A current of is passed through of solution of zinc sulphate for . What will be the molarity of ions after the deposition of zinc?
Step 1: Given data
Electric current flowing through zinc sulphate solution,
Time duration during which current flows through zinc sulphate solution,
Volume of the zinc sulphate solution,
Molarity of the zinc sulphate solution,
Step 2: Assumptions
Equivalent weight
Molecular weight
Valency
Number of moles of zinc deposited
Initial moles of the () present in the solution
Number of moles of zinc left
Molarity of () ions after the deposition of zinc,
Step 3: Calculation of the molarity of ions after deposition of zinc
The given electrochemical equation can be written as
From the above reaction, it is clear that the valency, ………….(s)
The weight () of the zinc deposited is given by the basic equation of “Faraday's first law of electrolysis”.
……………………….(a)
Where Z is the proportionality constant as is called as “electrochemical equivalent” and is related to the equivalent weight by the equation
………………………..(b)
Equivalent weight is related to the molecular weight and the valency by the equation
…………………………….(c)
Using equation (c) in the equation (b), we get
…………………(d)
Substituting equation (d) in equation (a), we get
…………………………………(e)
Substituting the equation (s) and given values in equation (e), we get
Number of moles of zinc deposited, …………………….(f)
Initial moles of () present in the solution will be equal to the product of the molarity of the zinc sulphate solution and its volume
Substituting the given values in the above equation, we get
…………..(g)
The number of moles of zinc left will be equal to the difference between the initial moles of () ions present in the solution and the number of moles of the zinc deposited
………………….(h)
Using equations (f) and (g) in equation (h), we get
The molarity of () ions after the deposition of zinc will be equal to the ratio of the number of moles of zinc left and the volume of the zinc sulphate solution.
Substituting the given and obtained values in the above equation, we get
Hence, option (B) is correct.