Estimation Of Chlorine In Plant Leaves Using Fundamental Principles Of Electrochemistry

Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

Chemistry Project Report

Estimation of Chloride Ion in Plant Leaves Using Fundamental Principles of Electrochemistry Indian Institute of Science Education & Research, Kolkata Semester III

Dec. 2008

By: Satyam Singhal (07MS-66) Jyothi V. Nair (07MS-72) Harsh Purwar (07MS-76) 1

Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

Contents Introduction

03

Aim of the Experiment

03

Theory

03

Experiment

03

Part I

03

Part II

04

Results

05

The Hits & Trials

05

The Actual Graphs

07

Discussion

08

Calculations

08

Conclusion

08

References

09

Acknowledgement

09

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Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

Introduction: Plants absorb water from the soil through their roots. Water contains dissolved salts many of which have the Cl- ions. These salts dissolved in water subsequently make their way to the leaves and much of it is retained in ionic form. Thus, chlorine estimation in leaves indirectly is a measure of salt concentration in the soil for an area.

Aim of the Experiment: To estimate the concentration of chloride ions present in the plant leaves by the standard principles of electrochemistry using a potentiometer.

Theory: Calomel half cell and Ag+/AgNO3 half cell are employed. From the Fundamental law of electrochemistry i.e. the Nernst Equation we have, 0 𝐸𝑐𝑒𝑙𝑙 = 𝐸𝐴𝑔/𝐴𝑔 + + 0.059 × 𝑙𝑜𝑔𝑐𝐴𝑔 + − 𝐸𝑆𝐶𝐸

where 𝑐𝐴𝑔 + is the concentration of AgNO3

Here we note that AgCl is a sparingly soluble salt in water. Now increase in the concentration of Cl- reduces the concentration of AgNO3 in the solution and hence the Ag+ ions. The reaction taking place is: 𝐴𝑔𝑁𝑂3 + 𝐶𝑙 − ⇋ 𝐴𝑔𝐶𝑙 + 𝑁𝑂3− 0 Reduction in concentration of Ag+ ion decreases 𝐸𝐴𝑔 + /𝐴𝑔 value. This in turn leads to lesser Ecell value. Change in Ecell is non-uniform being highly abrupt near the equivalence point. Reason being small amount of Cl- removes practically all the Ag+ ions responsible for the conduction.

Experiment: Part I  Collection of suitable leaves i.e. the ones’ easy to grind and prepare the extract from.  Weighing of the designated amount of sample leaves. 3

Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

 Preparation of extract using de-chlorinated water.  Simple calculation relating the amount of extract to the weight of the sample.

Part II  Obtain the extract from leaves.  Set up the experimental apparatus involving calomel half cell, Ag+/Ag half cell and 𝐸𝑐𝑒𝑙𝑙 measuring probe.  Release the leaf extract drop by drop from the burette into the Ag+/AgNO3 half cell solution.  Note down the 𝐸𝑐𝑒𝑙𝑙 value for every added drop of leaf extract.  𝐸𝑐𝑒𝑙𝑙 values start showing abrupt change subsequently.  Continue addition until this phase is over.  Plot the observed 𝐸𝑐𝑒𝑙𝑙 values against the volume of leaf extract added.  Also plot ∆𝐸𝑐𝑒𝑙𝑙 /∆𝑉 against 𝑉 where 𝑉 is the volume of the leaf extract added.  Calculate Cl- concentration using volume of AgNO3 solution used up till the equivalence point.

Inputs Concentration of AgNO3 used = 0.0001 N (prepared 100 mL by dilution) Weight of leaves used to prepare the extract = 10 g. Volume of leaf extract = Vol. {Grinded leaf (filtered) + H2O} = 50 mL.

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Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

Result: The Initial Trials Concentration of AgNO3 = 0.1N; AgNO3 in beaker; Distilled water in burette.

Concentration of AgNO3 = 0.001N; AgNO3 in beaker; Distilled water in burette.

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Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

Concentration of AgNO3 = 0.01N; AgNO3 in beaker; Distilled water in burette.

Concentration of AgNO3 = 0.001N; Distilled water in beaker; AgNO3 in burette.

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Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

Ecell (mV)

The Final Accurate Graph

Volume of Leaf Extract (mL)

Derivative of Ecell with respect to volume plotted against Vol. of leaf extract.

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Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

Discussion: Graph shows abrupt change for the volume range 20-24 ml. This represents the region wherein last traces of Ag+ responsible for conduction are removed. Solution in beaker gradually turns mildly white due the formation of insoluble or sparingly soluble salt AgCl. The trench in the derivative curve gives the volume of leaf extract used till the equivalence point i.e. 22 ml.

A few Calculations From the graph: The volume of the leaf extract used till the equivalence point is 22 mL. So, applying 𝑁𝐴𝑔 + 𝑉𝐴𝑔 + = 𝑁𝐶𝑙 − 𝑉𝐶𝑙 − we get: 0.0001 × 50 = 𝑁𝐶𝑙 − × 22 0.0001 × 50 ⇒ 𝑁𝐶𝑙 − = 𝑁 22 So, concentration of Cl- in leaf extract = 0.00023 N

Conclusion: Presence of considerable amount of chloride ion i.e. of the order of 10-4 N in 10g/50 mL of the croton plant leaves. This establishes the fact that chlorine is a trace element in plants.

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Indian Institute of Science Education & Research, Kolkata

Semester III – Dec. 2008

References: 

Our very own acquired knowledge along with the big creativity bank we have with us.  World Wide Web (Google search): For some discussion on the presence of chlorine in plant leaves.  Wikipedia: http://en.wikipedia.org/wiki

Acknowledgement:    

Prof. Sanjib Bagchi, HOD Chemistry Dr. Pradip Kumar Ghorai Dr. Debasish Haldar Mr. Saroj Naik, Lab Assistant

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