Comparison and Contrast Perhaps the most common assignment in a Composition course is the comparison and contrast essay. What could be easier?
These ions enter a water supply by leaching from minerals within an aquifer. Common calcium -containing minerals are calcite and gypsum.
A common magnesium mineral is dolomite which also contains calcium. Rainwater and distilled water are softbecause they contain few ions. Rain containing dissolved carbon dioxide can react with calcium carbonate and carry calcium ions away with it.
The calcium carbonate may be re-deposited as calcite as the carbon dioxide is lost to atmosphere, sometimes forming stalactites and stalagmites. Calcium and magnesium ions can sometimes be removed by water softeners. Carbonate hardness Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals calcium bicarbonate and magnesium bicarbonate.
The presence of the metal cations makes the water hard. However, unlike the permanent hardness caused by sulphate and chloride compoundsthis "temporary" hardness can be reduced either by boiling the water, or by the addition of lime calcium hydroxide through the process of lime softening.
Permanent hardness[ edit ] Permanent hardness is hardness mineral content that cannot be removed by boiling. Ions causing permanent hardness of water can be removed using a water softener, or ion exchange column. A major component of such scum is calcium stearatewhich arises from sodium stearatethe main component of soap: Synthetic detergents do not form such scums.
A portion of the ancient Roman Eifel aqueduct in Germany.
Hard water also forms deposits that clog plumbing. This precipitation formation of an insoluble solid is principally caused by thermal decomposition of bicarbonate ions but also happens in cases where the carbonate ion is at saturation concentration.
In boilers, the deposits impair the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat.
In a pressurized system, this overheating can lead to failure of the boiler. The softening of hard water by ion exchange does not increase its corrosivity per se. Similarly, where lead plumbing is in use, softened water does not substantially increase plumbo -solvency.
Calcium and magnesium hydroxides are both soluble in water. The solubility of the hydroxides of the alkaline-earth metals to which calcium and magnesium belong group 2 of the periodic table increases moving down the column.
Aqueous solutions of these metal hydroxides absorb carbon dioxide from the air, forming the insoluble carbonates, giving rise to the turbidity.
Hence, a common solution to the problem is, while maintaining the chlorine concentration at the proper level, to lower the pH by the addition of hydrochloric acid, the optimum value being in the range of 7.
Water softening It is often desirable to soften hard water.
Most detergents contain ingredients that counteract the effects of hard water on the surfactants.Click to share on Facebook (Opens in new window) Click to share on Twitter (Opens in new window) Click to share on Pinterest (Opens in new window).
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