Saturday, September 7, 2013

Acids and Bases Lab

Purpose- The purpose of this lab was to test for how different substances reacted with an acid (HCL) and a base (NaOH). We also tested for how resistant or susceptible each substance was to the acid and base. This determined if the substance was a buffer. In order to have a control group and a foundation for data comparison, we tested the effects of the base and acid on water. 

Introduction- In order to understand this lab, one must first be familiar with the properties of acids and bases. On the pH scale, the acids are at the lower ends of the scale (0-6), neutral substances in the middle (7), and basic substances in the upper end (8-14). The pH of a substance is determined to its relative hydrogen (H+) ion concentration and its relative hydroxide (OH-) concentration. Acids have a higher H+ concentration and bases have a higher OH- concentration. What this means is that acids are more likely to release or "donate" its H+ ions and bases are more likely to receive or "accept" H+ ions. 

 

             
     With the whole "donating and accepting" process in mind, the next step is to talk about substances that act as an equalizer of H+ ions. These substances are called buffers. Buffers absorb H+ ions and release it when needed, allowing it to balance and resist pH changes in that substance. 


Class Data





Material Tested Add
pH after adding this many drops



Material Tested Add
pH after adding this many drops









Graphs
Water's pH

















Orange juice pH

















Buffered Aspirin pH

















Chemical Added

Base=NaOH=red
Acid=HCl=blue

Method- During the lab, we followed an organized procedure. It is important to be as clear and organized as possible in the lab station, so we first labeled one of the 50mL beakers acid and the other base. The first substance we tested was the control group, water. We placed one of the probes that would record our data, the pH levels, into each beaker. Then, we added 5 drops of acid in one beaker and base in the other beaker. Stirring the HCl-water and NaOH-water solutions, we made sure that we would achieve the highest possible accuracy. After placing the probes in each solution, we were able to measure the changes in pH. We kept adding 5 more drops of acid and base until we reached 30 drops added in each solution. Cleaning the 50mL beakers and rinsing the probes, we made sure that we would not encounter any experimental error as we moved on from the control group to our next substance, orange juice. We followed the same procedure summarized above for orange juice and the buffered aspirin.


 

DiscussionThe pH of the acidic beaker and the pH of the basic beaker are at the opposite ends of the pH spectrum. The pH of the base is above 7 and the pH of the acid is below 7. The control group is ran with water in order to have a starting point of pH levels as we gradually add 5 drops until we reach 30.

Our results line up rather nicely with the class data. One other group tested the orange juice, and our data combined data did not vary significantly. After the first five drops of acid, the pH of the orange juice dropped to about 4.45 for both groups. After gradually adding the acid, the pH kept decreasing in order to signify the increased acidity. After thirty drops, the orange juice registered at about 4.36 pH. This shows that the already acidic orange juice does not act as a good buffer, and it reacts positively with the acid. It takes on acidic properties as the acid is added.
               Our validity for the buffered aspirin test is a little skewed. Our group, in the middle of the test, switched the probes so the basic probe went in to the acidic substance and vice versa. So our data up until the 15th drop is unreliable. However, as we cleaned and situated our probes into their proper places, we can see that the aspirin's reaction with the base and acid is as follows. The added acid greatly decreased its pH while the base increased it greatly. This goes to show that the buffered aspirin in fact is not a good buffer. It does not show that it has the potential to level out the pH levels due to its positive reactions with the acid and the base.
              
               Our data for the water test is somewhat reliable. The base increased its pH content but, somehow, the acid did not decrease it. In comparison with other groups, this should not be the case. The acid should have decreased the water's pH levels while the base should have (and it did) increase the pH levels. While starting out at the neutral 7 on the pH scale, as the base was added, the pH rose multiple degrees, sometimes even passing 11. The acid decreased the water's pH multiple degrees as well, for other groups. Ours, not so much. This could have been due to the fact that the probe wasn't working properly, or that we may have been taking our data wrong.



Conclusion-  We set out to complete this lab so that we could find which substance provides the best buffer. Buffers will not change pH very easily. According to our set of data and the class set of data, the substance that appears to provide the best buffer out of the substances tested is Orange Juice. This is because the total buffer range for Orange Juice in our set of data was .23, and some other team that tested Orange Juice calculated a total buffer change of .27. It was to our benefit of having access to the class data table, for we are know able to clearly see whether our data is validated by other experiments. .23 and .27 are very close values, so this serves to prove that there is a low chance that a significant experimental error occurred during our examination of Orange Juice. 




References-  

1 comment:

  1. Looking at your data...what determines whether or not a particular substance makes a good buffer? Is it a large discrepancy in pH between when you added acid and when you added base to the solution or is it a small one? What is the difference?

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