Friday, September 13, 2013

Acid and bases lab

Acid and Bases Lab

Purpose- The purpose of this lab was to find what were the best buffers in terms of the change in pH in our substance, which was Soduim Bicarbonate. The concept we tested was the effects these buffers had by adding acids and bases to a small portion of each substance. 

Introduction- This lab was about what substances were the best buffers in terms of pH by adding acids and bases to an equal portion of each substance. An acid is a substance that increases the hydrogen concentration of a solution. A base is a substance that increases the hydrogen ion concentration of a solution. Both the acidity or base can by measured by pH, which is a scale from 1 to 14 that measures the hydrogen ion concentration of a solution. If the concentration is measured from 1 to 6, it is acidic, 7 is neutral, and 8-14 is basic. Almost all substances have a pH, many are in our bodies. However, our bodies can't handle that type of dramatic change in pH, so buffers keep substances around the same pH. This experiment was to see what substance made the best buffer.

Methods- To begin the experiment, our group filled two 20 milliliter beakers full of water for a control test. We then put in five drops of acid into one, and five drops of a base into the the other. Then using the Vernier probes, we made a graph calculating the rise or fall of pH in each beaker, and we did increments of 5 drops at a time up until 30 drops. After our control test was done, we then did the same thing to Sodium Bicarbonate. On each graph, we measured the change in pH until 30 drops or acid or base was added to both beaker.
Danny measuring out 20 milliliters of Sodium Bicarbonate.

Data table-

The pH levels for both water and Soduim Bicarbonate after adding both acid and base


Graph of water in terms of change in pH. The X-axis is drops, and the Y-Axis is pH. The red is the base, and the blue is the acid.

The change in pH for Sodium Bicarbonate. The base is in red, and the acid is in blue.

Discussion- For our results, the Acid Sodium Bicarbonate beaker started at a pH of 8.32 and the Base started at 8.47. At the end of thirty drops, the Acid's pH was 8.43, and the Base's was at 8.94.  For the base, at first the pH jumped largely within the first 15 drops, from 8.47 to 8.77. After that, from 20 to 30 drops, the rapid climb of pH stopped, gaining only .1 pH in the last ten. While on the acid side, where we had predicted that the decline would be small, the pH of the Acidic Sodium Bicarbonate actually rose. However, the growth was very minimal, going only as high as 8.51 after 25 drops, then coming back down to 8.43. I feel our results may have been a bit jaded due to the fact that Danny and I were very quick to record the pH, which may have hurt the experiment. So I feel that if we were to do this lab again in the future, we would have to be more aware that we need to stay patient in our data recording. However, looking at our class's data table, sodium bicarbonate had the lowest change in buffer, changing only .11 from the original pH acid wise. Our base was also the smallest change in buffer, ranging only .47 from its original base. Despite these results, Danny and I did not predict these results. We had predicted that there would be a more severe change in the pH for both the acid and base, we especially didn't predict that the acid would increase due to the sodium bicarbonate.

Summary- The answer to our question is that sodium bicarbonate is the best buffer because of the small change in pH for both acids and bases. While most of the other substances had a total pH range of more than 1, sodium bicarbonate's total buffer range was 0.36. However, these results may be a bit jaded base on our quickness in collecting data, there is truth to the fact that sodium bicarbonate is a great buffer.

Resources -Campbell Biology, 9th edition, Class data table



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