Which of the following is the most effective buffer system for a pH value of 7.45? Assume all are 1M
A. Carbonic acid and sodium bicarbonate
B. Sodium bicarbonate and sodium carbonate
C. Sodium dihydrogen phosphate and disodium hydrogen phosphate
D Hydrogen cyanide and sodium cyanide
E. Ammonia and ammonium chloride
Would you agree with C?
yes. Are you guessing or do you know how to do this?
To determine which of the given buffer systems is most effective for a pH value of 7.45, we need to consider the components of each buffer system and their corresponding pKa values. The pKa value indicates the strength of an acid or base and is useful in determining the pH range over which a buffer is effective.
Let's analyze each option:
A. Carbonic acid and sodium bicarbonate: The pKa value of carbonic acid is around 6.37, which makes this buffer system effective for a pH range around 6.07-7.77. However, it is not the most suitable for maintaining a pH of 7.45.
B. Sodium bicarbonate and sodium carbonate: The pKa values of sodium bicarbonate and sodium carbonate are approximately 6.37 and 10.33, respectively. This buffer system would be effective in a pH range around 5.07-8.07, including a pH value of 7.45, making it a reasonable option.
C. Sodium dihydrogen phosphate and disodium hydrogen phosphate: The pKa value of sodium dihydrogen phosphate is around 7.2, and for disodium hydrogen phosphate, it is around 12.3. This buffer system is most effective in a pH range around 6.2-8.2. Therefore, it is a suitable option for maintaining a pH value of 7.45 and can be considered correct.
D. Hydrogen cyanide and sodium cyanide: The pKa value of hydrogen cyanide is approximately 9.21. This buffer system would be effective in a pH range around 8.21-10.21, so it is not the most suitable for maintaining a pH of 7.45.
E. Ammonia and ammonium chloride: The pKa value of ammonia is around 9.25. This buffer system would be effective in a pH range around 8.25-10.25, so it is not the most suitable for maintaining a pH of 7.45.
Based on the pKa values and the pH range over which each buffer system is effective, option C (Sodium dihydrogen phosphate and disodium hydrogen phosphate) is indeed the most appropriate choice for maintaining a pH of 7.45.