Water Flashcards
what does hardness in water do to soap
forms a scum instead of lather
what causes hardness
Ca2+ and Mg2+ ions
equation for formation of scum due to hardness in water
2(C17H35COONa) [sodium stearate/soap]+ Ca2+—->(C17H35COO)2Ca(↓)[calcium stearate/scum] +2(Na+)
when will lather be produced
when all the calcium or magnesium ions are gone, so a lot of soap must be used
hard water defn
water that does not form a lather easily with soap
two types of hardness and what causes them
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
how to remove both types of hardness
- distillation:water boiled off through Liebeg condenser (hydrogencarbonates and sulphates remain behind), expensive on large scale
- addition of washing soda crystals: carbonate ions in the crystals react with calcium ions (both) and remove them
- Ion exchange resin
how ion exchange resin work
- 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+) - 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
deionised vs distilled water
deionised- no ions, has dissolved gases and organic matter
distilled- no ions, no dissolved gases and organic material
advantages of hard water
- tastes better
- contains calcium which is good for bones teeth
3 good for brewing industry (beer)
disadvantages of hard water
- dirty looking scum produced with soap
- wastes soap
- produces scale that can block pipes and render heating appliances useless
what is standard solution in hardness testing experiment
EDTA ethylenediaminetetraacetic acid
what indicator is used in hardness testing experiment
Eriochrome Black T/ Solochrome Black T
hardness= wine/red
hardness removed=blue
what else added to hardness testing experiment
pH 10 buffer
how is EDTA stored and why
in plastic container sit has the ability to remove metal ions from glass
in hardness testing experiment what is all the hardness attributed to
calcium carbonate CaCO3
what does organic waste in water do
puts a demand on the dissolved oxygen which is necessary for aquatic life (plants and fish)
what decompose organic waste and how
bacteria and other organism and they use dissolved oxygen and convert waste into CO2 and H2O
Biochemical Oxygen Demand defn
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
BOD of clean water, treated sewage, raw sewage and silage effluent
clean water= 1-2 p.p.m.
treated sewage= 30p.p.m.
raw sewage= 400p.p.m.
silage effluent=54,000p.p.m.
