Document page
chemistry igcse acapprinted 71 · PDF 71
145 pagesrevision 46934
printed 71 · PDF 71
Page image rendered from the stored file at 110 dpi; it sharpens as you zoom. Outlines are placed from each region’s stored position on the page (612 × 792 pt).
readable
Source of this text: embedded text layer. The better of the embedded text and OCR is kept.
71
Uses of Water
Agricultural Uses: irrigation and as a drink for animals
Industrial Uses: as a coolant, as a solvent and as steam for electricity
Domestic Uses: drinking, cooking, sanitation, gardening
Impurities in Water
Some of these impurities are naturally occurring while some are the results of human actions.
Impurity
Beneficial or Harmful
Reason
Dissolved Oxygen
Beneficial
It is essential for the aquatic
life
Metal Ions (e.g. Ca, K, Na,
Mg, Pb, Al)
Some are beneficial while
some are harmful
Some are essential for life like
Ca, K, Na and Mg. Others are
toxic like Pb and Al
Plastics
Harmful
These may be harmful to
aquatic life in many ways
Harmful Microbes
Harmful
These are added in the water
through sewage and can lead
to several diseases
Nitrates and Phosphates from
Fertilisers
Harmful
It can lead to Eutrophication.
Treatment of Water
Untreated water contains both soluble and insoluble impurities. Insoluble impurities include soil,
plant debris, and other organic matter, while soluble impurities consist of dissolved calcium,
metallic compounds, and inorganic pollutants. The first step in water treatment is sedimentation
or filtration. Water is pumped into sedimentation tanks and left to sit for several hours, allowing
mud, sand, and other particles to settle at the bottom due to gravity, forming a sediment layer.
Afterward, the water is filtered through sand and gravel to eliminate smaller particles. The second
step involves filtration or treatment with carbon (charcoal), which removes unpleasant tastes and