 We're going to do a demonstration illustrating strong acids, weak acids, and buffers. We have three graduated cylinders. The graduate cylinder on the left contains two molar hydrochloric acid, a strong acid. The graduate cylinder in the center has two molar acetic acid, a weak acid. The graduate cylinder on the right contains a buffer mixture of two molar acetic acid and two molar sodium acetate. I'm going to add a little bit of universal indicator to each of the solutions. I'm now going to add some solid calcium carbonate to each one of the graduated cylinders. What we want to do is look at the rate at which the carbon dioxide is produced, which would be dependent upon the hydrogen ion concentration in each of the graduated cylinders. We see a very rapid evolution of carbon dioxide gas from the cylinder containing the hydrochloric acid. The strong acid solution has a high concentration of hydrogen ions. We'll add the same amount of calcium carbonate to the acetic acid. You can see that we're getting carbon dioxide produced, but at a much slower rate than the solution of hydrochloric acid. The two molar acetic acid has a much lower hydrogen ion concentration than the two molar hydrochloric acid. We will add the same amount of calcium carbonate to the buffer solution. The buffer solution contains the weak acid in the conjugate base, and it has a higher pH than the solution of just the weak acid. This results in a lower hydrogen ion concentration. We can see the very slow evolution of CO2 due to this lower hydrogen ion concentration.