Titration: Unknown Acid Concentration
Strong acid + strong base. V_a is known; C_a is hidden. Find the equivalence volume from the pH jump at several titrant concentrations and recover C_a from a fit of V_eq versus 1/C_b.
Goal
Determine C_a from C_a V_a = C_b V_eq. Plotting V_eq versus 1/C_b gives slope C_a V_a, so C_a = slope / V_a.
Equipment
- Burette (strong base)
- Pipette / flask (known V_a)
- pH meter
- Universal indicator
Experiment
Theory
At equivalence of a monoprotic strong–strong titration, moles of acid equal moles of base: C_a V_a = C_b V_eq (volumes in the same units). The pH jumps through 7 there. The bench never shows C_a, V_eq, or a “jump to equivalence” control.
Procedure
- Aliquot V_a is fixed and known. Acid concentration is hidden. You set the titrant C_b and the burette V_b.
- Watch the pH meter and indicator colour. When you judge the jump (equivalence), record — the row stores that V_b as your V_eq. The bench does not auto-detect the end point.
- The notebook computes 1/C_b. Repeat for at least 6 titrant concentrations from about 0.05 M to 0.20 M.
- Fit V_eq versus 1/C_b; C_a = slope / V_a. Compare with the reference.
Conclusion
The fitted acid concentration agrees with the hidden C_a. Main uncertainties: judging the end point by eye and assuming a sharp strong–strong jump.