To draw a titration pH curve for the titration of 25 mL of 0.1 N H₃PO₄ (phosphoric acid) with 0.1 N NaOH (sodium hydroxide), we can outline the main features of the curve.
Key Information:
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H₃PO₄ is a triprotic acid: It has three dissociable protons.
- First dissociation (strongest): KA1 ~ 7.5 x 10^-3
- Second dissociation: KA2 ~ 6.2 x 10^-8
- Third dissociation: KA3 ~ 4.8 x 10^-14
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Neutralization: The pH change will occur at three significant points corresponding to the neutralization of the three protons:
- First endpoint: pH ~ 4.7 (neutralization of the first proton)
- Second endpoint: pH ~ 7.2 (neutralization of the second proton)
- Third endpoint: pH ~ 12.5 (neutralization of the third proton)
Titration Process:
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Initial Point: Start with a pH of around 1.5 to 2, based on the concentration of the phosphoric acid.
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From 0 to 25 mL: As NaOH is added, the pH will rise gradually due to the neutralization of the first proton. The pH will steeply rise around the first equivalence point (at around 8.3 mL of NaOH added).
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Between First and Second Equivalence Points (8.3 to 25 mL NaOH): The pH will continue to rise more gradually but can show a noticeable rise around the second equivalence point (approximately 16.6 mL NaOH added).
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From 25 to ~33 mL: After the second equivalence point, the pH will rise steeply again before leveling off as it approaches the third equivalence point at around 25 mL (+ additional amounts of NaOH). The curve will again shift upward sharply near the pH of 12.5 as it transitions through the third equivalence point.
Titration Curve Sketching:
- Y-axis: pH (0 to 14)
- X-axis: Volume of NaOH added (0 to about 33 mL)
- Start at a low pH (around 2).
- Gradually increase and steeply rise around the first equivalence point (8.3 mL).
- Level off and then rise gradually toward the second equivalence point (approximately 16.6 mL).
- Steep rise at the second equivalence point and then level off before the third equivalence point.
- Sharp increase around the final pH point as excess NaOH is added.
In graphical form, the curve would show three notable points of steep ascent corresponding to the neutralization of each hydrogen ion from the phosphoric acid, with the overall trend being a gradual increase in pH.
Please note: To physically draw it, you'll use graphing tools but the above description should guide you in plotting the key features of this titration curve.
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