martinzoo

Today we did a acid-base titration experiment for Science. That means that we slowly added a base chemical (ammonia) to an acid chemical (vinegar) in small increments: we used teaspoons. This process was to determine how many teaspoons it took to take the acid to base.

Equal amounts of acids and bases can be added to each other to neutralize them if they are of a similar concentration. If you don’t know the concentration of your ingredients, this is one way to find out. We used 1/4 cup of vinegar, so if the concentrations were the same, it would have taken a 1/4 cup of ammonia to neutralize the vinegar.

You can do an online virtual acid-base titration experiment at this site.

*

Here are the supplies for this experiment: Household ammonia, distilled vinegar, red cabbage indicator (made from boiled water and red cabbage), a one teaspoon dropper, and several small bowls.

First we poured a 1/4 cup of vinegar into one of the bowls. Then we added enough of the red cabbage indicator to turn the vinegar bright red.

As you see here:

Next, to attempt to neutralize the acidity of the vinegar we started adding ammonia to the vinegar one teaspoon at a time, plotting our results on a graph as we went.

After three teaspoons it is still a red color.

Here, after 4 teaspoons, the vinegar solution is starting to turn purple, which indicates that it is near neutral.

We took the vinegar all the way to the base stage with the ammonia, and the results can be dramatically seen in this video. In the video we are at the fifth teaspoon, which was just at neutral. You can see how purple it looks. After adding two more teaspoons, we were at base with a nice green color.

And then, because GB was curious (this wasn’t part of the book’s experiment), we decided to see if we could reverse the process and take the obviously base vinegar/ammonia solution back to an acid state by adding vinegar…. same bowl… just more ingredients until it turned back to a red color. I didn’t think it would work because I thought we already had too many chemicals at work in the little bowl…. but it did.

I told him that he had acted exactly as a real scientist would have; he was curious about what would happen, made a guess about it based on the experiment he’d just done, and he did another experiment to find out if he was right.

In the end, we determined that 7 teaspoons was about half of what it should have taken to go from acid to neutral. But we went all the way to base with that, so our ammonia concentration was stronger than our vinegar concentration.