OC 30 & 31

test water for hardness (soap test) & understand that some dissolved compounds, including compounds of calcium, cause hardness in water, and that water hardness can be removed using an ion-exchanger

What is Hard water ??

ICE ?? ... no not this meaning of Hard water!

Hard water is water

that does not form a lather with soap easily

How to Test for Hardness in Water ???

OC 30 & 31

test water for hardness (soap test)

Use the definition above, to make a test for hard water.??

What do you need to do ?

How will you decide which type of water is the hardest ?


test tubes, test tube rack, soap flakes, different water samples.


  1. Take 4 test tubes, at the same height wrap it with sellotape
  2. Fill each test tube with a different water sample
  3. place these test tubes in a rack noting the type of water in each
  4. add one flake of soap to each test tube, liquid soap is not the same.
  5. place your thumb over the mouth of the test tube
  6. shake the test tube & water sample vigorously
  7. repeat for each sample
  8. observe the top surface of the water. Are there suds ? Do the suds go over the top of the sellotape ?
  9. If not add one more flake of soap and repeat until the suds go over the sellotape marker
  10. If 2 samples have the same number of drop of soap to make them suddsy you could compare the heights of the suds, and decide that the one with the least suds is harder
  11. Make a list in order of hardness, more soap = more hard

17/12/12 Our samples are

A = My Sample from _________

B = Tap Water

C = Sea Water

D = Boiled Water

E = CaCl2

Hard water is caused by Magnesium and / or Calcium ions.

These atoms get dissolved in the water as it passes over different soluble rock.

In the water the molecule disassociates (splits up) leaving the Calcium and / Magnesium atoms able to bond with the metal atoms on your kettles element or on your shower head especially in the presence of heat. This is usually called Limescale.

This limescale clogs water heating systems in hard areas, which means pipes inside the machines we use to heat water become covered in a stone like residue. This puts more pressure on pumps as they squeeze against ever increasingly narrow pipes. It also has to be heated up and takes the place of water in boilers, thus making cycles take longer times and being less efficient. Hard water is one of the main reason kitchen appliances break down.

The problems with Limescale are

  1. Reduced water flow in pipes
  2. Wasted energy heating the limescale.

What appliances at home will Limescale affect ?

Ca2+ + Sodium Stearate (soap) → soap scum

Mg2+ + Sodium Stearate (soap) → soap scum

Hard water areas of Ireland


Ways to Soften Water

There are 2 types of Hardness, temporary and permanent

Temporary hardness is removed by boiling,

but this boiling deposits limescale on elements, boilers and in pipes

this limescale is the cause of temporary hardness

We can soften water by removing the _________ and _______ Ions.

1. Distallation

Removes all __________ and _______ particles and hence softens water.

Distillation is the evaporation of water, where the water vapour is cooled quickly turning the vapour into liquid water again. All the suspended and dissolved particles are left in the boiler, leaving pure water (100% H2O)

Expensive to carry out on a large scale. Why ??


2. Addition of washing soda

Washing Soda.

Magic crystals from the depths of time that your nan used to use for everything from laundry to baking. Magic, safe, bio degradable, limescale-removing, de-greasing, water-softening, 90p-a-sack-from-pound-shop crystals that – apart from ruining aluminium – really do excel at pretty much every other task you throw at them.

Don’t confuse washing soda (or Sodium Carbonate) with caustic soda (the stuff you pour down drains that dissolves everything on contact). It’s actually a closer chemical relative to baking soda. And its fantastic stuff.

You can use a little to soften water and make your detergent go further. Or tip a cupful into your toilet to keep it clean and shiny. Its safe on clothes and plates. Its phosphate, bleach and enzyme free and is totally bio-degradable. It removes tea stains and I read somewhere that it kills greenfly – although you may want to check that one before you try it. Plant safety aside; for all i know, give it to greenfly and they may grow to the size of houses and develop a taste for human flesh.


Today’s tip for the day is dedicated to washing soda and to nans everywhere.

Ditch the sprays and hit the pound shops. Live clean and live simpler.

More washing-soda-goodness here and here.

And these guys have a pdf instruction leaflet available for download.

Go make your nan proud.


sodium + calcium → calcium

carbonate ions carbonate

(soluble) (soluble) (insoluble)

3. Ion-exchangers

An ion-exchanger works by replacing (exchanging) the ions that cause hardness with ions that do not cause hardness (Sodium Ions).

Softening can be carried out as a batch process by stirring a suspension of the ion exchange resin in the water for a period until equilibrium, or an acceptable level of hardness, is reached.

However, it is more convenient to operate a continuous flow process by passing the water downwards through a column of resin beads.

Theory: The exchange reaction for water softening with a sulphonated styrene-based resin in the form of sodium can be described below.

2Na+ R- + Ca 2+(aq) ↔ Ca2+ R-2 + 2Na+(aq)


for some serious Ion Exchange debate.

A good inexpemsive and easy way to bring your shower back to life is to soak the shower head for a number of hours in vinegar. The mild acid in the vinegar breaks down the calcium and magnesium salts so they can be rinsed off.

Watch out the water may be hotter than it was before ? an investigation

There are advantages to hard water

      1. It makes water taste better (to most people)
      2. It provides Calcium to your diet (good for bones and teeth)
      3. It makes better tasting Beer.
      4. It makes tanned leather products richer and softer.