Electrogravimetry in electrogravimetry the product is deposited quantitatively on an electrode by an electrolytic reaction and the amount of the product is determined by weighing the electrode before and after electrolysis. The material is deposited on an electrode by the application of a potential instead of chemical precipitation from a solution. Hence the name electrogravimetry (weighing of the product after electrolysis).

There are two types of electrochemical cells: 1. Electrochemical cells which generate an electric current are called voltaic cells or galvanic cells, and common batteries consist of one or more such cells. 2. Other electrochemical cells an externally supplied electric current is used to drive a chemical reaction which would not occur spontaneously. Such cells are called electrolytic cells. • Spontaneous reactions occur in galvanic (voltaic) cells; nonspontaneous reactions occur in electrolytic cells. • Both types of cells contain electrodes where the oxidation and reduction reactions occur. • Oxidation occurs at the electrode termed the anode and reduction occurs at the electrode called the cathode.

- These definitions apply to both galvanic and electrolytic cells. Cell Convention - The metal in the half-reaction where Oxidation is occurring is called the Anode - The metal in the half-reaction where Reduction is occurring is called the Cathode. - The Cathode is often labeled with a "+"; "this electrode attracts electrons" . - The Anode is often labeled with a "–"; "this electrode repels electrons" . - These definitions apply to both galvanic and electrolytic cells.

Galvanic or Voltaic Cells • Voltaic cell is a simple device with which chemical energy is converted into electrical energy. Voltaic cell is any cell that generates an electric current by an oxidation –reduction reaction. The redox reaction in a galvanic cell is a spontaneous reaction. • For this reason, galvanic cells are commonly used as batteries. Galvanic cell reactions supply energy which is used to perform work. The energy is harnessed by situating the oxidation and reduction reactions in separate containers, joined by an apparatus that allows electrons to flow. A common galvanic cell is the Daniell cell, shown below:

Electrolytic Cells The redox reaction in an electrolytic cell is nonspontaneous. Electrical energy is required to induce the electrolysis reaction ( Electrolysis is the process in which a reaction is driven in its nonspontaneous direction by the application of an electric current)

TYPES OF ELECTROGRAVIMETRIC METHODS Electrolytic precipitation or electrode position has been widely used for the determination of metals. In most applications, the metal is deposited on a weighed platinum cathode and the increase in mass is determined. There are two types of electrogravimetric methods 1- Constant current electrolysis and 2- Constant potential electrolysis.

1. Constant-current electrolysis :- In this case electrode position is carried out by keeping the current constant and applied potential is increased periodically as the electrolysis proceeds. The apparatus for constant current technique mainly consist of :- 1- 6 V battery as DC source of power, 2- Ammeter and voltmeter to measure the current and applied voltage respectively. 3- The voltage applied to the electrolytic cell is controlled with a resistor. 4- The cathode is usually cylindrical platinum gauze.

2. Constant potential electrolysis: This electrogravimetric method is also called or potentiostatic method. In this method potential of the working electrode is maintained at a constant level versus a reference electrode, such as the SCE. This technique requires additional equipment like electronic voltmeter, a potentiostat and a reference electrode.

Limitation of electrogravimetric methods. Though these techniques are simple but the sensitivity is the issue in these methods. Difficulty in determining the small difference in mass between the electrode itself and the electrode plus deposit. Another limitation with this technique is requirement of washing and drying of the electrode, therefore it is limited to electrode reaction involving the formation of insoluble substances.Thus, electrogravimetric methods are limited to detection of metals which can give smooth and adherent metal platings and deposits.

Applications of Electrogravimetry 1) Quantitative analysis :- This technique involves deposition of the desired metallic element upon a previously weighed cathode, followed by subsequent reweighing of the electrode plus deposit to obtain by difference the quantity of the deposited metal. 2) Separations – separate one species from another in solution by selectively plating it out and removing it from solution. This method is used to remove interferences particularly in electrochemical methods

3) Preconcentration – plating out metals from a large volume of solution (> 1 L) onto a small electrode effectively increases their concentration. Can also reoxidize metals back into a small volume of solution (e.g., 1 mL) & the ratio of volumes gives preconcentration factor (i.e., 1000). Can also use other methods for analysis of metal on solid electrode surface