Question

Which indicator is used to titrate sodium bicarbonate with hydrochloric acid?

• A. Starch
• B. Phenolphthalein
• C. EBT
• D. Methyl orange

Hint:

Think about the pH of the solution at the equivalence point of this titration.

Answer 1

The Correct Option is D

Step 1: Sodium bicarbonate, \(NaHCO_3\), is the salt of a weak acid (\(H_2CO_3\)) and a strong base. When titrated with HCl, a strong acid, the reaction is \(NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2\).

Step 2: At the equivalence point, the solution holds dissolved CO2 and carbonic acid, so the pH is acidic, around 3.5 to 4.

Step 3: The indicator must change color in this acidic range. Methyl orange changes color between pH 3.1 and 4.4, which matches the equivalence point.

Step 4: Phenolphthalein changes color between pH 8.2 and 10, so it would turn colorless well before the true endpoint and is not suitable here. \[\boxed{\text{Methyl orange}}\]