Soap is a basic substance, with a pH that ranges from 9 to 10. The pH scale is a measure of the acidity or basicity of a solution, and it ranges from 0 to 14. A solution with a pH of 0 is highly acidic, while a solution with a pH of 14 is highly basic. A solution with a pH of 7 is neutral, meaning it is neither acidic nor basic. Soap is basic because it contains alkaline substances, such as sodium hydroxide or potassium hydroxide, which are responsible for its cleaning properties. These alkaline substances help to neutralize acidic substances, such as grease and oil, making them easier to wash away. It's important to note that the pH scale is logarithmic, meaning that each increment on the scale represents a tenfold difference in acidity or basicity. For example, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5, and a solution with a pH of 3 is 100 times more acidic than a solution with a pH of 5. In general, a solution with a pH less than 7 is considered to be an acid, while a solution with a pH greater than 7 is considered to be a base. Solutions with a pH of 7 or less are considered to be strong acids, while solutions with a pH greater than 7 but less than 14 are considered to be weak acids. Similarly, solutions with a pH of 14 or greater are considered to be strong bases, while solutions with a pH greater than 7 but less than 14 are considered to be weak bases. It's worth noting that the pH of soap can vary depending on the specific type of soap and the ingredients used to make it. Some soaps may have a slightly lower or higher pH than others, depending on the ingredients and manufacturing process.