June 14th, 2007 <\/p>\n
Hardness is a term to describe water that doesn\u2019t allow soaping action, in other words no bubbles (lather) and no cleaning.\u00a0 The term \u2019soaping action\u2019 refers to the formation of micelles by negative ions joined to long carbon chains that dissolve in the fat or grease leaving the negative\u00a0charges outside the micelle structure.\u00a0These can then bond to the water molecules. In this way the hydrophobic grease is made to dissolve and lifts off the fabric or skin.<\/p>\n
Hardness\u00a0is due to Ca2+ or Mg2+ ions dissolved in the water. These ions react with the long negative ions of soap (stearate ions C17<\/sub> H35<\/sub> COO-) to make an insoluble grey compound which we call \u2019scum\u2019. As the reaction removes the necessary soap ions from the water it prevents lathering and the soap cannot perform its function. There are two subcategories of hardness: Temporary hardness is due to dissolved calcium (or magnesium) hydrogen carbonate Ca(HCO3)2, it can be removed by boiling the water, when the hydrogen carbonate ions decompose forming insoluble calcium (or magnesium) carbonate:<\/p>\n Ca(HCO3<\/sub>)2<\/sub> \u2013> CaCO3<\/sub> + CO2<\/sub> + H2<\/sub>0<\/p>\n Permanent hardness (due to dissolved calcium and magnesium sulphates and chlorides) must be removed by another method either:<\/p>\n 1. ion exchange using resins etc. Ca2+ + CO3(2-) \u2013> CaCO3(ppt)<\/p>\n
\nHardness can be removed by various means depending on the other ion that is dissolved with the Mg2+ or Ca2+ ions.<\/p>\n
\n1. Temporary
\n2. Permanent<\/p>\n
\n2. chemical precipitation<\/p>\n