A Better Preventer Of Rusting Biology Essay

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Iron is one of the most commonly used metals in our everyday life mostly in the field of construction. The main properties of iron that cause it to be so widely used are its tensile strength, its malleable and ductile nature and its high melting point. Despite all these properties, there is one major drawback that causes problems in almost everywhere it is used. Fresh iron surfaces are lustrous and silvery-grey in colour, but oxidize in moist air to form a red or brown coating of ferrous oxide which is called rust. The formation of rust on iron leads to its strength becoming weaker which can lead to disasters in the construction field.

Thus, there is a need to protect these properties from degrading. There are various methods, by which this degradation can be prevented or delayed such as painting, electroplating, etc. I decided to test the effectiveness of electroplating for the prevention of rusting by two different metals. Thus, my research question would be which out of the two metals, zinc or tin, is a better preventer of rusting.

Rust is a term used to signify the corrosion of iron. Corrosion is the oxidation of an iron to produce compounds of the iron mainly Fe2O3 through interactions with its environment. The general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture is rusting. Rusting can be explained by the following equation Fe(s) + O2 (g) + H2O (I) → Fe2O3. x H2O (s). Rusting is an electrochemical process that starts with the transfer of electrons from iron to oxygen. There are various factors that affect. Rusting of iron is a redox reaction involving both the loss and gain of electrons between the reactants.

Electroplating proves to be one of the most effective and relatively cheaper methods of protection. It is the process by which a metallic coating is deposited on an object (iron rods in this case) by putting a negative charge on a metal and exposing it to a solution containing a metal salt. The positively charged metal ions in the salt solution are attracted to the object and reduced to metallic form upon it. Electroplating is also known as electrodeposition as one metal is being deposited onto the surface of another. It is also a process of plating a superior metal on the surface another metal either to increase its attractiveness or to prevent it from corrosion.

Electroplating also changes the physical, chemical and mechanical properties of the work piece. The main problem with electroplating is that getting a uniform thickness throughout can be very difficult. The cations of the metal to be plated get attracted to external corners and protrusions but relatively unattracted to internal corners and recesses. These difficulties can be overcome with placing multiple anodes around the cathode at similar distances. It is also used to bestow a property of a metal on the surface of the metal on which it is being plated.

Electroplating plays an important role in the prevention of rusting. The metal to be plated forms a layer on the other metal forming a physical barrier between the metal and the external atmosphere thereby preventing further rusting. This is one of the most commonly used methods for the prevention of rusting.

Research Method

Research Question: - Prevention of rusting: Is plating of iron by tin more efficient than plating of iron by zinc.

Variables

Control variables:

Room temperature

Amount of oxygen and moisture

Duration of electroplating

Current and voltage at which the experiment is conducted

Concentration of electrolyte

Manipulated Variable:

Electrolyte

The material to be plated on the iron rod

Responding Variable: Gain in mass of the iron rod

Hypothesis: According to the metal reactivity series zinc is more reactive than tin. Thus the surface of tin, being less reactive, will slower the process of rusting. Therefore, tin will should be a better preventer of rusting that zinc.

Apparatus

Chemicals Measurements

6 Iron rods Each of diameter 2.08 cm and length of 3.10 cm

Zinc rod

Tin rod

Zinc sulphate solution 0.5 molar, 1 molar and 1.5 molar

Tin nitrate solution 0.5 molar, 1 molar, 1.5 molar

Conc. HCl 11.3 moldm-3

Distilled water

Silica gel 500 g

Petroleum jelly

Equipment

Battery of 2 Ampere current

Beaker

Wires

Desiccator

Boiling tubes

Measuring balance

Procedure

Preparing the iron rods for electroplating

Six cylindrical and identical iron rods were taken and their weights were measured. The iron rods were cleaned with san paper to remove the previously present rust. As all the rust could not be removed with the help of sand paper, the rods were taken and dipped in conc. HCl for a period of 24 hours. The rods were placed in conc. HCl to remove any rust that was previously present on the iron rod after it had been cleaned with sand paper. After a particular period of time they were cleaned in distilled water. The weight of all iron rods were measured after the coating of rust had been removed.

Preparing the electrolytes

The following method of was used to prepare 0.5 molar of zinc sulphate and tin nitrate. Then solutions of dilute zinc sulphate and tin nitrate were to be prepared. 6 beakers were taken and filled with 100 ml each of distilled water. In the first beaker the amount of zinc chloride that was added was its molar mass divided by 100. Thus a 1 molar solution of zinc chloride was prepared. Double the mass of the previous case was added to 100 ml of water for a 2 molar solution and half the taken for a 0.5 molar solution. The same procedure was followed to prepare 0.5, 1 and 2 molar solutions of tin nitrate. 3 iron rods were electroplated with the 3 different concentrated solutions of zinc sulphate while the other three were electroplated with 3 different solutions of tin nitrate.

Electrolytic setup

The apparatus was setup as shown in the below diagram. As shown by the diagram given below Zinc Sulphate was used as the electrolyte. The Iron rod acts as the anode while the Zinc rod acts as the cathode as they were connected to the positive and negative terminals of the battery respectively. A voltage of 8 volts was passed through the circuit and the current was maintained at 0.4 amperes with the help of the rheostat. The iron rod was rotated manually by 180° after 5 minutes to ensure that the plating was uniform. CLEAN RODS WITH SAND PAPER B4 DIPPED IN HCL TO REMOVE FURTHER RUST. Such a circuit was maintained for a period of 10 mins after which the rod was taken out of the setup, placed in a desiccator.

Preparing the iron rod for drying

Silica gel was placed at the base of the desiccator. Petroleum jelly was applied on the lid of the desiccator so that no air from outside was It acts as a drying agent and removes the water from the plated rod without reacting with it. After the rod was placed in the desiccator for a period of 24 hours it was taken out of the desiccator and its weight was recorded. The difference in mass is the mass of the metal that was electroplated on iron. A similar procedure was followed for all the rods except that the concentration of the solute was different on every occasion. To ensure that the layer of metal plated on iron remained uniform a low current was passed for a long period of time.

CA THODE

ANODE

+ Cell -

Iron rod Zinc rod

ZnSO4 solution

Electrolytic Cell

The rods were then placed on the window sill next to each other so that the moisture and oxygen supply they receive from the atmosphere is uniform. The weights of the rods were measured occasionally at 24 hours, 48 hours, 1 week, 2 weeks and 1 month. The data was collected and then recorded in the form of a table. This was done so that later on after the experiment was over, the amount of rusting that had occurred in all six rods could be calculated and compared. The difference between the weight measure after electroplating the metal on the iron rod and the weight of the iron rod after a month is the weight of the rust that has formed on the iron rod. We can compare this weight to find out which is the more efficient metal that should be used for coating and which is the best concentration of the solution that should be used.

Method of control

Control Variable

Method of control

Room temperature

All the rods were placed close to each other on the window sill. Thus any changes that occurred were uniform to all and thus its effect is cancelled out.

Amount of oxygen and moisture

All the rods were kept close to one another on the window sill. Thus the level of exposure of each rod to the amount of oxygen and moisture remained the same.

Duration of electroplating

Each rod was plated only for a period of 10 mins thereby maintaining it constant.

Current and voltage at which the experiment is conducted

The current and voltage was also maintained a constant for every experiment. The voltage was 8 volts and the current was kept at 0.4 amperes.

Concentration of electrolyte

The concentration of the electrolyte was maintained either at 0.5, 1 or 2 molar for both the metals.

DATA COLLECTION

Table 1

Sr. No.

Mass of iron rod (g) ± 0.0001 g

1

24.8282

2

24.7223

3

24.7755

4

24.6225

5

24.6259

6

24.7455

Table 2

Sr. No.

Mass of iron rod after removal of previously present rust (g) ± 0.0001 g

1

24.7560

2

24.6740

3

24.6869

4

24.4882

5

24.6090

6

24.6762

Table 3 - mass of iron rod after electroplating (± 0.001g)

0.5 molar

1 molar

2 molar

Tin Nitrate

24.7520

24.6865

24.7288

Zinc Sulphate

24.5203

24.6587

24.7667

Table 4 - mass of iron rod after 1 day (± 0.001g)

0.5 molar

1 molar

2 molar

Tin Nitrate

24.7535

24.7013

24.7337

Zinc Sulphate

24.5253

24.6538

24.7632

Table 5 - mass of iron rod after 2 days (± 0.001g)

0.5 molar

1 molar

2 molar

Tin Nitrate

24.7564

24.7019

24.7342

Zinc Sulphate

24.5289

24.6547

24.7635

Table 6 - mass of iron rod after 7 days (± 0.001g)

0.5 molar

1 molar

2 molar

Tin Nitrate

24.7578

24.7035

24.7356

Zinc Sulphate

24.5310

24.6552

24.7642

Table 7 - mass after 14 days (± 0.001g)

0.5 molar

1 molar

2 molar

Tin Nitrate

24.7613

24.7074

24.7394

Zinc Sulphate

24.5327

24.6558

24.7654

Table 8 - mass of iron rod after 30 days (± 0.001g)

0.5 molar

1 molar

2 molar

Tin Nitrate

24.7669

24.7102

24.7428

Zinc Sulphate

24.5336

24.6562

24.6568

Table 9 - mass of iron rod after 60 days (± 0.001g)

0.5 molar

1 molar

2 molar

Tin Nitrate

24.771

24.7135

24.745

Zinc Sulphate

24.5346

24.6573

24.7474

Table 10 - mass of rust (± 0.002g)

0.5 molar

1 molar

2 molar

Tin Nitrate

0.019

0.027

0.0162

Zinc Sulphate

0.0143

0.0097

0.0022

From the above tables we can see that the gain in mass of the iron rod is lesser for zinc than for tin. Thus, we can say that zinc is a better preventer of rusting than tin. When an electrolyte of zinc sulphate of concentration 2 molar, is used it proves to be the best electrolyte concentration.

DATA PROCESSING

Mass of iron rod after 2 months - mass of iron rod after electroplating = mass of rust

Table 1 - mass of rust

0.5 molar

1 molar

2 molar

Tin Nitrate

0.019

0.027

0.0162

Zinc Sulphate

0.0143

0.0097

0.0022

Uncertainties

All the uncertainties for the values recorded are ± 0.0001g.

But the uncertainty for the mass of rust is calculated by the adding the uncertainties of both the values.

Therefore,

Uncertainty in mass of rust = 0.0001+0.0001 = 0.0002g

We can compare the increase in mass of the iron rods in the form of a graph shown below. In the graph given below the green bar graphs indicate that zinc sulphate was used as the electrolyte and the red bar graphs indicate that tin nitrate was used as the electrolyte.

The numbers mentioned on the Y-axis represent the following-

Number

Name and concentration of electrolyte

1

Tin nitrate - 0.5 molar

2

Tin nitrate - 1 molar

3

Tin nitrate - 2 molar

4

Zinc sulphate - 0.5 molar

5

Zinc sulphate - 1 molar

6

Zinc sulphate - 2 molar

Thus from the graph we can clearly see that electroplating of the iron rod by zinc proves to be a better method of prevention of rusting as compared to tin. We can compare the mass of rust formed on the iron rod for different concentrations in the form of a table. By looking at the graph and at the table we can see that increase in mass of rust is the most when tin nitrate of concentration 1moldm-3 is used as the electrolyte and least when zinc sulphate of concentration 2 molar is used.

Electrolyte used

Conc. of electrolyte

Gain in mass on day 1

Gain in mass on day 2

Gain in mass on day 7

Gain in mass on day 14

Gain in mass on day 30

Gain in mass on day 60

Zinc sulphate

0.5 molar

0.005

0.0036

0.0021

0.0017

0.0009

0.001

Zinc sulphate

1 molar

0.0051

0.0009

0.0005

0.0006

0.0004

0.0022

Zinc sulphate

2 molar

0.0002

0.0004

0.0005

0.0004

0.0003

0.0004

Tin nitrate

0.5 molar

0.0015

0.0029

0.0014

0.0035

0.0056

0.0041

Tin nitrate

1 molar

0.0148

0.0006

0.0016

0.0039

0.0028

0.0033

Tin nitrate

2 molar

0.0049

0.0005

0.0014

0.0038

0.0034

0.0022

DATA ANALYSIS

From the graph we can see that electroplating the iron rod with zinc is a more effective method of preventing rusting than plating it with tin. This does not agree with the hypothesis that we started with. Thus there will be other reasons that play a more dominant role than the reactivity or the reactivity of the metals may be affecting it in some other manner than the one mentioned in the hypothesis. The results obtained can be explained in the following manner:-

Standard Electrode Potential

The rusting of iron stops after some time after it is plated with zinc because the Zinc layer on the Iron prevents corrosion by forming a physical barrier. When exposed to the atmosphere, Zinc reacts with Oxygen to form Zinc Oxide. The Zinc Oxide then reacts with the water molecules in the air to form Zinc Hydroxide. Finally, the Zinc Hydroxide reacts with Carbon Dioxide in the atmosphere to produce a thin, impermeable and an insoluble dull grey layer of Zinc Carbonate which sticks extremely well to the underlying Zinc thereby protecting it from further corrosion. The same reactions occur in the case of tin but it proves to be more effective in case of zinc. We can compare the gain in mass of the rod plated with zinc to the rod plated with tin.

Electrolyte used

Conc. of electrolyte

Gain in mass on day 1

Gain in mass on day 2

Gain in mass on day 7

Gain in mass on day 14

Gain in mass on day 30

Gain in mass on day 60

Zinc sulphate

0.5 molar

0.005

0.0036

0.0021

0.0017

0.0009

0.001

Zinc sulphate

1 molar

0.0051

0.0009

0.0005

0.0006

0.0004

0.0022

Zinc sulphate

2 molar

0.0002

0.0004

0.0005

0.0004

0.0003

0.0004

Tin nitrate

0.5 molar

0.0015

0.0029

0.0014

0.0035

0.0056

0.0041

Tin nitrate

1 molar

0.0148

0.0006

0.0016

0.0039

0.0028

0.0033

Tin nitrate

2 molar

0.0049

0.0005

0.0014

0.0038

0.0034

0.0022

Zn2+ + 2e- Zn -0.76 V

Sn2+ + 2e- Sn -0.14 V

Zinc has standard electrode potential value of -0.76 volts whereas tin has a standard electrode potential value of -0.14 volts. This means that tin is a more powerful oxidizing agent and less powerful reducing agent as compared to tin. Thus we can say that tin has a lower tendency to lose electrons as compared to zinc. Thus, zinc is a much more reactive metal as compare to tin. Zinc being more reactive reacts at a faster rate and stops further rusting before tin is able to do so. A combination of zinc-tin electroplating could prove to be even more effective than zinc plating. Moreover, tin being a stronger reducing agent has a higher gain in mass compare to that of zinc over the same period of time. Thus, the plating of iron with zinc becomes more effective than plating of iron with tin.

Sacrificial protection

Another reason to justify the effectiveness of zinc as compared to iron comes from the concept of sacrificial protection. In this method blocks of a more reactive metal are placed on the surface of iron that is to be protected (generally iron). The more reactive metal attracts electrons from the surroundings. This metal will feed the iron with electrons each time the iron is oxidized to iron ions thus preventing it from rusting. A metal is sacrificed (made to undergo corrosion) to prevent iron from rusting. This is a method mostly used to protect ships from getting rusted. Due to this property if a part of the coating of zinc on the iron rod wears off then due to the tendency of sacrificial protection, zinc will continue to rust and not iron.

Conclusion

Zinc is a better preventer of rusting as compared to tin when both are electroplated on iron.

Errors

The plating may not have been uniform throughout the rod. This could have led to increased rusting because of the uneven plating of the metal.

There were minor fluctuations in the current which was controlled by the rheostat. This also led to uneven plating on the iron rods.

Improvements

Multiple anodes should be placed at equal distances from the cathode around the iron rod. This would lead to a more uniform coating on the iron rod.

A new rheostat could be used to ensure that there are no minor fluctuations in the reading because of the errors in the device.

Scope for Further Research

There are two aspects into which further research could be done. Firstly, we could compare zinc plating and hot dip galvanization to find which of the two methods of protection of iron by using zinc is more effective. Another aspect is that we could compare different methods of prevention of rusting such as non - metallic coatings, alloying, anodic protection, and sacrificial protection to electroplating and find out which out of all these proves to be the best way of prevention of rusting.

We compare the two most common methods of prevention of rusting by zinc because we have already found out that zinc proves to be a better preventer of rusting than tin. The major difference between the two types of prevention could result from the fact that when an iron rod is dipped in molten zinc, zinc adheres well to the surface of iron and forms a coating that is thin as compared to the coating of zinc that is electroplated. This could prove to be a factor causing difference is results between zinc plating and hot dip galvanizing.

On the other hand, there are various methods of prevention of rusting such as alloying, anodic rusting and non-metallic coating to name a few. Non - metallic coating comprises of methods such as painting, varnishing, tarring, plastic coating, oiling, greasing, enamelling, etc. These method are used depending on the place where it has to be used for example we use greasing for the chain of the bicycle is a process in which the chain is manually coated with grease to avoid rusting. Painting another method for prevention is used for automobiles to increase its attractiveness and decrease the rate of rusting which is applying a coating of paint on the car to make a barrier between the iron and the atmosphere. Oiling of utensils in the kitchen is applying oil on the utensil for the same reason. When we compare electroplating to other methods of prevention of rusting, we have to keep in mind that it is practically not possible to electroplate huge structures with iron. Thus each method mentioned above is used specifically for a purpose. Anodic protection is a method in which the metal is intentionally oxidized under carefully controlled conditions to form a thin layer of oxide on the surface of the metal, which stops further oxidation. Alloying is a method of prevention where iron is alloyed together with different metals such as cadmium, carbon or nickel to enhance its physical properties.

Sites used

http://www.answers.com/topic/iron

http://en.wikipedia.org/wiki/Electroplating

Chemistry principles and practice by Reger Goode Mercer

http://en.wikipedia.org/wiki/Steel

http://en.wikipedia.org/wiki/Iron

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