What is pH value of pure water?

Appeared in: UPPSC 2022

Explanation

Pure water at 25°C has a neutral pH of 7.0.
Neutrality in water is defined by an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻).
The pH scale is a logarithmic scale from 0 to 14, where 7.0 is the midpoint representing a neutral solution.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain pH of pure water and the pH scale as background academic context rather than a clinical decision trigger.
Understanding pH is fundamental in nursing for interpreting arterial blood gas (ABG) results, as normal blood pH is tightly regulated between 7.35 and 7.45.
Deviations from the normal blood pH range lead to life-threatening conditions like acidosis (pH below 7.35) or alkalosis (pH above 7.45), which affect all cellular functions.
What if? If a patient's blood pH drops to 7.20, they are in a state of acidosis. The nurse's priority would be to assess respiratory status, administer prescribed buffers like sodium bicarbonate, and notify the physician immediately, as this indicates severe metabolic or respiratory dysfunction.

How to Approach the Question

This is a factual recall question testing a fundamental concept in chemistry and physiology.
Identify the keywords in the question: 'pH value' and 'pure water'.
Recall the definition of the pH scale, where 7.0 represents a neutral solution.
Recognize that 'pure water' is the universal standard for a neutral substance.
Evaluate the options based on this knowledge. Eliminate values below 7 as acidic and values above 7 as alkaline, leaving 7.0 as the only correct choice.

Concept Tested & Keywords

QsyEXsA2fpELEfy1mK4fH1

E6 Physiology Guyton 4SAE Part 2B p. 66-68

E6 textbook of Applied Biochemistry and Nutrition & DieteticsHarbans Lal (pp 26-464 of 479) p. 149-151

E6 Physiology Ganong 27e Vol 1 Part 1 p. 13-15

Practise the full UPPSC 2022

Attempt every question from this paper in a timed mock, then review the full solution for each one.