Wastewater chemistry basics: If the pH of sewage is measured to be exactly 7.0 at 25°C, how is it classified?

Introduction / Context:
pH is a measure of hydrogen ion activity and is fundamental to wastewater process control. It influences biological treatment, corrosion, scaling, and disinfectant efficacy. Understanding classifications helps operators quickly assess process health and potential risks.

Given Data / Assumptions:

• Measured pH = 7.0 at standard conditions.
• No temperature correction required for classification.
• Standard pH scale from 0 (acidic) to 14 (alkaline).

Concept / Approach:

On the conventional logarithmic pH scale, pH 7.0 represents neutral water at 25°C. Values below 7 indicate acidity; values above 7 indicate alkalinity. Raw sewage often falls between roughly 6.5 and 8.5 depending on source contributions.

Step-by-Step Solution:

Verification / Alternative check:

Cross-check with calibrated pH meter and buffer solutions (pH 4, 7, 10). Minor temperature effects do not alter categorical classification at exactly 7.0.

Why Other Options Are Wrong:

Acidic requires pH < 7; alkaline requires pH > 7; “none of these” does not apply because 7.0 is precisely neutral.

Common Pitfalls:

Assuming neutrality across temperatures without calibration; relying on indicator papers which may be less precise for operational decisions.

Final Answer:

Neutral