Comprehensive Study Notes on Titration Curves

Titration Curve Overview

  • A titration curve is a graphical representation showing how the pH of an acid solution changes as a base is added, or how the pH of a base solution changes as an acid is added.

Experiment Overview

  • This study focuses on the addition of a strong base to a strong acid solution.
  • Strong base used: 1 M NaOH (Sodium Hydroxide)
  • Strong acid used: 1 M HCl (Hydrochloric Acid)
  • Initial conditions: 25 mL of 1 M HCl in the beaker below a burette.
  • A pH meter is employed to monitor the pH of the solution.

Initial Conditions Before Addition

  • Before any NaOH is added:
    • Volume of HCl = 25 mL = 0.025 L
    • Moles of HCl = 1extmol/Limes0.025extL=0.025extmoles1 ext{mol/L} imes 0.025 ext{L} = 0.025 ext{moles}
    • Hydronium ion concentration ([H₃O⁺]): 0.1 M (derived from 1 M HCl)
    • Initial pH = 1

Monitoring Changes in pH

  • Adding 10 mL of NaOH:

    • Volume of NaOH added = 10 mL
    • Moles of NaOH = 1extmol/Limes0.01extL=0.01extmoles1 ext{mol/L} imes 0.01 ext{L} = 0.01 ext{moles}
    • New pH after addition = 1.37
    • Given the amounts, HCl is still in excess:
    • Moles of HCl remaining = 0.025−0.01=0.015extmoles0.025 - 0.01 = 0.015 ext{moles}

  • Adding 24 mL of NaOH:

    • Moles of NaOH with added volume:
    • Total volume = 24 mL
    • Moles of NaOH = 1extmol/Limes0.024extL=0.024extmoles1 ext{mol/L} imes 0.024 ext{L} = 0.024 ext{moles}
    • New pH = 2.69
    • At this point, the concentration of HCl is still present but in lower excess.

  • Adding 25 mL of NaOH (total):

    • Total moles of NaOH = 0.025extmoles0.025 ext{moles}
    • At this point, pH rises significantly to 7.
    • This point is termed the equivalence point:
    • At equivalence point:
      • Moles of NaOH = Moles of HCl = 0.025 moles
      • Reaction complete: ext{NaOH} + ext{HCl}
        ightarrow ext{NaCl} + ext{H}_2 ext{O}

Features Around the Equivalence Point

  • At the equivalence point (neutral pH = 7):
    • The solution has transitioned to being neutral due to complete neutralization of acid and base.
    • At this stage, only water and neutral salt (NaCl) remain in the solution.

After the Equivalence Point

  • Adding 26 mL of NaOH:

    • Total NaOH added = 26 mL
    • Resulting pH = 11.29
    • Small increments in NaOH lead to significant changes in pH due to excess base.

  • Adding 50 mL of NaOH:

    • Volume added = 50 mL
    • Resulting pH = 12.52
    • Moles of NaOH = 0.05 moles
    • The solution is now highly basic (as NaOH is in significant excess).

Titration Curve Characteristics

  • Shape of Curve:
    • The curve typically starts with a low pH (due to strong acid) and gradually rises with the addition of base.
    • Near the equivalence point, a sharp increase in pH is observed, resulting in an almost vertical section of the graph.
    • The pH at the equivalence point for strong acid-strong base titrations is always 7.
    • After the equivalence point, the curve appears as a reverse reflection of the section before the equivalence point.

Selection of Indicators

  • Suitable Indicators:
    • Effective indicators for this type of titration should change colors within the pH range of 3.6 to 10.4.
    • Recommended indicators include:
    • Bromothymol blue
    • Phenol red
    • Neutral red
    • These indicators are suitable since the pH at the equivalence point is 7, falling within these ranges.

Determining Equivalent Point Volume

  • To determine the volume of the base required to reach the equivalence point, a vertical line can be drawn from the equivalence point on the graph down to the x-axis, indicating that the volume needed in this case is 25 mL.

Conclusion

  • A titration curve provides a detailed insight into the acid-base reaction process, with key pH changes marked at significant points, particularly the equivalence point where neutralization occurs, illustrating the fundamental principles of acid-base chemistry.