When a water sample is acidified, what must be the final pH level?

• A. Neutral (7.0)
• B. 3.0
• C. 2.0
• D. Less than 2.0

Answer: (D)

Acidifying a water sample typically involves adding an acid to lower the pH of the solution. The final pH level in such cases is often required to be less than 2.0, especially in analytical or environmental testing contexts. This is because a pH level below 2 is strong enough to ensure that many metals and other compounds are kept in solution, allowing for more accurate testing or improvement in conditions for certain chemical reactions.

When a sample has a pH lower than 2.0, it indicates a highly acidic environment, which is beneficial for certain processes or analyses, such as preserving the sample's characteristics or ensuring that certain elements remain soluble. A pH of 3.0, while still acidic, may not be low enough for effective metal solubilization in certain contexts. Similarly, a neutral pH of 7.0 would not be suitable for acidified samples, as it implies no addition of acid has occurred, and conditions would not be conducive for analyses that require acidic environments. Thus, the requirement for the pH to be less than 2.0 stems from the necessity to maintain that strong acidity for proper treatment or analysis.