MEHRAN UNIVERSITY OF ENGINEERING AND TECHNOLOGY, JAMSHORO

DEPARTMENT OF METALLURGY AND DEPARTMENT OF METALLURGY AND MATERIALS ENGINEERINGMATERIALS ENGINEERING

The potential difference across an electrochemical cell is the potential difference measured between two electronic conductors connected to the electrodes.

In the external circuit, the electrons will flow from the most negative point to the most positive point.

By convention, the current will flow in the opposite direction.

Since the electrode potential can be either positive or negative, the electrons in the external circuit can also be said to flow from the least positive electrode to the most positive electrode.

A voltmeter may be used to measure the potential differences across electrochemical cells but cannot measure directly the actual potential of any single electrode.

Nevertheless, it is convenient to assign part of the cell potential to one electrode and part to the other.

Iron is connected to copper and then immersed in a solution containing both Fe2+ and Cu2+ charge.

I. Which metals corrodes?II.Write equations to describe the reactions

which occurs at each electrode, assuming each electrode has a valency of 2.

III.Calculate the maximum possible potential of the resulting corrosion cell.

A Reference electrode is an electrode which has a stable and well-known electrode potential.

The high stability of the electrode potential is usually reached by employing a redox system with constant (buffered or saturated) concentrations of each participants of the redox reaction.

There are many ways reference electrodes are used. The simplest is when the reference electrode is used as a half cell to build an electrochemical cell.

This allows the potential of the other half cell to be determined.

Since only differences in potential can be measured, a benchmark electrode is required, against which all other electrode potentials can be compared.

The particular reference electrode used must be stated as part of the units.

The electrode reaction2H+ + 2e- = H2

is defined as having an electrode potential, EH+/H2 of zero volts, when all reactants and products are in the standard state.

The standard chemical potential of H+ at 1 molar (M) concentration is by definition equal to zero.

The standard state is defined as 298 K, 1 bar pressure for gases and a concentration 1 molar (1 mol dm-3) for ions in aqueous solution.

1) Platinized platinum electrode

2) hydrogen blow3) solution of the acid

with activity of H+ = 1 mol dm-3

4) hydroseal for prevention of the oxygen interference

5) reservoir through which the second half-element of the galvanic cell should be attached.

As a direct result of this, the standard hydrogen electrode (SHE) is commonly used as a reference electrode.

When coupled with an electrode, the potential difference measured is the electrode potential of that electrode, as the SHE establishes by definition the zero point on the electrochemical scale.

The standard hydrogen electrode consists of a platinum electrode suspended in a sulphuric acid solution with a one molar concentration of H+.

Purified hydrogen is bubbled through to equilibrate the 2H+ + 2e- = H2 electrode reaction.

This historically important reference electrode is called the standard hydrogen electrode (SHE) if a standard solution of acid is used.

"By definition" the equilibrium potential of this electrode is zero at any temperature."

The SHE is also called by many "normal hydrogen electrode" (NHE) in reference to a solution containing one equivalent of protons.

However, the SHE can be somewhat inconvenient to use because of the need to supply hydrogen gas.

Therefore, other reference electrodes are much preferred for practical considerations.