Soft water lathers well when mixed with soap, but hard water does not. Both hard water and soft water lather well with soapless detergents, eg washing-up liquid.
To investigate hardness in water:
- Put a known volume of water into a boiling tube.
- Add soap solution, one drop at a time, and shake the mixture for 10 seconds.
- Record the number of drops of soap needed to make a lather. The greater the number of drops needed to make a stable lather, the harder the water.
- To separate temporary and permanent hard water samples, boil the water.
- Repeat steps two and three with the boiled samples.
|Water sample||Volume of soap before boiling (cm3)||Volume of soap after boiling (cm3)||Conclusion|
|B||15||2||Temporary hard water|
|C||15||15||Permanent hard water|
|D||15||10||A mixture of temporary and permanent hard water|