Hard and Soft Water

THINK! What is water hardness? What would be the definition of removing water hardness?

To get rid of water hardness, you need to get rid of the dissolved calcium (and magnesium) ions.

We already know one way to get the calcium in temporary hard water to precipitate out-can you remember? Heat it The limescale that precipitates out takes the calcium ions with it- filter these off and the water it leaves behind is now soft Problem with this heating/filtering method? Far too expensive to heat all the water you need and filter it before using it Even if you could afford it, this won’t work with permanently hard water.

The key is to remember its only Calcium and Magnesium ions that are the issue. If you can swap those ions for something else, you have softened the water.

There are 2 practical ways to soften water- and they work with temporary or permanently hard water.

1) Washing Soda This product is Sodium carbonate. It puts extra carbonate ions into the water They react with the calcium ions The calcium carbonate precipitates out The sodium ions are left in the water but these don't cause hardness, therefore that's no problem.

Washing Soda This product is designed to reduce the soap you need Most modern washing powder has washing soda in it anyway

2) Ion exchange column These columns work by swapping ions you don’t want (In this case calcium and magnesium) for ones you don't mind e.g. sodium.

2) Ion exchange column The columns are filled with resin beads covered in the ions you want. As the water filters through the calcium and magnesium ions swap with the sodium and calcium and magnesium are left on the beads.

2) Ion exchange column These columns need replenishing with more sodium ions after a while. This is easy to do with NaCl- eg adding salt to compartment in the dishwasher.

Softening Challenge!

Peer assess - Have you included? Step-by-step method (1) Variables (2) Risk assessment (1) Description of testing the water before (1) Description of passing water through each resin, or shaking with resin and filtering (1) Description of testing the water after (1) Explanation of how you will decide which resin is the best (1)