Water

Ms. Sterling
 The unique
Properties of
water
Colourless, tasteless, and odourless
liquid.
Boils at 100°C and freezes at 0°C.
Polar molecules with partial positive
and negative charges.
Hydrogen atoms have partial
positive charges.
Oxygen atoms have partial
negative charges.
 the unique properties of water
The maximum density of water occurs at 4°C
Density is the mass divided by volume of a substance.
If the volume of a fixed mass decreases, its density increases.
If the volume increases, its density decreases.
When liquids become solids, the solid volume is less than the liquid
volume, making it denser.
Water, when cooled to 4°C, contracts and becomes denser.
If cooled below 4°C, it expands until freezing at 0°C, making solid ice
less dense than the liquid water.
This ice floats on the liquid, allowing aquatic organisms to survive
under the ice.
the unique properties of water
Water has a high specific heat capacity
The specific heat capacity of a substance is the amount of
heat needed to raise a unit mass's temperature by 1°C.
Water has a high specific heat capacity, requiring a lot of
heat energy to increase its temperature by 1°C.
This means water can absorb a lot of heat energy without
its temperature changing significantly.
Living organisms can survive in extreme temperatures due
to their 60%-70% water content.
Large bodies of water like lakes and seas do not experience
extreme temperature fluctuations, preventing extreme
fluctuations in aquatic environments.
 the unique properties
Water has a high heat of vaporisation
of water
High heat of vaporisation required to convert liquid to gas.
Water molecules' hydrogen bonds make it less volatile.
Evaporation from living organisms removes significant heat energy, making
sweating and transpiration effective cooling methods.
Water has a relatively high melting point and boiling point
Ice's melting point and boiling point are higher due to hydrogen bonds.
Water exists as a liquid between 0°C and 100°C, allowing aquatic organisms to
thrive.
Lakes, rivers, and seas provide suitable environments for aquatic life.
Water dissolves a large number of substances
Water, a 'universal solvent', dissolves a wide range of substances due to its polar
nature.
It aids in chemical reactions in cells, facilitating respiration.
It dissolves useful substances like food and mineral salts, allowing their
absorption and transportation.
It dissolves waste products like urea, aiding in their excretion.
However, water's solvent properties can lead to issues like hardness, pollution,
and leaching of mineral salts from soil.
 the unique
Water Hardness
properties of water
Hard water is hard and doesn't lather easily with soap.
It's caused by dissolved calcium and magnesium salts.
Soap in hard water forms unpleasant scum, wasting soap and discolouring
clothes.
Types of Water Hardness
Temporary hardness: Water hardness that can be removed by boiling.
Permanent hardness: Hardness that cannot be removed by boiling.
Temporary hardness is caused by dissolved calcium hydrogencarbonate and
magnesium hydrogencarbonate.
Water Pollution
Water dissolves harmful substances in the environment, leading to pollution.
Main pollutants include heavy metal ions, sulfur dioxide and nitrogen oxides,
nitrate and phosphate ions, pesticides, and organic waste.
Leaching
Leaching is the loss of water soluble substances from the soil as water passes
through it.
Rainwater or irrigation water dissolves water soluble mineral salts, making the
soil less fertile.
The treatment of water for domestic
purposes
Water from reservoirs, lakes, rivers, and aquifers is piped to homes and must be
treated to remove contaminants and make it safe for consumption. Drinking water,
or bottled water, is safe enough for humans to consume. Various methods are used
to treat water for safe use.
Large-Scale Water Treatment Process
Flocculation and Sedimentation
Addition of chemicals like alum to water to form larger floc particles.
Sedimentation allows floc to settle within the water supply.
Filtration
Clear water is passed through filters to remove remaining particles, including
bacteria and viruses.
Filters are beds of gravel, sand, and charcoal with varying compositions and
pore sizes.
Chlorination
Chlorine gas is added to destroy bacteria and viruses in the water supply.
Chlorine is toxic, so only small amounts are added.
Monochloroamine (NH2CI) is now used as an alternative due to its stability,
effectiveness, and lack of gaseous chlorine.
 The treatment of water for domestic
purposes
Water treatment in homes can be done using various methods to ensure safe drinking water.
Filtration removes suspended sediment and dissolves organic compounds, odours, and unpleasant tastes.
Chlorination adds sodium chlorate(I) solution or calcium chlorate(I) tablets to the water, which can be found in chlorine bleaches.
Boiling water for 15 minutes kills microorganisms but does not leave an unpleasant taste. To ensure the water is safe to drink, add ten drops of chlorine
bleach to 5 dm of water, stir, and leave for 30 minutes. After boiling, the water should be cooled before drinking.
Softening Hard Water: Methods and Benefits
Boiling
Removes temporary hardness by decomposing dissolved calcium and magnesium ions into insoluble calcium and magnesium carbonate, water, and
carbon dioxide.
Calcium carbonate, also known as limescale, is removed from the water.
Addition of sodium carbonate
Also known as washing soda, sodium carbonate precipitates out dissolved calcium and magnesium ions as insoluble calcium and magnesium
carbonate.
Removes both temporary and permanent hardness.
Ion-exchange Water Softening Device
Water is passed through an ion-exchange column containing an ion-exchange resin known as zeolite.
Calcium and magnesium ions displace sodium ions and are absorbed into the zeolite.
Calcium and magnesium ions are periodically removed from the zeolite by passing a highly concentrated solution of sodium chloride (brine).
Distillation
Boils water and condenses the steam to form pure distilled water.
Can be used to desalinate sea water in areas with water shortage.
Not economical due to high energy consumption and residue buildup in the heating vessel.
Reverse osmosis
Water is forced through a semi-permeable membrane under pressure.
Removes ions causing water hardness and other ions and any dissolved organic matter.
Most desalination plants use reverse osmosis to desalinate sea water or brackish water to produce fresh water.