Chemistry | Electrochemistry | Galvanic cell (Full lesson)

The video begins with a greeting and an introduction to redox reactions in the context of galvanic cells. The presenter explains that 'redox' is a portmanteau of 'reduction' and 'oxidation,' with reduction being the gain of electrons and oxidation being the loss of electrons. The fundamentals of these reactions are explored, emphasizing electron transfer. The structure of a galvanic cell is also introduced, consisting of electrodes, a wire, a voltmeter, and an electrolyte. A salt bridge made of a highly soluble salt and porous plugs is mentioned as a key component that allows ions to move and maintain electrical neutrality.

The presenter discusses the importance of nitrates as soluble electrolytes in galvanic cells and contrasts them with less soluble alternatives like silver chloride and some sulfates. The function of the salt bridge, made of a concentrated salt solution, is explained in terms of its semi-permeable nature, allowing liquid flow but not solids. The theoretical aspects of redox reactions are further elaborated, with a focus on mass gain during reduction and mass loss during oxidation. The concept of the anode and cathode in a galvanic cell is introduced, with reduction occurring at the cathode and oxidation at the anode.

The video explains that galvanic cells convert chemical energy into electrical energy through spontaneous reactions. The necessity for these reactions to occur without an external energy source is highlighted. The roles of the anode and cathode are further clarified, with the anode undergoing oxidation and the cathode undergoing reduction. The terms 'oxidizing agent' and 'reducing agent' are introduced, explaining their functions in facilitating electron transfer within the cell.

The presenter delves into the concept of the standard hydrogen electrode as a reference point for measuring the tendency of substances to gain or lose electrons. The standard reduction potential table is introduced, showing how values tend to become more negative as one moves down the table. The video also explains the conditions under which standard reduction potentials are measured, such as a temperature of 25 degrees Celsius, a concentration of one mole per cubic decimeter, and a pressure of one atmosphere.

The video illustrates how to determine the direction of electron flow in a galvanic cell using the standard reduction potential table. It is shown that electrons flow from the anode (which undergoes oxidation) to the cathode (which undergoes reduction). The process of identifying the anode and cathode based on their respective standard potentials is demonstrated using zinc and silver as examples.

The presenter uses a zinc-copper cell to exemplify the working principle of a galvanic cell. The electrolytes for each half-cell are identified, and the importance of matching the correct copper ion is emphasized. The function of the salt bridge in neutralizing excess ions and completing the circuit is discussed. The video concludes with an overview of how the cell operates, with zinc undergoing oxidation and copper ions being reduced to metallic copper at the cathode.

The process of identifying the anode and cathode in a cell and determining the overall cell reaction is explained. By comparing the standard reduction potentials, the presenter shows how to write the half-reactions for the anode and cathode and combine them to form the net cell reaction. The mnemonic 'A B C' is used to help remember the process, with 'A' representing the anode, 'B' as a bridge (or the middle part), and 'C' for the cathode.

The video details the flow of electrons from the anode to the cathode and how this movement is represented in the half-reactions. The anode half-reaction is reversed to represent oxidation, while the cathode half-reaction remains the same to represent reduction. The net cell reaction is derived by ensuring the number of electrons lost at the anode equals the number gained at the cathode. The formation of zinc ions and copper metal is described, along with the mass changes at the electrodes.

The presenter explains the role of the salt bridge in neutralizing excess ions and allowing the movement of ions to complete the circuit. The movement of cations and anions in relation to the electron flow is discussed, with cations moving towards the cathode where electrons are gained. The accumulation of zinc ions in the salt bridge and the resulting neutralization process are also explained.

The video concludes with a demonstration of how to write the standard cell notation, which includes the anode and cathode reactions and the salt bridge. The presenter summarizes the operation of the galvanic cell, emphasizing the continuous nature of the reactions and the resulting changes in mass at the electrodes. The concept of spectator ions, which do not participate in the reaction, is introduced. The video ends with an encouragement to the viewers to work hard and prepare for upcoming exams.