Chapter 19: Problem 57
The passage of a current of 0.750 A for 25.0 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 approximately \( 31.6 \, \text{g/mol} \)
Step by step solution
01
Convert time to seconds
The time, given in minutes, must be converted to seconds since the standard unit of time in physics is seconds. Given that 1 minute equals 60 seconds, the conversion is done by multiplying: \( 25.0 \, \text{minutes} \times 60 = 1500 \, \text{seconds} \)
02
Calculate the total charge
Now we can calculate the total charge passed using the formula \( q = It \) where \( I \) is the current and \( t \) is the time in seconds. Substituting the known values more the formula: \( q = 0.750 A \times 1500 s = 1125 C \)
03
Use Faraday's law
Faraday's first law of electrolysis states that the amount of substance deposited is directly proportional to the charge passed through the circuit. The relationship is given by \( Q = n \times F \), where \( Q \) is the total charge, \( n \) is the number of moles, and \( F \) is Faraday's constant (96485 C/mol). Re-arranging for \( n \), we have \( n = Q / F = 1125 C / 96485 C/mol = 0.01166 mol \)
04
Calculate molar mass
The molar mass is obtained by dividing the mass of the substance by the number of moles. The mass in the problem was given as \( 0.369 \, g \). Therefore, the molar mass \( M = mass/moles = 0.369g / 0.01166 mol = 31.6 g/mol \)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Faraday's Law of Electrolysis
Understanding Faraday's law of electrolysis is essential for anyone dealing with electrochemical processes. This fundamental principle, discovered by Michael Faraday, explains how electric charge is related to the amount of a substance undergoing electrolysis - a chemical reaction driven by an electric current.
Faraday's law states that the amount of substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electric charge passed through the electrolyte. It can be split into two parts - the first law gives us the qualitative aspect indicating the relationship between mass and charge, whereas the second law provides a quantitative measure which says the mass of the substances altered at an electrode during electrolysis is proportional to the molar mass of the substance when the charge passed is constant.
To apply Faraday's first law to a real-world problem, consider charging passed in an electrolysis circuit. This charge, measured in coulombs, is the product of current (in amperes) and time (in seconds). From the charge, one can determine the number of moles of electrons or the amount of the substance reacted by using Faraday's constant, which is equivalent to the charge of one mole of electrons (approximately 96485 C/mol). This process is pivotal in calculating the quantities involved in electrochemical reactions.
Faraday's law states that the amount of substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electric charge passed through the electrolyte. It can be split into two parts - the first law gives us the qualitative aspect indicating the relationship between mass and charge, whereas the second law provides a quantitative measure which says the mass of the substances altered at an electrode during electrolysis is proportional to the molar mass of the substance when the charge passed is constant.
To apply Faraday's first law to a real-world problem, consider charging passed in an electrolysis circuit. This charge, measured in coulombs, is the product of current (in amperes) and time (in seconds). From the charge, one can determine the number of moles of electrons or the amount of the substance reacted by using Faraday's constant, which is equivalent to the charge of one mole of electrons (approximately 96485 C/mol). This process is pivotal in calculating the quantities involved in electrochemical reactions.
Chemical Electrolysis Calculation
Calculating the outcomes of chemical electrolysis entails several steps that hinge on the principles of Faraday's laws. Beginning with the basics, in an electrolytic cell, the passage of an electric current causes a chemical reaction which results in the deposition or dissolution of material on the electrodes.
For chemical electrolysis calculations, the following steps are typically involved:
By diligently following these steps, the calculation of amounts in electrolysis becomes systematic and accurate, providing critical information for various applications, from metal purification to electroplating industries.
For chemical electrolysis calculations, the following steps are typically involved:
- Convert all units to the standard scientific units (e.g., time to seconds, mass to grams).
- Determine the total charge passed using the formula: \( q = It \), where \( q \) represents the charge in coulombs, \( I \) is the current in amperes, and \( t \) is the time in seconds.
- Apply Faraday’s law to find the number of moles of electrons or the substance involved using the formula: \( n = Q / F \), where \( n \) is the number of moles, \( Q \) is the total charge, and \( F \) is Faraday’s constant.
- Using the number of moles calculated, one can then determine the mass of the substance deposited or dissolved at the electrodes.
By diligently following these steps, the calculation of amounts in electrolysis becomes systematic and accurate, providing critical information for various applications, from metal purification to electroplating industries.
Molar Mass Determination
Molar mass determination is a fundamental concept in chemistry that enables the identification of the amount of substance in a given mass. Molar mass is the mass of one mole of a substance and it is expressed in grams per mole (g/mol).
To calculate the molar mass from the electrolysis data:
In the case presented in the original exercise, after finding out the number of moles of copper deposited, we simply take the mass of copper deposited and divide by the number of moles to find its molar mass. It’s worth noting that precise and accurate measurements during each step of the calculation are critical because any error will directly affect the final determination of molar mass. This concept is not only crucial in the context of electrolysis but also across various chemical and physical processes to determine the composition and quantities of substances.
To calculate the molar mass from the electrolysis data:
- Determine the mass of the deposited or reacted substance.
- Calculate the number of moles using Faraday's law and the charge passed during electrolysis.
- Divide the mass by the number of moles as per the formula: \( M = \frac{mass}{moles} \).
In the case presented in the original exercise, after finding out the number of moles of copper deposited, we simply take the mass of copper deposited and divide by the number of moles to find its molar mass. It’s worth noting that precise and accurate measurements during each step of the calculation are critical because any error will directly affect the final determination of molar mass. This concept is not only crucial in the context of electrolysis but also across various chemical and physical processes to determine the composition and quantities of substances.