Textbook Question
Which of the following mixtures has the higher pH? (a) Equal volumes of 0.10 M HCN and 0.10 M NaOH (b) Equal volumes of 0.10 M HClO4 and 0.10 M NaOH
18. Aqueous Equilibrium
Intro to Acid-Base Titration Curves
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What is the pH at the equivalence point when titrating a 0.200 M solution of sodium hydroxide (NaOH) with 0.200 M HBr?
A
9.0
B
3.0
C
7.0
D
5.5
Verified step by step guidance1
Identify the type of titration: This is a strong acid (HBr) titration with a strong base (NaOH). In such titrations, the pH at the equivalence point is typically neutral, which is pH 7.0.
Write the balanced chemical equation for the reaction: \( \text{NaOH} + \text{HBr} \rightarrow \text{NaBr} + \text{H}_2\text{O} \). This shows that NaOH and HBr react in a 1:1 molar ratio.
Determine the moles of NaOH and HBr: Since both solutions have the same concentration (0.200 M) and react in a 1:1 ratio, the moles of NaOH will equal the moles of HBr at the equivalence point.
At the equivalence point, all the NaOH has reacted with HBr to form water and NaBr, a neutral salt. Therefore, the solution is neutral, and the pH is 7.0.
Conclude that for strong acid-strong base titrations, the pH at the equivalence point is always 7.0, regardless of the concentrations, as long as they are equal and the reaction goes to completion.
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