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GYANESH TIWARI

Roll No.6261924

XII (SCIENCE)

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CONTENTS

I. AcknowledgementII. Certificate

III. AimIV. Materials Required

V. TheoryVI. Procedure

VII. ObservationsVIII. Conclusions

IX. Precautions

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Acknowledgement

It is my duty to record my sincere thanks

and deep sense of gratitude to myrespected teacher Mr. Sanjay Mishra

for his valued guidance , interest andconstant encouragement for the

fulfillment of the project.

Gyanesh Tiwari

Class- XII (science)

6261924

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CertificateCertified that this is the bonafide

work of Gyanesh Tiwari of class XII ofK.V. A.F.S Rajokri N.D. 38 . He has

performed these experiments duringacademic year 2009-10.

The student’s initiative, cooperativeness& participation during the practical

classes were excellent. His aestheticpresentation, visual appeal, expression &

neatness were excellent.

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His content accuracy, creativity,originality & analysis of different

perception were excellent.

Mr. Sanjay Mishra

T.Signature:-

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AIMTo study of the effect of metal

coupling on the rate of corrosions.

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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.

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Theory:• Corrosion is a serious problem of some

metals like iron, zinc, aluminium and alloyslike brass which are commonly used in day

to day life.

• Apart from reducing the life of articlesmade up of these metals or alloys the

chemical substances formed out ofcorrosion have serious public health

problems.

• Replacement of machines or their partsand many other articles in industrial andpublic dealing lead to huge expenditure.

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• Hence, how to reduce or avoid corrosionof articles made up of metals or alloys hasbeen a major subject of study in the field

of chemistry and electro-chemistry.iC

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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 differentbeakers.

(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

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(vi) Then take iron + brass, iron +aluminium, iron + zinc, aluminium + zinc

and

brass + zinc and keep them in differentbeakers.

(vii) Allow the reactions to occur for 24hours.

(viii) Note the maximum and minimumtemperatures.

(ix) Now at the end of reaction take out themetals and keep them in sun for

sometime so that they get dried up quickly

(x) Take the weights of each specimen andnote the difference.

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(xi) Similarly repeat 1,2,3,4,5,6,7 and 8steps in a basic solution.

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Observations:

S.No. Specimen (with acid) Initial Weight(in gm)

Final Weight(in gm)

1. Brass 8 52. Iron 8 63. Zinc 8 6.504. Aluminium 8 7.105. Iron + Aluminium 15 12.306. Brass + Zinc 15 13.007. Iron +Zinc 15 14.10

Specimen (with Base)8. Brass 8 5.809. Zinc 8 6.20

10. Iron 8 7.1011. Aluminium 8 7.6012. Brass + Aluminium 15 12.9013. Brass + Zinc 15 13.6014. Iron + Aluminium 15 14.40

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Results :1. The rate of corrosion observed in acidicmedium or the mass consumed during the

corrosion is in the decreasing order frombrass to aluminum. Brass has the highest

corrosion rate while aluminium has theleast corrosion rate.

Brass > Iron > Zinc > Aluminium

2. When coupling of these metals wasdone each couple showed some difference

in their corrosion with respect to eachmetal kept alone. Iron + Aluminium couplehas the highest rate of corrosion while iron

+Zinc couple has the lowest rate ofcorrosion.

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Rate of corrosion of each couple is in theorder of

Iron + Aluminium > Brass + Zinc> Iron +Zinc

3. Rate of corrosion in basic medium is inthe 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 therate of corrosion was in the decreasing

order from

Brass+ Aluminium > Brass + Zinc > Iron +Aluminium

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5. Temperature and time of reaction wereconstant i.e., temperature was 21° C and

time of

reaction was 24 hours.iC

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Conclusions:• Corrosion is a serious problem of some

metals like iron, zinc, aluminium and alloys

like brass which are commonly used in dayto day life.

• Apart from reducing the life of articlesmade up of these metals or alloys the

chemical substances formed out ofcorrosion have serious public health

problems.

• Replacement of machines or their partsand many other articles in industrial and

public dealing lead to huge expenditure.

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• Hence, how to reduce or avoid corrosionof articles made up of metals or alloys has

been a major subject of study in the fieldof chemistry and electro-chemistry.

• The study of the rate of corrosion ofdifferent 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 fullagreement with the well known electro-chemical reaction. Some of the typical

reactions as occur with iron are illustrated.

(a) The reactions at respective electrodesare:

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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 andwill form H2 gas. While OH. anion will also

react with some of the iron and will formFe(OH)3 which is observed in the form of

rust.

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(b) The e.m.f of these metals are in theorder 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 copperhas the e.m.f. 0.42V during the forwardreaction or oxidation reaction. While in

backward reaction the e.m.f. value is .0.42.This is because during oxidation reaction

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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+ ionswhich react with metals and H2 gas is

evolved. This is because all the metals arehighly electronegative in nature. When

these two come in contact they react veryeasily and form stable compounds. Thus

the rate of corrosion is very high.

The rate of corrosion in basic medium isvery less as compared to acidic medium.

This is

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shown because of following factors:

(i) Ex: sodium hydroxide .NaOH which is inequilibrium with Na+ and OH. ions.

NaOH . Na+ + OH When

NaOH comes in contact with water the twoions immediately dissociate. The hydrates

Na+ ions will take the H+ ion.

The electropositive characters here will bethe main factor in the slow rate of

corrosion.

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Na being more electropositive than themetal mentioned above, most of OH- ions

will be

taken by Na+ when compared to the othermetals 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 theconversion of H+ to H2 gas state. That is

why

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there will not be replaceable ‘H’ ion. Ifthere is no replaceable H+ ion then the

corrosion will

be possible. Hence the rate of corrosion isvery slow.

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Bibliography:-

1) NCERT text book2) WIKIPEDIA

3) APC Lab Manual4) www.icbse.com

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