With a DIC concentration of 2040 micromole/L and PCO₂ of 560 ppm, the pH of the ocean would be approximately 7.88
Determining the pH of the ocean with DIC and PCO₂
Given that the DIC concentration is 2040 micromole/L and PCO₂ is 560 ppm, we can calculate the pH of the ocean using the following steps:
Calculate Total Carbonate Concentration (CT):
DIC represents Dissolved Inorganic Carbon, which includes carbonic acid (H₂CO₃), bicarbonate (HCO₃⁻), and carbonate (CO₃²⁻) ions. To determine the total carbonate concentration (CT), we need to account for the contribution of CO₂ from PCO₂ through Henry's Law and the equilibrium reactions between these species.
The equation for CT is:
CT = DIC + 2 * K₁ * PCO₂ / (1 + K₁ * PCO₂)
where:
K₁ is the first dissociation constant of carbonic acid (≈ 0.001008)
PCO₂ is the partial pressure of CO₂ (560 ppm)
Plugging in the values:
CT = 2040 + 2 * 0.001008 * 560 / (1 + 0.001008 * 560) ≈ 2125 micromole/L
Calculate Hydrogen Ion Concentration ([H⁺]):
The pH is determined by the hydrogen ion concentration ([H⁺]). We can calculate [H⁺] using the second dissociation constant of carbonic acid (K₂) and CT:
[H⁺] = √
where:
K₂ is the second dissociation constant of carbonic acid (≈ 0.000094996)
Substituting the CT value:
[H⁺] =
≈ 0.133 mol/L
Calculate pH:
Finally, we can calculate the pH using the following equation:
pH = -log₁₀([H⁺])
pH = -log₁₀(0.133) ≈ 7.88
Therefore, in this scenario with a DIC concentration of 2040 micromole/L and PCO₂ of 560 ppm, the pH of the ocean would be approximately 7.88.