[H⁺][OH⁻] = 10⁻¹⁴ mol²/L²
Neutral water has [H⁺] = 10⁻⁷, so pH = 7.
Neutralisation
Acid + Base → Salt + Water
HCl + NaOH → NaCl + H₂O.
Acid + metal
Acid + Metal → Salt + H₂↑
Zn + 2HCl → ZnCl₂ + H₂.
Acid + carbonate
Acid + Carbonate → Salt + CO₂ + H₂O
CO₂ turns lime water milky.