Lesson 4 unite 1 :Water

Water

Lesson objectives

• At the end of this lesson, The student should be able to :

1- Identify the importance of water and its sources.

2-Identify the bonds between its atoms and water molecules.

3- Identify the physical and chemical properties of water.

4-Explain the abnormality of physical properties of water.

5-Identify the electrolysis of water.

6-Explain why water is neutral.

7-Identify the water pollutants and their harms.

8-Identify how to keep water from pollution.

9-Appreciate the importance of water in our life.

•  Importance of water and its sources

1-The basic  fields for using water in the world
are: agriculture, industry, and personal uses.

2-Most of fresh water is used in planting crops field.

Sources of water in nature are :

(rivers , seas , oceans) rains, wells and springs

 * For more information about source of water , please visit these sites:

•  Water structure :

* Molecule is composed of the combination of one 

oxygen atom with two hydrogen atoms to form two

single covalent bonds , the angle between them is

104.5º.

*Due to large electronegativity of oxygen compared

with hydrogen a weak electrostatic attraction is 

originated between water molecule which is called 

 hydrogen bond.

*Although these hydrogen bonds are weaker than

the covalent bonds in the same molecules, they

are considered to be the most important factors

which are responsible for abnormality of water

properties.

* For more information about  water structure  , please visit this site:

• Properties of water :

1-Good polar solvent :Some substances dissolve

 in water, while others don’t dissolve in it.

Water is a good polar solvent for most ionic compounds

 (as table salt) and for some covalent compounds (as 

sugar) which form hydrogen bonds with water.

2- Rising of its boiling and melting points:

According to the position of oxygen in group 6A of the

 periodic table, it was supposed that the boiling of water

  is less than (100°C) and the freezing point is less than

 zero celsius . but the pure water in the normal
  
atmospheric pressure boils at (100°C) and

freezes at zero.The abnormality of the physical 

properties of water and from which high boiling and

freezing point, is due to the presence of hydrogen bonds.

  3- Water has low density when it freezes :

 The density of water when it is in a solid state is lower

than its density when it is in a liquid state because when

the temperature decreases less than 4 °C , the water 

molecules are collected by hydrogen bonds 

forming large-sized hexagonal crystals with many 

spaces between them so ice floats o n t he surface of 

 water in the frozen zones which make marine organisms

 be still alive.

 4- Rising of its latent heat:

 Rising of water latent heat , makes it resists the change 

from a state to another This property makes water one

 of the most important liquids used in extinguishing 

fires , as it consumes  a large amount of heat of

combustion media during its vaporization process

 5- Rising of its specific heat The high specific 

heat of water makes it absorbs or loses a large amount 

 of heat without changing its temperature therefore 
 
the temperature of human body doesn’t change by

changing the atmospheric temperature.

6- Weakness of its ionization:Ionization: is the

 process of converting the molecules of some covalent 

compounds into ions ,the pure water is considered from

 weak ionized substances. Water is neutral because when

 it ionize , it gives equal numbers numbers of positive 

hydrogen ions.

H+ which is responsible for the acidic properties and 

negative hydroxide ions.

(OH)– which is responsible for the basic properties.

H2O H+ + OH–

7- It has neutral effect on both of litmus papers

8- Its resistance to analysis:At normal 

conditions, water isn’t analyzed into two elements or by

 the effect of heat, it helps to keep water solutions in the

 cells of living organisms generally.

* For more information about  water structure and properties  , please visit this site:

*The process of electrolysis of water

 

* Water Pollution

*Water pollution is divided into (4) main parts

1- Biological pollution:

It is originated from mixing of human and animal wastes

with water and that causes many diseases such

as Bilharzia, typhoid and that hepatitis.

2- Chemical pollution:

It is originated from discharging of factories wastes in

 canals , rivers and sea.,the increase of some elements

  concentration causes great harms. Eating  fish which 

contains high ratios of lead causes the death of brain 

cells, drinking water which contains high ratio of 

mercury leads to blindness.arsenic increases the rate of 

infection by liver cancer.

 3- Thermal pollution

It is originated from the rise of temperature of some

marine zones which use water for cooling the nuclear

reactors which destroy the marine organisms found in

them due to separation of dissolved oxygen in water

4- Radiant pollution

It is originated from leakage of radioactive substances

from the nuclear reactors or dumping of the atomic

wastes in seas and oceans.

* For more information about  water pollution  , please visit this site:

Protection of water from pollution

1- Getting rid of the phenomenon of discharging of sewage,
factories wastes and dead animals in rivers or canals.

2-Development of water purification stations
and making periodic analysis to determine the rate of
its validity for drinking.

3-Spreading environmental awareness among people
about protection of water from pollution.

4-Disinfecting drinking water tanks above buildings
periodically. 

5-Don’t store the tap water in empty plastic bottles of
mineral water because they react with chlorine gas
which is used in disinfecting of water, so the rate of
cancer infection increases

* For more information about  water protection  , please visit this site:

•  please visit this video because it shows this lesson in detail: