Elemental sulfur (S₈) itself is almost insoluble in water (solubility ~0.063 mg/L at 20°C), so pure sulfur powder does not have an intrinsic “pH value” — pH is a property of aqueous solutions.
When sulfur powder is mixed with water to form a suspension, the measured pH is typically weakly acidic to near-neutral, generally in the range of pH 6.0 – 7.0, due to slow surface oxidation of sulfur particles that form trace amounts of sulfurous acid (H₂SO₃) and sulfuric acid (H₂SO₄).
Typical measured values:
- Reagent-grade sulfur powder (≥99.0% purity): ~pH 6 for a 10 g/L suspension at 20°C
- Industrial/agricultural-grade sulfur saturated solution: ~pH 6.8
- High-purity nano sulfur: ~pH 7 ± 0.5 (near neutral)
The exact pH varies with particle size, purity, surface oxidation level, and concentration. In agricultural applications, elemental sulfur is used to gradually lower soil pH because soil microbes oxidize it into sulfuric acid over time.
