Why ph range is between 0 to 14 | Why Are pH Values Only In A Range of 0-14

Value of pH is determined between 0 and 14 that shows the alkalinity and acidity of the solution. pH 7 is considered as neutral.

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.

The general definition of the pH val ue 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. 

This verified by calculations involving formulae that express can be mathematical 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.

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 which expresses pH value of 7 in 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.

Why Are pH Values Only In A Range of 0-14

A pH outside the conventional 0-14 range is possible, but various limitations caused by the instruments and the solution itself restrict us from measuring such a substance.

We often label water as a neutral solution with a pH of 7. Also, any solution that seems acidic is said to have a pH of less than 7, while one that is basic is said to have a pH greater than 7. However, what are these numbers and what do they tell us about the solution? Is it true that a solution can only have pH values in the range 0f 0-14?

A pH outside the conventional 0-14 range is possible, but various limitations caused by the instruments and the solution itself restrict us from measuring such a substance.

We often label water as a neutral solution with a pH of 7. Also, any solution that seems acidic is said to have a pH of less than 7, while one that is basic is said to have a pH greater than 7. However, what are these numbers and what do they tell us about the solution? Is it true that a solution can only have pH values in the range 0f 0-14?

What is the pH scale?

The pH scale is used to determine whether a substance is acidic or basic, and to calculate how strong a chemical it is. A pH value is a number that ranges from 1 to 14 for most common chemicals, with seven being the middle or neutral point. Values below 7 are indicators of acidity, which increases as the number decreases, while values above 7 indicate alkalinity, which increases as the value increases. One interesting thing to note here is that the pH scale is not a linear scale. In other words, an acid with a ph of 3 is not twice as strong as an acid with a pH of 6. An important distinction to understand is that the pH scale is a logarithmic scale.

The formal definition of pH reveals that is simply a measure of the activity of hydrogen ions in a given solvent. Activity here means that their movement is free, which is only possible if the chemical has ionized, thus releasing ions into the solution.

pH formula

The formula to calculate pH looks something like this: pH=−log10[Hsolvated].

This is a logarithmic equation with a base 10. On this scale, a substance with a ph of 3 is ten times more acidic than a substance with a pH of 4, and 100 times more acidic than a substance with a pH of 5. Similarly, a substance with a pH of 9 is ten times more alkaline than a substance with a pH of 8, and 1000 times more alkaline than a substance with a pH of 6.

What does the p in pH stand for?

The story behind the discovery of the pH scale is quite interesting. The concept of pH was first introduced by a chemist named Soren Peder Lauritz, who worked at the Carlsberg Laboratory in Copenhagen, Denmark. The first mention of this term looked something like this— p­H—a small p with an H in the subscript.

While the H represents the hydrogen ion concentration upon which the entire concept revolves, the exact meaning of the p is highly disputed. The scale basically measures a potential difference between different solutions by counting the negative power of ten. Both of these words—”power” and “potential”—start with p in all three languages (French, German and Danish) that Sorensen spoke and published his research in. Given that ambiguity, the meaning of the p remains one of the great mysteries in the field of chemistry, although not something overly critical to the concept itself.

Can we have pH values outside the 0-14 range?

Theoretically speaking, the pH scale should actually range from negative infinity to positive infinity. This claim is according to its definition, which states that the pH of a substance is the value defined by the negative logarithm of the hydrogen ion concentration. However, in reality, most solutions you would find in a standard laboratory have a pH value between 0-14. This is because, in order to reach pH levels below 0 or above 14, one would require extraordinarily acidic or basic solutions, respectively.

A saturated sodium hydroxide solution (NaOH) solution is supposed to have a pH of 15 based on its molarity. However, the chemical will not be able to solvate entirely due to the presence of water, which acts as a hindrance to the solvation (breakdown) of larger molecules. This will, in turn, result in a decline in the release of hydroxide ions (OH–), which are ions that absorb the hydrogen ions, increasing the pH of the solution.

Is a negative pH possible?

Achieving a negative pH rating is definitely possible. In practice, any acid that yields a concentration of hydrogen ions with molarity greater than one will show a negative pH when calculated. However, whether or not an acid actually has a negative pH value isn’t something that can be verified effectively in a lab.

To put this in perspective, consider a 12 M solution of hydrochloric acid (HCL). This chemical should have a pH of -1.08, which is one unit above the standard pH scale, but we cannot measure it with any known instrument. Litmus paper (the most common means of measuring pH) only indicates whether the pH value is above or below seven. As such, pH meters are necessary to establish the actual value. However, even glass-electrode pH meters fail in such extreme tasks because of something called acid error, which causes even these highly advanced devices to measure a pH that is higher than the true value. Even if we improve the efficiency of these instruments and achieve “perfection” (which seems almost impossible), there is still one final problem—effective concentration.

What is effective concentration?

Strong acids never fully dissociate in water to release the number of hydrogen ions required to bring the meter of the device to a negative value. Accentuating this problem is the effective concentration of hydrogen ions, which is always less than the true concentration, as there is very little water per unit of acid in strong and concentrated acid solutions. Water helps in the breakdown of acids, releasing hydrogen ions in the process. This is because water is a dipole molecule and creates net effective dipole movement. However, in the absence of water, the acid molecules don’t break down as much as they should, which makes the pH much higher than you would expect based on their molarity.