Sodium hydroxide $(NaOH)$ was added to pure water $(H_2O)$. Which most likely were the pH values of the water before and after the sodium hydroxide was added to it?
A. before = 7, after = 9
B. before = 7, after = 4
C. before = 4, after = 7
D. before = 9, after = 7
Answer (2)
Pure water has a neutral pH of 7.
Adding sodium hydroxide (NaOH), a strong base, increases the pH.
The pH after adding NaOH will be greater than 7.
The most likely pH values are before = 7 and after = 9, so the answer is b e f ore = 7 , a f t er = 9 .
Explanation
Initial pH of Water Pure water has a neutral pH.
Effect of Adding NaOH Sodium hydroxide (NaOH) is a strong base. When added to water, it increases the concentration of hydroxide ions (OH-), which raises the pH.
Expected pH Change Since pure water has a pH of 7, and adding NaOH will make the solution more basic, the pH after adding NaOH will be greater than 7.
Conclusion Therefore, the most likely pH values are before = 7 and after = 9.
Examples
Understanding pH is crucial in many real-world applications. For example, in agriculture, knowing the pH of the soil helps farmers choose the right crops and fertilizers. Similarly, in water treatment, maintaining the correct pH level ensures that the water is safe for consumption and doesn't corrode pipes. In medicine, the pH of our blood is tightly regulated to ensure proper bodily functions. This problem illustrates a fundamental concept in chemistry that has wide-ranging implications.
The addition of sodium hydroxide (NaOH) to pure water will raise the pH from the neutral value of 7 to a higher value, commonly around 9. Thus, the most likely pH values before and after the addition are before = 7 and after = 9. The chosen multiple-choice option is A. before = 7, after = 9.
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