WATER
CONTENT
· Types, Uses and Structure of Water.
· Laboratory Preparation of Water.
· Test for Water
· Causes/ Removal of Hardness of Water.
· Purification of Water for Municipal Supply.
WATER
Water is said to be a universal solvent , because it can dissolve almost all other substances.
SOURCES OF WATER
The following are the sources of water: the sources of water may be grouped into two
1. Natural water: Rainwater, Well water, Spring water and Sea water, rivers and lakes
2. Treated water: Distilled water, Pipe – borne water, deionized water and chlorinated water
STRUCTURE OF WATER
Because of the repulsion between the two lone pairs of electrons in the oxygen atom the two bonding pair are pushed towards each other resulting to a V-shape or angular shape or bent shape for water.
O
∕ \
H H
LABORATORY PREPARATION OF WATER
When dry hydrogen gas is lighted in air. It burns with a faint blue flame to give steam, which condenses when it comes in contact with any cold surface to form water.
PHYSICAL PROPERTIES OF WATER
1. Water has a boiling point of 100oC and freezes at 0oC
2. It has a maximum density of 1gcm-3 at 4oC
3. It is neutral to litmus.
4. It is a liquid at room temperature
CHEMICAL PROPERTIES
1. Water reacts with electropositive metals like K, Na and Ca to form alkali and liberate hydrogen gas. E.g Na(s)+ H2O(aq) →NaOH(aq) + H2(g)
Mg & Zn react with steam to form an alkaline solution while Cu, Hg, Ag, Au, do not react with water
2. Non-metal especially the halogens chlorine reacts with water to form acid solution
i. H2O(aq) + Cl2(g) →HCl(aq) + HOCl(aq)
ii. H2O(aq) +Br2(g) →HBr(aq) + HOBr(aq)
TEST FOR WATER
When few drops of water are added to
1. White anhydrous copper (II) tetraoxosulphate (VI), it turns blue.
2. Blue cobalt (II) chloride, it turns pink.
NOTE: These two tests are not specific for water. They only indicate the presence of water. Any aqueous solution or substance containing water will give a positive test for water
HARDNESS OF WATER
Hard water is any water that does not form lather (foam) readily with soap.
There are two types of hardness / hard water
I. Temporary hardness or temporary hard water
II. Permanent hardness/ permanent hard water.
I. Temporary hardness is caused by the presence of Ca(HCO3) or Mg(HCO3) in any water sample and these can be removed by boiling the water.
II. permanent hardness is caused by the presence of CaSO4 or MgSO4 or CaCl2 or MgCl2 it can not be removed by boiling
REMOVAL OF TEMPORARY HARDNESS
1. Physical method: By boiling
heat
Ca(HCO3)2(aq) →
CaCO3(s) + H2O(l) + CO2(g)
2. Chemical method: By using calculated amount of slaked lime (calcium hydroxide solution)
Ca(HCO3)2(aq) + Ca(OH)2(aq) →2CaCO3(s)+ 2H2O(l)
3 Addition of washing soda :-
Ca(HCO3)2(aq) + Na2CO3(aq) → CaCO3(s)+ NaHCO3 (aq)
EFFECTS OF TEMPORARY HARDNESS:
Hard water causes
1. Furring of kettles and boilers.
2. Stalagmite and stalactites in caves.
Removal of permanent hardness:
1. by physical method : Distillation
2.By chemical method only
i. Addition of washing soda
Na2CO3(aq) + CaSO4(aq) →CaCO3(s) + Na2SO4(aq)
ii. Addition of caustic soda
2NaOH(aq) +CaSO4(aq) → Ca(OH)2(s)+ Na2SO4(aq)
iii. Ion exchange resin
CaSO4(aq) +
Sodium zeolite →Calcium zeolite + NaSO4(aq)
(insoluble)
ADVANTAGES OF HARD WATER
i. Hard water taste better than soft water because of the presence of ions
ii. Calcium salts in it helps to build strong teeth and bones.
iii. It provides CaCO3, that crab and snail use to build their shells.
iv. It does not dissolve Lead, hence it can be supplied in lead pipes.
DISADVANTAGES OF HARD WATER
1. It causes furring of kettles and boilers.
2. It wastes soap.
3. It cannot be used in dying and tanning.
4. Effects is seen in stalactites and stalagmite
TREATMENT OF WATER FOR MUNICIPAL/ TOWN SUPPLY
The following are the processes involved in the treatment of river water for town supply
1. Coagulation: Chemicals like potash alum, KAl(SO4)2, or sodium aluminate III, NaAlO2 is added to water in a large settling tank.
2. Sedimentation: The coagulated solid particles or flocs are allowed to settle in the settling tank to form sediments at the bottom of the tank.
3. Filtration: The water above the sediment still contains some suspended particles. The water is passed through a filter bed to remove the remaining fine dirt particles.
4. Chlorination (Disinfection): Chemicals like chlorine is then added to the water to kill germs.
5. Calculated amount of iodine to prevent goiter and fluorine to prevent tooth decay are added as food supplements to prevent goiter and tooth decay respectively.
The treated water is then stored in a reservoir and distributed to the town.
OBJECTIVE QUESTIONS
1. Treated town water undergoes the following steps except
(A). coagulation
(B). precipitation
(C). sedimentation
(D). chlorination
2. Water is temporarily hard because it contains
A. CaSO4
B MgSO4
C. Chlorine
D. Ca(HCO3)2
3. Temporary hardness of water is removed by the use of one of the following
A. boiling
B. use of use of Ca(OH)2
C. use of Na2CO3
D. use of alum
4. A substance that turns white anhydrous CuSO4 blue is
A. water
B. liquid ammonia
C. hydrochloric acid
D. molten Sulphur
5. Distilled water is different from deionized water because
A. distilled water is a product of condensed steam while deionized water is filtered laboratory water
B. distilled water is always pure and sold in packs while deionized is not packaged for consumption
C. distilled water is condensed steam but deionized water is produced using ion-exchange resins which absorbs undesired ions.
D. distilled water is man-made while deionized water is both natural and artificial
6.
THEORY QUESTIONS
1.a i Mention two compounds that causes permanent hardness in water
ii. State two ways of removing permanent hardness in water
iii. List two advantages of hard water
b.(ai ) State the steps involved in the treatment of river water for town supply.
ii. Write two equations to show the removal of permanent hardness of water.
iii. Name two cations that causes hardness of water?
c.i. Give two methods of removal removal removal
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