Two acids X and Y of the same concentrations were reacted with 0.1 mole of aqueous sodium hydroxide.
Which one of the following statements explains why a larger volume of X would be required to achieve the end-point as compared to Y?
A) X is a strong acid and Y is a weak acid.
B) X is a weak acid and Y is a strong acid.
C) X is a monobasic acid and Y is a dibasic acid.
D) X is a dibasic acid and Y is a monobasic acid.
Answer: C
- Strong acids ionise completely in water. Weak acids ionise partially in water.
- However, when acids react with sodium hydroxide, all the hydrogen ions will be completely reacted (regardless of whether the acid is strong or weak).
→ A and B are not correct.
- Monobasic acid contains 1 mole of hydrogen ion per mole of acid; dibasic acid contains 2 moles of hydrogen ions per mole of acid.
- Since a dibasic acid contains more hydrogen ions, we will require less of it to react away 1 mole of sodium hydroxide.
→ Y is a dibasic acid.
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