In Part C of Lab 8, you will prepare a phosphate buffer of a certain pH using the direct method. The questions below are to give you practice carrying out the necessary calculation for preparing the buffer from the correct phosphate compound. When you next come to lab to complete Part C of Lab 8, you will need to carry out this calculation again based on the actual mass of Na₂HPO4 7 H₂O that you weigh out. (a) Select a pH for your buffer solution. (Please make sure you and your lab partner(s) select the same pH, or someone will need to redo their calculations in lab.) --Select- (b) Based on the pH selected, will you need to use Na3PO4 12 H₂O or NaH2PO4 H₂O in order to generate a buffer of the desired pH? 2- 3- Hint: To answer this, you will need to determine pK values corresponding to the mixtures of the HPO anion with both phosphate anions PO4 and H2PO4 and evaluate which of these mixtures is closer to your target pH value. Na3PO4 12 H₂O NaH2PO4 H₂O • (c) Assuming you use exactly 3.000 g Na₂HPO4 7 H2O to make your buffer solution, what mass of the other phosphate compound will you need to add in order to generate the desired pH? Hint: You will need to use the Henderson-Hasselbalch Equation for this calculation. Pay attention to the correct molar masses for the phosphate compounds, as well (including the H₂O molecules!). (Enter your answer to the closest 0.001 g.) g
In Part C of Lab 8, you will prepare a phosphate buffer of a certain pH using the direct method. The questions below are to give you practice carrying out the necessary calculation for preparing the buffer from the correct phosphate compound. When you next come to lab to complete Part C of Lab 8, you will need to carry out this calculation again based on the actual mass of Na₂HPO4 7 H₂O that you weigh out. (a) Select a pH for your buffer solution. (Please make sure you and your lab partner(s) select the same pH, or someone will need to redo their calculations in lab.) --Select- (b) Based on the pH selected, will you need to use Na3PO4 12 H₂O or NaH2PO4 H₂O in order to generate a buffer of the desired pH? 2- 3- Hint: To answer this, you will need to determine pK values corresponding to the mixtures of the HPO anion with both phosphate anions PO4 and H2PO4 and evaluate which of these mixtures is closer to your target pH value. Na3PO4 12 H₂O NaH2PO4 H₂O • (c) Assuming you use exactly 3.000 g Na₂HPO4 7 H2O to make your buffer solution, what mass of the other phosphate compound will you need to add in order to generate the desired pH? Hint: You will need to use the Henderson-Hasselbalch Equation for this calculation. Pay attention to the correct molar masses for the phosphate compounds, as well (including the H₂O molecules!). (Enter your answer to the closest 0.001 g.) g
Principles of Modern Chemistry
8th Edition
ISBN:9781305079113
Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Chapter15: Acid–base Equilibria
Section: Chapter Questions
Problem 57P
Related questions
Question
Transcribed Image Text:In Part C of Lab 8, you will prepare a phosphate buffer of a certain pH using the direct method. The questions below are to give you practice carrying out the necessary calculation for preparing the buffer from the correct phosphate compound. When
you next come to lab to complete Part C of Lab 8, you will need to carry out this calculation again based on the actual mass of Na₂HPO4 7 H₂O that you weigh out.
(a) Select a pH for your buffer solution. (Please make sure you and your lab partner(s) select the same pH, or someone will need to redo their calculations in lab.)
--Select-
(b) Based on the pH selected, will you need to use Na3PO4 12 H₂O or NaH2PO4 H₂O in order to generate a buffer of the desired pH?
2-
3-
Hint: To answer this, you will need to determine pK values corresponding to the mixtures of the HPO
anion with both phosphate anions PO4
and H2PO4 and evaluate which of these mixtures is closer to your target pH value.
Na3PO4 12 H₂O
NaH2PO4 H₂O
•
(c) Assuming you use exactly 3.000 g Na₂HPO4 7 H2O to make your buffer solution, what mass of the other phosphate compound will you need to add in order to generate the desired pH?
Hint: You will need to use the Henderson-Hasselbalch Equation for this calculation. Pay attention to the correct molar masses for the phosphate compounds, as well (including the H₂O molecules!).
(Enter your answer to the closest 0.001 g.)
g
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