The pH value of thiourea depends on its concentration and the solvent it is dissolved in. In general, thiourea is a weak base and it can form acidic or basic solutions depending on the pH of the surrounding environment.

For example, a 0.1 M solution of thiourea in water has a pH of around 4-5, which is slightly acidic. This is because thiourea can undergo protonation in water, releasing H+ ions and forming the thiourea cation (SCN2H+).

On the other hand, if thiourea is dissolved in a strongly acidic solution, such as 1 M HCl, the pH of the solution will be lower and thiourea will be protonated to a greater extent, forming more SCN2H+ ions.

Conversely, if thiourea is dissolved in a strongly basic solution, such as 1 M NaOH, the pH of the solution will be higher and thiourea will be deprotonated, forming the thiourea anion (SCN-).

Therefore, the pH value of thiourea can vary depending on the concentration of thiourea, the solvent, and the presence of other substances that can affect the protonation/deprotonation equilibrium of thiourea.