Volumetric Analysis and Acid-Base Chemistry
Volumetric Analysis and Acid-Base Chemistry
This domain tests titration calculations, standard solutions, indicator choice and acid-base definitions. The exam expects precise burette readings, correct mole ratios and a clear calculation from concordant titres.
Core rules
- A standard solution has a known concentration, prepared using a primary standard such as anhydrous sodium carbonate or potassium hydrogen phthalate.
- n = cV; at the equivalence point, moles of acid and base are in the ratio of the balanced equation.
- For a strong acid–strong base titration, phenolphthalein or methyl orange is suitable. For weak acid–strong base, phenolphthalein is preferred; for weak base–strong acid, methyl orange is preferred.
- Rinse the burette with the titrant, the pipette with the solution being measured, and the conical flask with distilled water.
- Use concordant titres within about 0.10 mL; the rough titration is not included in the average.
Worked example
25.0 mL of HCl is titrated with 0.100 M NaOH. Concordant titres average 23.40 mL. n(NaOH) = 0.100 × 0.02340 = 2.34 × 10^-3 mol. HCl + NaOH → NaCl + H2O is 1:1, so n(HCl) = 2.34 × 10^-3 mol. c(HCl) = n/V = 2.34 × 10^-3 / 0.0250 = 0.0936 M.
Traps
Read the bottom of the meniscus at eye level and record initial and final readings. Do not average non-concordant titres. Do not use the conical flask volume as the volume of acid unless the acid was pipetted into it. Match the indicator to the titration type, not just to colour.