The pH of the blood is lower in veins and higher in arteries. The pH of the venous blood is 0.02 to 0.04 lower than the pH of the arterial blood (pH of Arterial blood: 7.35-7.45 and pH of Venous blood: 7.31-7.41). During respiration, CO2 releases from the tissue to the vein and the CO2 combined with H2O to form H2CO3. Venous HCO3 concentration is higher than arterial HCO3. As HCO3 is acid, the pH of the vein is lower in veins and higher in arteries.