A student wishes to set up an electrolytic cell to plate copper onto a belt buckle. Predict the length of time it will take to plate out 2.5g of copper from a copper (II) nitrate solution using a 2.5-A current. At which electrode should the buckle be attached?
To solve this problem, we need to use Faraday's laws of electrolysis. Faraday's first law states that the amount of substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passing through the electrolyte. Faraday's second law states that the mass of a substance deposited or liberated during electrolysis is directly proportional to the molar mass of the substance.
To predict the length of time it will take to plate out 2.5g of copper, we need to calculate the total amount of charge required.
First, let's determine the molar mass of copper (Cu). The molar mass of copper is 63.55 g/mol.
Next, we can use Faraday's second law to calculate the amount of charge required to plate out 2.5g of copper.
Charge (Q) = (Mass of substance plated / Molar mass of substance) * Faraday's constant
The Faraday's constant is 96500 C/mol.
Q = (2.5g / 63.55 g/mol) * 96500 C/mol
Q = 3825.28 C
Now we can use Faraday's first law to calculate the time required.
Time (t) = Charge (Q) / Current (I)
t = 3825.28 C / 2.5 A
t ≈ 1530.11 seconds
t ≈ 25.5 minutes
Therefore, it will take approximately 25.5 minutes to plate out 2.5g of copper.
As for the electrode, the buckle should be attached to the negative electrode (cathode). Since copper (II) ions are positively charged, they will be attracted to the negatively charged electrode and get reduced, resulting in the plating of copper onto the buckle.