Question

At temperature of 25 Celsius

c. If the partial pressure of CO2 (Pco2) has increased to 500 ppm 10-3.30 atm, state and justify the assumptions needed in order to calculate the pH: Verify the assumptions made in order to calculate the pH if the pH of the water is 5.58 d.

This is an open system.

Answer 1

Part c.

CO₂(g) + H₂O(l) ----> H₂CO₃(aq)

According to ideal gas equation:

P = CRT

i.e. 10^-3.3 atm = C * 0.0821 L.atm/mol.K * 298 K

i.e. C = 2.05*10^-5 M

Therefore, [H₂CO₃] = 2.05*10^-5 M

Formula: pH = 1/2 (pKa - Log[H₂CO₃])

i.e. pH = 1/2 (6.37 - Log(2.05*10^-5))

i.e. pH = 1/2 (6.37 + 4.69)

Therefore, pH = 5.53