Every drop counts.
At equivalence, acid and base have reacted in their balanced-equation proportions. The end point is the experimental signal, often a colour change. They should be close, but they are different concepts.
A strong acid–strong base titration has an equivalence pH of 7 at 25 °C. A weak acid–strong base titration has a buffer region and an equivalence pH above 7. At half-equivalence for a weak monoprotic acid, pH = pKa.
In conductometric titration of HCl with NaOH, highly mobile is replaced by less mobile Na⁺ before equivalence, reducing conductivity. Excess OH⁻ raises conductivity afterwards. Use the intersection of the two trends to locate equivalence.
Add a little. Watch a lot.
25.00 mL of 0.100 M monoprotic acid + 0.100 M NaOH, 25 °C. Ideal charge-balance calculation. Equivalence is at 25.00 mL. Pink approximates a phenolphthalein endpoint; the blue tint is only schematic.
Explore: Follow the curve through equivalence and explain the chemistry on either side.
25.00 mL HCl requires 18.60 mL of 0.1000 M NaOH at equivalence. Calculate the HCl concentration.
- n(NaOH) = 0.1000 × 0.01860 = 0.001860 mol.
- n(HCl) = 0.001860 mol.
- c(HCl) = = 0.07440 mol .
Answer: 0.0744 mol
Assumed knowledge
n = cV and converting mL to L; accurate volumetric measurements.
Learning checkpoints & source
YOUR SYLLABUS CHECKPOINT- Read equivalence points and buffer regions.
- Use titration data to calculate concentration.
- Interpret conductivity changes.