Question

Who do you figure out alkalinity in chemisty?

Answer 1

Alkalinity has been defined in a number of ways . However, in the simplest sense - " Alkalinity is considered as the quantitative capacity of an aqueous solution to neutralize an acid. "

Figuring out Alkalinity :

Alkalinity is equal to the stoichiometric sum of the bases in solution. Since in nature carbonate alkalinity causes most of the total alkalinity ( A_T), due to common occurence and dissolution of carbonate rocks, and also presence of carbon di- oxide in the environment. Besides this there happen to be other common natural components which do contribute to alkalinity . A few of them are borate , hydroxides, phosphate, silicates , dissolved ammonia ,and conjugate bases of some organic acids.

Alkalinity is usually given in the unit m Eq / L ( milliequivalent per liter ). Commercially , it is reported as

"parts per million of equivalent calcium carbonate ( ppm CaCO3 ) " , or typically as mg / L as CaCO₃

It is reported as total alkalinity (A_T ) which is stoichiometrically equal to,

A_T  =[ HCO₃^- ] _T + 2[CO₃^2- ]_T + [ B (OH)₄^- ]_T + [OH^- ]_T + 2[PO₄^-2 ]_T + [ SiO (OH)₃^- ]_T

- [ H⁺ ] - [HSO₄^-  ]

Determination of Alkalinity - Take 100ml of filtered sample in a conical flask and add to it a few drops of phenolphthalein indicator. Now, titrate the solution with 0.02N HCl till colorless. Add a few drops of methyl orange indicator at a stage when the solution becomes colorless and again titrate till a reddish orange color is obtained,indicating the end point. The nature of alkalinity is then predicted from such titration as below-

1. If titration to the phenolphthalein end point is zero, tha alkalinity may be regarded as due to bicarbonate alone.
2. When there is no further titration to methylorange end point after phenolphthalein end point the alkalinity is solely due to the hydroxide.
3. When phenolphthalein end point titration is half the total titration, only carbonate alkalinity is expected to be present.
4. When the phenolphthalein end point is greater than half the total titration , the alkalinity is due to both carbonate and hydroxide.

5. When phenolphthalein end point is less than half the total titration, the alkalinity is due to carbonate and bicarbonate.  

........Further , it is noteworthy that alkalinity is sometimes incorrectly used interchangeably with basicity. For example the pH of a solution can be lowered by addition of CO2 . This will reduce the basicity; however , alkalinity will remain unchanged.