Calculation of the pH value of rainwater in equilibrium with an atmosphere containing 0.1 ppm of SO2?
Thread Content
The concentration of sulfur dioxide in the atmosphere at 25 degrees Celsius is 0.1 ppm. What is the pH value of rainwater that is in equilibrium with this concentration? Assuming that the rainwater before equilibrium, free of dissolved gases, is pure water, and given the Henry constant and acid dissociation constant of sulfur dioxide
It’s also related to rainfall. The greater the rainfall, the lower the concentration.
Once the concentration of SO2 is determined, its partial pressure in the air is also determined. According to the gas-liquid equilibrium relationship—Henry’s law, the equilibrium partial pressure P* = Ex, where x is the molar fraction of SO2 in rainwater； The concentration of H ions in rainwater is then calculated based on the ionization constant of sulfurous acid. Theoretically, primary and secondary ionizations as well as the ionization of water itself need to be taken into account, but these latter two can be ignored in terms of order of magnitude ； By taking the negative logarithm of the H-ion concentration, the pH value can be calculated!