Page 110 - [B._MURPHY,_C._MURPHY,_B._HATHAWAY]_A_working_meth

94 Chapter 7
chloride, NaCl,,,,, not only are the Na+ and the C1- ions
present, but also H20, i.e. H20 S H+ + OH-.
4. Determine which substances/species are present at the cathode
and which substances/species are present at the anode ('CNAP'):
Cathode is - ve, attracts + ve species
Anode is + ve, attracts - ve species
This procedure is modified further if water is present.
5. Examine the species at both electrodes carefully. If the electro-
lysis is that of a molten substance, this step can be ignored and
you can go directly to step 6. If, however, the electrolysis is that
of an aqueous solution, there will be a choice of two reactions at
both the cathode and the anode. To determine which reduction
half-reaction and which oxidation half-reaction actually occur,
the following rules of thumb should be applied:
I. Cathode reaction (reduction: M"+ + ne 3 M'):
Write down the Electrochemical Series in detail:
Little Lithium Li
Potty Potassium K
Sammy Sodium Na
Met Magnesium Mg - ve
A Aluminium A1
Mad Manganese Mn
Zebra Zinc Zn
In Iron Fe
Lovely Lead Pb
Honolulu Hydrogen H 0.00 v
Causing Copper cu
Strange Silver Ag + ve
Gazes Gold Au

(a) If the element is above zinc in the Electrochemical Series, then
H2cg, will be discharged at the cathode, according to the
following reduction half-reaction: