(Unit 3)Electrochemistry

• Electrochemistry is a field of chemistry that deals with the relationship between electrical energy and chemical energy
• All electrochemical reactions involve the transfer of electrons and are therefore redox reactions
• Devices that convert chemical energy to electrical energy or electrical energy to chemical energy are called electrochemical cells
• Electrochemical cells can be classified as electrolytic cells and galvanic or voltaic cells
• In electrolytic cells, electrical energy is used to do chemical work and produce new chemical substances
• Galvanic cells induce chemical changes that produce electrical energy
• Examples of galvanic cells include flashlight batteries, wrist watches, cameras, and car batteries
• Electrolysis is used to manufacture metals like sodium, aluminum, non-metals like chlorine, hydrogen, compounds like sodium hydroxide and sodium hypochlorite
• Electrochemistry has practical applications in the production of dry cells and lead storage batteries used in the automotive industry
• Metallic conduction occurs by movement of electrons under applied potentials in solid or molten metallic forms without undergoing chemical change
• Non-metals are generally non-conductors of electricity because they do not have freely moving electrons
• Graphite is a form of carbon that conducts electricity due to the movement of electrons through its hexagonal layers
• Electrolytic conductors, or electrolytes, transmit electricity in molten state or in aqueous solution
• Strong electrolytes ionize almost completely in aqueous solution, while weak electrolytes ionize only slightly
• When electrical potential is applied through electrolytes, positive ions move towards the cathode and negative ions move towards the anode
• Ionic compounds are non-conductors of electricity in the solid state because their ions are held at fixed positions and cannot move
• Electrodes in an electrolysis cell can be chemically active or inert, with examples of active electrodes being zinc and magnesium, and inert electrodes being platinum and graphite
• Anode is the electrode connected to the positive terminal of the source and is positively charged
• Cathode is the electrode connected to the negative terminal of the source and is negatively charged
• During electrolysis, ions of the electrolyte migrate to electrodes of the opposite charge
• Cations are attracted to the cathode and discharge by gaining electrons, which is called reduction
• Anions are attracted to the anode and discharge by losing electrons, which is called oxidation
• Cathode is where reduction occurs and anode is where oxidation takes place
• Oxidation half-reactions occur at the anode and reduction half-reactions at the cathode
• Net reaction in the electrolytic cell is known as cell reaction or redox reaction
• Electrolysis is a process using electric energy to bring about an oxidation-reduction reaction
• Electrolysis can be defined as the decomposition of an electrolyte using electricity
• Electrolysis of molten electrolytes involves dissociation of ionic solids into positive and negative ions
• During electrolysis of molten electrolytes, cations move towards the cathode and gain electrons, while anions move towards the anode and lose electrons
• In the electrolysis of molten sodium chloride, sodium metal is deposited at the cathode and chlorine gas is liberated at the anode
• Positive ions are called cations and negative ions are called anions
• Oxidation and reduction reactions proceed simultaneously in a redox reaction
• Galvanic cells are electrochemical cells where spontaneous redox reactions generate electricity
• Primary galvanic cells cannot be recharged, examples include Daniel’s cell, zinc-carbon dry cell, and fuel cells
• Galvanic cells contain two electrodes in contact with an electrolyte, which can be in the form of a solution or paste
• In a Daniel cell, zinc atoms lose electrons at the anode and copper ions gain electrons at the cathode
• Salt bridge in a galvanic cell maintains electrical neutrality between the two solutions and allows electrical contact between them
• Purpose of the salt bridge is to maintain electrical neutrality, allow electrical contact, and prevent mixing of the two solutions
• To design and construct a simple galvanic cell
• Materials required:

  • 1.0 M solution each of ZnSO4 and CuSO4
  • Concentrated KCl solution
  • Zinc and copper strips
  • Electric wires
  • Beakers
  • A salt bridge
  • A tomato or lemon
  • Magnesium ribbon
  • Zinc, iron, and aluminum metals