Electroplating Practice Problems

Illustrate a cell representation of the electrolysis of a concentrated aqueous solution of hydrochloric acid. Use inert electrodes. Label which are the anode, cathode, positive and negative electrodes, and the direction of ion and electron flow. Show the balanced equations for the important reactions involved.

What are the cathode, anode and overall cell reaction for the electrolysis, in a cell with inert electrodes, of the aqueous solution of a KClO₂ salt?

ClO₂⁻(aq) → ClO₂(g) + e⁻ E° = −0.95 V

K⁺(aq) + e⁻ → K(s) E° = −2.92 V

Magnesium can be acquired by the electrolysis of molten MgCl₂. Calculate the required current to acquire 650 g of Mg in a span of 2 hours.

The electrochemical process of anodizing is used to add color and also a corrosion-resistant coat to metals like aluminum and titanium. Unlike aluminum anodizing, titanium anodizing requires a significantly thinner oxide layer. This thin layer of titanium oxide works by interfering with the wavelength of the incident light which results in different colors. The reactions involved in this process are:

Cathode (reduction): 4 H⁺(aq) + 4 e^– → 2 H₂(g)

Anode (oxidation): Ti(s) + 2 H₂O(l) → TiO₂(s) + 4 H⁺(aq) + 4 e^–

The thickness and the various color of the oxide layer can be controlled by changing the voltage. The higher the voltage applied, the higher the current generated, and the thicker the oxide layer formed. Calculate the time it will take to produce a dark green titanium oxide film with a thickness of 0.13 µm on a square sheet of titanium metal with an edge length of 20.0 cm. The density of titanium oxide is 4.23 g/cm³ and the current used is 0.25 A. 

An aqueous metal nitrate [M(NO3)₃] solution was subjected to electrolysis using a current of 25.0 A. If 408 g of the metal is produced in 400 min, what is the identity of the metal ion (M³⁺)?

What are the cathode, anode and overall cell reactions for the electrolysis, in a cell with inert electrodes, of the aqueous solution of a NiMnO₄ salt?

What are the cathode, anode and overall cell reaction for the electrolysis, in a cell with inert electrodes, of the aqueous solution of a CrI₂ salt?

Which of the following are the end products of the overall process that takes place when an aqueous BaI₂ solution is electrolyzed?

How many kilowatt-hours of electricity are needed to obtain 1.0×10³ kg (1 metric ton) of chromium through the electrolysis of Cr³⁺, given that this process has a 40% efficiency and the applied voltage is 5.10 V?  

(a) Assuming that the electrolytic cell has 78% efficiency, what is the mass of Cs formed from the electrolysis of molten CsCl using a current of 2.5×10³ A for a period of 12 h? (b) Determine the minimum voltage needed to drive the reaction.

Cs⁺ + e^– → Cs                E°_red = –3.03 V
Cl₂ + 2 e^– → 2 Cl^–         E°_red = –1.36 V

An ammeter, which measures electrical current, is created by a student using the electrolysis of water into hydrogen and oxygen gases. If the student wants to collect 15.5 mL of water-saturated H₂(g), how long should an electrical current of 0.670 amperes be run through the device? The temperature of the system is 27.0 °C, and the atmospheric pressure is 850 torr.

Active metals such as Mn are obtained via the electrolysis of molten salts. Why can't we use aqueous solutions to obtain active metals via electrolysis?

True or False. We can obtain potassium metal from the electrolysis of an aqueous solution of KF because K⁺ ions are reduced to K(s)

What happens at the anode when molten KF is electrolyzed?

The MBr₃ is a metal bromide salt. What is the molar mass of the metal if 2.56 g of the metal is deposited when MBr₃ undergoes electrolysis for 18.4 minutes with a 3.29 A current?

In the electrolysis of an aqueous solution of Pb(IO₃)₂, what are the half-reaction equations that occur at the anode and cathode?

For the electrolysis of a molten mixture of LiF and LiCl, determine the products formed.

A 250 mL of a 0.250 M NaCl solution with an initial pH of 7.00 was subjected to electrolysis. A 15.0 mL portion of the solution was set for analysis after 20 minutes of the process. 32.6 mL of a 0.150 M HCI solution was used to reach the endpoint.

Calculate the current (in A) running through the cell

It matters to be specific as to whether a molten or an aqueous solution will be subjected to electrolysis since the products vary for each case. List the products that will be formed when aqueous NaCl is electrolyzed in a cell with inert electrodes and briefly account for the difference. 

Identify the metals that can be used for the cathodic protection of iron: Ni, Mg, Co, Zn, Cd

Molten carbonate fuel cells (MCFC) are newly developed fuel cells that commonly use molten lithium and potassium carbonates as electrolytes. The half-reactions in the cell are shown below: 

Anode: H₂(g) + CO₃^2–(l) → H₂O(l) + CO₂(g) + 2 e^–

Cathode: 1/2 O₂(g) + CO₂(g) + 2 e^– → CO₃^2–(l)

(a) What is the mass of hydrogen gas (in grams) needed to generate a constant current of 12.4 A for 10.0 h? 

(b) What is the volume (in liters) of the hydrogen gas if the required conditions are 650°C and 1406 mmHg?

What amount of a constant current (in amperes) is needed to generate silver at a rate of 20.0 kg/h using the smelting process?

Which of the following best describes cathodic protection?

Which of the following best explains how galvanizing prevents or minimizes rusting of steel?

3.25 g of Li is consumed at the battery's anode during the discharge of a Li-ion battery with an overall reaction of Li(s) + CoO₂(s) → LiCoO₂(s). What amount of electrical charge in coulombs is transferred from Li to CoO₂?

When a current is passed through an HCl solution, bubbles come out of the solution as H⁺ becomes H₂ gas. Determine the pH of a 4.18 L of 0.378 M HCl solution after passing through 27.5 A for 39 minutes.

A solution of Pb²⁺ is produced from dissolving 0.617 g of impure lead sample in strong acid. This solution needed 0.0263 L of 0.0568 M solution of NO₃^- to reach the equivalence point where NO₃^- is reduced to NO gas. What is the mass percent of lead in the sample if there is no other reducing agent?

Would coating iron with cadmium (Cd) metal prevent the corrosion of iron?

Would coating iron with tin (Sn) metal prevent the corrosion of iron?

At the cathode of an electrolytic cell, cadmium can be electroplated with the following half-reaction: 

Cd²⁺(aq) + 2 e^- → Cd(s)

Calculate the mass of cadmium plated onto the cathode when a 3.2 A current goes through the cell for 56 min.

Calculate the amount of time to redissolve 231 g of Ag at a charging current of 8.93 A in a rechargeable battery based on a concentration cell constructed of two Ag/Ag⁺ half-cells.

Calculate the amount of time needed to run a current of 7.2 A for 436 mg of Cu to be electroplated 

Cu²⁺(aq) + 2 e^– → Cu(s)

Identify the solid formed and the amount in grams when 15 A of current is applied for 10 minutes to an electrolytic cell that uses the two half-reactions below:

Mg ²⁺(aq) + 2e⁻  →  Mg(s)   E ⁰ = − 2.38

Li ⁺(aq) +  e⁻  →  Li(s)           E  ⁰ = − 3.04

Using a current of 8.20 A, an aqueous solution containing Ga³⁺ was subjected to electrolysis. Calculate the mass of Ga(s) plated out after 3.00 days.

Ga³⁺(aq) + 3 e^– → Ga(s)         E°_red = –0.549 V

A sodium/nickel chloride battery operates at a temperature range of 270°C-350°C using molten metals and salts. Sodium acts as the anode and nickel acts as the cathode. A beta-alumina ceramic wall serves as a barrier between the electrodes which is conductive for sodium ions but not for electrons. The cell has a voltage of overall cell reaction is 2.58 V and the cell reaction is as follows:

Na(s) | Na(sol'n), NaCl(soln) || Ni(sol'n), NiCl₂(sol'n) | Ni(s)

Calculate the mass of nickel produced (in kilograms) if a 12.3 kW sodium/nickel chloride battery produces a current in a span of 45.0 minutes.

Ordinary alkaline battery half-reactions can be written as 

anode: Zn(s) + 2 OH⁻(aq) → Zn(OH)₂(s) + 2 e⁻

cathode: MnO₂(s) + H₂O(l) + e⁻ → MnO(OH)(s) + OH⁻(aq)

Consider a hypothetical battery composed of the same anode as the ordinary alkaline battery and a cathode where CoO₄²⁻ ion from Na₂CoO₄ is reduced to solid Co(OH)₃ in a basic solution. Because the hypothetical battery's cathode can provide more charge per unit mass than an ordinary alkaline battery of the same size and weight, it should last longer. Compare quantitatively the amount of coulombs of charge released when 15.0 g of Na₂CoO₄ is reduced to Co(OH)₃ with the amount of coulombs of charge released when 15.0 g of MnO₂ is reduced to MnO(OH).

If 300.0 g of Sn(NO₃)₂(s) has to be transformed into Sn(s) and SnO₂(s) in order to charge an experimental Sn(NO₃)₂(s) battery, how much coulombs of electrical are needed?

Calculate the time (in hours) it will take to produce 1.50×10³ kg of potassium when a sample of molten KF was subject to electrolysis using a constant current of 2.50×10⁴ A. Determine the volume (in L) of F₂ gas produced at STP.

The unit used to express the capacity of batteries is milliamp-hours (mAh). A fresh alkaline battery has a normal capacity of 2500 mAh and starting voltage of 1.50 V. When the battery has delivered its rated capacity, its voltage decreases to 0.75 V during discharge. Estimate the total maximum electrical work that the battery could perform during discharge if we assume that voltage declines linearly as current is withdrawn.

The cathode LiMn₂O₄ in Li-ion batteries can be replaced by LiFePO₄. The use of LiFePO₄ has received widespread market approval because of its low cost, non-toxicity, and iron's natural abundance. During the charging of a certain battery with a LiFePO₄ cathode, about 40.8% of the lithium migrates from the cathode to the anode. To migrate the same amount of lithium to the graphite anode, what fraction of the lithium in LiMn₂O₄ would have to migrate in a battery that uses a LiMn₂O₄ cathode?

The cathode LiMn₂O₄ in Li-ion batteries can be replaced by LiFePO₄. The use of LiFePO₄ has received widespread market approval because of its low cost, it is non-toxic, and iron's natural abundance. Determine which material has a higher percentage of lithium and identify which cathode will deliver greater power upon discharging.

A rechargeable battery is made up of two Au/Au³⁺ half-cells. The initial concentrations of Au3+ in each half-cell are 1.50 M and 1.25×10^–3 M, respectively, and each cell has a volume of 2.50 L. Calculate the time it will take to redissolve 1.25×10² g of gold charging at a current of 11.5 amps?

A concentration cell made of two Fe²⁺/Fe³⁺ half-cells serves as the foundation for the construction of a rechargeable battery. Each half-cell has a 1.5 L capacity, and there are 2.05 M and 1.4x10^-3 M Fe³⁺ concentrations inside each half-cell. How much iron is plated onto the cathode when it is operated at 1.9 A for 6.7 hours?

A battery works on the reduction of Pb²⁺ and the oxidation of barium. In separate 1.00 liter half-cells, 1.50×10^–4 M of Ba²⁺ and 2.00 M of Pb²⁺ are initially present. Calculate the time the battery can deliver 6.00 A before it goes dead.

Consider an alkaline battery with 2.63 g of Zn. Calculate the mass of Zn(OH)₂ formed assuming all the zinc metal undergoes oxidation using MnO₂.

For a Nickel-Cadmium battery, calculate the optimal mass ratio Cd to NiO(OH).

Iridium is an impurity found in a mixture of palladium and silver metals that have undergone electrorefining. The oxidation state of iridium is Ir³⁺ and its standard reduction potential is as follows:

Ir³⁺(aq) + 3 e^– → Ir(s)   E°_red = 1.156 V

Using this information, what is likely to happen to iridium impurities during electrorefining? When palladium is oxidized, do the impurities remain at the bottom of the refining bath (unchanged) or do they dissolve as ions? If they dissolve in the solution, will they plate out on the cathode?

Pd²⁺(aq) + 2 e^– → Pd(s)   E°_red = 0.951