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Chemistry Project to Study Effect of Metal Coupling on Corrosion

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To study of the effect of metal coupling on the rate of corrosion

GYANESH   TIWARI

Roll No.6261924

XII (SCIENCE)

CONTENTS

  1. I.        Acknowledgement
  2. II.        Certificate
  3. III.        Aim
  4. IV.        Materials Required
  5. V.        Theory
  6. VI.        Procedure

VII.  Observations

  1. VIII.    Conclusions
  2. IX.    Precautions

Acknowledgement

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.

Gyanesh Tiwari

Class- XII  (science)

6261924

Certificate

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

T.Signature:-

AIM

To study of the effect of metal coupling on the rate of corrosions.

Materials required:

Apparatus:

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

Box.

Chemicals:

Hydrochloric acid and Sodium hydroxide.

Theory:

• 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.

Procedure:

(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

beakers.

(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.

Observations:

S.No. Specimen (with acid) Initial Weight (in gm) Final Weight (in gm)
1. Brass 8 5
2. Iron 8 6
3. Zinc 8 6.50
4. Aluminium 8 7.10
5. Iron + Aluminium 15 12.30
6. Brass + Zinc 15 13.00
7. Iron +Zinc 15 14.10
Specimen (with Base)
8. Brass 8 5.80
9. Zinc 8 6.20
10. Iron 8 7.10
11. Aluminium 8 7.60
12. Brass + Aluminium 15 12.90
13. Brass + Zinc 15 13.60
14. Iron + Aluminium 15 14.40

Results :

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.

Conclusions:

• 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:

At cathode:

Fe . Fe2+ + 2e.

in acid the equilibrium is

HCl . H+ + Cl .

At anode:

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

rust.

(b) The e.m.f of these metals are in the order of Al:Zn:Fe . The values are

e.m.f

Al .Al3++3e-

Zn .Zn2++2e-

Fe . Fe 2++ 2e-

1.66V

0.76V

0.44V

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.

Bibliography:-

1) NCERT text book

2) WIKIPEDIA

3) APC Lab Manual

Email id: tgyanesh@gmail.com

Now in LPU, a 2010 Presentation.

Thank you.

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