Classify water using pH: identify the correct statements about neutrality, acidity, and alkalinity with respect to pH values.
-
AAt pH = 7, water is neutral
-
BAt pH < 7, water is acidic
-
CAt pH > 7, water is alkaline
-
DAll the above
-
EOnly (a) and (b)
Answer
Correct Answer: All the above
Explanation
Introduction / Context:pH is a master variable in water quality affecting corrosion, coagulation, disinfectant efficacy, and taste/odor. Correct classification of water based on pH is essential in environmental and municipal engineering.
Given Data / Assumptions:
- pH scale ranges nominally from 0 (strongly acidic) to 14 (strongly alkaline).
- Pure water at 25°C has pH ≈ 7 (neutral).
Concept / Approach:By definition, pH = −log10[H+]. At 25°C, [H+] = 10^−7 mol/L corresponds to neutral pH 7. Values below 7 indicate higher proton activity (acidic), and values above 7 indicate lower proton activity (alkaline/basic).
Step-by-Step Solution:
Confirm neutrality at pH 7 (true).Recognize acidity for pH < 7 (true).Recognize alkalinity for pH > 7 (true).Therefore, the inclusive correct choice is 'All the above'.Verification / Alternative check:Any standard water chemistry text or drinking-water standards describe these pH classifications.
Why Other Options Are Wrong:
- Options listing subsets omit one or more correct statements; the complete statement is required.
Common Pitfalls:
- Confusing alkalinity (as titratable carbonate/bicarbonate capacity) with simply having pH > 7; while related, they are distinct concepts.
Final Answer:All the above