Acids, Bases and Buffers Lab
The experimental results for part one is as follows:
Part One Data Table
| Initial pH| Final pH|
Test Tube A| 6| 1|
Test Tube B| 4| 4|
Test Tube C| 4| -----|
Test Tube D| 4| 4|
Test Tube E| 6| 11|
The experimental results for part two is as follows:
Part Two Data Table
| Before CO2 was Added| After CO2 was Added|
Colour| Blue/green| Light green/yellow|
pH Level| 8.0pH| 5.0pH|
For thousands of years, people have known lemon juice, vinegar, and many other foods taste sour. However, it was not until a few hundred years ago that it was discovered that these foods tasted this way because they were all acids. In the seventeenth century, the Irish writer and amateur chemist Robert Boyle first labeled substances as either acids or bases. He noted that acids tasted sour, are corrosive to metals, change litmus red, and become less acidic when mixed with bases. On the contrary, bases felt slippery, changed litmus blue, and became less basic when mixed with acids. In the late 1800s, the Swedish scientist Svante Arrhenius believed that acids are compounds that contain hydrogen and can dissolve in water to release hydrogen and can dissolve in water to release hydrogen ions into solution. He also defined bases as substances that dissolve in water to release hydroxide ions into solution. Finally, in 1923, the Danish scientist Johannes Bronsted and the Englishman Thomas Lowry altered Arrhenuis’ theory slightly, saying acids and bases are substances that are capable of splitting off or taking up hydrogen ions respectively. In 1909, the Danish biochemist Sören Sörensen invented the pH scale for measuring acidity. The pH scale ranges from 0 to 14, where substances with a pH between 0 and less than 7 are acids, substances with a pH greater than 7 and up to 14 are bases, and a substance is considered neutral when they have a pH level of 7.
In part one of the acids, bases and buffers lab, only the pH levels of test tube A changed over the course of the experiment. The initial pH in test tube A was 6, and the final pH was 1. This shows that when 5mL of the 0.1M hydrochloric acid was added, the pH level dropped, causing the substance in test tube A to become more acidic. The hydrochloric acid completely ionized in the water, making it as strong as H3O+ due to the leveling effect of water. While in test tube B, the initial and final pH levels remained at 4 even though 5mL of 0.1M hydrochloric acid was added to the buffer solution. When the hydrochloric acid was added to this buffer, the added hydronium ion reacted with the strongest base in the medium, namely the acetate ion, and formed more acetic acid. This reaction consumed the added hydronium ion, preventing the pH levels from rising drastically and was responsible for the buffering effect. As a result of adding acid to the buffer, the concentration of acetate decreased and the concentration of acetic acid increased. The solution acted as a buffer because nearly all of the added hydronium ion is consumed by reaction with acetate. Thus, because of the buffer solution in test tube B, the pH levels remained the same while the pH levels in test tube A decreased.
In test tube D, the initial pH and final pH remained constant at a level of 4. The results remain the same because of the buffer. When sodium hydroxide was added to the buffer solution, the hydroxide ions were removed when they reacted with the acetic acid molecules. This prevented the pH of the solution from significantly rising, which it would have if the buffer solution was not present. While in test tube E, the initial pH was 6 and the final pH was 11. This is so because sodium hydroxide was added to the distilled water, resulting in the solution to become basic since the concentration of OH- decreased. The final test tube, which was test tube C, had an initial pH of 4. This would be considered the control, as it acted as a constant for the other test tubes to be compared to throughout the experiment. It was important to have test tube C to stay constant so that in the end, all of the test tubes would have different solutions in them. For example, in the end test tube A contained an acidic solution, test tube B had a buffered solution where an acidic solution was added, test tube D had a buffered solution where a basic solution was added, test tube E had a basic solution, and finally test tube C had a buffered solution which was left untouched. Thus, test tube C played an important role in the lab.
Buffering is extremely important in the human system. One of the uses of buffering in the body is to control the pH levels in the blood. This buffer system is composed of carbonic acid and the bicarbonate ion. When the blood becomes more basic than it should be, the carbonic acid is released, which brings the blood back up to the pH level it should be. Also, when carbonic acid is used, it forms the bicarbonate ion after the hydrogen has been donated. The same applies when the blood becomes too acidic. The bicarbonate ion is released bringing the pH back up to where it should be and producing carbonic acid. Other examples of buffering takes place during biochemical reactions involved in vital processes like metabolism, respiration, the transmission of nerve impulses and muscle contraction and relaxation take place within a narrow pH range. Without the buffering systems, human beings would not be able to survive.
http://www.chemguide.co.uk/physical/acidbaseeqia/buffers.html http://www.science.uwaterloo.ca/~cchieh/cact/applychem/waterchem.html http://www.visionlearning.com/library/module_viewer.php?mid=58