Chemistry Project to Study Effect of Metal Coupling on Corrosion
To study of the effect of metal coupling on the rate of corrosion
- I. Acknowledgement
- II. Certificate
- III. Aim
- IV. Materials Required
- V. Theory
- VI. Procedure
- VIII. Conclusions
- IX. Precautions
It is my duty to record my sincere thanks
and deep sense of gratitude to my respected teacher Mr. Sanjay Mishra for his valued guidance , interest and constant encouragement for the fulfillment of the project.
Class- XII (science)
Certified that this is the bonafide work of Gyanesh Tiwari of class XII of K.V. A.F.S Rajokri N.D. 38 . He has performed these experiments during academic year 2009-10.
The student’s initiative, cooperativeness & participation during the practical classes were excellent. His aesthetic presentation, visual appeal, expression & neatness were excellent.
His content accuracy, creativity, originality & analysis of different perception were excellent.
Mr. Sanjay Mishra
To study of the effect of metal coupling on the rate of corrosions.
Beakers-15, Iron sheets of 2# size-6, Aluminium rods of 2# size-6, Brass rods of
2# size-6, Zinc sheets of 2# size-6, Measuring cylinders, Chemical Balance, Weight
Hydrochloric acid and Sodium hydroxide.
• Corrosion is a serious problem of some metals like iron, zinc, aluminium and alloys like brass which are commonly used in day to day life.
• Apart from reducing the life of articles made up of these metals or alloys the chemical substances formed out of corrosion have serious public health problems.
• Replacement of machines or their parts and many other articles in industrial and public dealing lead to huge expenditure.
• Hence, how to reduce or avoid corrosion of articles made up of metals or alloys has been a major subject of study in the field of chemistry and electro-chemistry.
(i) Mix 9 ml. of conc. HCl with 241 ml. of water to form 250 ml. of solution.
(ii) Take this solution in seven different beakers.
(iii) Mark each beaker serially from 1 to 7.
(iv) Take the weights of three iron sheets, three aluminium rods, three brass rods and
three zinc sheets.
(v) Now keep iron sheets, aluminium rods, zinc sheets and brass rod in separate
(vi) Then take iron + brass, iron + aluminium, iron + zinc, aluminium + zinc and
brass + zinc and keep them in different beakers.
(vii) Allow the reactions to occur for 24 hours.
(viii) Note the maximum and minimum temperatures.
(ix) Now at the end of reaction take out the metals and keep them in sun for
sometime so that they get dried up quickly
(x) Take the weights of each specimen and note the difference.
(xi) Similarly repeat 1,2,3,4,5,6,7 and 8 steps in a basic solution.
|S.No.||Specimen (with acid)||Initial Weight (in gm)||Final Weight (in gm)|
|5.||Iron + Aluminium||15||12.30|
|6.||Brass + Zinc||15||13.00|
|Specimen (with Base)|
|12.||Brass + Aluminium||15||12.90|
|13.||Brass + Zinc||15||13.60|
|14.||Iron + Aluminium||15||14.40|
1. The rate of corrosion observed in acidic medium or the mass consumed during the
corrosion is in the decreasing order from brass to aluminum. Brass has the highest
corrosion rate while aluminium has the least corrosion rate.
Brass > Iron > Zinc > Aluminium
2. When coupling of these metals was done each couple showed some difference in their corrosion with respect to each metal kept alone. Iron + Aluminium couple has the highest rate of corrosion while iron +Zinc couple has the lowest rate of corrosion.
Rate of corrosion of each couple is in the order of
Iron + Aluminium > Brass + Zinc> Iron + Zinc
3. Rate of corrosion in basic medium is in the decreasing order from Brass to Aluminium.
The order of rate of corrosion is as below:
Brass > Zinc >Iron > Aluminium
4. When these metals were coupled the rate of corrosion was in the decreasing order from
Brass+ Aluminium > Brass + Zinc > Iron + Aluminium
5. Temperature and time of reaction were constant i.e., temperature was 21° C and time of
reaction was 24 hours.
• Corrosion is a serious problem of some metals like iron, zinc, aluminium and alloys
like brass which are commonly used in day to day life.
• Apart from reducing the life of articles made up of these metals or alloys the
chemical substances formed out of corrosion have serious public health problems.
• Replacement of machines or their parts and many other articles in industrial and
public dealing lead to huge expenditure.
• Hence, how to reduce or avoid corrosion of articles made up of metals or alloys has
been a major subject of study in the field of chemistry and electro-chemistry.
• The study of the rate of corrosion of different metals or alloys showed gradual
decrease in their masses in acidic medium. The decrease is in the order of brass,
iron, zinc, aluminium.
• The present experiments are in full agreement with the well known electro-chemical reaction. Some of the typical reactions as occur with iron are illustrated.
(a) The reactions at respective electrodes are:
Fe . Fe2+ + 2e.
in acid the equilibrium is
HCl . H+ + Cl .
The water which is in equilibrium
H2O . H+ + OH.
Here the Fe2+ cation will readily take Cl- and form FeCl3. While H+ of acid will
be reacting with another H+ of water and will form H2 gas. While OH. anion will also
react with some of the iron and will form Fe(OH)3 which is observed in the form of
(b) The e.m.f of these metals are in the order of Al:Zn:Fe . The values are
Fe . Fe 2++ 2e-
Brass which is an alloy of zinc and copper has the e.m.f. 0.42V during the forward reaction or oxidation reaction. While in backward reaction the e.m.f. value is .0.42. This is because during oxidation reaction the e.m.f values of zinc and copper are .0.76 and + 0.34, respectively. That is why the value differs.
(c) In acid there are replaceable H+ ions which react with metals and H2 gas is
evolved. This is because all the metals are highly electronegative in nature. When
these two come in contact they react very easily and form stable compounds. Thus
the rate of corrosion is very high.
The rate of corrosion in basic medium is very less as compared to acidic medium. This is
shown because of following factors:
(i) Ex: sodium hydroxide .NaOH which is in equilibrium with Na+ and OH. ions.
NaOH . Na+ + OH When
NaOH comes in contact with water the two ions immediately dissociate. The hydrates
Na+ ions will take the H+ ion.
The electropositive characters here will be the main factor in the slow rate of corrosion.
Na being more electropositive than the metal mentioned above, most of OH- ions will be
taken by Na+ when compared to the other metals i.e., the rate of corrosion is slow with
Na+ \ Fe2+ || OH\OH-
While H+ + electron = H
H + H = H2 gas.
(ii) The availability of e- is very less for the conversion of H+ to H2 gas state. That is why
there will not be replaceable ‘H’ ion. If there is no replaceable H+ ion then the corrosion will
be possible. Hence the rate of corrosion is very slow.
1) NCERT text book
3) APC Lab Manual
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Now in LPU, a 2010 Presentation.