The pH of salt water solution, specifically when the salt is formed from a strong acid and a strong base, like common table salt (sodium chloride or NaCl), is neutral at 7.
Understanding the pH of Salt Water
When salts dissolve in water, they can sometimes affect the acidity or basicity of the solution. This happens through a process called hydrolysis, where the ions of the salt react with water molecules. However, not all salts cause hydrolysis.
Why Some Salt Water is Neutral
Based on chemical principles, particularly information highlighting the behavior of salts from strong acids and strong bases:
- Origin of the Salt: Salts formed from the reaction of strong acids and strong bases, such as sodium chloride (NaCl) which comes from hydrochloric acid (HCl - strong acid) and sodium hydroxide (NaOH - strong base), behave differently in water.
- No Hydrolysis: Salts that are from strong bases and strong acids do not hydrolyze. This means the ions of these salts do not significantly react with water to produce excess hydrogen (H⁺) or hydroxide (OH⁻) ions, which are the drivers of pH changes.
- Ion Behavior: When a salt like NaCl dissolves, it dissociates into its constituent ions (Na⁺ and Cl⁻).
- Alkaline metal cations (like Na⁺ from NaOH) do not alter the H⁺ concentration in the water.
- Halide anions (like Cl⁻ from HCl) do not attract the H⁺ from water molecules.
- Result: Neutral pH: Because neither the cation nor the anion affects the balance of H⁺ and OH⁻ ions in pure water, the solution's pH remains unchanged. The pH will remain neutral at 7.
- Example: This is why NaCl is a neutral salt. A solution of NaCl in pure water will have a pH of approximately 7, which is the definition of a neutral solution.
Key Takeaway
For salt water solutions made from neutral salts like NaCl, the pH remains at 7.
| Salt Type | Source Acids/Bases | Hydrolysis Affects pH? | Typical pH |
|---|---|---|---|
| Neutral Salts (e.g., NaCl) | Strong Acid & Strong Base | No | 7 |
| Other Salts (not covered here) | Varied | Yes | Can be >7 or <7 |
It's important to note that while pure NaCl salt water is neutral, the pH of actual salt water found in nature (like the ocean) can vary slightly due to the presence of other dissolved substances, gases, and biological activity, but the fundamental principle for a pure strong acid/strong base salt solution remains a pH of 7.
