• cuigm371
In summary, according to the homework statement, the pH range that this electrodeposition can be conducted in order to avoid hydrogen gas evolution and nickel hydroxide precipitation is 4.22 to avoid hydrogen gas evolution. If the pH range is not within this range, nickel hydroxide precipitation will occur.
cuigm371

## Homework Statement

Hey guys,
I am preparing a technical exam and am facing an exam problem below:

Ni is electrodeposited from an aqueous sulphate solution that has a composition that fluctuates from 1 to 0.01M due to changes in the feed composition of the process.
a) what is the pH range that this electrodeposition can be conducted in order to avoid hydrogen gas evolution and nickel hydroxide precipitation? Given:
Ni 2+ + 2e- <-> Ni , E0 = -0.25V
Ni 2+ + 2H2O <-> Ni(OH)2 (s) + 2H+ log K = -12.73

## Homework Equations

Ksp= [Ni(OH)2] * [H+]^2/[Ni+]

## The Attempt at a Solution

a. pH range: take Eh-PH of H2O with respect to H2/H+ where:
[H2/H+] = -0.0592 pH = E0 = -0.25 V
so pH = 0.25/0.0592 = 4.22 to avoid hydrogen gas evolution

For Ni(OH)2 precipitation:
Ksp= [Ni(OH)2] * [H+]^2/[Ni+]^2 = 10^(-12.73)

this is where I was stuck- how to calculate the [Ni(OH)2] and the [Ni+]? using 1M and 0.01M respectively?

Last edited:
Your formula for Ksp is wrong.

Borek said:
Your formula for Ksp is wrong.

Thank you for pointing out. the formula should've been:

Ksp= [Ni(OH)2] * [H+]^2/[Ni+] = 10^(-12.73)

I still am not clear what to do next. Could you please advise?

No, this is still not a correct formula for solubility product. It is not a matter of a wrong exponent, it is conceptually wrong (and that's what stops you from solving the problem).

Ni(OH)2 <-> Ni 2+ + 2 (OH)-
and Ksp = [Ni2+] [OH-]^2/[Ni(OH)2]

this seems more reasonable. Correct?

No, you are making the same error again and again. Please check with your textbook.

Borek said:
No, you are making the same error again and again. Please check with your textbook.

I believe it is right as below. THANK YOU VERY MUCH!

H+ + OH- = H2O Kw
Ni(OH)2= Ni2+ + 2OH- Ka

so, for Ni2+ + 2H2O = Ni(OH)2 + 2H+
K = Kw^2/Ka

Borek said:

Refer to the textbook page attached.

Ni(OH)2 = Ni2+ + 2(OH)-
Ks = [Ni]2+ x (OH)-^2 = 10^(-12.73)
Ni+ ranges from 1 to 0.01M, so OH- can be calculated accordingly. Is this right now?

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Yes, when you have a correct formula for Ksp it is as trivial as solving for OH- and converting it to pH.

Borek said:
Yes, when you have a correct formula for Ksp it is as trivial as solving for OH- and converting it to pH.

Thank you very much indeed!
looking back I think I was confused initially by the way it was given,
Ni 2+ + 2H2O <-> Ni(OH)2 (s) + 2H+

and forgot to go to the definition of the solubility product. this is a good lesson learned.

## 1. What is nitrate electrodeposition?

Nitrate electrodeposition is a process used in electrochemistry to deposit a thin layer of metal or metal oxide onto a conductive surface. It involves using an electric current to reduce nitrate ions in a solution, causing them to form a solid layer on the surface of an electrode.

## 2. Why is nitrate electrodeposition important?

Nitrate electrodeposition has many practical applications, including in the production of electronic devices, coatings for corrosion protection, and in the manufacturing of batteries and fuel cells. It is also used in research and development for studying the properties and behavior of various materials.

## 3. What are the main challenges in nitrate electrodeposition?

One of the main challenges in nitrate electrodeposition is controlling the thickness and quality of the deposited layer. Other challenges include maintaining a stable and uniform electric field, preventing unwanted side reactions, and ensuring the purity of the solution and electrode materials.

## 4. How is the nitrate electrodeposition process optimized?

The nitrate electrodeposition process can be optimized by carefully controlling the experimental parameters such as the composition and concentration of the electrolyte solution, the electric current and voltage, and the temperature. The use of additives and modifiers can also improve the quality and properties of the deposited layer.

## 5. What are the potential environmental concerns with nitrate electrodeposition?

Nitrate electrodeposition can generate waste products and byproducts, such as excess metal ions and toxic gases. Proper disposal and treatment of these waste materials is important to minimize their impact on the environment. Additionally, the use of certain chemicals and materials in the process may also pose environmental risks, and alternative, more sustainable methods are being researched and developed.