WATER
Water=excellent solvent- used in many chemical reactions- easily contaminated/polluted
Hard Water= water that will not easily form lather with soap
Temporary Hardness= hardness can be removed by boiling- caused by presence of Calcium and Magnesium hyrdrogencarbonate
found where there is limestone (CaCO3)calcium carbonate in the earth
CO2 in the air reacts with rainwater to form carbonic acid.
Carbonic acids react with CaCO3 forming calcium hydrogencarbonate Ca(HCO3)2 which is soluble in water.
H2CO3 + CaCO3 r Ca(HCO3)2 to remove temporary harness by boiling: Ca(HCO3)2 + heat r CaCO3 + CO2 +H2O
Forms calcium carbonate which is precipitated out and called limescale
Soap is a sodium salt of Stearic Acid = long chain fatty acid
Soap scum is formed when the Ca2+ ion reacts with the soap.
This causes an insoluble salt (Calcium Stearate) to precipitate out and thus forms a scum
Soap softens hard water by removing the Ca2+ ions from the water
Permanent Hardness cannot be removed by boiling
Caused by presence of Ca2+ and Mg2+ ions of sulphate and chloride
Can be removed by ion exchange and distillation
Distillation involves boiling water + then cooling the vapour
removes all dissolved solids and liquids
expensive on a large scale
Addition of washing soda hydrated sodium carbonate can be used to soften the water as the carbonate ion reacts with the Ca2+ ions and remove them as insoluble CaCO3
Ca2+ + CO32- r CaCO3
Ion exchange units that are involved in water softening have cation-exchange resin which exchanges positive ions (Ca2+ and Mg2+) in water for Na+ ions
Ca2+ ions remain on the resin
resin loses all Na+ ions but can be regenerated by passing concentrated NaCl solution throught the column