Chapter 8: Problem 31
A \(100.0 \mathrm{~mL}\) dilute solution of \(\mathrm{Ag}^{+}\) is electrolyzed for \(15.0\) minutes with a current of \(1.25 \mathrm{~mA}\) and the silver is removed completely. What was the initial \(\left[\mathrm{Ag}^{+}\right]\) ? (a) \(2.32 \times 10^{-1}\) (b) \(2.32 \times 10^{-4}\) (c) \(2.32 \times 10^{-3}\) (d) \(1.16 \times 10^{-4}\)
Short Answer
Step by step solution
Calculate the total charge passed through the solution
Determine the amount of silver deposited
Calculate initial concentration of \(\mathrm{Ag}^+\)
Express the answer in scientific notation
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Faraday's Laws of Electrolysis
Faraday's first law states that the amount of a substance altered at an electrode during electrolysis is directly proportional to the amount of electricity that passes through the circuit. This principle helps us quantify the changes occurring during the electrolytic process. The second law points out that for the same quantity of electricity passed through different electrolytes, the amount of substances liberated is proportional to their equivalent weights.
These laws help us calculate things like how much metal is deposited during electroplating. For instance, in our example problem, Faraday's first law allows us to determine the moles of silver deposited by using the charge that passed through the solution and dividing it by Faraday's constant. Understanding these laws provides the foundation to approach and solve quantitative electrolysis problems effectively.
Calculating Concentration
To calculate the concentration, you need to know the amount of solute (in moles) and the volume of the solution. In the context of our electrolysis problem, after using Faraday's law to find the moles of silver deposited, we then calculate the initial concentration of silver ions by dividing these moles by the total volume of the solution in liters.
Why are these calculations crucial? They are used in preparing solutions for reactions, pharmaceutical formulations, and any chemical process where the exactness of reactant concentration is necessary for consistency and desired outcomes. Through practice, students can master this basic and essential technique, enhancing their lab competencies and their grasp of the underlying principles.
Quantitative Aspects of Electrolysis
In our specific exercise, this involves calculating the total charge passed (using the current and the time), then relating that charge to the number of moles of silver deposited. Once the moles are known, the initial concentration before electrolysis can be calculated. This process shows the interconnection between charge, moles, and concentration, all of which are key to understanding and solving problems related to electrolysis.
Gaining a solid grasp of these quantitative relationships not only aids in solving textbook problems but also prepares students for practical applications in industries where precise chemical deposition is required, thereby highlighting the vital role of electrolysis in various scientific and engineering fields.