Draw the titration curve of H2C6H6O6 (ascorbic acid, diprotic) titrated with NaOH.

We can't draw structures or curves on this board but here is a link. It will look much like the titration curve for carbonic acid; I suspect you have a curve for Na2CO3 in your text. This would be the reverse of that.

http://www.google.com/imgres?q=titration+curves&hl=en&client=firefox-a&hs=sb2&sa=X&rls=org.mozilla:en-US:official&biw=776&bih=416&tbm=isch&prmd=imvnsfda&tbnid=A96RfAsc8VNp7M:&imgrefurl=http://www.sparknotes.com/chemistry/acidsbases/titrations/section1.html&docid=ki9lKNqM3PHweM&imgurl=http://img.sparknotes.com/figures/3/3a5994498f24d59f5d5d762b40844a2a/polycurve.gif&w=322&h=289&ei=q2NhT5PBMqre2QXIreyFCA&zoom=1&iact=hc&vpx=444&vpy=25&dur=6606&hovh=213&hovw=237&tx=171&ty=146&sig=110994422192062145360&page=1&tbnh=83&tbnw=92&start=0&ndsp=10&ved=1t:429,r:3,s:0

To draw the titration curve of ascorbic acid (H2C6H6O6) titrated with NaOH, we need to understand the step-by-step process of the titration and the behavior of the acidic and basic components involved.

Step 1: Understanding the Components
Ascorbic acid is a diprotic acid, meaning it can donate two protons (H+ ions) per molecule. In water, it partially dissociates into H+ ions and the ascorbate ion (C6H6O62-). NaOH is a strong base and completely dissociates into Na+ and OH- ions in water.

Step 2: Initial State (Before Titration)
In the beginning, we have a solution of ascorbic acid (H2C6H6O6) in water. It contains the ascorbic acid molecules and a small amount of H+ ions due to partial dissociation.

Step 3: Titration Start
We start adding NaOH solution (the titrant) to the ascorbic acid solution (the analyte) gradually. NaOH reacts with ascorbic acid in a neutralization reaction:

H2C6H6O6 + 2NaOH → Na2C6H6O6 + 2H2O

In this reaction, each molecule of ascorbic acid reacts with two molecules of NaOH, resulting in the formation of sodium ascorbate (Na2C6H6O6) and water.

Step 4: Initial Equivalence Point
As NaOH is a strong base, it neutralizes the first proton (H+) of ascorbic acid quickly. This point is called the Initial Equivalence Point (IEP) or the first half-equivalence point. At this point, half of the ascorbic acid has reacted, and the solution contains equal amounts of ascorbic acid and the corresponding salt, sodium ascorbate (Na2C6H6O6). The pH of the solution at this stage is relatively low, indicating an acidic medium.

Step 5: Intermediate Stage
As we continue to add NaOH, it reacts with the second proton (H+) of ascorbic acid:

H2C6H6O6 + 2NaOH → Na2C6H6O6 + 2H2O

During this stage, the pH of the solution starts increasing rapidly as the remaining ascorbic acid is neutralized. The solution becomes more basic as the concentration of the ascorbate ion (C6H6O62-) increases.

Step 6: Final Equivalence Point
This is the point where the second proton of ascorbic acid is neutralized completely by NaOH. It is called the Final Equivalence Point (FEP) or the second half-equivalence point. At this point, all of the ascorbic acid has been converted into sodium ascorbate. The pH of the solution is relatively high, indicating a basic medium.

Step 7: Beyond the Equivalence Point
If we continue to add NaOH after the FEP, the pH of the solution remains constant at a high value, indicating the excess of the strong base (NaOH) in the solution.

To draw the titration curve, plot the pH of the solution on the y-axis and the volume of NaOH added on the x-axis. Connect the points based on the behavior described above. Initially, the pH will be low, then increase sharply, reach a maximum at the FEP (pKa2), and remain relatively constant after that.

Keep in mind that the exact placement and shape of the curve will depend on the concentration of the ascorbic acid and NaOH solutions, as well as the specific pKa values of ascorbic acid.