experiment 32 Galvanic cells, the nernst equation

objectives

- to measure the relative reduction potentials for a number of redox couples
-to develop an understanding of the movement of electrons, anions, and cations in a galvanic cell
-to study the factors affecting cell potentials
-to estimate the concentration of ions in solution using the Nernst equation

in galvanic cells, redox rxns occur ?

Spontaneously

in electrolytic cells, redox rxns occur ?

Non - Spontaneously and require energy to occur

interface

the boundary between two phases; in this case, the boundary that separates the solid metal from an aqueous solution

redox couple

an oxidized and reduced form of an ion/substance appearing in a reduction or oxidation half-reaction, generally associated with galvanic cells

galvanic cell

makes for the spontaneous transfer of electrons: forces e- to pass externally through a wire ( an external circuit ) for reduction

half cell

half cell consists of an electrode, usually the metal (reduced state) of the redox couple, and a solution containing the corresponding cation (oxidized state) of the redox couple ; a part of the galvanic cell that hosts a redox couple

external circuit

the movement of charge as electrons move through a wire connecting the two half cells, forming one half of the electrical circuit in a galvanic cell

salt bridge

paper moistened with a salt solution, or an inverted tube containing a salt solution, that bridges two half cells to complete the solution part of an electrical circuit

internal circuit

the movement of charge as ions through solution from one half cell to another, forming one half of the electrical circuit in a galvanic cell

cathode

silver electrode at which reduction occurs

anode

copper electrode at which oxidation occurs

why is the anode designated negative?

bc an oxidation process donates electrons to the copper electrode to provide a current in the external circuit, the anode is negative

why is the cathode positive?

a reduction process accepts electrons from the circuit and supplies them to the silver ions in the solution so the cathode is positive

cell potential

cell potential of a galvanic cell is due to the difference in tendencies of the two metals to oxidize (donate electrons) or of their ions to reduce (accept electrons)

reduction potential

the tendency for an ion (or molecule) to accept electrons, the value used to identify the relative ease of reduction for a half reaction

potentiometer/multimeter

placed in the external circuit between the two electrodes, measures the cell potential (e cell), a value that represents the differences between the tendencies of the metal ions in their respective half cells to undergo reduction

the measured cell potential corresponds to the standard cell potential when...

the concentrations of all ions are 1 mol/L and temperature of all solutions is 25 C

Nernst equation

e cell = e cell - (0.0592/n)logQ