Passage
Within the renal system, two buffers operate to counter the production of excess H⁺ from luminal H₂CO₃. They are located within the tubular lumen, and maintain urinary pH levels between 4.5 and 8.0.The first of these is a phosphate buffer, which serves as the primary buffer for urine because its pK_a is very close to extracellular fluid pH of 7.4. The phosphate buffer operates according to Reaction 1. H₂PO₄⁻ is excreted in urine.
Reaction 1During acidosis when tubular pH is low, the phosphate buffer system becomes saturated. An ammonia buffer system then becomes the primary buffer, and NH₄⁺ is excreted in urine.
Reaction 2Titratable acid (TA) is the total acid in urine, and it can be found using Folin's method. Under normal physiological conditions, TA is approximately equal to the amount of phosphate in urine, which is a product of serum phosphate concentration and glomerular filtration rate. This makes TA a good indicator of kidney function.Folin's method involves back titration of a urine sample to a pH of 7.4 using a strong base. In a typical procedure, potassium oxalate is added to remove calcium from the sample prior to titration with 1.0 M NaOH. The titration continues until the solution reaches a pH of 7.4 (measured by a pH meter) . The amount of base required for the titration can then be used to calculate the amount of H₂PO₄⁻ in the urine sample.
-A phosphate buffer system based on Reaction 1 is made that contains 5 M H₂PO₄⁻ and 0.5 M HPO₄²⁻. Will the pH of this system fall within the pH range for urine?

Question

Passage
Within the renal system, two buffers operate to counter the production of excess H⁺ from luminal H₂CO₃. They are located within the tubular lumen, and maintain urinary pH levels between 4.5 and 8.0.The first of these is a phosphate buffer, which serves as the primary buffer for urine because its pK_a is very close to extracellular fluid pH of 7.4. The phosphate buffer operates according to Reaction 1. H₂PO₄⁻ is excreted in urine.

Passage Within the renal system, two buffers operate to counter the production of excess H<sup>+</sup> from luminal H<sub>2</sub>CO<sub>3</sub>. They are located within the tubular lumen, and maintain urinary pH levels between 4.5 and 8.0.The first of these is a phosphate buffer, which serves as the primary buffer for urine because its pK<sub>a</sub> is very close to extracellular fluid pH of 7.4. The phosphate buffer operates according to Reaction 1. H<sub>2</sub>PO<sub>4</sub><sup>−</sup> is excreted in urine. <strong>Reaction 1</strong>During acidosis when tubular pH is low, the phosphate buffer system becomes saturated. An ammonia buffer system then becomes the primary buffer, and NH<sub>4</sub><sup>+</sup> is excreted in urine. <strong>Reaction 2</strong>Titratable acid (TA) is the total acid in urine, and it can be found using Folin's method. Under normal physiological conditions, TA is approximately equal to the amount of phosphate in urine, which is a product of serum phosphate concentration and glomerular filtration rate. This makes TA a good indicator of kidney function.Folin's method involves back titration of a urine sample to a pH of 7.4 using a strong base. In a typical procedure, potassium oxalate is added to remove calcium from the sample prior to titration with 1.0 M NaOH. The titration continues until the solution reaches a pH of 7.4 (measured by a pH meter) . The amount of base required for the titration can then be used to calculate the amount of H<sub>2</sub>PO<sub>4</sub><sup>−</sup> in the urine sample. -A phosphate buffer system based on Reaction 1 is made that contains 5 M H<sub>2</sub>PO<sub>4</sub><sup>−</sup> and 0.5 M HPO<sub>4</sub><sup>2−</sup>. Will the pH of this system fall within the pH range for urine? A) Yes; pH = 5.8 B) Yes; pH = 6.8 C) No; pH = 9.1 D) No; pH = 10.1

Reaction 1During acidosis when tubular pH is low, the phosphate buffer system becomes saturated. An ammonia buffer system then becomes the primary buffer, and NH₄⁺ is excreted in urine.

Reaction 2Titratable acid (TA) is the total acid in urine, and it can be found using Folin's method. Under normal physiological conditions, TA is approximately equal to the amount of phosphate in urine, which is a product of serum phosphate concentration and glomerular filtration rate. This makes TA a good indicator of kidney function.Folin's method involves back titration of a urine sample to a pH of 7.4 using a strong base. In a typical procedure, potassium oxalate is added to remove calcium from the sample prior to titration with 1.0 M NaOH. The titration continues until the solution reaches a pH of 7.4 (measured by a pH meter) . The amount of base required for the titration can then be used to calculate the amount of H₂PO₄⁻ in the urine sample.
-A phosphate buffer system based on Reaction 1 is made that contains 5 M H₂PO₄⁻ and 0.5 M HPO₄²⁻. Will the pH of this system fall within the pH range for urine?

Quizplus · Accepted Answer

11ecba2d_1212_f719_a3bf_eb2afc40c898_MD0008_00 A buffer system resists changes in pH when OH⁻ or H⁺ is added to the solution. Buffer systems accomplish this by containing large amounts of a mixture of either a weak acid (HA) with its conjugate base (A⁻) or a mixture of a weak base (B) with its conjugate acid (HB⁺), which can neutralize lesser amounts of any additional H⁺ or OH⁻ that may be introduced into the system. The Henderson-Hasselbalch equation is used to find the pH of a buffer system. This equation comes from the equilibrium relationship for the dissociation of a weak acid: 11ecba2d_1212_f71a_a3bf_77af7cc4ed63_MD0008_00 Then the equilibrium relationship is described by the equation: 11ecba2d_1212_f71b_a3bf_412019b945c9_MD0008_00 Rearranging this equation gives: 11ecba2d_1212_f71c_a3bf_97ba772a6789_MD0008_00 Because pH = −log[H⁺] and pK_a = −log K_a, applying logarithm rules to both sides of the equation gives the Henderson-Hasselbalch equation: 11ecba2d_1212_f71d_a3bf_1900148f9ceb_MD0008_00 For the phosphate buffer system (Reaction 1), the pK_a is 6.8. The concentration of H₂PO₄⁻ (HA) is 5 M and the concentration of HPO₄²⁻ (A⁻) is 0.5 M. Substituting these values into the equation gives: 11ecba2d_1213_1e2e_a3bf_ab794745f2a4_MD0008_00 11ecba2d_1213_1e2f_a3bf_912c235bff71_MD0008_00 The pH of the buffer system is 5.8, which is between 4.5 and 8.0 (the acceptable pH range for urine). (Choice B) A value of 6.8 is obtained by assuming the pH is the same as the pK_a. In a buffer system, the pH differs from the pK_a based on the ratio of the concentrations of a weak acid and its conjugate base. (Choice C) A value of 9.1 is obtained if the pK_a is assumed to be the pH of the system and the ammonia buffer system is used instead of the phosphate buffer system. (Choice D) A value of 10.1 is obtained if the pK_a of the ammonia buffer system is plugged into the Henderson-Hasselbalch equation rather than the pK_a of the phosphate buffer system. Educational objective: A buffer resists changes to pH. A buffer system is comprised of a weak acid (or weak base) and its conjugate. The pH of a particular buffer system can be found using the Henderson-Hasselbalch equation.

Passage Within the Renal System, Two Buffers Operate to Counter the the Production