Chemical Characteristics of water | |||||||||||
Acidity:Acidity or alkalinity is measured by pH. PH measures the concentration of Hydrogen ions in water. Ionization of water is
HOH H+ + OH-
In neutral solutions [OH] = [H] hence pH = 7If acidity is increased, [H] increases and pH reduces from 7 (because H is log of [H]). The value of pH of water is important in the operations of many water and waste water treatment processes and in the control of corrosion. | |||||||||||
Alkalinity:The values of pH higher than 7, shows alkalinity. The alkaline species in water can neutralize acids. The major constituents of alkalinity (or causticity) are OH-, CO32- and bicarbonates HCO3 ions. Alkalinity in water is usually caused by bicarbonate ions.Hardness of water: Definition of hard waterHardness is the property that makes water to require more soap to produce a foam or lather. Hardness of water is not harmful for human health but can be precipitated by heating so can produce damaging effects in boilers, hot pipes etc by depositing the material and reducing the water storage and carriage capacity.Absolute soft water on the other hand is not acceptable for humans because it may cause ailments, especially to heart patients. Hardness in water is commonly classified in terms of the amount of CaCO3 (Calcium Carbonate) in it.
Table 1 - Degree of Hardness
Low level of hardness can be removed just by boiling but high degree of hardness can be removed by addition of lime. This method has also the benefit that iron and manganese contents are removed and suspended particles including micro-organisms are reduced.
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Arches An arch is an opening spanned by a collection of wedge shaped pieces ( voussoirs ) which stay in position by pressing in on one another. The joints between the pieces appear to radiate from some central point lying within the opening, and sometimes from points which lie outside, so every type of arch has a characteristic curvature. The simplest and visually most natural shape for an arch is the semicircle but many other designs have been used. How an Arch "Works" The central voussoir ( keystone ) is traditionally the last to be set into position to "lock" the whole thing into a strong and stable structure. A keystone is not always necessary, however; there may be a joint at the apex instead, as is common in Gothic arches. Gravity tries to pull the keystone downwards, but the thrust is carried on either side by the voussoirs immediately flanking it. These in turn have their total thrust carried through the whole semicircle of pieces in a sideways direc...
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