Electrochemistry is the study of the movement of electron which generate electricity in a chemical reaction. Electrochemistry also defined as the study of chemistry which concerned on the interconversion of chemical and electrical energy. As the electron move from one element to another element, the reaction is known as redox reaction. Electrochemistry is the theory which can apply in many fields such as physical, chemical, biological science and so on. The example of the electrochemical cell is battery and it is commonly use in our daily life in order to provide electric current. The application of the theory of electrochemistry is the cell phone, electric cars, remote control, laptops and so forth.
There are two type of cell in electrochemistry which are voltaic cell and electrolytic cell. Voltaic cell is also known as galvanic cell or chemical cell. Electrolytic cell, a type of cell which use electrical energy to produce chemical energy. Galvanic cell is a type of cell which produce electrical energy from chemical energy. The galvanic cell has two different metals, act as electrodes, immersed in two separate electrolyte solutions and connected to each other with wires. The electrolyte solutions are separated by salt bridge or porous pot that does not react with the electrodes in galvanic cell. The function of salt bridge or porous pot is to separate two electrolyte solutions but allow ions to pass through a complete circuit. The value of potential difference depends on the distance of two metals in the electrochemical series. The longer the distance between the two metals in electrochemical series, the larger the voltage will be. Electrochemical series, an arrangement of metals according their tendency to donate electrons and forms ions. The higher the position of metals in electrochemical series, the more electropositive is the metal. Moreover, the metals that are located higher in electrochemical series which is more electropositive will act as the negative terminal (anode), while the metals that are located lower in electrochemical series which is more electronegative will act as the positive terminal (cathode). At the anode (negative terminal), will release the electrons and dissolve to form metal ions; whereas at the cathode (positive terminal), will gain the electrons and be discharged to form metal atoms. The electrons will flow through the external circuit from the negative terminal to the positive terminal. Finally, the example of galvanic cell include Daniel cell, dry cell, lead-acid accumulator and alkaline cell.
Electrolytic cell Galvanic cell
Both cells consist of an electrolyte
Both cells consist of two electrodes
Both cells involve chemical changes on electrodes
Anode of both cells undergo oxidation while cathode undergo reduction
The electron flow in both cells flow from anode to cathode in external circuit
Electrolytic cell converts electrical energy to chemical energy Galvanic cell converts chemical energy to electrical energy
The anode of electrolytic cell is positive terminal The anode of galvanic cell is negative terminal
The cathode of electrolytic cell is negative terminal The cathode of galvanic cell is positive terminal
Electrolytic cell consists of battery Galvanic cell does not consist of battery
Electrolytic cell can be two similar or different electrode immersed in electrolyte Galvanic cell can be two different electrodes immersed in electrolyte
Theory of Electroplating
Definition of Electroplating
Electroplating, known as electrodeposition, a process that coating a thin layer of non- reactive metal on the surface of the reactive metals by electrolysis. The process of breaking down chemical compounds into their constituent elements by using electric current is known as electrolysis.
Importance of Electroplating
The purpose of electroplating to improve the appearance of the metal which known as aesthetic. For example, jewellery often plated with gold or silver to make it more attractive and valuable. Rusting of metals occur when they interact with water and oxygen. Electroplating will protect the metal from corrosion or rust. Metals that often use as the protective layer are tin, zinc, nickel, and others. For instance, food container is plated by tin to prevent it from rusting easily. Next, some electroplating is both aesthetic and protection. For instance, wheel rims are often plated by chromium to make them shininess and for protection. Moreover, electroplating can enhance electrical conductivity. For instance, gold plated and silver plated are used to manufacture electrical components such as computers, cell phone, and others. Finally, electroplating can increase the thickness, lifespan, prevent tarnishing of an object.
Materials that commonly used to plate an object
Not every material are suitable for electroplating. The most common materials that suitable for electroplating are chromium, nickel, tin, zinc, cadmium, gold, silver, copper, palladium, platinum, ruthenium and brass.
The process of Electroplating
In the electroplating process, two different electrodes are needed to immerse into the electrolyte. Electrodes can be classified into 2 which are inert electrode and active electrode. The inert electrode such as platinum and carbon do not take part in chemical reactions during electrolysis; whereas active electrode such as copper, silver, and mercury take part in chemical reaction during electrolysis. The two electrodes are known as anode and cathode. Anode is the positive electrode that connected to the positive terminal of the battery; whereas cathode is the negative electrode that connected to the negative terminal of the battery. In this process, the anode must be made of plating metal; whereas cathode must be the object or metal to be plated.
Redox reaction, a chemical reaction that both oxidation and reduction occur together. Oxidation is a process of an atom losing an electron; whereas reduction is a process of atom gaining an electron. In this process, oxidation takes place at the anode; whereas reduction takes place at the cathode.
The example of half equation at anode and cathode:
Anode: Cu Cu2+ + 2e-
Cathode: Cu2+ + 2e- Cu
Furthermore, the electrolyte solutions must be based on what the object plated. For example, to copper plate an object, the electrolyte solutions must be in copper-based solution such as copper sulphate solution. If not, the electroplating process will be failed.
When the switch is turned on, the current is passed through the electrolyte and causes the electrolyte to splits into a positive ion and a negative ion. The positive ion will be attracted to the cathode to gain electron; whereas the negative ions will be attracted to the anode to lose an electron. When the positive ions at the cathode gain electron, it will become atom and form a thin layer on the object.
During the electroplating process, the size of the anode decreases because of the loss of electrons, the size of the cathode increases because of the gaining of electrons. Finally, to achieve a higher quality of electroplating which is attractive, resistant to corrosion and lasting, the metals need to be plated should be cleaned before the process, then a small electric current should be used, time taken for the electroplating must be longer, a dilute electrolyte should be used and the metals to be plated should be rotated slowly and consistently.
Example of Electroplating
Electroplating of Copper
The first example of electroplating is copper electroplate. The electrolyte use in copper electroplating is acidified copper sulphate solution. Thick rod of impure copper act as an anode while thin rod of pure copper act as cathode. When the switch is turn on, the current pass through the solution. As the result, acidified copper sulphate solution splits into copper ions (Cu²?) and sulphate ions (SO?²?). The copper ions from the electrolyte attracted towards the cathode. The copper ions gain two electrons from cathode and deposit as pure copper atoms on thin copper rod. At the same time, copper atom from anode lose two electrons and converted into copper ions. Copper ions dissolve in the electrolyte solution. As the result, the concentration of electrolyte remains the same. The copper atoms from anode get deposited on cathode repeatedly. Hence, the size of anode decreases and size of cathode increases. The equation take place at anode is Cu Cu²?+ 2e while cathode is Cu²?+ 2e Cu. All the pure copper from anode deposit on the cathode. The impurities in the impure copper rod settle down as anode mud at the bottom of container.
The overall redox equation is Cu + Cu²? Cu²? + Cu.
054665The nickel electrode act as the anode whereas the spoon that needs to be plated act as cathode. Oxidation (loss of electrons) take place at the anode; whereas reduction (gain of electron) take place at the cathode. Nickel (II) sulphate solution (NiSO4) is used as the electrolyte. The nickel electrode contains nickel atom. The spoon is made of iron which never reacts because metal atom cannot be reduced. When the switch is turned on, the current passed through the NiSO4 solution and causes NiSO4 solution split into nickel ion (Ni2+), water (H2O) and sulphate ions (SO2-4). The nickel electrode (anode) loss 2 electrons (oxidation) to form nickel ions (Ni2+), the 2 electrons will be transferred to the iron spoon (cathode). The Ni2+ ions from the NiSO4 solution attracted toward the iron spoon (cathode) and gain 2 electrons (reduction) to form nickel atom.
Anode (oxidation): Ni Ni2+ + 2e-
Nickel dissolves from the anode by releasing electrons to form Ni2+ ions. Nickel electrode becomes thinner.
Cathode (reduction): Ni2+ + 2e- Ni
Ni2+ ions are discharged by accepting electrons to form nickel atom. Nickel metal is deposited on the surface of the iron spoon.
Overall Redox Equation: Ni2+ + Ni Ni + Ni2+
Next, the nickel atom will keep on forming and coat the surface of the iron spoon by forming a layer of nickel atom. When Ni2+ ions are getting used up, they will not be depleted because of the presence of the nickel electrode. The nickel anode becomes thinner because of the losing of electrons. If the nickel electrode disintegrates too much, it will replace by a new nickel. Last but not least, the thin layer of nickel deposited on the iron spoon become thicker because of the gaining of electrons. Finally, to ensure the nickel plated on the iron spoon is attractive and resistant to rusting, make sure to clean the iron spoon before plated, then small electric current is used and time taken for electroplating is longer.
Factor affect the Electroplating
There are some factors affect electroplating. The first factor is strength of electric current. Stronger the current, the rate of electrons moves through the circuit increases, the rate of electroplating also increases. Furthermore, the second factor is concentration of electrolyte. Higher the concentration of the electrolyte solution, higher the rate of electroplating.
Applications of Electroplating in Daily life
A lot of things in daily life have applied with the electroplating. For instance, the astronaut who makes the First American Spacewalk in 1965 was wearing a gold plated visor to protect his eyes from solar radiation. The next example is the jewellery such as a ring, necklace, bracelet and others can be plated with gold or silver to make it more attractive and valuable. The third example is that the tin cans for the food storage are plated by tin to make it resistant to corrosion and long lasting. The final example is the bath taps which plated by the chromium for protection and to make it more attractive.
Safety Precautions of Electroplating
To prevent injured when undergoing the process of electroplating, a few safety precautions must be aware and follow. During the electroplating process, safety goggles and gloves should be used to prevent skin infections. Then, the acid and cyanide solutions cannot be mixed because it will produce hydrogen cyanide gas which is a poisonous gas that is harmful to our body. Moreover, cannot eat and drink during the process. Last but not least, cannot store the electrolyte in any container that made of metal because the electrolyte will react with the metal substances. Finally, the electrolyte cannot come into contact with any household cleaning materials because the reaction will release toxic gases.
Effect of electroplating towards environment
There are some effects of electroplating towards the environment. The example of effect is air pollution, water pollution, soil erosion and affect human health.
The uses of acid, alkaline and other material will contribute odour smell to environment. Fuses and vapour which is toxic may release through electroplating activities. The gasses and fumes released may affect air quality and will associated human health problems. For example, cryolite which is dust particle that escape into air may lead to air pollution too. Besides that, during the process of electroplating, it will release poisonous gasses such as chlorine gas and bromine gas which is poisonous to the environment.
The process of electroplating also causes water pollution. When mercury is used in the electrolysis of aqueous sodium chloride solution, it may seep into the water if disposed carelessly and it may contribute to mercury poisoning. Furthermore, electroplating process emits poisonous waste chemical of chromium salt and nickel salt which may change the pH of water resources and it will also affect the aquatic organism even the ecosystem as the aquatic organism cannot live in the extreme pH. Water waste and sludge release from the electroplating industry also increase water pollution.
Electroplating process also lead to soil erosion. When the impurities of electrolysis such as red mud which obtained during electrolysis of bauxite may cause soil to be polluted if it is disposed carelessly. The process of electroplating also brings some harmful effect to human being such as human diseases. For instance, aluminium metal may lead to Alzheimer’s disease. This disease will cause some problems with memory, thinking and behavior of people. Moreover, if human expose to hexavalent chromium will lead to eye irritation and damage, perforated eardrums, respiratory irritation. If expose to nickel will cause kidney damage and liver damage.
Finally, filtration is one of the ways to disposed the waste product of electroplating because it will help to filter and remove the accumulation of solid so that it does not polluted the environment.
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