A. Discussion Questions: nitial pH of the ammonia/ammonium ion buffer so differe
ID: 1032297 • Letter: A
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A. Discussion Questions: nitial pH of the ammonia/ammonium ion buffer so different than the initial pH of the acetic acid/acetate ion buffer? In your answer include the relative strengths of the acid in each of the buffers as well as the acid dissociation constants and their relationship to pl. Buffers are only effective in controlling pH when there are significant concentrations of the acid and its conjugate pase or the base and its conjugate acid. Essentially they control pH within a range of +/- 1 pH unit of the pka of he acid or base. Similarly, to stay within this range there must be sufficient "buffer capacity" (moles of H fronm the acid and its conjugate or moles of OH form the base and its conjugate) to neutralize the added acid or base. Remember: adding base neutralizes the acid component of a buffer and increases pH; adding acid neutralizes the base component of a buffer and decreases the pH. If the additions are within the capacity of the buffer to neutralize the acid or base, the buffer will minimize the pH change which will remain in the range of the buffer. When the additions of acid or base exceed the capacity of the buffer, the pH will exceed the buffer range. Complete the following table for the titrations of buffer solutions A, B and C. (Use the full descriptive name of each buffer in the headings.) Tabulate how many milliliters of each titrant, NaOH and HCL, were required to cause a 1.00 pH unit change from the initial pH. 2. Table 9-3 Buffer Titrant acetic acid (A e buffer NaOH HCA A and B) that were studied? Were the buffer capacities similar for each titrant? 8mL 5NML 2mL 8mL a. What conclusions can you draw regarding the buffer capacities for the two 0.060 M buffers (solutions b. What conclusions can you draw about the buffer capacities for the two acetic acid/acetate ion buffers (solutions A and C)? Was there a correlation of their capacities? Were there any surprises here?Explanation / Answer
1. the initial pH of the buffer is dependent upon the pKa of the acid component in the buffer.
As the acid component in the buffer in acetic acid has pKa 4.75 and the acid component of the ammonium buffer is 9.25. The initial pH of the acetate buffer is much lower than the ammonium buffer.
2. From the table
(a). The acetate buffer resists the pH change by the adiition of base much strongly than the addition of acid. Higher volume of base NaOH is used than acid HCl. This is due to the lower initial pH of the buffer.
Whereas, in case of ammonium buffer, the higher initial pH of the buffer resists pH change in basic medium such that by addiiton of base, but shows a fast pH change by acid HCl addition.
(b) The buffer capacity of acetic acid/acetate C is same in both acid HCl or base NaOH addition because the compoent acid/base in the biffer is lower. Whereas, the buffer capacity of buffer solution A, with higher acid/base component is also higher. So it needs more base to neutralize the acid component of the buffer.
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