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Hydroxide ion is a strong enough acid to deprotanate a certain indicator to give

ID: 1056623 • Letter: H

Question

Hydroxide ion is a strong enough acid to deprotanate a certain indicator to give a red colored compound. Phenoxides, however like the phenoxide obtained when acetaminophen reacts with hydroxide ion, are not strong enough bases to deprotonate that same indicator so the indicator does not turn red. A drop of this indicator is added to 2.00 liters of a solution of acetaminophen. After adding 22.6ml of 1.20M NaOH to this solution, the indicator turns red. What is the molarity of the original acetaminophen solution ? Hydroxide ion is a strong enough acid to deprotanate a certain indicator to give a red colored compound. Phenoxides, however like the phenoxide obtained when acetaminophen reacts with hydroxide ion, are not strong enough bases to deprotonate that same indicator so the indicator does not turn red. A drop of this indicator is added to 2.00 liters of a solution of acetaminophen. After adding 22.6ml of 1.20M NaOH to this solution, the indicator turns red. What is the molarity of the original acetaminophen solution ?

Explanation / Answer

From the law of dilution,

V1M1=V2M2

Here, V1 is the volume of NaOH and M1 is the molarity of NaOH.

V2 is the volume of acetaminophen and M2 is the molarity of acetaminophen.

22.6 mL*1.2 M = 2000 mL*M2

M2 =0.01695 M

Therefore, the molarity of the original acetaminophen solution is 0.01695 M