gyanesh tiwari roll no.6261924 xii (science)projects.icbse.com/chemistry/465.pdfwhen coupling of...
TRANSCRIPT
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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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