Question

Which of the following cause alkalinity in natural water?
(A)Sodium carbonate
(B)Potassium carbonate
(C)Potassium bicarbonate
(D)All of the above

Answer 1

Hint:We know that the alkalinity of water refers to its capacity to neutralize acids or to resist changes in pH range. It is a measure of the concentrations of three basic ions: carbonates ($C{{O}_{3}}^{2-}$ ), bicarbonates ($HC{{O}_{3}}^{-}$), and hydroxides ($O{H}^{-}$) in water. So we will check whether these given compounds are having any of these ions or not.

Complete step-by-step answer:-Alkalinity is the capacity of water to resist acidification or it can be said as a measure of the capacity of water to neutralize acids present in the body. It is measured on a pH scale that ranges from 0 to 14 where 0 to 6.99 is acidic, 7 is neutral and above 7, upto 14 is alkaline or basic.
-The alkalinity of water is primarily due to the presence of carbonates ($C{{O}_{3}}^{2-}$ ), bicarbonates ($HC{{O}_{3}}^{-}$), and hydroxides ($O{H}^{-}$) ions. Also to increase the pH of the natural lake water we can use these salts which is also known as ‘Liming’.

-The presence of carbonate and bicarbonate salts can be easily tested by adding hydrochloric acid which will liberate carbon dioxide gas. This gas is then passed through a container of lime juice which turns into white color.
(A)Sodium carbonate: When we add HCl to the salt, it starts bubbling and carbon dioxide is liberated which is then certainly passed through a beaker of lime juice. The juice color gets changed to white and hence this salt contains carbonate or bicarbonate ions.
(B)Potassium carbonate: Here also when we add HCl to the salt, it starts bubbling and carbon dioxide is liberated which is then certainly passed through a beaker of lime juice. The juice color gets changed to white and hence this salt contains carbonate or bicarbonate ions.
(C)Potassium bicarbonate: Here also when we add HCl to this salt, it starts bubbling and carbon dioxide is liberated which is then certainly passed through a beaker of lime juice. The juice color gets changed to white and hence it contains carbonate or bicarbonate ions.
-From the above data we may conclude that all the three salts cause alkalinity in natural water.

Hence the right option is: (D) All of the above.

Note:-Using these salts to increase the pH of natural lake waters is only a temporary solution. Another alternative is “Continuous Laminar Flow Inversion and Oxygenation”, a process of continuous lake inversion and lake aeration from surface to bottom.
-The alkalinity of natural water is generally determined by the soil and bedrock through which it passes.