An equivalent of any substance is equal in weight to its formula weight.

• A. True
• B. False
• C. It depends on the reaction and the number of reactive units
• D. It equals the mole mass

Answer: (C)

Equivalent weight depends on how a substance participates in a reaction. An equivalent is the amount of substance that reacts with or supplies one unit of reactive capacity (such as one H+ in acid-base reactions or one electron in redox reactions). Because different reactions involve different numbers of reactive units, the mass that corresponds to one equivalent changes with the reaction.

For example, a monoprotic acid like HCl donates one proton, so one equivalent equals its formula weight (molar mass). A diprotic acid like H2SO4 can furnish two protons, so one equivalent is half the formula weight. In redox, the number of electrons transferred determines the equivalent weight, so the molar mass divided by that number gives the equivalent weight.

Thus, the statement is not generally true; the correct idea is that the weight of one equivalent depends on the reaction and the number of reactive units involved.