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EC > Water > Flashcards

Water Flashcards

1
Q

Earth is mostly covered by water, so why is there water scarcity?

A

Only 2.5% of the world’s water is freshwater, most of it locked in glaciers and ice caps.

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2
Q

What percentage of freshwater is available for human use?

A

Only 1% of freshwater is readily available for human use.

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3
Q

What are the two main categories of impurities in water?

A

Dissolved Impurities & Suspended Impurities

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4
Q

Give examples of Inorganic Dissolved Salts (Cations)

A

Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+), Potassium (K+)

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5
Q

Give examples of Inorganic Dissolved Salts (Anions)

A

Chloride (Cl-), Sulfate (SO4^2-), Nitrate (NO3-)

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6
Q

What are some gases that can dissolve in water?

A

Carbon Dioxide (CO2), Oxygen (O2), Nitrogen (N2)

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7
Q

What type of organic matter can be found dissolved in water?

A

Decomposing plants and animals

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8
Q

Give an example of a suspended inorganic impurity.

A

Clay particles

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9
Q

Give an example of a suspended organic impurity.

A

Oil globules

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10
Q

What is the size range of colloidal impurities?

A

10-4 – 10-6 mm

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11
Q

Give an example of a colloidal impurity

A

Clay

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12
Q

What are some micro-organisms that can be found in water?

A

Bacteria, Fungi, Algae

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13
Q

Effects of Impurities in natural water

A

➢ Colour
➢ Taste and odour
➢ Turbidity and sediments
➢ Micro-organisms
➢ Dissolved minerals matters
(a) hardness
(b) Alkalinity
(c) Total solids
(d) corrosion
➢ Dissolved gas
➢ Silica contents

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14
Q

How is water hardness originally defined?

A

Water hardness is defined as the soap-consuming capacity of a water sample.

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15
Q

What causes the soap-consuming capacity of water?

A

The presence of certain salts of calcium, magnesium, and other heavy metals dissolved in the water.

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16
Q

What are soaps generally composed of?

A

Soaps are generally composed of sodium salts of fatty acids such as oleic acid, palmitic acid, and stearic acid.

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17
Q

How do calcium and magnesium in hard water react with soap?

A

They react with the sodium salts of long-chain fatty acids present in the soap to form insoluble scums of calcium and magnesium soaps.

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18
Q

Give examples of fatty acids found in soap.

A

Oleic acid (CH3(CH2)7CH=CH(CH2)7COOH), palmitic acid (CH3(CH2)14CO2H), and stearic acid (CH3(CH2)16CO2H).

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19
Q

What are some characteristics of hard water?

A

Hard water does not produce good lather or foam with soap, consumes more soap, and contains bicarbonates, chlorides, and sulfates of calcium and magnesium. Other metal ions such as Fe2+, Mn2+, and Al3+ also contribute to hardness, but are present in water only in traces.

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20
Q

What happens when hard water is treated with soap like sodium stearate?

A

No lather will be formed because sodium stearate reacts with salts of calcium and magnesium, giving insoluble calcium and magnesium stearate.

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21
Q

What happens when soft water is treated with soap?

A

It produces more lather and consumes less soap.

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22
Q

Why does soft water produce more lather and consume less soap?

A

Due to the absence of dissolved salts of calcium and magnesium in the water.

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23
Q

What are the products formed when sodium stearate reacts with water in the absence of calcium and magnesium?

A

Sodium hydroxide (NaOH) and stearic acid (C17H35COOH).

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24
Q

What causes temporary hardness in water?

A

Temporary hardness is caused by the presence of dissolved bicarbonate of calcium and magnesium and other heavy metal ions.

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25
Q

How can temporary hardness be removed from water?

A

Temporary hardness can be removed by boiling the water, which decomposes bicarbonates into insoluble carbonates and hydroxides that settle at the bottom of the vessel.

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26
Q

Name two compounds responsible for temporary hardness.

A

Calcium bicarbonate and magnesium bicarbonate

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27
Q

What causes permanent hardness in water?

A

Permanent hardness is caused by the presence of chlorides and sulphates of calcium, magnesium, iron, and other heavy metal ions.

28
Q

Can permanent hardness be removed by boiling water?

A

No, permanent hardness cannot be removed by boiling water.

29
Q

Name two compounds responsible for permanent hardness.

A

Calcium chloride and magnesium chloride

30
Q

Name two additional compounds that contribute to permanent hardness.

A

Calcium sulphate and magnesium sulphate

31
Q

Why is hardness often expressed in terms of the equivalent of calcium carbonate?

A

Hardness is expressed in terms of the equivalent of calcium carbonate because it is an insoluble salt that can be most easily precipitated in water treatment.

32
Q

What is the principle behind the Complexometric/EDTA method for determining water hardness?

A

The principle involves titrating a water sample with the sodium salt of EDTA using Eriochrome Black-T as an indicator, keeping the pH at 9.0 - 10.0, and observing the color change from wine-red to blue when EDTA complexes the calcium and magnesium salts completely.

33
Q

What steps are involved in the standardization of EDTA solution?

A

Rinse and fill the burette with EDTA solution, pipette out into a conical flask, add 4-5 ml of buffer solution and 2 drops of EBT indicator, and titrate with EDTA solution until the color changes from wine-red to blue. The volume of EDTA used is.

34
Q

How do you calculate total hardness in ppm?

A

Total Hardness = M3 × Molecular weight of CaCO3 (100) × One Litre (1000ml)
= M3 × 105 ppm

35
Q

How is temporary hardness calculated?

A

Temporary Hardness = Total Hardness - Permanent Hardness

36
Q

What is water softening?

A

Water softening is the process of removing hardness, primarily caused by calcium (Ca) and magnesium (Mg) ions, as well as iron (Fe), manganese (Mn), strontium (St), and aluminum (Al).

37
Q

Why is water hardness problematic?

A

Hardness in the range of 300-500 mg/L as CaCO3 is considered excessive and can lead to consumer objections and other issues. Even levels above 150 mg/L may result in consumer objection.

38
Q

What range of hardness is considered moderate?

A

A hardness level of 60-120 mg/L as CaCO3 is considered moderate.

39
Q

What are the primary methods of softening water?

A

Softening can be done by precipitation of Ca and Mg, or by ion exchange of Ca/Mg with ions such as Na.

40
Q

What is the principle behind the precipitation method in water softening?

A

The soluble hardness-causing impurities are converted into insoluble precipitates, which can be removed by settling and filtration.

41
Q

What is the lime-soda process in water softening?

A

In the lime-soda process, calculated amounts of lime and soda are added to hard water. Soluble calcium and magnesium salts are converted into insoluble compounds such as calcium carbonate and magnesium hydroxide, which can be removed by settling and filtration.

42
Q

How does lime remove temporary hardness?

A

Lime removes temporary hardness by precipitating bicarbonates of calcium and magnesium into insoluble carbonates and hydroxides.

43
Q

How does lime remove permanent magnesium hardness?

A

Lime reacts with permanent magnesium hardness, converting magnesium salts into insoluble magnesium hydroxide

44
Q

What is ion exchange in water softening?

A

Ion exchange involves replacing calcium and magnesium ions with sodium ions using a resin, effectively removing the hardness-causing ions from the water.

45
Q

What is the purpose of adding coagulants in the lime-soda process?

A

Coagulants like alum, aluminum sulfate, and sodium aluminate are added to help the finely divided precipitates settle down more easily.

46
Q

How does sodium aluminate as a coagulant benefit water treatment?

A

Sodium aluminate aids in the removal of silica and oil from water.

47
Q

What is the benefit of mixing lime and soda with water at 80°C?

A

The reaction proceeds faster, softening capacity is increased, no coagulant is needed, dissolved gases are driven out, viscosity is lower for easier filtration, and the process produces water with low residual hardness (15-30 ppm).

48
Q

Why is the high-temperature lime-soda process advantageous?

A

It increases reaction speed, improves softening capacity, negates the need for coagulants, drives out dissolved gases, lowers water viscosity for easier filtration, and produces water with low residual hardness.

49
Q

What are the economic benefits of the lime-soda process?

A

The lime-soda process is very economical and can reduce the need for coagulants when combined with sedimentation/coagulation.

50
Q

How does the lime-soda process affect the pH of treated water?

A

It increases the pH of the treated water.

51
Q

Besides removing hardness, what additional benefit does the lime-soda process offer?

A

It reduces the quantities of minerals in the water and significantly decreases the amount of pathogenic bacteria due to the alkaline nature of treated water.

52
Q

What are the operational challenges of the lime-soda process?

A

Efficient and economical softening requires careful operation and skilled supervision.

53
Q

What is a significant issue with the lime-soda process?

A

Disposal of the large amount of sludge generated poses a problem.

54
Q

What is the limitation of the lime-soda process regarding hardness removal?

A

It can only remove hardness up to 15 ppm, which is not sufficient for boiler use.

55
Q

What is the purpose of ion-exchange resins in water treatment?

A

Ion-exchange resins are used for separation, purification, and decontamination processes, such as water softening and water purification.

56
Q

What are ion-exchange resins made of?

A

Ion-exchange resins are insoluble, cross-linked, long-chain organic polymers with micro-porous structures. Functional groups attached to the chains are responsible for the ion exchange properties.

57
Q

What are cation exchange resins and their functional groups?

A

Cation exchange resins contain acidic functional groups (-COOH, -SO3H) and can exchange their H+ ions with other cations. Example: styrene-divinyl benzene copolymer after sulphonation and carboxylation.

58
Q

What are anion exchange resins and their functional groups?

A

Anion exchange resins contain basic functional groups (-NR3+OH-) and can exchange their anions with other anions. They may be made of styrene divinyl benzene or amine-formaldehyde copolymerization.

59
Q

What is the role of cation exchange resins in water softening?

A

Cation exchange resins remove cations like Ca2+ and Mg2+ from water, releasing equivalent amounts of H+ ions.

60
Q

What is the role of anion exchange resins in water softening?

A

Anion exchange resins remove anions like Cl- and SO4^2- from water, releasing equivalent amounts of OH- ions.

61
Q

What is deionized or demineralized water?

A

Deionized or demineralized water is water that has been treated to remove all cations and anions, resulting in ion-free water.

62
Q

What happens to the hydrogen and hydroxide ions in the ion exchange process?

A

Hydrogen ions (H+) from cation exchange and hydroxide ions (OH-) from anion exchange combine to form water (H2O).

63
Q

How is a cation exchange column regenerated?

A

By passing a solution of dilute HCl or H2SO4 through the column.

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Q
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EC (10 decks)

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