In this video, we're going to review buffer solutions. So recall from your previous chemistry courses that buffers are substances that resist changes to pH, and this is true even when small to moderate amounts of a strong acid or base are added. In other words, when small to moderate amounts of a strong acid or base are added to a buffer solution, the pH of that buffer solution is only going to change a little bit in comparison to the pH change that we would see if the same amount of a strong acid or base were added to an unbuffered solution. Down below in our example, we have 4 different scenarios numbered 1, 2, 3, and 4. In the first two scenarios on the left, we're adding a small amount, just 1 milliliter of a strong acid, hydrochloric acid, with a concentration of 0.1 molar. In the first scenario over here, notice that the solution in our Erlenmeyer Flask is an unbuffered solution. When we add this little bit of a strong acid to the unbuffered solution, notice that the pH drops significantly. The pH indicator inside of the solution changes color from a blue color to a pink color to show the change in the pH that we see in this unbuffered solution.
On the right, we're here in scenario 2 where we have a buffered solution. When we add the same exact amount, the same exact small amount of a strong acid, notice that the pH remains relatively stable and the pH indicator does not change color. It has a blue solution up above and it remains blue to show that the pH remains relatively stable and does not change. The point here is to show that the buffered solution is able to resist changes in pH.
In scenarios 3 and 4, in a similar way, we're adding a small amount, this time of a strong base, sodium hydroxide, with a concentration of 0.1 molar. In scenario 3, we have an unbuffered solution, and when we add that small amount of a strong base to the unbuffered solution, notice that the pH increases significantly. The solution is unbuffered. You'll notice there is a color change from a blue color up above to a purplish color down below to show that the pH changed. Again, with the buffered solution, when we add that same small amount of a strong base to the buffered solution, notice that the pH remains relatively stable. We have the same color up above and down below: light blue, to show there is no significant color change. Again, the major takeaway here is that buffers can resist changes in pH.
Now, on the right, we're reminding you guys that the Henderson-Hasselbalch equation can be used to prepare buffer solutions. Recall from our previous lesson videos that the Henderson-Hasselbalch equation is expressed as follows: pH=pKa+logconcentrationofconjugatebaseconcentrationofconjugateacid. In our next practice videos, we'll be able to practice utilizing the Henderson-Hasselbalch equation while preparing buffer solutions. I'll see you guys in that practice video.
