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Water Flashcards

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1
Q

Write the chemical name and molecular formula of water

A

The chemical name of water is dihydrogen oxide.
It’s molecular formula is H²O.

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2
Q

Water covers nearly ____ of the earth’s surface.

A

Three-fourths

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3
Q

In what states of matter does water exist?

A

Water exists in all three states of matter:
solid (ice),
liquid (water),
and gas (water vapor).

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4
Q

How is water present in the atmosphere?

A

In the atmosphere, water is present in the form of water vapor, which condenses to form clouds, fog, mist, etc.

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5
Q

Where is the major portion of water on Earth found?

A

The major portion of water on Earth is found in the form of ice, snow, in polar regions, and high mountains as polar ice, caves, and glaciers.

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6
Q

What is hydroelectricity?

A

The electricity produced by using the flow of water from a dam is called hydroelectricity.

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7
Q

What is the largest source of water on Earth and what percentage of the Earth’s surface does it cover?

A

Oceans and seas, covering nearly 71% of the Earth’s surface.

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8
Q

Why is water from oceans and seas not suitable for direct consumption?

A

It contains a very high proportion of dissolved substances, mainly common salt.

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9
Q

What are the sources of water in rivers and lakes, and what impurities do they contain?

A

Rivers and lakes get water from rain and melting snow and contain dissolved impurities like salt and suspended impurities like clay, sand, twigs, and microbes.

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10
Q

What is the purest form of natural water?

A

Rainwater is the purest form of natural water.

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11
Q

Why is the first shower of rain considered impure?

A

It dissolves gases and collects particles, smoke, and germs from the air as it falls.

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12
Q

What distinguishes spring and well water in terms of purity and taste?

A

Spring and well water are underground sources, usually free from suspended impurities and germs, and the taste varies due to different dissolved substances.

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13
Q

Seas/oceans contain ____ of total water available on the earth.

A

97.4%

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14
Q

What is desalination?

A

The process of removal of dissolved salts from sea/ocean water.

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15
Q

Why is water called the source of life?

A

No living being can survive without water, therefore it is rightly called the source of life.

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16
Q

What are the key reasons water is important in our daily lives?

A

1.Drinking to satisfy biological needs.
2.Providing a medium for biochemical reactions.
3.Regulating body temperature.
4.Everyday uses (cooking, cleaning, bathing, washing).
5.Growing crops, germinating seeds, and photosynthesis in plants.
6.Providing nutrients to plants and animals.
7.Controlling Earth’s climate.
8.Various manufacturing purposes.
9.Generating electricity.

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17
Q

Define water cycle

A

The changes of water from one state to another in nature, resulting in its continuous circulation from earth’s surface to the atmosphere and from the atmosphere back to the earth’s surface is called water cycle.

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18
Q

What is the process of water interchange in nature, and what does it help balance?

A

The interchange of water from one state to another involves evaporation, condensation, and precipitation. This process helps balance the amount of water in the atmosphere and on Earth’s surface, supporting plant and animal life.

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19
Q

Importance of water cycle

A
  1. Helps in regulating the climate on earth.
  2. Makes water available in various forms on earth.
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20
Q

Why do clothes not dry quickly on a humid day during the rainy season?

A

On a humid day, the air contains a lot of water vapor, which reduces the rate of evaporation from surfaces like clothes, making them take longer to dry.

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21
Q

What is potable water?

A

The which which is fit for consumption by human beings and other animals.

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22
Q

What are the key physical properties of pure water?

A

•Colorless, transparent, tasteless, and odorless.
•Freezes at 0°C and boils at 100°C.
•Ice melts at 0°C

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23
Q

How does atmospheric pressure affect the boiling point of water?

A

The boiling point decreases with lower atmospheric pressure and increases with higher pressure.

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24
Q

Why does water boil at a lower temperature and take longer to cook food in hilly areas?

A

In hilly areas, lower atmospheric pressure decreases the boiling point of water, causing food to cook more slowly.

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25
Q

Why does food cook faster in a pressure cooker?

A

The increased pressure inside the cooker raises the boiling point of water, requiring more heat to cook food faster.

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26
Q

How does a skater glide on ice?

A

The pressure under a skater’s shoe melts the ice, which refreezes after the skater moves, allowing the skater to glide on the thin layer of water.

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27
Q

How do impurities affect the freezing point of water?

A

Impurities lower the freezing point of water. For example, adding salt to ice creates a freezing mixture with a melting point of about -15°C.

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28
Q

Why is alcohol added to water in car radiators?

A

Alcohol is added to prevent the water from freezing in cold weather.

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29
Q

How do impurities affect the boiling point of water?

A

Impurities raise the boiling point of water. For example, adding salt raises the boiling point, which aids in cooking.

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30
Q

Why does water make an excellent cooling agent?

A

Water heats up and cools down slowly, making it effective for absorbing heat and preventing overheating in car engines, nuclear reactors, and machinery.

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31
Q

What is the anomalous expansion of water?

A

Water expands on cooling below 4°C, making its density decrease, unlike most substances that contract and increase in density.

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32
Q

Why does ice float on water?

A

Ice is less dense than liquid water, causing it to float.

33
Q

How does the anomalous expansion of water benefit aquatic life in cold regions?

A

Ice forms on the surface, insulating the water below and protecting aquatic life from freezing temperatures.

34
Q

At what temperature is water’s density maximum?

A

Water’s density is maximum at 4°C.

35
Q

At what temperature is water’s density maximum?

A

Water’s density is maximum at 4°C.

36
Q

Why do water pipes burst in winter?

A

Water expands as it freezes, increasing its volume by about 9% and creating pressure inside pipes, which can cause them to burst.

37
Q

Why is water termed as the universal solvent?

A

Because it dissolves almost all kinds of solids,liquids, and gaseous substances.

38
Q

What is a solution?

A

A solution is a homogeneous mixture of two or more substances whose composition can be varied.

39
Q

Define solute

A

A solute is a substance that dissolves in other substances.

40
Q

Define solvent

A

A solvent is a medium in which a solute dissolves.

41
Q

Define miscible and immiscible liquids

A

The liquids which dissolves in water are called miscible liquids and which do not dissolve is called immiscible liquid.

42
Q

How does temperature affect the solubility of a solid solute and a gas in water?

A

Solubility of a solid solute increases with temperature; solubility of a gas decreases with temperature.

43
Q

Why does boiled water taste flat?

A

Because boiling reduces the solubility of gases, which affect the taste and aroma of water.

44
Q

How does pressure affect the solubility of a solid in water?

A

Pressure has practically no effect on the solubility of a solid in water.

45
Q

How does pressure affect the solubility of a gas in water?

A

The solubility of a gas increases with higher pressure and decreases with lower pressure.

46
Q

Why does a carbonated drink release gas with a hissing sound when opened, and why is it bottled under high pressure?

A

Carbonated drinks are bottled under high pressure to keep a large amount of carbon dioxide dissolved. When the bottle is opened, the pressure decreases, causing the gas to escape rapidly and create a hissing sound.

47
Q

What are the benefits of dissolved gases in natural water?

A

Dissolved oxygen is crucial for marine life, carbon dioxide supports photosynthesis in aquatic plants and helps form shells of marine animals, and nitrogen is converted into nitrogenous compounds by bacteria to nourish water plants.

48
Q

Why are dissolved salts important in natural water?

A

Salts like common salt (sodium chloride) are essential for the proper growth and development of the human body and add taste to drinking water.

49
Q

Saturated solution

A

A solution that cannot dissolve any more of the solute at a given temperature.

50
Q

Unsaturated solution

A

A solution in which more of the solute can be dissolved at a given temperature.

51
Q

Super-saturated solution

A

A saturated solution that contains more solute than it can hold at room temperature.

52
Q

Suspension

A

A suspension is a heterogeneous mixture in which solid particles, with a size about 10-⁷m are dispersed in a medium that eventually get settled down.

53
Q

Colloid

A

A colloid is a homogeneous looking heterogeneous mixture in which particles with size ranging from 10-¹⁰m to 10-⁷m are dispersed in a continuous medium. These particles remain suspended throughout the medium.

54
Q

Solution

A

A solution is a homogeneous mixture in which the particle size is less than 10-¹⁰m.

55
Q

Define water of crystallisation

A

The fixed amount of water which is in a loose chemical combination with one molecule of a substance in it’s crystal form.

56
Q

Crystal

A

A crystal is a homogeneous solid of definite geometrical shape in which particles are arranged symmetrically.

57
Q

Crystallisation

A

The process by which crystals of a substance are seperated by cooling its hot super-saturated solution.

58
Q

What are anhydrous substances and give examples?

A

Anhydrous substances do not contain water of crystallization. Examples include crystalline substances like common salt, potassium nitrate, and sugar, as well as amorphous powdered solids like calcium carbonate, zinc carbonate, and copper oxide.

59
Q

What are efflorescent substances and give examples?

A

Efflorescent substances lose water of crystallization when exposed to air. The process is called efflorescence. Examples include washing soda, which changes from a white crystalline substance to a white powder, and Glauber salt.

60
Q

What are deliquescent substances and give examples?

A

Deliquescent substances absorb water from the atmosphere, become moist, and lose their crystalline form, eventually forming a solution. Examples include caustic soda, magnesium chloride, calcium chloride, and iron chloride.

61
Q

Why does table salt turn moist during the rainy season?

A

Table salt turns moist because it contains impurities like magnesium chloride and calcium chloride, which are deliquescent. Sodium chloride itself is not deliquescent.

62
Q

What are hygroscopic substances and give examples?

A

Hygroscopic substances absorb moisture from the atmosphere without dissolving in it. Examples include concentrated sulfuric acid, phosphorus pentoxide, quicklime, calcium chloride, and silica gel.

63
Q

What is the purpose of using silica gel pouches?

A

Silica gel pouches are used as drying agents to absorb moisture and keep items dry, such as in water bottles, camera lenses, shoe boxes, and medicine containers.

64
Q

What is the reaction of metals with water?

A

Active metals like sodium, potassium, magnesium, and calcium react with water to produce hydrogen gas and metal hydroxides. For example:
•Sodium reacts with cold water to form sodium hydroxide and hydrogen gas.
•Calcium reacts with cold water to form calcium hydroxide and hydrogen gas.
•Magnesium reacts with steam to form magnesium oxide and hydrogen gas.
•Iron reacts with steam to form iron oxide and hydrogen gas.

65
Q

How does water react with non-metals and non-metallic oxides?

A

1.Non-metals like carbon react with steam to produce water gas (CO + H₂).
2.Chlorine gas reacts with water to form hydrochloric acid and release oxygen gas.
3.Non-metallic oxides like carbon dioxide, sulfur dioxide, and nitrogen dioxide dissolve in water to produce acidic solutions (e.g., carbonic acid, sulfurous acid).

66
Q

What is the effect of heat or electrolysis on water?

A

Water decomposes into hydrogen and oxygen gases when heated above 2000°C or when an electric current passes through it.

67
Q

How can water be tested for purity?

A

Water can be tested for purity by its boiling point (100°C) and freezing point (0°C). It can also be tested using anhydrous substances: adding water to anhydrous copper sulfate turns it blue, and adding water to anhydrous cobalt chloride turns it pink.

68
Q

What is soft water and how can it be identified?

A

Soft water forms a lather easily with soap and does not produce a white sticky scum. Rainwater and distilled water are examples of soft water.

69
Q

What is hard water and how can it be identified?

A

Hard water does not form a lather easily with soap and forms a white sticky scum or precipitate. It is often obtained from certain natural sources.

70
Q

What is temporary hard water?

A

Temporary hard water contains bicarbonates of calcium and magnesium. It can be easily softened by boiling.

71
Q

What is permanent hard water?

A

Permanent hard water contains sulphates and chlorides of calcium and magnesium. This type of hardness cannot be removed by boiling.

72
Q

What are the advantages of hard water.

A

Hard water adds taste due to dissolved salts and provides calcium and magnesium, which are essential for healthy bones and teeth.

73
Q

What are the disadvantages of hard water and methods to remove its hardness?

A

Disadvantages include:
1. Wastes soap in laundry.
2. Leaves scale or fur, damaging containers.
3. Affects textile industries and dyeing.
4. Not ideal for cooking

Methods to remove hardness:
1. Boiling: Removes temporary hardness by converting bicarbonates to insoluble carbonates.
2. Adding Sodium Carbonate (Washing Soda):Removes permanent hardness by forming insoluble carbonates from calcium and magnesium salts.

74
Q

What is water pollution and its causes?

A

Water pollution is the contamination of water making it unfit for use due to undesirable changes. Causes include:

1.Chemical wastes from industries and agriculture.2.Thermal wastes from power plants.
3.Sewage and garbage discharge.
4.Waterborne diseases from polluted water.

75
Q

How can we prevent water pollution?

A

Prevention methods include:
1. Improve sanitation facilities to avoid open defecation.
2. Treat domestic sewage before discharge.
3. Treat industrial waste before release.
4. Reduce use of non-biodegradable substances.
5.Avoid washing near water sources.
6. Plant trees along riverbanks.
7. Cover wells and regularly purify water bodies.
8. Dispose of animal carcasses hygienically.

76
Q

What are the effects of water scarcity on plants?

A

Water scarcity causes plants to dry out, leading to loss of green cover. This impacts food supply, oxygen production, and increases drought frequency. Without plants, life on earth would be severely affected.

77
Q

What are the effects of water scarcity on plants?

A

Water scarcity causes plants to dry out, leading to loss of green cover. This impacts food supply, oxygen production, and increases drought frequency. Without plants, life on earth would be severely affected.

78
Q

What are some methods for managing and conserving water?

A

Methods for water management and conservation include:
1. Constructing dams and reservoirs.
2. Avoiding leaving taps running.
3. Recycling water in industries.
4. Planting trees to increase water seepage.
5. Practicing rainwater harvesting.
6. Repairing leaking taps and pipes.
7. Recycling polluted water for irrigation.
8. Using biodegradable fertilizers and pesticides.
9. Implementing efficient irrigation methods like drip irrigation.

Chemistry (5 decks)

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