Water Flashcards
1
Q
What is water?
A
“One of the most common substances known and a good solvent for many substances
2
Q
What does natural water include?
A
“Rainwater
3
Q
Why is rainwater considered the purest form of natural water?
A
“It is formed as a result of the condensation of water vapour in the atmosphere
4
Q
What does spring water contain?
A
“A considerable amount of mineral salt
5
Q
What does well-water contain?
A
“A lot of clay and other mineral salts.”
6
Q
What are the guidelines for wells used as a source of drinking water?
A
“They should be sited away from sources of underground water pollution like pit latrines
7
Q
What do river water, lake water, and sea-water contain?
A
“A lot of dissolved air
8
Q
What is treated water?
A
“Water prepared for special purposes
9
Q
What is distilled water?
A
“Chemically pure water
10
Q
What is deionized water?
A
“Water prepared using exchange resin.”
11
Q
What is distilled water used for?
A
“Preparing reagents and analytical work in the laboratory
12
Q
How is pipe-borne water prepared?
A
“In a water-treatment plant.”
13
Q
What does pipe-borne water usually contain?
A
“It is germ-free but contains mineral solutes like sodium chloride.”
14
Q
Where does the water treated in water-treatment plants come from?
A
“Rainfall
15
Q
What methods are used to purify water in water-treatment plants?
A
“Coagulation
16
Q
How is treated water distributed?
A
“To towns and cities via underground pipes for domestic and industrial uses.”
17
Q
What chemicals are used in the coagulation or flocculation process?
A
“Potash alum ($KAl(SO_{4}){2}$) or sodium aluminate(III) ($NaAlO{2}$).”
18
Q
What happens during coagulation?
A
“Impurities clump together to form big particles of dirt or flocs which settle down rapidly.”
19
Q
What is the purpose of a filter bed in water treatment?
A
“To remove the remaining fine particles of dirt.”
20
Q
What chemical is used to kill germs in water treatment?
A
“Chlorine.”
21
Q
What other chemicals may be added to treated water and why?
A
“Iodine and fluorine
22
Q
Where is treated water stored before distribution?
A
“In a reservoir.”
23
Q
What is hard water?
A
“Water that will not form lather readily with soap and contains dissolved calcium or magnesium salts.”
24
Q
What is soap?
A
“The sodium or potassium salt of an organic acid
25
What happens when soap is added to hard water?
"The dissolved salts react with the soap molecules to form an insoluble scum."
26
Why is hard water wasteful?
"A large amount of soap has to be used to precipitate and remove the calcium and magnesium ions before lather can form."
27
How has the problem of hard water been overcome in recent years?
"By the introduction of detergents
28
How does water acquire hardness?
"When it dissolves gypsum ($CaSO_{4}.2H_{2}O$)
29
What is the reaction when carbon (IV) oxide dissolves limestone?
"$CaCO_{3}(s) + CO_{2}(g) + H_{2}O(l) \rightarrow Ca(HCO_{3})_{2}(aq)$"
30
What are the two types of hard water?
"Temporarily hard and permanently hard water."
31
How can temporary hardness be removed?
"By boiling."
32
What causes temporary hardness?
"The presence of dissolved calcium hydrogentrioxocarbonate (IV) ($Ca(HCO_{3})_{2}$)."
33
What happens when temporary hard water is boiled?
"The calcium hydrogentrioxocarbonate (IV) decomposes to form insoluble calcium trioxocarbonate (IV) ($CaCO_{3}$)
34
How else can temporary hardness be removed?
"By using slaked lime ($Ca(OH)_{2}$)."
35
What is the reaction when slaked lime is used to remove temporary hardness?
"$Ca(HCO_{3})_{2}(aq) + Ca(OH)_{2}(s) \rightarrow 2CaCO_{3}(s) + 2H_{2}O(l)$"
36
What are the effects of temporary hardness?
"Furring of kettles and boilers
37
What causes the furring of kettles and boilers?
"The gradual deposition of calcium trioxocarbonate (IV) from the decomposition of calcium hydrogentrioxocarbonate (IV)."
38
What are stalagmites and stalactites?
"Pillars of limestone found in caves
39
How does the experiment to compare the hardness of various water samples work?
"By measuring the amount of soap solution required to produce a permanent lather in different water samples."
40
What does the amount of soap solution used indicate?
"The degree of hardness of the water sample
41
How is permanent hardness removed?
"By using chemicals to precipitate the calcium and magnesium ions from solution."
42
What type of chemicals are used to remove permanent hardness?
"Soluble sodium compounds which form insoluble precipitates with the calcium and magnesium ions."
43
Name some common chemicals used in the removal of permanent hardness.
"Washing soda
44
What happens when washing soda is added to permanently hard water?
"It removes the calcium and magnesium ions as insoluble calcium and magnesium trioxocarbonates (IV) respectively."
45
What are the reactions when washing soda is added to permanently hard water?
"$Na_{2}CO_{3}(aq) + CaSO_{4}(aq) \rightarrow CaCO_{3}(s) + Na_{2}SO_{4}(aq)$ and $Na_{2}CO_{3}(aq) + MgSO_{4}(aq) \rightarrow MgCO_{3}(s) + Na_{2}SO_{4}(aq)$"
46
What happens when caustic soda is added to permanently hard water?
"It removes the calcium and magnesium ions as insoluble calcium and magnesium hydroxides respectively."
47
What are the reactions when caustic soda is added to permanently hard water?
"$2NaOH(aq) + CaSO_{4}(aq) \rightarrow Ca(OH)_{2}(s) + Na_{2}SO_{4}(aq)$ and $2NaOH(aq) + MgSO_{4}(aq) \rightarrow Mg(OH)_{2}(s) + Na_{2}SO_{4}(aq)$"
48
What is permutit or zeolite?
"An ion-exchange resin used for softening water
49
How does permutit or zeolite soften water?
"It exchanges sodium ions for calcium and magnesium ions in the water."
50
What is an example of the reaction between calcium tetraoxo-sulphate(VI) and sodium zeolite?
"$CaSO_{4} + Na_{2}Zeolite \rightarrow CaZeolite + Na_{2}SO_{4}$"
51
How is permutit regenerated after use?
"By pouring a strong solution of common salt through the resin."
52
What is an example of the reaction for permutit regeneration?
"$CaCl_{2} + Na_{2}Zeolite \rightarrow CaZeolite + 2NaCl$"
53
What are the advantages of hard water?
"It tastes better than soft water
54
What are the disadvantages of hard water?
"It requires more soap for washing
55
What is water pollution?
"A big problem in the present day world that threatens aquatic life
56
What is the main cause of water pollution?
"The indiscriminate dumping of solid and liquid wastes into water bodies."
57
What are common water pollutants?
"Refuse and sewage
58
Why are many towns and villages located near rivers?
"For convenience since transport is easy and water supply is available."
59
What is a common practice in towns and villages for waste disposal?
"Dumping refuse and human wastes into the river."
60
Where does human waste from water-closet lavatories go?
"Either into septic tanks or sewers."
61
What are sewers?
"Large underground pipes for carrying waste or sewage."
62
Where do sewers often empty waste?
"Directly into rivers and seas without any treatment."
63
What are examples of harmful chemical wastes?
"Detergents
64
What happens to fertilizers and insecticides used in agriculture?
"They are washed by rain into the soil and eventually reach water bodies like lakes
65
What is a characteristic of many harmful chemical wastes like detergents and insecticides?
"They are non-biodegradable."
66
What are the effects of non-biodegradable wastes?
"They cause long-term pollution problems."
67
What is a major source of water pollution in coastal towns?
"Crude oil spillage from ships
68
What are the methods for controlling water pollution?
"Proper disposal of refuse and sewage
69
How should refuse and sewage be disposed of to prevent water pollution?
"By using modern incinerators and recycling plants
70
How should industrial wastes be treated to prevent water pollution?
"By treating them chemically to neutralize harmful substances before being discharged into water bodies."
71
What type of insecticides and fertilizers should be used to prevent water pollution?
"Non-poisonous ones
72
What role does public education play in water pollution control?
"Educating people on the causes and dangers of water pollution."
73
What legal measures should be taken to control water pollution?
"Laws should be enacted to prohibit the pollution of water bodies
74
What is a solution?
"A homogeneous mixture of two or more substances."
75
What are the two components of a solution?
"Solute and solvent."
76
What is a solute?
"The substance that is dissolved."
77
What is a solvent?
"The dissolving medium."
78
What is an example of a solution?
"Sodium chloride dissolved in water."
79
What is an aqueous solution?
"A solution in which water is the solvent."
80
What is solubility?
"The amount of solute necessary to saturate 100g of solvent at a particular temperature."
81
What is a saturated solution?
"A solution that contains as much dissolved solute as it can hold at a given temperature."
82
What is an unsaturated solution?
"A solution that contains less solute than it can hold at a given temperature."
83
What is a supersaturated solution?
"A solution that contains more solute than it can normally hold at a given temperature; it is usually unstable."
84
What are the factors affecting solubility?
"Temperature and nature of solute and solvent."
85
How does temperature affect the solubility of solids in liquids?
"The solubility of solids in liquids generally increases with an increase in temperature."
86
How does temperature affect the solubility of gases in liquids?
"The solubility of gases in liquids decreases as the temperature rises."
87
What is the nature of solute and solvent in terms of solubility?
"Like dissolves like
88
What is crystallization?
"The process by which crystals are obtained when a solute separates out of a saturated solution."
89
What is used to represent the solubility of a solute?
"A solubility curve."
90
What is the x-axis on a solubility curve?
"Temperature."
91
What is the y-axis on a solubility curve?
"Solubility."
92
What does a solubility curve show?
"The variation of solubility of a solute with temperature."
93
What is the importance of solubility curves?
"They are used to compare the solubilities of different substances at different temperatures
94
What is the effect of stirring on the rate of dissolution?
"Stirring increases the rate of dissolution."
95
What is the effect of particle size on the rate of dissolution?
"The smaller the particle size
96
What is the effect of temperature on the rate of dissolution?
"The higher the temperature
97
What is dialysis?
"The process by which a true solution is separated from a colloidal solution by the use of a parchment membrane."
98
What is a true solution?
"A homogeneous mixture where solute particles are small molecules or ions (crystalloids)."
99
What is a colloidal solution?
"A false solution where solute particles are larger than in a true solution but not visible to the naked eye."
100
What is the Tyndall effect?
"The scattering of light rays by colloidal solutions."
