This summary of the video was created by an AI. It might contain some inaccuracies.
00:00:00 – 00:06:39
The video provides a comprehensive tutorial on solving for non-standard cell voltage using the Nernst equation, which is represented as ( E = E^{text{standard}} – frac{0.0257}{n} ln Q ). The instructor begins by determining the standard cell voltage (( E^{text{standard}} )) through the difference between the voltages of the cathode and anode half-reactions involving Chromium 3+ and Calcium 2+, respectively. The standard voltage is found to be 2.124 volts. Moving forward, the number of electrons exchanged (n) is established by balancing the redox reaction, which involves six electrons. The reaction quotient (Q) is then calculated using the given molar concentrations of calcium and chromium ions, yielding a value of 46.5. Finally, the instructor demonstrates the correct sequence of calculations, ultimately arriving at a non-standard cell voltage of 2.11 volts, and underscores the necessity of manually inputting the unit (volts) in the final answer.
00:00:00
In this part of the video, the instructor demonstrates how to solve the ALEKS problem of calculating non-standard cell voltage using the Nernst equation. The Nernst equation is given as ( E = E^{text{standard}} – frac{0.0257}{n} ln Q ). The instructor notes that another version of the equation uses a logarithm base 10 instead of the natural logarithm. To solve, the standard cell voltage (( E^{text{standard}} )), the number of electrons exchanged (n), and the reaction quotient (Q) are needed.
First, the instructor calculates the standard voltage (( E^{text{standard}} )) using the formula ( E^{text{standard}} = E_{text{cathode}} – E_{text{anode}} ). The reduction reaction, occurring at the cathode, involves Chromium 3+ reducing to Chromium. This specific reaction is identified from a table of half-reactions with a voltage of -0.744 volts.
Next, the oxidation reaction at the anode involves Calcium 2+ converting to solid Calcium, with a half-cell voltage of -2.868 volts. The standard cell voltage (( E^{text{standard}} )) is calculated as ( -0.744 – (-2.868) = 2.124 ) volts.
00:03:00
In this part, the video explains how to determine the number of moles of electrons (n) exchanged in a redox reaction by examining the half-reactions, specifically focusing on the calcium reaction where initially two electrons are exchanged. However, after adjusting the stoichiometric coefficients to match the overall reaction, it is determined that six electrons are actually exchanged. The video then calculates the reaction quotient (Q) by using the molar concentrations of products and reactants, excluding pure solids and liquids. The product (calcium ion) is cubed, and the reactant (chromium ion) is squared based on their coefficients. Given concentrations of calcium (6.48) and chromium (2.42) are used in the calculation, resulting in Q equals 46.5. With this information, the video proceeds to solve for the standard electromotive force (E), integrating the calculated values.
00:06:00
In this part of the video, the speaker explains the steps to correctly enter a series of calculations into a calculator for determining a value in volts. They emphasize the importance of taking the natural logarithm of 46.5 first, then multiplying the result by 0.0257, dividing by 6, and subtracting from 2.124. The final answer, rounded to three significant figures, is 2.11 volts. The speaker also highlights that the unit must be manually entered as it isn’t built into the problem.