Chapter 18: Problem 59
The passage of a current of 0.750 A for \(25.0 \mathrm{~min}\) deposited \(0.369 \mathrm{~g}\) of copper from a \(\mathrm{CuSO}_{4}\) solution. From this information, calculate the molar mass of copper.
Short Answer
Expert verified
The molar mass of copper is \(63.3 g/mol\).
Step by step solution
01
Convert time to seconds
Given that the time of passage of current is 25.0 min, this should be converted to seconds since time in the formula for Faraday's laws of electrolysis is in seconds. Therefore, it will be \(25.0 min \times 60 s/min = 1500 s\)
02
Substitute known variables into the mass formula
The mass of the substance can be expressed using Faraday's formula as \( m = ZIt \), where \( m = 0.369 g \), \( I = 0.750 A \) and \( t = 1500 s \)
03
Calculate the electrochemical equivalent
From the mass formula, we can calculate for Z (electrochemical equivalent) as \( Z = \frac{m}{It} = \frac{0.369 g}{(0.750 A)(1500s)} = 3.28 \times 10^{-4} g/C \)
04
Substitute electrochemical equivalent into the equivalent formula
The electrochemical equivalent can be expressed as \( Z = \frac{M}{nF} \) where n is the number of electrons involved per molecule (for copper n=2) and F is Faraday's constant (\(96485 C/mol\)). This can be rearranged into \( M = ZnF \)
05
Calculate the molar mass
Substitute for Z, n and F into the formula for molar mass as \( M = (3.28 \times 10^{-4} g/C)(2)(96485 C/mol) = 63.3 g/mol \)
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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 laws of electrolysis are pivotal in understanding the relationship between the amount of electrical charge passed through a substance and the amount of substance that is deposited or dissolved at the electrodes during electrolysis. According to the first law, the mass of a substance altered at an electrode during electrolysis is directly proportional to the amount of electricity that passes through the electrolyte. Simply put, the more electricity you use, the more substance gets deposited.
The second law states that the amounts of different substances deposited by the same quantity of electricity are proportional to their equivalent weights. This means that if two different substances are deposited using the same electrical charge, the ratio of their masses will be equal to the ratio of their molar masses divided by their respective charges involved in the ions or atoms deposited. These foundational principles guide the calculation process in our exercise to determine the molar mass of copper from an electrolysis procedure.
By using these laws, we can create a bridge between the practical aspect of electrolysis and the theoretical calculations necessary to find the molar mass of substances such as copper. This understanding is essential for students conducting experiments or tackling problems that involve electrochemistry.
The second law states that the amounts of different substances deposited by the same quantity of electricity are proportional to their equivalent weights. This means that if two different substances are deposited using the same electrical charge, the ratio of their masses will be equal to the ratio of their molar masses divided by their respective charges involved in the ions or atoms deposited. These foundational principles guide the calculation process in our exercise to determine the molar mass of copper from an electrolysis procedure.
By using these laws, we can create a bridge between the practical aspect of electrolysis and the theoretical calculations necessary to find the molar mass of substances such as copper. This understanding is essential for students conducting experiments or tackling problems that involve electrochemistry.
Electrochemical Equivalent
The concept of the electrochemical equivalent (Z) is essential when dealing with electrolysis calculations. It represents the amount of a substance that is deposited or dissolved at an electrode per unit charge passed. In simpler terms, it tells you how many grams of a substance you'll get for every coulomb of charge that flows through the electrolyte.
Mathematically, it is expressed as \( Z = \frac{m}{It} \) where \( m \) is the mass of the substance deposited, \( I \) is the current, and \( t \) is the time. It's a key intermediate in calculating the molar mass of a substance after electrolysis, as it connects the flow of electricity to the physical mass deposited. In our example, we calculated the electrochemical equivalent of copper to be \( 3.28 \times 10^{-4} g/C \).
Furthermore, the electrochemical equivalent can be linked to the concept of a mole and Faraday’s constant, allowing us to deduce the molar mass of the electroplated substance. Through this, students see firsthand how theoretical concepts yield practical and quantifiable results, bridging the gap between abstract numbers and actual laboratory outcomes.
Mathematically, it is expressed as \( Z = \frac{m}{It} \) where \( m \) is the mass of the substance deposited, \( I \) is the current, and \( t \) is the time. It's a key intermediate in calculating the molar mass of a substance after electrolysis, as it connects the flow of electricity to the physical mass deposited. In our example, we calculated the electrochemical equivalent of copper to be \( 3.28 \times 10^{-4} g/C \).
Furthermore, the electrochemical equivalent can be linked to the concept of a mole and Faraday’s constant, allowing us to deduce the molar mass of the electroplated substance. Through this, students see firsthand how theoretical concepts yield practical and quantifiable results, bridging the gap between abstract numbers and actual laboratory outcomes.
Molar Mass of Copper
Molar mass is a fundamental concept in chemistry, representing the mass of one mole of a substance, where one mole corresponds to Avogadro's number (approximately \(6.022 \times 10^{23}\)) of atoms or molecules of the substance. The molar mass of copper is particularly important in the context of electrolysis because it lets us calculate how much copper can be deposited as a function of the electrical charge passed through a solution of its salts, like copper sulfate (\(\mathrm{CuSO}_{4}\)).
In the exercise, after determining the electrochemical equivalent, we used it to find the molar mass of copper. We put the value of Z, the number of electrons transferred (\(n\)), which is 2 for Cu\textsuperscript{2+}, and Faraday's constant (\(F\)) into the formula \( M = ZnF \), revealing a molar mass of \(63.3 g/mol\) for copper. This value is consistent with the atomic mass of copper found on the periodic table, providing a beautiful demonstration of how abstract electrochemical principles translate into tangible chemical properties.
Understanding the molar mass is not only crucial for solving textbook problems but also for practical applications. It is used in stoichiometric calculations and can help predict the outcomes of various chemical reactions involving copper, which is why it's a staple in chemical education and a key piece of knowledge for students in the field.
In the exercise, after determining the electrochemical equivalent, we used it to find the molar mass of copper. We put the value of Z, the number of electrons transferred (\(n\)), which is 2 for Cu\textsuperscript{2+}, and Faraday's constant (\(F\)) into the formula \( M = ZnF \), revealing a molar mass of \(63.3 g/mol\) for copper. This value is consistent with the atomic mass of copper found on the periodic table, providing a beautiful demonstration of how abstract electrochemical principles translate into tangible chemical properties.
Understanding the molar mass is not only crucial for solving textbook problems but also for practical applications. It is used in stoichiometric calculations and can help predict the outcomes of various chemical reactions involving copper, which is why it's a staple in chemical education and a key piece of knowledge for students in the field.