Determination of the electro-chemical equivalent of copper by using an ammeter & copper voltametre

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Abstract

The electrochemical equivalent, sometimes abbreviated Eq, of a chemical element is the mass of that element (in grams) transported by 1 coulomb of electricity. The weight of a substance (such as an element) deposited or evolved during electrolysis by the passage of a specified quantity of electricity and usually expressed in grams per coulomb, the value for copper as the usual standard being 0.0003281 gram.[1] Here by using an ammeter & copper voltameter, the electro chemical equivalent of copper will be determined. the initial and final mass of copper deposited in cathode will be find out and the time will be calculated too & at last with the help of required formulae we can find out the electrochemical equivalent of copper that is 2.52×10^-4 gm/coulomb with an error of 23.23%

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Introduction

Electrochemical equivalent: An electrochemical equivalent (ECE) is the amount of a substance in grams produced or consumed by the passage of one coulomb of electricity in an electrochemical reaction. A voltmeter is used to measure the electrochemical equivalent of an element. ECE is mainly used for determining the kinetics of corrosion rates and to estimate the oxidizing power in specific environments. Electrochemical equivalent can be abbreviated as Eq (grams per coulomb).[2]

Electrochemical equivalent of some elements are :

 

Element	Electrochemical equivalent
Silver	0.0011181
Copper	0.0003281
Hydrogen	0.0000104

Ammeter: Ammeter, instrument for measuring either direct or alternating electric current, in amperes. An ammeter can measure a wide range of current values because at high values only a small portion of the current is directed through the meter mechanism; a shunt in parallel with the meter carries the major portion.[3]

Voltameter: A voltameter or coulometer is a scientific instrument used for measuring quantity of electricity (electric charge). The SI unit of quantity of electricity is the coulomb. The voltameter should not be confused with a voltmeter, which measures electric potential. The SI unit for electric potential is the volt.[4]

Copper voltameter: This is similar to the silver voltameter but the anode and cathode are copper and the solution is copper sulfate, acidified with sulfuric acid. It is cheaper than the silver voltameter, but slightly less accurate.[5]

Theory

Faraday’s first law of electrolysis states that, the amount of substance liberated at an electrode is directly proportional to the quantity of electricity passed.[6]

or, W ∞ Q

Where,

W = amount of substance liberated in gram.

Q = quantity of electricity passed in coulomb.

Since, Q = I.t

Where,

I = Current in ampere and

t = time in seconds

Hence, 

    W∞I.t or W = ZI.t = ZQ … … … … … … … … … … … … … … … (1)

Where, Z = Proportionality constant, called electrochemical equivalent.

If I = 1 ampere and t = 1 second then Z = W Therefore electrochemical equivalent may be defined as, “The mass of substance (in grams) liberated at the electrode on passing current of 1 ampere for 1 second or on passing 1 coulomb of electricity is called electrochemical equivalent of the substance”.

From eqn (1),

Knowing, W, I & t, Z can be determined

Apparatus

1) Copper voltameter

2) Battery

3) Rheostat

4) Stop watch

5) Key

6) Connecting wires

7) Balance with weight box etc.

Experiment data table

Data for determining the ammeter reading with time

Calculation

A. Mass of copper deposited

Initial mass of the cathode, W1 = 27.6 gm

Final mass of the cathode, W2 = 28.6 gm

Mass of copper deposited, W = (W2 – W1) = (28.6 - 27.6) = 1 gm

B. Data for finding equivalent weight of copper

Time for required current pass, t = 1800 sec

Mean current, I = 2.197 amp

Percentage of error

Result

The electrochemical equivalent of given copper is found 2.52 × 10^-4 gm/coulomb with an error of 23.23%

Discussion

We complete the experiment successfully. Though we followed all the procedures carefully, there’s noted some fault that’s why we have an error of 23.23%. to avoid those fault we should follow these statements. 

The cathode plate should be throughly cleaned after rubbing with sand paper.

Only that much of current should be passed as is obtained from the calculation of the area of the immersed part of the cathode plate.

Only a fresh solution of CuSO4 should be used. To prepare the solution about 25 g of CuSO4 crystals should be dissolved in 100 cm3 water. A few drops of sulphuric acid (H2SO4) should be added to make it more conducting.

The plate should be hold from its upper end so as to avoid touching its surface.

Cathode plate should be washed immediately after it is taken out of the solution.[7]

Conclusion

The experiment of determination of the electro-chemical equivalent of copper by using an ammeter & copper voltametre was done successfully. Copper voltameter is a new term. There are many kinds of voltameter and copper voltameter is one of them. It consists of three copper plates suspended from an insulating cover in a glass jar. Two of these, called the anode, are hung on each side of the centre plates and are connected to one binding post.[8] The centre plate is the cathode and is so mounted that it may be taken out of or put into the holder without being touched by the fingers. The plates are mounted on hard rubber top.

References

[1]. http://www.mynoteslibrary.com/html/Chemistry_IX_Faraday.htm

[2]. https://www.merriam-webster.com/dictionary/electrochemical%20equivalent

[3]. https://www.britannica.com/technology/ammeter

[4]. https://en.wikipedia.org/wiki/Voltameter

[5]. https://en.wikipedia.org/wiki/Voltameter

[6]. http://www.sciencehq.com/chemistry/faradays-law-electrolysis.html

[7]. http://learnphysics-dhruv.blogspot.com/2015/03/copper-voltameter-to-determineelectro.

html

[8]. Practical physics, Dr. Giasuddin ahmed and Md. Shahabuddin, page- 394