Video: EC17-18-S2-Q10B

What is the name for the mass of a substance that has the ability to lose or gain one mole of electrons during chemical reactions?

02:41

Video Transcript

What is the name for the mass of a substance that has the ability to lose or gain one mole of electrons during chemical reactions?

Firstly, let’s have a think about what it means to lose or gain a mole of electrons. Let’s imagine we have a reduction process, where a substance A is gaining electron, forming A⁻. If we have one mole of electrons being gained in this process, we must start out with one mole of A. The same is true if we’re dealing with a one-electron oxidation process. But what if we’re dealing with a two-electron reduction. We still have one mole of electrons. However, we only have half as many moles of the starting material. A similar scenario occurs with the three-electron reduction.

Now we can see what happens when we try to calculate the mass of each substance. In the case of the one-electron reduction, we have one mole of A. Therefore, we have one times the molar mass of A, in grams. In the case of the two-electron and three-electron reductions, the molar mass of each substance has to be divided by the number of electrons in the equation. In all three cases, we’ve worked out the mass in grams, required to generate one mole of electrons. Another way of expressing one mole of electrons is one equivalent.

Hopefully, all of this should jog your memory as to the name for the mass of a substance that has the ability to lose or gain one mole of electrons during chemical reactions, the gram equivalent mass of a substance. Historically, the gram equivalent mass of a substance was of great importance because molar masses weren’t necessarily known. And chemists needed to be able to dispense precise amounts of ingredients to produce a desired result.

This definition of the gram equivalent mass of a substance is in fact only applicable to redox processes. The gram equivalent mass of a substance can be defined in acid-based chemistry as the mass in grams that will react with or generate one mole of protons. Or it can be defined in general chemistry as the mass of a substance that will react with one mole of hydrogen atoms.

In any case, the gram equivalent mass of a substance is the answer we’re looking for.

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