How Is pH Calculated?

The pH scale ranges from zero to 14.
••• Calculator image by Alhazm Salemi from Fotolia.com

pH Measurement

The pH scale measures the concentration of hydrogen ions and hydroxide ions to determine how basic or acidic a solution is on a scale between zero and 14. If you want to know how to calculate pH, you must understand that the higher the number, the more basic the solution. Conversely, the strongest acids have numbers closer to zero. Acidic solutions have a greater concentration of hydrogen ions, and basic solutions have a higher concentration of hydroxide ions. Because pH is based on logarithms, a decrease of one means the acid is 10 times more acidic, and an increase in one means it is 10 times more basic.

Water (H2O) can disassociate into one hydrogen ion and one hydroxide ion. Therefore, it is neither acidic nor basic and has a pH of seven. Hydrogen ions are represented as H+ and hydroxide ions are represented by OH-.

How to Calculate the pH of a Solution

There are two ways to calculate pH of a solution. One is with hydrogen and the other is hydroxide. Calculate the concentration of hydrogen (H+) ions by dividing the molecules of hydrogen ions by the volume, in liters, of the solution. Take the negative log of this number. The result should be between zero and 14, and this is the pH. For example, if the hydrogen concentration is 0.01, the negative log is 2, or the pH. The stronger the acid, the more corrosive the solution.

Using Hydroxide Concentration to Calculate pH

The pH of a solution also can be determined by finding the pOH. Determine the concentration of the hydroxide ions by dividing the molecules of hydroxide by the volume of the solution. Take the negative log of the concentration to get the pOH. Then subtract this number from 14 to get the pH. For example, if the OH- concentration of a solution was 0.00001, take the negative log of 0.00001 and you get five. This is the pOH. Subtract five from 14 and you get nine. This is the pH.

Related Articles

What Is the pH of Distilled Water?
How to Calculate the pH of Ammonia Water Using KB
How to Calculate Hydrogen Ion Concentration
What Does pH Mean in Chemistry?
What Is pH of Sodium Carbonate in Water?
How to Calculate Alkalinity After Titration
General Characteristics of Acids & Bases
What Is the Function of Litmus Paper?
How to Find the Half Equivalence Point in a Titration...
How to Calculate Total Alkalinity
How to Calculate the pH of a Strong Acid
How Can You Tell If a Substance Is Acidic?
How to Find pH for a Given Molarity
What Is the pH of Distilled Water?
The Effects of Temperature on the pH of Water
What pH Numbers Are Considered Acidic, Base & Neutral?
Physical Properties of Household Ammonia
How to Make a 50% Normal Solution of Hydrochloric Acid
How do I Calculate the Amount of Acid to Reduce Water...
How to Convert pKa to Ka