Irresistible Lab Report Chem 109
Abstract A buffer is a solution that resists changes in pH when H+, OH-, or H20 is added. By using standard lab equipment, a lab pro diagnostic tool, and acidic and basic solutions, the pH can be found. By recording the pH while adding a base or an acid gradually to a buffer solution you can find the capacity of each buffer to resist drastic changes in pH. The best buffers will keep a solution from becoming either too acidic or basic with the addition of a strong base or acid. Introduction
The objective of the Irresistible lab is to determine the capacity of each solution (unbuffered and buffered both) and how much they resist changes to pH. This is accomplished by having ten graduated beakers: two containing pure water, two with . 1 M Sodium Chloride, two with 1 gram of solid sodium acetate dissolved in acetic acid, two with 5 grams of solid sodium acetate dissolved in acetic acid, and two with 10 grams of solid sodium acetate dissolved in acetic acid. These are split into two groups of five containing one of each solution.
The pH of each solution is then measured and a pipette is used to distribute 1 mL of HCl, a strong acid, at a time to each solution in the first set, with the pH being measured and recorded until a drastic change is recorded. The procedure will be repeated with the other set of solutions using NaOH, a strong base. I would predict that the pure water and sodium chloride solutions would not have a very strong buffering capacity and therefore would almost immediately drop or raise the pH level depending on whether a base or acid was added.
As far as the mixture of sodium acetate and acetic acid, I would predict that they would be a better buffer than the previous solutions. There are varying amounts of sodium acetate, but I don’t predict that they will have much different results as far as buffering solutions goes. This is because they all have the same amount of acetic acid, which will act as the main buffer. I predict that this will be the limiting reagent out of those solutions. Method I began by preparing ten beakers, labled 1-10 and added 50 mL of water to numbers 1 and 6. In 2 and 7 I added 50 mL of . 1 M NaCl.
I added sodium acetate to the rest of the beakers: 1 gram to 3 and 8, 5 grams to 4 and 9, and 10 grams to 5 and 10. I then filled the beakers that contained the solid sodium acetate with 50 ml of . 10 M acetic acid. Specifics can be found on page 84 of the lab manual. Though the lab manual instructed to use a pipet, we did not have an accurate 1 mL pipet or a graduated pipet, so we instead prepared two graduated burets with 1 M Sodium Hydroxide and 1 M hydrochloric acid. Using a standardized pH probe with a Lab Pro to measure changes in pH, we added 1 mL of HCl at a time and recorded the changes.
The same was done for the NaOH. Results We only added a small amount of HCl to the water and sodium chloride. We did not continue to add more HCl after a significant drop in pH was recorded. We added a total of 2 mL of HCl to both H20 and NaCl before the pH changed. The 1 gram solution of sodium acetate and acetic acid changed after a 8 mL, and the other two never dropped before we reached our total of 10 mL HCl. The Effect of Acidon Solutions 50 ml H2050 mL . 1 M NaCl1 g CH3COONa5 g CH3COONa10 g CH3COONa TrialpH 07. 516. 374. 745. 75. 97 11. 591. 384. 545. 455. 88 21. 121. 184. 375. 355. 75 3 4. 185. 245. 68 4 3. 985. 155. 59 5 3. 765. 075. 51 6 3. 455. 015. 46 7 2. 984. 935. 41 8 1. 634. 865. 34 9 4. 815. 31 10 4. 775. 26 We repeated the procedure with the second set of solutions, but replaced hydrochloric acid with sodium hydroxide. Like the last set, both sodium chloride and water changed pH almost instantly. It took one mL to reach a significant rise in pH. The other three solutions all took a total of 4 mL to rise to a pH of a little over 13. 6. The Effect of Base on Solutions Trial50 ml H2050 mL . 1 M NaCl1 g CH3COONa5 g CH3COONa10 g CH3COONa 06. 777. 34. 845. 6255. 934 112. 9913. 1355. 7836. 164 2 5. 366. 1456. 444 3 6. 267. 9557. 53 4 13. 0613. 1413. 14 5 Discussion The point of this lab was to determine the capacity of each solution as a buffer. By adding a strong acid to the solution we were essentially measuring the amount of hydrogen atoms that could be absorbed by the solution (buffered) before the limit was reached and they were abundant in the solution (pH).
The same was measured by lack of the hydrogen atoms and abundance of hydroxide ions in solution when the base was added. As seen in the graph above, water has little to no buffering capacity. Because it contains a hydrogen and hydroxide ion, it should have some buffering capabilities, but I suspect that the fact that the acid was strong quickly overcame the capacity. Similar results with the sodium chloride show that it’s buffering capacity is not good. The 1 gram of sodium acetate reached its capacity at 8 mL of HCl, and the other two never dropped off.
This shows that they were continuing to buffer past the 10 mL of HCl. The graph above shows the same solutions with the addition of Sodium Hydroxide. Once again water and NaCl do not buffer well and at 4 mL of NaOH all three sodium acetate solutions reached capacity. In a lab like this, errors are very likely. There is the absence of ionized water, for one, to consider. This could easily skew results because the water could be contaminated. Unfortunately the equipment is old and could be faulty. And also those doing the experiment could have bad techniques because we are so new at this.
The lab was also open, and the contaminates could easily mess up the results. If I were to do this lab again, I would do more with the varying concentrations of sodium acetate to acetic acid solutions. Obviously they were the best buffers, but I would test different ratios and concentrations along with different volumes of acetic acid. With more experimentation, conclusions could be more easily drawn between the relationship of these two. Conclusion Buffers are very important in all aspects of life. In the body they keep the blood from becoming too acidic or basic, for example.
I’ve learned that not all solutions make good buffers, water for example, did not stand up to the strength of the sodium hydroxide or hydrochloric acid. In conclusion: without buffers, our whole world would be acidic and basic, no neutrals around. References Kautz, J. , D. Kinnan, and C. McLaughlin. 2011-2012. Chemistry 110 Laboratory Manual “Taking things apart… Putting things together”. Plymouth, MI: Hayden-McNeil Publishing. Gilbert, T. R. , R. V. Kriss, N. Foster, G. Davies. 2004. Chemistry The Science In Context. New York, NY: W. W. Norton & Company