Hard Water Testing
Observe how hard water reacts with soap to form insoluble scum, while soft water produces a good lather. This demonstrates why hard water reduces soap's effectiveness.
Add soap solution to both tubes and shake to observe the difference between soft and hard water reactions.
The Science Behind Hard Water and Soap
Hard water contains dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions that react with soap:
- Soap molecules (e.g., sodium stearate C17H35COO-Na+) dissolve in water
- In hard water, soap anions react with Ca²⁺/Mg²⁺ to form insoluble salts (scum)
- This precipitation removes soap from solution, reducing its cleaning power
- Soft water produces a good lather as soap remains dissolved
1. With calcium ions: 2C17H35COO- + Ca2+ → (C17H35COO)2Ca↓
2. With magnesium ions: 2C17H35COO- + Mg2+ → (C17H35COO)2Mg↓
3. In soft water: Soap molecules remain dissolved and form micelles
- Hard water requires more soap for effective cleaning
- Scum forms bathtub rings and clogs pipes
- Hard water reduces water heater efficiency
- Water softeners replace Ca²⁺/Mg²⁺ with Na⁺ ions
