With the titration of a diprotic acid, we now have to keep in mind the existence of 2 equivalence points as well as all the equations and calculations involved between those two. If we take a look here, we're going to say, as always, we should determine what the equivalence volume will be in terms of our titrant. Here, our diprotic acid will serve as the analyte and our strong base will serve as the titrant. Because we have the existence of 2 equivalence points, we're going to have to find 2 equivalence volumes. We're going to say here first that molarity of my acid times the volume of my acid equals molarity of the base times the first equivalence point. When we input the values, we have 0.100 M × 100 mL = 0.050 M × the first equivalence point . Divide both sides here by 0.050 M. Our first equivalence volume would be 200 milliliters. That's how much it takes to get to the 1st equivalence point. To get to the 2nd equivalence point, we would just need another 200 milliliters. We would need 400 milliliters total to get to the second equivalence point.

All right. Now, before we've added any strong base, we essentially just have a weak diprotic acid. With a weak diprotic acid, we have to employ the chart. From that information, we can set up our equilibrium expression. With this first point in our before we get to our real titration, we're dealing with the removal of the first acidic hydrogen. This first acidic hydrogen from our sulfuric acid solution will be donated to water. We'll create bisulfite as a product as well as H3O+. Because we're talking about removing the first H⁺ ion, that means we're dealing with Ka1 for sulfuric acid is equal to 1.6 × 10-2. We'd use that Ka value here within our equilibrium expression. Remember, we can always do the 5 percent approximation method to see if I ignore the minus x within my equilibrium expression? You would take the initial concentration of your weak diprotic acid which is 0.100 M and you divide it by the k that we're using which is 1.6 × 10-2. If you do that, you'll find that this ratio is not greater than 500. Therefore, you would not be able to ignore this minus x. We would keep the minus x and as a result have to use the quadratic formula to solve for x itself. Once you have that value for H⁺, you could just take the negative log and from that, you can find the pH which is 1.48. Just remember, at this point, the titration technically hasn't begun yet. Once we start adding our strong base to our sulfuric acid solution, then our titration can commence. We're going to have to be aware of where exactly within the titration are we dealing with calculations. Are we dealing with at the equivalence point, before the equivalence point, or after to add KOH to our sulfuric acid solution.