Acids and Bases Lab

Purpose: The purpose of this lab is to see how certain substances react to certain pHs, also to find buffers. The relationships between the dependent and independent variables is that the independent variable is water, the dependent variable is the sodium bicarbonate, orange juice, spinach, and other substances. We did this to figure out which buffers work best.

Introduction: Buffers are aqueous (dissolved in water) solutions with a very stable pH. Even when acids or bases are added to it, it resists changes in pH. Buffers are made by adding a weak acid or base and its conjugate. They are able to remain in the solution without neutralizing each other. As hydrogen ions are added to the buffer, they are neutralized by the base, and hydroxide ions are neutralized by the acids. This prevents the addition of acids or bases from having any significant effect on the pH of a solution.

Methods: In this lab, we used vernier lab quest probes to track the pH of the substances as we added acids and bases. We set up the lab by cleaning off the probes and setting them in a beaker about half way full of clean water. We then took our first substance (water) and put 20 mL in two beakers. We set the probes into these beakers and tracked their starting pH. After we had found that, we began adding acid to one beaker and a base to the other beaker 5 drops at a time. Every 5 drops we would record on our lab quest the change in the pH. We then rinsed off the probes and cleaned the beakers. After all cleaning was done we repeated the adding of acid and base to the 2 other substances, Gelatin and sodium bicarbonate.

Data:

                                                                Sodium Bicarbonate
Graphs and Charts:

Gelatin

 Water

Discussion: By taking a quick glance at our data you can see that the best buffer we tested was the sodium bicarbonate. The increase in pH was very small. When we added acid, the pH only decreased by .34.  This is quite small in comparison to our worst buffer, water whose difference was 4.01!  While looking at our data, some trends I noticed were in water, the pH increased very quickly when NaOH was added. This must be partly due to the fact that NaOH dissolved well in water. I would question the validity of our data however, because as you can see this trend doe not just occur in water it occurs in Gelatin too. If you took a look at our data table for gelatin, our starting pH was off by a whole 3.23. Also, our sodium bicarbonate was off by .56.We should have payed closer attention to the starting pH and not just assumed it was the same. Next lab, we need to be more alert to our data and if we see a mistake correct it so as to have the most accurate data possible. Even though this data may have screwed up the numbers a bit, it still shows the trend that Gelatin is in fact not a good buffer. The pH still had a high change of 1.65 for the NaOH and 3.50 for the HCL.  If we quickly take a look at the trend of the sodium bicarbonate you see that the numbers remain fairly close to their starting pH. The base beaker started at 9.17 and ended at 9.35, while the acid beaker started at 8.61 and ended at 8.27. Overall, I feel that our data could have been much mo accurate and would have made the trends much more obvious to us. Despite these mistakes, we can see that some substances make better buffers than others.

References:
Helmestine, Anne M. "Buffers." About.com. chemistry.about.com, 21 Mar. 2011. Web. 08 Sept. 2013. 

Reece, Jane B., and Neil A. Campbell. "Chapter 3.3." Campbell Biology / Jane B. Reece ... [et Al.]. Boston: Benjamin Cummings, 2011. N. pag. Print.