The passage of an electric current through a conducting solution causes chemical reactions. This is known as the chemical effect of electric current. Some of the chemical effects of electric current are the following:
• Formation of bubbles of a gas on the electrodes
• Deposition of metal on electrodes
• Change in colour of solutions
The process of decomposition of a chemical compound in a solution when an electric current passes through it is called electrolysis. The solution that conducts electricity due to the presence of ions is called an electrolyte. Two electrodes are inserted in the solution and are connected to the terminals of a battery with a switch in between. This arrangement is called an electrolytic cell. The electrode that is connected to the positive terminal of the battery is called the anode, and the other connected to the negative terminal is called the cathode. The electrolyte contains ions, which are charged. The positively charged ions are called cations and the negatively charged ions are called anions. Cations, being positively charged, get attracted to the negatively charged cathode and move towards it. On the other hand, anions, being negatively charged, get attracted towards the positively charged anode and move towards it. This is how ions move in an electrolyte and thus conduct electric current. A chemical reaction takes place at the electrodes. The reaction depends on the metals of which the electrodes are made and the electrolyte used. As a result of this reaction, we may observe bubbles at the electrodes due to production of gases, deposition of metal on the electrodes or change in the colour of the electrolyte.
During electrolysis, the concentration of the electrolyte remains unchanged; the number of electrons extracted at the cathode is equal to the number of electrons supplied at the cathode; Since metal atoms are deposited on the cathode, the mass of the cathode increases and the mass of the anode decreases by an equal amount.
Elecrolysis is used in refining and extraction of metals from impure samples. This process is called electrorefining. It is also useful in coating one metal with another. This process is called electroplating.
The most common application of electrolysis is electroplating. Electroplating is a process of coating one metal with another using an electric current. In this process, there exists an electrolyte, through which current passes. Two electrodes are inserted in the electrolyte and are connected to the terminals of a battery with a switch in between. The metal to be used for coating is chosen as the anode and the object to be electroplated is chosen as the cathode. The electrolyte is a salt of the anode metal which gets dissociated into its respective ions. The positive ions are called cations, and the negative ions are called anions. The current in the solution is due to the flow of these ions. The anions move towards the anode, and the cations move towards the cathode. The cations are converted into atoms at the cathode and form a layer on it, which we call electroplating. To compensate for the loss of ions in the solution, the atoms of the anode dissociate into the solution, forming the ions. When electric current passes through the circuit for 20-25 minutes, the metal from the anode gets deposited on the cathode.
Electroplating is done in industries to have an anti-reactive coating on the parts of machines so that they do not react with the raw material, to have an anti-corrosive coating for the machines so that they do not get corroded, and to have a heat-resistive coating for parts like boilers to resist the heat produced by the machinery. Gold plating is one of the most common applications of electroplating in ornament-making.
Group.chem.iastate.edu has created a simulation on electrolysis which gives a set up for electrolysis. Here one can change the electrodes, the electrolyte, the masses of the metals, the voltage applied and so on and see what happens.
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Sepuplhs.org has developed an animation of the electrolysis set up. It explains all the parts of the set up, like anode, cathode, electrolytic solution, battery, etc.
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