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{title2=$m=MQ/(zF)$}
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<Faraday's laws of electrolysis> state that the <mass> of material formed or consumed by a specified <electrode> reaction is proportional to the transported <electric charge>, and that equal <electric charge> produces <masses> proportional to $M/z$ for different reactions. Here $M$ is the product's <mass> per <mole>, and $z$ is the positive number of <Electrons> transferred per product entity. For complete use of the <electric charge> in that reaction,
$$
n_{e^-}=\frac QF,\qquad n_{\mathrm{product}}=\frac{Q}{zF},\qquad m=\frac{MQ}{zF}.
$$
The first relation uses the <Faraday constant>; the second uses <half-reaction> <stoichiometry>; the third converts <amount of substance> to <mass>. For equal transported <electric charge> in two ideal cells,
$$
\frac{m_1}{m_2}=\frac{M_1/z_1}{M_2/z_2}.
$$
The number $z$ belongs to the balanced <half-reaction>, rather than to the metal's name alone: <copper> deposited from $\mathrm{Cu}^{2+}$ needs $z=2$. These modern forms of both laws are given in KIT's practical.<Elektrolyse, Bestimmung von e by Karlsruhe Institute of Technology, Faculty of Physics teaching laboratory>{ref}

If other same-direction <electrode> reactions share the measured <electric current>, define an integrated current efficiency $\eta=Q_{\mathrm{product}}/Q$. Provided the product is neither subsequently consumed nor lost, the retained <mass> is
$$
m=\eta\frac{MQ}{zF},\qquad
\eta=\frac{\int I_{\mathrm{product}}(t)\,dt}{\int I(t)\,dt}.
$$
Here $0\leq\eta\leq1$ follows from the specified same-direction partition of <electric current>. It is not a universal bound on every signed partial-current convention: IUPAC notes that simultaneous <oxidation> and <reduction> at one <electrode> can produce a current-efficiency ratio above one.<IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book) by International Union of Pure and Applied Chemistry/current efficiency>{ref} When efficiency varies during a run, use the charge-weighted ratio above, rather than an unweighted average over <time>. If deposition removes material from a multicomponent <chemical solution>, specify which <chemical species> is being counted and balance its <half-reaction> before choosing $z$.

Michael Faraday's accessible 1834 paper, Experimental Researches in Electricity, Seventh Series, §783 states proportionality between chemical action and the quantity of electricity passed. In §§789–791 he describes connecting a molten tin-chloride cell in series with a water-decomposition charge indicator, weighing the receiving <electrode> before and after, and comparing the deposited metal with the indicator's gas readout. The common series <electric current> makes these two readouts comparable. This was a quantitative test of chemical equivalents, rather than merely an observation that a deposit appeared. It is historical evidence, not a suggested classroom procedure; the modern <Electron>-counting derivation above uses concepts unavailable to Faraday.<Experimental Researches in Electricity, Seventh Series by Michael Faraday>[§783; §§789–791; pp. 101–103]{ref}


 Faraday's laws of electrolysis (source code)