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Data Post-Lab Summary Note : some questions will display a variable like "nCount" or "SyInput" instead of an actual number in the data summary. Q# Question Text 4) Data Entry - No Scoring Part I. What is your assigned pH value for the ACIDIC buffer solution? Enter your pH value to the hundredth of a pH unit, e.g. 4.70. pH = Your Answer: 4.9 No Points Possible 5) Scoring Scheme: 3-3-2-1 Part I. What volume in mL of 2.5 M sodium acetate is needed to make 250 mL of the acetic acid/acetate ion buffer that has an acetate ion concentration of 0.20 M? You should report your value to 2 significant figures. Volume = Your Answer: 20 You Scored 3 points out of 3 Possible 6) Scoring Scheme: 3-3-2-1 Part I. What is the concentration of the acetic acid in the 250 mL acetic acid/acetate ion buffer solution at your assigned pH? You should report your value to 2 digits. Molarity = Your Answer: 0.14 You Scored 3 points out of 3 Possible 7) Scoring Scheme: 3-3-2-1 Part I. What volume in mL of the 6 M acetic acid solution is needed to prepare the 250 mL acetic acid/acetate ion buffer solution at your assigned pH? You should report your value to 3 digits. Volume = Your Answer: 5.77 You Scored 3 points out of 3 Possible 8) Data Entry - No Scoring Part I. What is the assigned pH value for your NEUTRAL buffer solution? Enter your pH value to the hundredth of a pH unit, e.g. 7.40. pH = Your Answer: 7.1 No Points Possible 9) Scoring Scheme: 3-3-2-1 Part I. What volume in mL of the 2.5 M stock sodium dihydrogen phosphate is needed to prepare 250 mL of the neutral buffer that was 0.10 M in sodium dihydrogen phosphate? You should report your value to 2 significant figures. Volume = Your Answer: 10 You Scored 3 points out of 3 Possible 10) Scoring Scheme: 3-3-2-1 Part I. What is the concentration of the sodium hydrogen phosphate in the dihydrogen phosphate ion/hydrogen phosphate ion buffer solution at your assigned pH? You should report your value to 2 significant figures. Molarity = Your Answer: 0.079 You Scored 3 points out of 3 Possible 11) Scoring Scheme: 3-3-2-1 Part I. What mass in grams of sodium hydrogen phosphate heptahydrate is needed to make the 250 mL dihydrogen phosphate ion/hydrogen phosphate ion buffer at your pH? You should report your value to 2 significant figures. Mass (g) = Your Answer: 5.3 You Scored 3 points out of 3 Possible 12) Data Entry - No Scoring Part I. What is the assigned pH value for your BASIC buffer solution? Enter your pH value to the hundredth of a pH unit, e.g. 10.70. pH = Your Answer: 10.4 No Points Possible 13) Scoring Scheme: 3-3-2-1 Part I. What mass of sodium hydrogen carbonate is needed to make the buffer solution 0.10 M in sodium hydrogen carbonate? You should report your value to 3 significant figures. Mass (g) = Your Answer: 2.1 You Scored 3 points out of 3 Possible 14) Scoring Scheme: 3-3-2-1 Part I. What is the concentration of the sodium carbonate in the hydrogen carbonate ion/carbonate ion buffer solution at your assigned pH? You should report your value to 2 significant figures. Molarity = Your Answer: 0.12 You Scored 1 point out of 3 Possible 15) Scoring Scheme: 3-3-2-1 Part I. What mass of anhydrous sodium carbonate is required to make the 250 mL hydrogen carbonate ion/carbonate ion buffer at your assigned pH? You should report your value to 3 significant figures. Mass (g) = Your Answer: 3.17 You Scored 1 point out of 3 Possible 16) Scoring Scheme: 3-3-2-1 Part I. Why was your measured pH level of the buffer solutions different from the calculated values? You Scored 3 points out of 3 Possible Your Register to View Answerall of the above 18) Scoring Scheme: 3-3-2-1 Part II. What volume of the 6 M HCl stock solution is needed to prepare 100 mL of 0.2 M HCl? You should report your value to 2 digits. Volume = Your Answer: 3.3 You Scored 3 points out of 3 Possible 19) Scoring Scheme: 3-3-2-1 Part II. What volume of the 6 M NaOH stock solution is needed to prepare 100 mL of 0.2 M NaOH? You should report your value to 2 digits. Volume = Your Answer: 3.3 You Scored 3 points out of 3 Possible 22) Data Entry - No Scoring. Part III. Let's begin comparing corresponding graphs. Take the two graphs of the acidic buffer, one of the titration with HCl and the other of the titration with NaOH. Place the graph of the HCl titration on top of the graph of the NaOH titration. Line up these two graphs along the y-axis (pH) and the x-axis (volume). Flip the top graph 180, keeping the pH axis aligned. After the flip, the volume axis will be lined up end-to-end with the zero values superimposed. You should now have a curve that looks like an "S" lying on its side and one of the graphs will be face down. Hopefully your graph paper is "see through." Find the pH range over which the buffer effectively neutralizes the added strong acid and strong base and maintains a reasonably constant pH. This is referred to as the buffer range. To which of the following ranges is the buffer range of the acidic buffer closest? You Scored 0 points out of 0 Possible Your Register to View Answer3.7 - 5.7 23) Data Entry - No Scoring. Part III. Now, take the two graphs of the neutral one buffer, of the titration with HCl and the other of the titration with NaOH. Place the graph of the HCl titration on top of the graph of the NaOH titration. Line up these two graphs along the y-axis (pH) and the x-axis (volume). Flip the top graph 180, keeping the pH axis aligned. After the flip, the volume axis will be lined up end-to-end with the zero values superimposed. You should now have a curve that looks like an "S" lying on its side and one of the graphs will be face down. Hopefully your graph paper is "see through." Find the pH range over which the buffer effectively neutralizes the added strong acid and strong base and maintains a reasonably constant pH. This is referred to as the buffer range. To which of the following ranges is the buffer range of the neutral buffer closest? You Scored 0 points out of 0 Possible Your Register to View Answer6.2 - 8.2 24) Data Enrty - No Scoring. Part III. Next, take the two graphs of the basic buffer, one of the titration with HCl and the other of the titration with NaOH. Place the graph of the HCl titration on top of the graph of the NaOH titration. Line up these two graphs along the y-axis (pH) and the x-axis (volume). Flip the top graph 180, keeping the pH axis aligned. After the flip, the volume axis will be lined up end-to-end with the zero values superimposed. You should now have a curve that looks like an "S" lying on its side and one of the graphs will be face down. Hopefully your graph paper is "see through." Find the pH range over which the buffer effectively neutralizes the added strong acid and strong base and maintains a reasonably constant pH. This is referred to as the buffer range. To which of the following ranges is the buffer range of the basic buffer closest? You Scored 0 points out of 0 Possible Your Register to View Answer9.3 - 11.3 25) Scoring Scheme: 3-2-1-1 Part III. Considering the ranges of pH of each buffer, which of the following equations best defines the buffer range in terms of pH and pKa? You Scored 3 points out of 3 Possible Your Register to View AnswerpH = pKa +/- 1 26) Scoring Scheme: 3-2-1-1 Part III. Buffer capacity is defined as the amount of acid or base that can be added to a buffer before any substantial change in pH. At what pH is the buffer capacity at its maximum? You Scored 1 point out of 3 Possible Your Register to View AnswerpH = pKa 27) Free Response (2 points) Part III. Finally, take the two graphs of the acetic acid solution, one of the titration with HCl and the other of the titration with NaOH. Place the graph of the HCl titration on top of the graph of the NaOH titration. Line up these two graphs along the y-axis (pH) and the x-axis (volume). Flip the top graph 180, keeping the pH axis aligned. After the flip, the volume axis will be lined up end-to-end. You should now have a curve that looks like an "S" lying on its side and one of the graphs will be face down. Hopefully your graph paper is "see through." How do these graphs compare to the graphs of the acid buffer? For example, starting at the pH in the middle of "S" curve of each graph, compare how much HCl or NaOH is added before the pH has changed by 1 unit? Enter your paragraph in the text box provided. Your Answer: In the graph, the pH changes by more than 1 Text Answers to be Scored by your TA unit. The similarity is that they both change very quickly towards the end of the titration. It takes more solution to change the pH in the acetic acid solution. 28) Free Response (2 points) Part III. Compare the acidic buffer graph to the graph of pH vs. volume of NaOH added to the mixture of the acid buffer + HCl in step 8 of Part IV in the laboratory procedure. What are the differences, if any? How do the buffer ranges of the two graphs compare? Enter your paragraph in the text box provided. Your Answer: In the acidic buffer with HCl it needed alot more Text Answers to be Scored by your TA titrant for the pH to change. The pH changes much more rapidly towards the end when the NaOH titrant is used as opposed to the HCl titrant. 29) Free Response (2 points) Part III. Consider the titration curve you plotted for the "Titration of a Weak Acid" experiment. How does the titration curve compare to the graph involving the acetic acid/acetate ion buffer in this experiment? Does the titration curve include a buffer region? If so, where is the buffer region? If not, why not? Enter your paragraph in the text box provided. Your Answer: This curve itself is shaped like an "S", like the Text Answers to be Scored by your TA other curves when they are combined. The buffer region is towards the middle where the slope is small. 30) Concluding Remarks (2 points) After reflecting on the nature of buffer solutions and their effectiveness over different pH ranges, compose a few paragraph summary of this experiment. Enter your paragraph in the text box provided. Your Answer: In the experiment, we saw the effects of buffer solutions on titrations. In the titrations it took a lot more HCl to reach the pH change we needed than NaOH. But in general, the buffer worked best with the opposite titrant (acid with base, or base with acid) ... View Full Document

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