 We're going to look at the buffering action of Alka-Seltzer. What we want to look at first is a solution that is not a buffer. We have some distilled water, and we've added a little bit of Bromthymol blue to it. Bromthymol blue is blue and basic solution, yellow and acidic solution, and green and neutral solution. I'm going to add some one molar HCl to the solution. The solution immediately turns yellow. The solution has turned fairly acidic. The pH has dropped rapidly. I'm again going to start with 100 milliliters of distilled water, and I'm going to add an Alka-Seltzer tablet. I'm also going to add a couple of drops of Bromthymol blue. Add one molar HCl. After adding 60 drops, the solution turns yellow. The buffer has maintained a relatively constant pH for a long time.