Water

The material here is very straightforward, and very relevant to everyday life. Several of the mandatory experiments (two of which are titrations) pertain to water and it is important to have an understanding of the principles of these.

Technical terms, Definitions and Laws


Hardness in water

Make sure you know the causes of both temporary and permanent hardness, and how and why temporary hardness is removed. Also learn what happens when soap reacts with hard water.

Hard water; causes and remedies
Temporary hardness caused by calcium hydrogencarbonate, Ca(HCO3)2
Permanent hardness caused by calcium sulfate, CaSO4

Methods of removal
(i) Ion exchange
(ii) Precipitation with sodium carbonate
(iii) Distillation (uneconomic method)


Water for Domestic Use

The stages in the purification process are as follows: (Make sure you know and understand what happens in each.)
1. Mechanical separation
2. Flocculation
3. Filtration
4. Chlorination
5. Fluoridation
6. Testing, and pH adjustment if necessary


Sewage Treatment

There are three main stages in the treatment process. Make sure you know and understand what happens in each.
1. Screening and settlement
2. Chemical oxidation and biological decomposition
3. Phosphate removal (by precipitation)


Experiments

The experiments in this section are the determination in water of:

  • Suspended and dissolved solids
  • Hardness
  • Dissolved oxygen (Winkler method)
  • BOD
  • Colorimetric measurement of dissolved chlorine
  • pH

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