The pH value of sulfuric acid is not a single fixed number; instead, it varies depending on its concentration.
How Concentration Affects Sulfuric Acid pH
The pH of any acid solution, including sulfuric acid (H₂SO₄), is fundamentally determined by the concentration of hydrogen ions (H⁺) it releases into the water. Sulfuric acid is a strong acid, meaning it dissociates significantly in water to produce H⁺ ions.
- Higher Concentration: A more concentrated sulfuric acid solution contains more acid molecules dissolved in a given amount of water. This leads to a higher concentration of H⁺ ions, resulting in a lower pH value (more acidic).
- Lower Concentration: A more dilute sulfuric acid solution (less acid, more water) will have fewer H⁺ ions, leading to a higher pH value (less acidic, but still acidic).
Therefore, stating a single pH value for "sulfuric acid" without specifying the concentration is incomplete.
Specific pH Value Under Standard Conditions
According to one reference, a specific pH value can be provided when the concentration and environmental conditions are defined.
Under the standard conditions of 1 mMol/L (millimolar) concentration, 25°C temperature, and 1 atmospheric pressure, the pH value of sulfuric acid is 2.75.
Key Condition and Value Summary
Here is a summary of the specific condition and the corresponding pH value mentioned:
| Condition | pH Value |
|---|---|
| 1 mMol/L, 25°C, 1 atm | 2.75 |
It is crucial to remember that the 2.75 pH value is specific to this particular 1 mMol/L concentration under the noted standard conditions.
Practical Considerations
- The pH of concentrated sulfuric acid solutions (e.g., laboratory reagent concentration, which is typically around 98%) is extremely low, often negative, indicating a very high acidity far beyond the 0-14 pH scale usually shown for dilute solutions.
- For dilute solutions with concentrations significantly less than 1 mMol/L, the pH will be higher than 2.75, approaching 7 (neutral) as the concentration decreases, but it will always remain acidic (pH < 7).
