If a solution of pure water and sodium hydroxide is titrated with H2SO4 for the alkalinity measurement. Then the correct option would be...a.The Phenolphthalein alkalinity will be the total alkalinityb.The Phenolphthalein alkalinity will be the bicarbonate alkalinityc.The Methyl orange alkalinity will be the total alkalinityd.The Phenolphthalein alkalinity will not be the total alkalinity
Question
If a solution of pure water and sodium hydroxide is titrated with H2SO4 for the alkalinity measurement. Then the correct option would be...a.The Phenolphthalein alkalinity will be the total alkalinityb.The Phenolphthalein alkalinity will be the bicarbonate alkalinityc.The Methyl orange alkalinity will be the total alkalinityd.The Phenolphthalein alkalinity will not be the total alkalinity
Solution
The correct option is d. The Phenolphthalein alkalinity will not be the total alkalinity.
Here's why:
Alkalinity is a measure of the ability of a solution to neutralize acid without changing the pH significantly. It is usually expressed in terms of equivalent concentration of calcium carbonate (CaCO3).
In a solution of pure water and sodium hydroxide (NaOH), the alkalinity is due to the hydroxide ions (OH-) from the NaOH. When titrated with sulfuric acid (H2SO4), these hydroxide ions are neutralized to form water.
Phenolphthalein is an indicator that changes color at a pH of 8.2, which is the pH at which all the hydroxide ions have been neutralized. Therefore, the Phenolphthalein alkalinity is the concentration of hydroxide ions.
However, the total alkalinity includes not only the hydroxide ions, but also any bicarbonate (HCO3-) and carbonate (CO3 2-) ions that may be present. In a solution of pure water and NaOH, there are no bicarbonate or carbonate ions, so the total alkalinity is the same as the Phenolphthalein alkalinity.
But in a solution that contains bicarbonate or carbonate ions, the total alkalinity would be higher than the Phenolphthalein alkalinity. Therefore, the Phenolphthalein alkalinity will not be the total alkalinity.
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