Flashcards in C3 - Hardness Of Water Deck (18):
What happens when you react hard water with soap?
Scum is produced.
What happens when you heat hard water?
Scale is produced.
What is scale and how does it affect appliances?
It blocks pipes and reduces efficiency.
What ions make water hard?
Ca2+ and Mg2+.
How is hard water made?
Rain falls on limestone, chalk and gypsum & dissolves the ions.
What is a benefit of having Ca2+ in water?
It is good for teeth & bones.
What is there a lesser risk of in hard water areas?
What ion causes temporary water hardness?
The hydrogencarbonate ion HCO3.
What ion causes permanent water hardness?
How is temporary water hardness removed?
Why is temporary water hardness removed by boiling?
Calcium hydrogencarbonate thermally decomposes to produce insoluble calcium carbonate (scale).
What can be added to soften both permanent and temporary hard water?
Why does adding sodium carbonate remove water hardness?
The added carbonate ions react with Ca2+ and Mg2+ to form an insoluble precipitate.
The ions are no longer in the water.
What method can you use to soften both temporary and permanent hard water?
Passing it through an ion exchange column.
How does an ion exchange column work?
The Ca2+ and Mg2+ ions are exchanged for sodium or hydrogen ions.
How can you compare water hardness?
Using a titration experiment.
Describe the process of comparing water samples using a titration.
1) 50cm3 soap solution in burette.
2) 50cm3 water in flask.
3) add 1cm3.
4) put in bung & shake for 10 seconds.
5) repeat until a lasting lather is formed for 30+ seconds.
6) repeat with other samples.
7) boil fresh samples & repeat.