The plot on the left shows you a calculated titration curve (a plot of pH vs. vol. base added) on a scale of pH=0 to 13 while the volume of added 1M NaOH runs from 0 to 100 mL.
The sliders below allow you to change the volume (v0 in mL) of a dilute acid sample that you titrate, it's initial concentration (c0 in M) and the pKa value of the acid.
Finally, you can switch between a mono-protic acid and a bi-protic acid in the popup menu at the bottom. We'll get to that later...

For the prelab, please draw sketches and write short answers into your lab note book. The comparison of three acids in question 2 to 4 might work well in a table format.

1. Strong Acid
When you first load the applet, the default values are set to a 50mL sample of a 0.3 M strong acid (pKa = 0). Fairly normal looking titration curve...
Vary the volume of your sample (v0). Then set the volume back to the initital value and vary the initial concentration. How does the equivalence point move? How does the equivalence volume depend on v0 and c0? Do you see any differences? Why or why not?

2. Weak Acid
Move the sliders back such that the curve shoots up roughly in the middle of the plot. Now vary the pKa value slowly and observe what happens to the plot. Draw a sketch of the titration curve for three qualitatively different cases (for example HCl, Acetic Acid, and the Ammonium Ion) in your lab note book.

3. Equivalence Point
The point with the steepest slope is the equivalence point. What is the chemical identify of the solution at this point for the three acids you picked in 2?
Once pKa is larger than 2, the applet also prints the pH value for the equivalence point.
Write down the pH of the equivalence point for your three acids. How does the pH of the equivalence point depend on the initial concentration of your acid sample?

4. Half-Equivalence point
A second point is marked as well: at half the amount of base added which is needed for a complete reaction. This is called the half equivalence point.
What is the chemical composition of your solution at this point for your three acids?
Given your chosen initial concentration, what is the concentration of these chemical species?
How does the pH of this point depend on the pKa value and the initial concentration?

5. Biprotic Acids
Switch the pull-down menu at the bottom to "Two Stage". This will add a second slider for the equilibrium constant for the second stage of acid dissociation for a biprotic acid. Because there are twice the number of protons per acid molecule now, you will have to reduce the volume of acid added to your sample to see the full curve in the window (for example V0 = 25 mL, c0 = 0.3 M). With both acid dissociation constants set to pKa1=0 and pKa2=0 the plot does not look much different from the initial plot for HCl.

a. Look through table C-20 at the end of your text book. Identify the polyprotic acids. What is a typical difference between pKa1 and pKa2? Why is pKa2 always larger than pKa1?

b. Adjust the pKa sliders to the values for carbonic acid (H2CO3), the stuff that makes drinks fizzy. There are now two steep parts in the titration curve. Write down the corresponding equilibria.

c. Four special points are marked. The two equivalence points (in the steep parts) and two half-equivalence points. Which chemical species are (mainly) present at each of those four points?

d. Reduce the volume of acid sample titrated (V0) until the curve moves close to the left edge (5 – 10 mL). Now vary the concentration of the acid sample titrated (c0). Which marked pH values change? Why only those?

e. Can you find the pKa values again in the marked points on the plot? Which pKa value is identical to the pH at which marked point? Move the sliders to identify the connections if you are not sure.

f. On which pKa values does the pH of the two equivalence points depend?

g. A simple mathematical operation connects pKa1 and pKa2 to the pH at the first equivalence point. Can you identify it?