Final answer:
The pH value at which a solution is more than 99% basic is significantly higher than 7, likely around 12 to 13, which indicates a strong base. Indicators like phenolphthalein can signal when a solution is basic by changing color at certain pH levels.
Step-by-step explanation:
To determine at which pH value a solution is more than 99% basic, we need to understand the pH scale and how pH relates to the concentration of hydroxide ions (OH-) in a solution.
The pH indicates the acidity or basicity of a solution: a pH less than 7 is acidic, a pH of 7 is neutral, and a pH greater than 7 is basic. As a solution becomes more basic, its pH value increases. A solution with a pH significantly above 7 indicates a strong base.
A pH indicator, such as phenolphthalein, changes color at specific pH values, which can be used to estimate the pH of a solution. For instance, phenolphthalein is pink at a pH of 10 and above, indicating a basic solution.
The pH at the equivalence point when titrating a weak acid with a strong base is much greater than 7, showing the solution is strongly basic. When bases are added to neutral water (pH 7), the pH can rise to a value between 12 and 13, signifying a strongly basic solution with a high percentage of hydroxide ions.