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Investigating Faraday’s Law of Electrolysis – Lab Report

Investigating Faraday’s Law of Electrolysis

Introduction

Electrolysis also referred to as an electrochemical action, has been defined as a process where an electric current is used to break down or decompose ionic substances (Harwood and Lodge 103).  An example of Electrolysis is the decomposition of water into hydrogen and water by the passage of an electric current through water. Electrolysis takes place only under certain circumstances. For example, electrolysis can be performed when there is the free motion of ionic substances. Ions are in a position to move when they are either melted or dissolved in water. The major conditions that need to be satisfied for a substance to undergo electrolysis are that the substance needs to be a good conductor of electricity, liquid, and a definite chemical compound (Gore 72). Liquid alloys such as those of alloys of sodium and potassium, and mercury and tin do not undergo electrolysis. Similarly, liquid compounds of two elements which are non-metallic such as chloride of sulfur, and bisulphide of carbon do not undergo electrolysis.   Investigation of electrolysis by Michael Faraday led to what is popularly known as the Faraday Laws of Electrolysis. Faraday First Law of Electrolysis state that the amount of substance that is liberated or lost at the electrode during the process of electrolysis is directly proportional to the amount of electricity passed (Sivasankar 88). Faraday’s Second Law of Electrolysis states that when the same amount of electricity is used to perform electrolysis in different substances, a number of chemical changes are proportional to their equivalent chemical weights (Sivasankar 88). Does Faraday’s Laws of Electrolysis hold true? Is the mass of the liberated mass equivalent to the amount of current consumed?

Objective of the Experiment

The aim of this experimental investigation is to investigate Faraday’s Law of Electrolysis. Specifically, the objectives of this experiment were to:

  • Measure the mass of the electrode (iron nail)
  • Measure the amount of electric current
  • Measure the time
  • To establish a relationship between the mass of the electrode liberated and the amount of electricity passed

Materials

In this experiment, the following materials were used:

  • Dry cells
  • Conductors
  • Timing watch
  • Ammeter
  • Graduated jar
  • 2M copper sulfate solution (Electrolyte)
  • Distilled water
  • Electronic balance
  • Five iron nails

 

Methods

  • The masses of the iron nails were measured using the electronic balance.
  • The experiment was then set up as shown in 1 with the current switched off.
  • The stopwatch was then set to zero.
  • The switch was then turned on for 60 seconds.
  • After 60 seconds, the current was switched off.
  • The electrode (iron nail) was then carefully wiped dry and its mass measured. The mass was recorded on a table.
  • Procedure (iii) to (vi) was repeated five times.
  • After procedure (vii) was completed, the copper sulfate solution was discarded, and a another diluted solution was introduced into the jar.
  • Procedure (iii) to (vi) was repeated five times, but the duration was 120 seconds
  • After procedure (ix) was completed, the copper sulfate solution was discarded, and a fresh solution was introduced into the jar and diluted.
  • Procedure (iii) to (vi) was repeated five times, but the duration lasted 180 seconds
  • After procedure (xi) was completed, the copper sulfate solution was discarded, and a freshly diluted solution was introduced into the jar.
  • Procedure (iii) to (vi) was repeated for five times but the duration lasted for 240 seconds
  • After procedure (xiii) was completed, the copper sulfate solution was discarded, and a freshly diluted solution was introduced into the jar.
  • Procedure (iii) to (vi) was repeated for five times but the duration lasted for 300 seconds
  • Finally, the experimental setup was dismantled, and the dry cells and copper sulfate solution was disposed of safely.

This method was used because it meets all the condition for electrolysis and therefore it is a viable method for investigating Faraday’s Laws of Electrolysis. 2M solution of copper sulfate is highly concentrated, and electrolysis might not take place because there is no free motion of ions; a condition that must be satisfied for electrolysis to take place.  Consequently, the copper sulfate solution had to be diluted. During the process of electrolysis, it was found that the copper sulfate solution began to fade at the area around electrodes. This had a tendency of reducing the electrical conductivity. To ensure that the electrical conductivity remained constant, the solution was stirred continuously. In the experiment, it was very important to ensure that certain variables such as the current passing through the electrolyte, the concentration of the electrolyte, and the copper conductors were maintained constant. The major reason was to ensure that the only variables were time and mass of the iron nail. This made the analysis of the variables easier since only two variables. Although the materials used do not pose any safety concerns, all safety guidelines were observed throughout the experiment. At the end of the experiment, the electrolyte, and the dry cells were disposed of safely.

Results

The data collected was recorded in the tables as shown.

Independent Variable Dependent Variables
Time (Seconds)

±0.5s

Initial Mass of Iron Nail (g) ±0.01g Final Mass of Iron Nail (g) ±0.01g Difference in Mass of Iron Nail (g) ±0.01g
60.0 0.405 0.406 0.001
0.407 0.408 0.001
0.418 0.420 0.002
0.405 0.407 0.002
0.406 0.407 0.001
120.0 0.392 0.395 0.003
0.424 0.428 0.004
0.414 0.417 0.003
0.392 0.396 0.004
0.402 0.406 0.004
180.0 0.409 0.414 0.005
0.405 0.410 0.005
0.409 0.415 0.006
0.417 0.423 0.006
0.413 0.419 0.006
240.0 0.407 0.415 0.008
0.406 0.413 0.007
0.419 0.426 0.007
0.402 0.408 0.006
0.410 0.418 0.008
300.0 0.407 0.416 0.009
0.422 0.431 0.009
0.411 0.421 0.010
0.412 0.425 0.013
0.396 0.405 0.009

Table 1: Independent and dependent variables

 

Controlled variables Quantity Uncertainty
2M Copper Sulfate Solution 100cm3 ±1cm3
Distilled water 100cm3 ±1cm3
Copper strips 10cm2  
Voltage of dry cells 3.0V  
Current of dry cells 0.3A  

Table 2: Controlled variables

 

Independent Variable Dependent Variables
Time (Seconds)

±0.5s

Average difference in Mass of Iron Nail (g) Uncertainty (g)
60.0 0.0014 0.0005
120.0 0.0036 0.0005
180.0 0.0056 0.0005
240.0 0.0072 0.0010
300.0 0.010 0.0020

 

 

Table 3: Processed Data of variables

 

 

Fig 1: Time (s) against average difference in mass of iron nail (g)

Discussion

Before electrolysis began, during the process of electrolysis, and after the electrolysis, qualitative observations were made. Before being immersed in the copper sulfate solution, it was observed that the color of the iron nails was silver. When the iron nails were immersed in copper sulfate solution, and the current turned on, it was observed that one of the electrodes turn its color from silver to reddish brown. Upon removal from the electrolyte, the original silvery iron nail had been coated with a reddish-brown copper oxide while the other iron nail had been eaten away. Before the onset of electrolysis, the color of copper sulfate solution was blue. However, after some time, the blue color gradually faded. A graph of time against the mass of the iron nail showed that time and amount of current consumed has a linear relationship. The data collected, however, were not uniform even for the same duration of time. This might be due to the errors during the measurement of time or mass of the iron nail. The other limitation might be the accumulation of the copper oxide coating on the surface of the iron nail. Copper oxide is a poor conductor of electricity, and this had a tendency of increasing electrical resistance and therefore slowed down the buildup of the copper oxide coating on the surface of the iron nail.

Conclusion

The physical changes that were observed confirm that three conditions must be fulfilled for electrolysis as stated by Gore (72). According to Gore (72), an ideal substance for electrolysis needs to be a liquid, a chemical compound, and a good conductor of electricity. The change of color of the iron nails and change in mass also suggest that electrolysis took place. A graph of time against the mass of iron nail revealed that the mass of the iron nail is proportional to the time. This shows that more time the current was passed through the electrolyte, the more the deposits of copper oxide on the surface of the iron nails. Given that time is a function of the amount of electricity passed through the electrolyte, it can be concluded that the amount of electricity passed through the electrolyte is in direct proportion to the mass of the copper oxide deposited on the surface of the iron nails. The behavior of the graph, therefore, compare well with a theoretical statement of Faraday’s First Law of Electrolysis which states that the quantity of a substance that is either dissolved, liberated or deposited during the process of electrolysis is proportional to the amount of electricity that is passed through the electrolyte (Sivasankar 88). To generate more accurate results in future, it might be necessary to use the more precise balance for measuring the mass of iron nails. During the whole process, the dry cells used were not changed. In future, there is a need to ensure that the current and voltage is constant by changing the dry cells after every five consecutive trials. It will also be necessary to record the masses of the electrode that is consumed or dissolved instead of the one that is increasing in mass. One reason is that some copper oxide falls off from the iron nail as it is removed from the electrolyte and during wiping it to dry. Therefore, the final mass of the coated iron nail might be less than what it would have weighed if all the copper oxide had been included. If the nail eaten away is to me weighed, it is also necessary to continuously scrub the electrode where the copper oxide is deposited to ensure that there is no buildup of resistance to the flow of the electric current. As time goes, the conductivity of the electrolyte might change. It might be therefore necessary to find a way where the electrolyte conductivity is held constant probably by draining the electrolyte continuous without necessarily disconnecting the flow of current.

 

Works Cited

Gore, G. Electrolytic Separation, Recovery, and Refining of Metals. Wexford College Press, 2003.

Harwood, Richard and Ian Lodge. Cambridge IGCSE Chemistry Coursebook. Cambridge University Press, 2014.

Sivasankar, B. Engineering Chemistry. Tata McGraw-Hill Publishing Company, 2008.

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