Hard water is water that contains a lot
of dissolved compounds, usually
Calcium and Magnesium
Water becomes hard when it flows
through chalk or limestone rock
What happens
to rainwater?
1) Rain water reacts with Carbon Dioxide
in the air to form Carbonic Acid (slightly
acidic rainwater)
2) If the Slightly acidic water runs through a city with a high
amount of limestone, it reacts to form Calcium Hydrogen
Carbonate, which is dissolved in water to form hard water
The more Ca2+ ions
present in the water,
the harder it is
The harder the water, the more drops
of soap solution (Wanklyns) is needed
to form a lather
Permanents hard water
remains hard when boiled
Temporary hard water is
softened when boiled
Making hard water soft
To soften hard water you need to remove the
dissolved Calcium and Magnesium ions which
make the water hard
Boiling
By boiling the temporary hard
water you cause the Hydrogen
Carbonate ions to breakdown
into Hydrogen and Carbonate
ions. The carbonate ions that
are formed react with the
Calcium or Magnesium ions,
forming either Calcium
Carbonate or Magnesium
Carbonate which are
precipitates
Adding Sodium Carbonate
By adding Sodium Carbonate to the temporary hard water, we are in
effect adding Carbonate ions to the water. The carbonate ions react
with the Calcium ions (which are making the water hard in the first
place) to form Calcium Carbonate which is a precipitate
Ion exchange columns
Water for life
Untreated water
Microbes cause
diseases such as
Cholera and
Tetanus and can
cause health
problems
Chemicals that make the
water smell, make the
water unpleasant to
drink
Solid things (i.e
insects or toilet
paper) block pipes
and taps and may
carry microbes
Salts, such as nitrates, cause
diseases such as Cholera and
Tetanus
Treating water
Microstainers
Large rotating sieves which
remove solids including algae
Sand Filters
Football pitch sized
beds of sands, and 1m
deep, as water trickles
through solids and
harmful bacteria are
removed
Chlorine is
added to kill
bacteria
Ozone kills bacteria and
destroys pesticides
Fluorides and filters
Carbon Filter
Removes chlorine
from water and
compounds with bad
tastes and smells
Contains activated carbon. Has tiny
holes to increase surface area.
Unwanted substances stick to the
Carbon (ADSORPTION)
Silver Filter
Ions destroy bacteria
Catalytic action of silver ions
with oxygen provides a sanitiser
which means we don't have to
use as much chlorine
Ion Exchange resin
Lead, Copper or
Cadmium ions are
removed
They replace some
dissolved substances in
water to improve taste
and quality
FOR
1 part/million
Protect us from
tooth decay or
heart disease
AGAINST
Ethically wrong
Cant set safe limits
of fluoride so people
may take more than
is safe
Excess fluoride affects the brain
and has been associated with
Alzheimar's disease in old people