# Optional Experiment

Chronocoulometry (CC) is a technique in which the CA *i-t* is integrated to give charge, Q, vs. time, *t*, where Q = ∫ *i* d*t*. The current, *i*, is the rate of electrolysis at any given time, *t*, and Q is the amount of charge transferred to time, *t*. In the case of an electron-transfer reaction, we can integrate the Cottrell relationship, denoting the Q due to a diffusing species as Q_{diff}.

\[Q_{diff}=\dfrac{2nFAC^b\, D^{1/2}\,t^{1/2}}{π^{1/2}}\tag{6}\]

The total charge, Q_{T}, is comprised of two other components: the Q_{dl} due to charging the double layer, as already discussed, and Q_{ads}, due to electrolysis of any electroactive species adsorbed on the electrode surface [i.e., Q_{T} = Q_{diff} + Q _{dl} + Q_{ads}]. Since the latter two terms are time independent (involves charge only of the surface), a plot of Q vs. t^{1/2} should be linear with the extrapolated intercept at *t* = o due to Q_{dl} + Q_{ads}.

With the *i-t* data from the chronoamperometry of ferricyanide reduction or FCA oxidation, obtain Q values at times of 50 mS, 100 mS, 200 mS and 300 mS. Plot Q vs. *t*^{1/2} and obtain the intercept value, which is due to Q_{dl}. Is this value reasonable for the charging of the double-layer?