What is h2so3 ph?

Sulfurous Acid (H₂SO₃) and pH

Sulfurous acid (H₂SO₃) is a weak diprotic acid formed in solution when sulfur dioxide (SO₂) dissolves in water. It is not a stable compound and cannot be isolated in pure form. Its presence and behavior are observed in aqueous solutions.

• Formation: SO₂(g) + H₂O(l) ⇌ H₂SO₃(aq)

• Acidity: As a diprotic acid, it undergoes two ionization steps:

  • H₂SO₃(aq) + H₂O(l) ⇌ HSO₃⁻(aq) + H₃O⁺(aq) (K_a1 ≈ 1.7 x 10⁻²)
  • HSO₃⁻(aq) + H₂O(l) ⇌ SO₃²⁻(aq) + H₃O⁺(aq) (K_a2 ≈ 6.4 x 10⁻⁸)

• pH Calculation: The pH of a sulfurous acid solution depends on its concentration and the equilibrium constants. Because it is a weak acid, a simple calculation is not sufficient; you must use the K_a values to determine the hydronium ion concentration ([H₃O⁺]).

• Influence of Concentration: Higher concentrations of dissolved SO₂ will generally lead to lower pH values (more acidic). However, due to the equilibria involved, the relationship is not linear.

• pH Range: The pH of sulfurous acid solutions can vary significantly, but typically falls in the range of 1 to 5, depending on concentration.

• Important Note: The concentration of [H₂SO₃] at any instant is very small. The major species at equilibrium are SO₂, HSO₃⁻ and H₃O⁺. Often it is more accurate to consider it as solution of hydrated SO₂.