This analytical technique relies heavily on Faraday’s laws of electrolysis. These fundamental laws state that electricity and chemical reactions are directly linked. The total electrical charge passed is proportional to the number of reacting molecules.
The standard math formula for this law is Q = nFN. In this formula, Q is the charge and n is the electrons per molecule. F represents Faraday’s constant and N is the moles of the chemical.
To work properly, the reaction must have exactly 100 percent current efficiency. This means every single electron must go toward the intended chemical change. No electrical energy can be wasted on unintended side reactions in the liquid.
Chemists use two main ways to run this specific test. The first way holds the voltage constant until the chemical reaction completely stops. The second way keeps the current constant and measures how much time passes.
Because machines can measure electrical charge with incredible accuracy, this method is highly precise. This high precision makes coulometry perfect for finding trace amounts of metals or water. Chemists consider this process to be a fully absolute measurement method.
This means you do not need to compare it to a known calibration standard. You only need to trust the basic fundamental laws of physics and chemistry. Students often forget that time is a crucial part of the final measurement. Electrical charge is just the steady electrical current multiplied by the total time.