Water

Question 1

what does hardness in water do to soap

Answer 1

forms a scum instead of lather

Question 2

what causes hardness

Answer 2

Ca2+ and Mg2+ ions

Question 3

equation for formation of scum due to hardness in water

Answer 3

2(C17H35COONa) [sodium stearate/soap]+ Ca2+—->(C17H35COO)2Ca(↓)[calcium stearate/scum] +2(Na+)

Question 4

when will lather be produced

Answer 4

when all the calcium or magnesium ions are gone, so a lot of soap must be used

Question 5

hard water defn

Answer 5

water that does not form a lather easily with soap

Question 6

two types of hardness and what causes them

Answer 6

temporary hardness: calcium/magnesium hydrogencarbonate (Mg/Ca)CO3, enters when carbonic acid/acid rain reacts with limestone, removed by boiling as calcium hydrogencarbonate forms insoluble calcium carbonate(responsible for scale on kettles etc)
permanent hardness: calcium/magnesium sulfate (Mg/Ca)SO4, can’t be removed by boiling

Question 7

how to remove both types of hardness

Answer 7

1. distillation:water boiled off through Liebeg condenser (hydrogencarbonates and sulphates remain behind), expensive on large scale
2. addition of washing soda crystals: carbonate ions in the crystals react with calcium ions (both) and remove them
3. Ion exchange resin

Question 8

how ion exchange resin work

Answer 8

1. when hard water passes through the ions that cause hardness (calcium/ magnesium) are swapped with sodium ions (resin does become full of swapped ions and must be soaked in solution of sodium chloride)
   Na2R+Ca2+—>CaR=2(Na+)
2. removes all ions to produce deionised water, two resins; cation and anion exchange, cation resin exchanges H+ ions with positive ions and anion resin exchanges negative ions with OH-
   RH+cation–>H+ +spent resin
   ROH+anoin–>OH-+spent resin
   H+ +OH- —> H2O

Question 9

deionised vs distilled water

Answer 9

deionised- no ions, has dissolved gases and organic matter

distilled- no ions, no dissolved gases and organic material

Question 10

advantages of hard water

Answer 10

1. tastes better
2. contains calcium which is good for bones teeth
   3 good for brewing industry (beer)

Question 11

disadvantages of hard water

Answer 11

1. dirty looking scum produced with soap
2. wastes soap
3. produces scale that can block pipes and render heating appliances useless

Question 12

what is standard solution in hardness testing experiment

Answer 12

EDTA ethylenediaminetetraacetic acid

Question 13

what indicator is used in hardness testing experiment

Answer 13

Eriochrome Black T/ Solochrome Black T
hardness= wine/red
hardness removed=blue

Question 14

what else added to hardness testing experiment

Answer 14

pH 10 buffer

Question 15

how is EDTA stored and why

Answer 15

in plastic container sit has the ability to remove metal ions from glass

Question 16

in hardness testing experiment what is all the hardness attributed to

Answer 16

calcium carbonate CaCO3

Question 17

what does organic waste in water do

Answer 17

puts a demand on the dissolved oxygen which is necessary for aquatic life (plants and fish)

Question 18

what decompose organic waste and how

Answer 18

bacteria and other organism and they use dissolved oxygen and convert waste into CO2 and H2O

Question 19

Biochemical Oxygen Demand defn

Answer 19

the amount of dissolved oxygen consumed by biochemical action when a sample of water is kept in the dark, at 20 degrees, for 5 days

Question 20

BOD of clean water, treated sewage, raw sewage and silage effluent

Answer 20

clean water= 1-2 p.p.m.
treated sewage= 30p.p.m.
raw sewage= 400p.p.m.
silage effluent=54,000p.p.m.