pH Value, pH Scale and Its Measurement between 0 and 14

Curiosity is the first and foremost trait of a science student. Remember when your chemistry teacher in high school taught you about the pH scale? Remember how you were told pH value is measured between 0 and 14? Well, if you are reading this, you're probably a science enthusiast and probably do have the basic traits of a science student. So if you did wonder why pH is measured only on a scale of 0 to 14 and not negative values or in 100s, you can get the answer to that question here.

The answer is, well, pH is not actually measured between 0 and 14. Most commonly found solutions have their pH value lying between this range, but in fact, the pH value of a solution can be lesser or greater than this range.

Definition of pH Value

The general definition of the pH value of a solution is the negative base-10 log of the concentration of hydronium ion in the solution.

In the pharmaceutical industry, we're used to not more than 1M in concentration under normal cases. With that being said, the pH value could be on 2 extremes in that case. One far end is not more than 1M of hydrogen ions, which results in a pH value of not more than 0. While on the other end is not more than 1M of hydroxide ions which results in a pH value of not more than 14.
Related: Working Principle of pH Meter

This can be verified by mathematical calculations involving formulae that express equilibrium constant and dissociation constant of the dissociation of water into hydrogen and hydroxide ions which are positive and negative respectively.

Well, with that on one hand, we also must remember that nature ain't a very good fan of following rules that humans lay down. So rest assured, the concentration of solutions in nature need not necessarily be less than 1M.

Why is the pH value measured between 0 and 14?

The pH value goes out of the 0-14 range when the concentration of the solution exceeds 1M. While in basic practice the pH value is the negative log of hydrogen ion concentration, what chemistry graduates would know is that technically the value is a measure of the activity of hydrogen ion. While that is hard to estimate or experimentally find out, the former method suits for most cases with appreciable accuracy.

So if you're wondering about what other factors that could influence the pH value of a solution, one major factor would be the temperature at which the test of the pH of the solution is carried out. Why? I hope you would not ask that question, because we believe that as a science enthusiast you know that temperature is a villain who interferes and alters results in most experiments and tests. So obviously, the temperature would affect the equilibrium and dissociation rates, which would directly result in a change of pH value. For example, water that expresses pH value of 7 at room temperature would express a different pH at a different temperature.

We end this article with a practical implication of this theory. Even the slightest or drop or hike in the pH value of a person's blood is a sign that they are sick because it would have been caused by a hike or a drop in body temperature which had altered the dissociation rates of the blood solution.

Frequently Asked Questions (FAQs) on pH Value and Its Measurement

Q: What is the full form of pH?

The full form of pH is the "Potential of Hydrogen".

Q: What is the significance of pH measurement?

pH measurement is very useful because it provides basic information of acidity or alkalinity of the solution. pH value of the solution is used in various areas like chemistry, biology environmental science and medicine discovery. In pharmaceuticals, pH is used in tablet manufacturing, chemical analysis, water quality determination and effluent treatment plant.

Q: What is the pH scale and pH scale range?

pH scale is a logarithmic range of hydrogen ion concentration that measures the acidity and alkalinity of the solutions. pH scale ranges between 0 and 14. Solutions with pH below 7 are considered acidic and with pH above 7 are considered basic while pH 7 is considered neutral.

Q: What does the ph scale measure?

pH scale measures the acidity or alkalinity of the solution in terms of hydrogen ion concentration. pH value provides information about the solution about its acidity and alkalinity that can be used in various aspects.

Q: How is the pH value determined?

pH is measured using a pH meter or pH strip indicator or pH paper. pH meter measures the voltage difference between two electrodes and this voltage is coveted to ph value in numbers between 0 and 14. pH indicator paper changes its color based on the pH of the solution, red color in acidic solution and blue color in basic solution. The intensity of the dark color shows the higher and lower pH value. pH strip indicator does not show any number but its color is matched with the standard color to determine the approximate pH value.

Q: What does a pH value below 7 indicate?

A pH value below 7 indicates that the solution is acidic and a lower value shows the more acidic solution. The solution with 3 pH is more acidic than the solution having a pH value of 5.

 

Q: What does a pH value above 7 indicate?

A pH value above 7 indicates that the solution is basic in nature and a higher value shows the more acidic solution. The solution with pH 12 is more basic in nature than the solution with a pH value of 8.

Q: What does a pH value of 7 indicate?

The solution with a pH value of 7 is considered neutral. It indicates that the solution is neither acidic nor basic and has a balance of hydrogen and hydroxyl ions. At 25° C, distilled water is considered neutral.

Q: Can pH values exceed the range of 0 to 14?

pH value of the aqueous solution always remains between 0 and 14. In extreme conditions or nonaqueous solution pH value may exceed this range.