Why is the pH of arterial blood higher than venous blood?
pH is lower, i.e. acidity is higher in venous blood besause of presence of dissolved carbodioxide, which forms carbonic acid.
Before discussing the answer, we must remember that a very small difference in pH is encountered between arterial and venous blood.
Carbonic acid in blood plasma dissociates as positive and negative ions, as follows:
Presence of free hydrogen ions increase acidity, lowers pH of venous blood.
To handle this issue, DCT of nephrons in kidney discharges hydrogen ions in urine. Tubular cells also reabsorb more of bicarbonates to maintain alkaline blood pH.