Sodium sulphate is a salt that, when dissolved in water, dissociates into sodium ions (Na+) and sulphate ions (SO42-). The pH value of a solution is a measure of its acidity or basicity, and it is determined by the concentration of hydrogen ions (H+) in the solution.

Sodium sulphate is a neutral salt, which means that it does not produce a significant change in the pH of a solution. This is because the sodium ions and sulphate ions do not react with water to produce hydrogen ions or hydroxide ions (OH-), which are responsible for the acidic or basic properties of a solution.

Therefore, the pH value of a sodium sulphate solution is typically around 7, which is considered neutral. However, it's important to note that the exact pH value may vary slightly depending on the concentration of sodium sulphate and the presence of other substances in the solution.