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When one coulomb of electricity is passed through an electrolytic solution, the mass deposited on the electrode is equal to:
A. equivalent weight
B. molecular weight
C. electrochemical equivalent
D. one gram

Last updated date: 13th Jun 2024
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Hint: We have to mark the option which is coined for the term mentioned in the question. One coulomb of electricity when passed through an electrolytic solution, electrolysis occurs and some ions are deposited at the electrodes.

Complete answer: Let’s define all the terms given in option and then choose the appropriate answer.
A. Equivalent weight: Equivalent weight is the mass of one equivalent, that is the mass of a given substance which will combine with or displace a fixed quantity of another substance. The equivalent weight of an element is the mass which combines with or displaces 1.008 gram of hydrogen or 8.0 gram of oxygen or 35.5 gram of chlorine. It is also known as gram equivalents.

B. Molecular weight: The molecular weight also called as molecular mass (m) is the mass of a given molecule: it is measured in Daltons (Da or u). Different molecules of an equivalent compound may have different molecular masses because they contain different isotopes of a component.

C. Electrochemical equivalent: Electrochemical equivalent (ECE) may be defined as “the mass of the ion deposited by passing a current of one Ampere for one second (i.e., by passing Coulomb of electricity)”. Its unit is gram per coulomb.
It is represented by Z.

D. One gram: A gram is a unit of mass in the metric system defined as one thousandth $1\times {{10}^{-3}}$of a kilogram. Originally, the gram was defined as a unit equal to the mass of one cubic centimetre of pure water at ${{4}^{\circ }}C$ (the temperature at which water has maximum density).
So, the correct answer is “Option C”.

Note: The molecular mass and relative molecular mass are distinct from but associated with the molar mass.
The molar mass is defined because the mass of a given substance divided by the quantity of a substance and is expressed in g/mol. The molar mass is typically the more appropriate figure when handling macroscopic (weigh-able) quantities of a substance.
Don’t get confused between equivalent weight and electrochemical equivalent as both are completely different things.