To answer this question, we need to understand the effect of adding sodium hydroxide ([tex]\( NaOH \)[/tex]) to pure water ([tex]\( H_2O \)[/tex]) on its pH levels. Here's a step-by-step explanation:
1. Understanding pH Levels:
- pH is a measure of how acidic or basic (alkaline) a solution is.
- The pH scale ranges from 0 to 14.
- A pH of 7 is considered neutral, which is the pH of pure water.
- A pH value less than 7 indicates an acidic solution.
- A pH value greater than 7 indicates a basic (alkaline) solution.
2. Effect of Sodium Hydroxide ([tex]\( NaOH \)[/tex]) on pH:
- Sodium hydroxide is a strong base.
- When [tex]\( NaOH \)[/tex] is added to water, it dissociates into sodium ions ([tex]\( Na^+ \)[/tex]) and hydroxide ions ([tex]\( OH^- \)[/tex]).
- The hydroxide ions increase the basicity of the solution, thereby increasing the pH.
3. Initial pH of Pure Water:
- Pure water has a neutral pH of 7.
4. Possible Changes in pH After Adding [tex]\( NaOH \)[/tex]:
- Since [tex]\( NaOH \)[/tex] is a base, adding it to water will raise the pH above 7.
- The final pH will depend on the amount of [tex]\( NaOH \)[/tex] added, but it will definitely be higher than the initial pH of 7.
Given these points:
- The initial pH of pure water is 7.
- After adding [tex]\( NaOH \)[/tex], the pH increases as the solution becomes more basic.
Thus, the most likely pH values before and after the addition of sodium hydroxide are:
- Before: [tex]\( 7 \)[/tex] (neutral)
- After: [tex]\( 9 \)[/tex] (basic)
Therefore, the correct choice is:
- Before = 7, After = 9
