Ask a New Question
Menu

What are nanoprotic and polyprotic acids Draw tifration curves (pH vs. volume of titrant) for:

(6) 10 ml 0.1 M Na,CO, with 0.1 M HCI

(ii) 25 ml 0.1 N HPO, with 0.1 N NaOH.

1 answer

Understanding the difference between monoprotic and polyprotic acids is crucial in the context of titration curves.

Definitions

  1. Monoprotic Acids: These acids can donate only one proton (H⁺) per molecule. Examples include hydrochloric acid (HCl) and acetic acid (CH₃COOH).

  2. Polyprotic Acids: These acids can donate more than one proton per molecule. Examples include sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and carbonic acid (H₂CO₃).

Titration Curves

Here, two different titrations will be described visually. Unfortunately, I can't create actual graphical figures, but I can help you understand how to plot these curves and what they would generally look like.

(i) Titration of 10 mL 0.1 M Na₂CO₃ with 0.1 M HCl

  • Starting State: 10 mL of Na₂CO₃ (a weak base, having two acidic protons to donate).
  • Titrant: 0.1 M HCl (a strong acid).

Titration Curve Shape:

  • As you add HCl, the pH will start high (around 10 for Na₂CO₃ in solution).
  • When you start adding HCl, you will first reach the first equivalence point where Na₂CO₃ is converted to NaHCO₃ (sodium bicarbonate).
  • The first equivalence point occurs at a pH of around 8.3.
  • After this point, further addition of HCl transforms NaHCO₃ into CO₂ and water, significantly decreasing the pH until it reaches below 7.
  • The second equivalence point would be observed where this transition occurs—typically, this would be near pH 4.7 for the conversion of sodium bicarbonate to carbonic acid.

The curve would exhibit a significant drop in pH around these equivalence points, forming the characteristic “S” shape.

(ii) Titration of 25 mL 0.1 N H₃PO₄ with 0.1 N NaOH

  • Starting State: 25 mL of H₃PO₄ (a triprotic acid).
  • Titrant: 0.1 N NaOH (a strong base).

Titration Curve Shape:

  • The pH starts relatively low because the solution contains H₃PO₄ (pH about 1.5-2).
  • The three pKa values of phosphoric acid are approximately 2.15, 7.2, and 12.4.
  • Initially, as NaOH is added, you will go through three distinct regions:
    1. The first equivalence point will occur around pH 2.15.
    2. The second equivalence point will occur around pH 7.2.
    3. The third equivalence point will occur around pH 12.4, marking the complete neutralization to PO₄³⁻.

The overall shape of the curve would show three significant jumps in pH at the three equivalence points, forming a step-like function on the graph.

Conclusion

In both titrations, you'll see different curves due to the nature of the acids—monoprotic vs. polyprotic. The key points of inflection in the titration curves are where the pH changes dramatically and are indicative of the neutralization events that are taking place.