Question

1 a) A sudden increase in lactic acid levels during exercise can lead to metabolic acidosis. Acidosis is commonly treated by administering NaHCO, intravenously. Using the bicarbonate-carbon dioxide buffer system, qualitatively explain the effect of this procedure on blood pH. [6 points)

Answer 1

Buffer systems consist of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffer systems prevent radical change in pH of the system by absorbing excess H⁺ or by absorbing excess OH^-.

1. Muscles during heavy exercise start doing anaerobic respiration and generate lactic acid. Lactic acid easily dissociates into lactate ion and hydrogen ion (H⁺). These H⁺ ions cause metabolic acidosis. Muscles pump the generated lactate ions and H⁺ ions into the blood this reduces the blood pH. Our blood has the capacity to maintain blood pH in an optimal range with the help of various kinds of buffer systems. The bicarbonate-carbonic acid buffer system is the most important one. Bicarbonate ions along with the sodium form sodium bicarbonate(NaHCO_3).

NaHCO₃+ Lactic acid →  H2CO₃ + Sodium lactate

(sodium bicarbonate) + (acid) → (Carbonic acid) + (salt)

H₂CO₃ —> CO₂ + H₂O ( Removed by the lungs)

(weak acid) →(Carbon dioxide) + (water)

b) Phosphate buffer system

Phosphates in blood exist in two forms i.e. Sodium dihydrogen phosphate (Na₂H₂PO₄^-) a weak acid and sodium monohydrogen phosphate (Na₂HPO₄^2-) a weak base. When Na₂HPO₄² react with an acid it picks up a hydrogen ion to form Na₂H₂PO₄ and a salt. When Na₂HPO₄²reacts with a base it reverts back to the weak base and form water.

Example:

HCL + Na₂HPO₄ →NaH₂PO₄ + NaCl

(strong acid) + (weak base) → (weak acid) + (salt)

NaOH + NaH₂PO₄→Na₂HPO₄ + H2O

(strong base) + (weak acid) → (weak base) + (water)