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Electrochemistry

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Electrochemistry

In this article, you will learn the basics of electrochemistry. More importantly, you will learn why electrochemistry is so important to many industries. Electrochemistry has a large number of applications, all of which depend on the control of redox reactions.

  • You will learn what electrochemistry is.
  • We shall cover what redox reactions are and how to control the flow of electrons in them.
  • We'll go over the two types of electrochemical cells.
  • Next, we'll see what the applications of electrochemistry are.
  • Finally, we'll look at how to set up an electrochemical experiment.

Electrochemistry Definition

What is electrochemistry?

At its simplest, electrochemistry is the study of the relationship between electricity and chemical reactions.

Electrochemistry involves the study of the transfer of electrons and concerns mainly redox reactions.

Redox reactions are reactions that include reduction and oxidation.

Redox Reactions

Redox reactions are studied by splitting them into reduction reactions and oxidation reactions.

In the context of electron transfer, the following can be assumed:

reduction is the gain of electrons

oxidation is the loss of electrons

You can remember these by the acronym OIL RIG, which opens up as Oxidation is Loss and Reduction is Gain.

So electrochemistry concerns the transfer of electrons in redox reactions. But how?

Electrochemistry is the study and quantification of the controlled release of energy in redox systems. Redox reactions can proceed spontaneously and in an uncontrolled fashion if you mix your reagents in a beaker. But if you separate the reagents and allow a circuit to be formed, then the reaction can be controlled.

Remember that redox concerns the transfer of electrons in a system, so connecting reagents through a circuit allows the electrons to flow through wires.

So, allowing the redox reaction to be separated allows one to control the flow of electrons and thus, electricity through the system, which comprises the basis of electrochemistry. You can also think of electrochemistry as the chemistry which generates electric circuits and potential.

Electrochemistry Experiments

Here we will cover some key experiments for you to understand the concept of electrochemistry, and more importantly, how electrochemistry was developed.

For example, take the displacement reaction of copper and zinc:

CuSO4 (aq) + Zn (s) → Cu (s) + ZnSO4 (aq)

The reaction above is a redox reaction, as copper gains electrons, while zinc loses electrons. Normally, performing this reaction would lead to an instant transfer of electrons, here from the zinc to the copper. But what if you separate the two reagents in two cells and connect them through a circuit?

Below you can see a diagram of a set-up to perform such an experiment.

Electrochemical copper-zinc cell. Source: researchgate.net

In the above diagram, you can see how the two reagents are separated physically, but connected by two connections. These are an external circuit, which connects the metal electrodes, as well as a salt bridge. The salt bridge provides anion flow, so that during the reaction, both electrons and anions can be mobile.

A salt bridge is crucial, as without it the movement of negative ions, in this case the anions, will not occur and the circuit will not be complete.

Can you see how the redox reaction is still happening, yet it is happening in two half-reactions in each cell? This is because they are happening partially and separate, but connected through the circuit. Through this way, we can control the reaction and monitor it.

Monitoring the reaction occurs by placing a voltage meter in the circuit, to quantify the flow of electrons.

Other types of Electrochemical experiments

In the reaction above, the one pictured in the diagram above, is called a voltaic cell, or galvanic cell. This type of cell occurs when the reaction being performed is spontaneous, that is if the reactions thermodynamically are able to react with each other without external intervention.

But what if the two reagents do not react spontaneously? You can still perform the experiment and create two cells connected into a circuit, but in this scenario you will need to supply energy into the system. By applying a current into the system, you will make a non-spontaneous reaction proceed for desired outcomes. This type of reaction is called electrolysis and is usually performed in an electrolytic cell.

A key difference between spontaneous reactions and non-spontaenous reactions is that in spontaneous reactions, energy is released, while in non-spontaneous reactions, energy must be supplied to the system through heat or electricity or other means.

Applying this to redox and electrochemistry contexts, a reaction is spontaneous if it generates current in the circuit. While in a non-spontaneous reaction, you will need to supply current, such as in an electrolytic cell.

Electrochemistry Principles

So what does electrochemistry rely on? What do you need to study electrochemistry?

Electrochemistry relies on a closed and complete circuit.

This means that the circuit created between the two reagents must be complete with an external circuit for the electrons, and a salt bridge for the anions. Electron flow, and thus electricity, will not occur if the circuit is only connected through an external wire.

There always needs to be a loop for the circuit to be complete.

Electrochemical cells are half-reactions of the full redox reaction.

Each part of an electrochemical cell represents one half-reaction of the full redox reaction. The reduction takes place on one side, where a metal will gain electrons and become solid from an aqueous state. In the other half cell, the oxidation reaction takes place, where the solid metal will give up electrons to become aqueous.

In electrochemical cell notation, the half cell that undergoes oxidation is written first (on the left), which is then followed by the half cell that undergoes reduction. This way you can see the transfer of electrons clearly, as it will be from the one half cell to the other in the direction of oxidation to reduction, showing the elements that lose electrons and those that gain those electrons.

Electrochemistry Techniques

So what type of equipment and methodology do you need to set up your own electrochemical cell?

These are the types of equipment that you will be using in any type of electrochemical experiment:

  1. two beakers (glass, unreactive)
  2. two inert electrodes (such as platinum)
  3. a wire to connect electrodes
  4. a salt bridge (filled with an inert electrolyte)
  5. voltmeter (voltage meter) or battery

So, how do you assemble your experiment? First you need to measure out your reagents, and determine the stoichiometric relations for the redox reaction to proceed. Usually, you will create specific concentrations of solutions which you will then use for your electrochemical reactions. Alternatively, if you are performing a non-aqueous electrochemistry experiment, such as electrolysis of molten salts, you will not need to create specific solutions.

After you have created your half cells, connect the circuit through the wire and salt bridge, and make sure you hook up the voltage meter or battery to it. This will either supply energy into the reaction or measure the energy of the system.

A note on the electrodes you use. Based on the type of reaction you will be performing, you will either use metal electrodes of the aqueous metal species, or inert electrodes. Inert electrodes are able to facilitate any type of electrochemical reaction without interfering with the system or stoichiometry of the redox reaction. This depends on whether the half cell reaction is able to have its own metal electrode or relies on an inert one.

Applications of Electrochemistry

Here we will cover some common applications of different types of electrochemistry. These include both applications for electrolysis and other electrochemical cell reactions.

Voltaic Cell Applications

Some common applications of electrochemistry are to produce solid metal crystals from solutions. Many different metals are found as salts in natural states from the ground. By dissolving them in solutions and then performing electrochemical redox reactions, we can produce the solid metal.

Producing these materials and metals is critical for all different types of industries. This includes the technology industry and any manufacturing industry.

Electrolysis Applications

Some common applications of electrolysis are to refine metals and impurities. By applying a current to a lump of impure metal you can purify it, resulting in a sludge of impurities in the bottom of your beaker. This can be used to turn any precious metal into a more precious one, as it will increase its purity.

Another key application of electrolysis is electroplating.

Electroplating is coating a metal object with a very thin layer of another metal.

Electroplating allows for metals to be deposited onto another metal object. This is usually performed with precious metals, such as silver or gold. Here, the object you want to electroplate can be silverplated for example, giving it a silver coat. This is done to use as little of the precious metal as possible on the object you want to cover.

The object you want to electroplate also has to be a metal, as that object will act as one of the electrodes hooked up to the electrical wire. The reduction reaction will occur on the metal object, and the previous metal will be deposited onto the object from the aqueous solution.

Electrochemistry - Key takeaways

  • Electrolysis is the study of the relationship between electricity and chemical reactions.
  • Splitting a redox reaction into cells allows for a controlled flow of electrons (electricity) through an external circuit.
  • Voltaic cells quantify spontaneous redox reactions by the electricity (energy) of the system.
  • Electrolysis allows non-spontaneous reactions to proceed by applying energy into the system.
  • Some applications of electrochemistry are: purifying metal, producing solid metals, and electroplating

Frequently Asked Questions about Electrochemistry

Electrochemistry is the study of the relationship between electricity and chemical reactions.

One example of electrochemistry is electrolysis, which can be used to electroplate metal objects. 

The applications of electrolysis are electroplating, refining metals, and producing solid metals from solutions. 

EMF is the electromotive force, which quantifies the energy a certain half cell produces in volts. 

The basics of electrochemistry rely on splitting redox reactions into the half-reactions of oxidation and reduction to control the flow of electrons. 

Final Electrochemistry Quiz

Question

Define electrochemistry in terms of electricity. 

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Answer

Electrochemistry is the relationship between electricity and chemical reactions. 

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Question

Why do electrochemical reactions require two electrodes? 

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Answer

This allows for the redox reaction to be split between the reduction and oxidation reaction. 

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Question

If a redox reaction is spontaneous, will it produce a current? 

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Answer

Yes

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Question

What type of electrochemical cell will be required for a spontaneous redox reaction?

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Answer

Voltaic (galvanic) cell

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Question

What are the two types of electrochemical cells?

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Answer

Voltaic (galvanic) cell and electrolytic cell. 

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Question

What type of redox reactions do electrolytic cells facilitate?

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Answer

Electrolysis is used for non-spontaneous redox reactions. 

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Question

What acronym can we use to remember redox processes?

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Answer

OIL RIG

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Question

Expand on the acronym OIL RIG

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Answer

Oxidation of loss, Reduction is gain. This statement concerns electrons. 

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Question

What are some common applications of voltaic cells?

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Answer

Production of solid metals from salt solutions. 

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Question

What are some common applications of electrolytic cells?

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Answer

Refining metals and impurities, production of metals from molten salts, and electroplating.

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Question

What are the most important types of equipment you will require for an electrochemical experiment. 

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Answer

Electrodes

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Question

Why is the salt bridge so important for electrochemical experiments?

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Answer

The salt bridge completes the circuits and allows anions to move from one half-cell to another. 

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