LC Chem 9.2 Water Hardness

Created by dkilroy 

Upgrade to
remove ads

chemistry

Hard water

Water that will not easily form a lather with soap.

Ca2+ or Mg2+ ions

Causes of Hardness

ppm CaCO3

Units and substance in which water hardness is usually expressed

Temporary

Hardness that can be removed by boiling

Calcium and Magnesium Hydrogencarbonates

Causes of Temporary hardness

Temporary hardness

Caused by the action of water and carbon dioxide on limestone

Boiling

Causes a chemical reaction which removes the Ca2+ ions from the water to soften the water

Limescale

Soap scum caused by hard water that clogs pipes and boilers

Permanent

Hardness that cannot be removed by boiling

Calcium and Magnesium Chlorides and Sulfates

Causes of Permanent hardness

Advantages of Hard Water

1. Provides calcium for teeth and bones.
2. Nicer taste.
3. Good for brewing and tanning.

Disadvantages of Hard Water

1. Blocks pipes, leaves scale on kettles and boilers.
2. Wastes soap.
3. Produces scum.

Removes Hardness from Water

1. Distillation.
2. Using washing soda.
3. Ion exchange resin

Distillation

Boiling the water and then cooling the vapour to remove all dissolved solids and dissolved liquids

Washing soda

Addition of hydrated sodium carbonate, Na2CO3.10H2O. The carbonate ions react with the calcium ions in the water and removes them as insoluble calcium carbonate. Ion exchange resin Substance which swaps the ions in water which cause hardness for ions which do not cause hardness

Cation exchange

Resins which swap the positive ions in the water (Ca2+ and Mg2+ ions) for Na+ ions: Ca2++ Na2R --> CaR + 2Na+

Anion exchange

Resins which swap the negative ions in water for OH- ions: Cl- + ROH --> RCl + OH-

Mixed resin

Replaces all the dissolved salts with water molecules so the water is deionised

edta

Used to estimate the total hardness of a water sample as it forms metal complexes with alkaline earth metal ions Ca2+ and Mg2+ but not with alkali metal ions

Ethylenediaminetetraacetic acid

Full name of edta

9-10

pH needed for the estimation of the total hardness of a water sample using edta

Eriochrome Black T

Indicator used in the estimation of the total hardness of a water sample using edta

Wine red to Blue

Colour change observed in the estimation of the total hardness of a water sample using edta

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set