Electrical Resistance Of Different Electrolytes Biology Essay

Hewlett-Packard

Extended Essay

Physics

Rushabh

[Pick the date]

Research Question: To investigate how a change in the distance between electrodes and altering the area of electrodes submerged in an electrolyte affects the electrical resistance of electrolytes.

Abstract – 231 words

Essay – 3907 words

Research Question:

To investigate the electrical resistance of different electrolytes/solutions.

Abstract:

The aim of the research was to study the electrical resistance of different electrolytes (Salts and Acids) under different conditions, i.e. varying the distance between electrodes and also changing the area of electrodes immersed in the electrolyte.

In order to measure the resistance Ohm’s Law was used in which varied potential difference was applied across the electrolyte and the corresponding current flowing through the electrolyte was recorded. By the use of Ohm’s Law the resistance was measured from the V-I curve in different cases. The comparison of resistance of different salts and different acids were made.

The effect of shape and size of electrode on the electrical resistance was studied by varying the distance between the electrodes and also by changing the area of the electrodes immersed in the electrolyte.

The trend obtained in case of salts and acids could be explained on the basis of the mobility (drift speed) and mass of the ions. In metals the conductivity is decided by the mobility of free electrons whereas in electrolytes the electrical conductivity depends on the mobility of negative ions and also the positive ions. In case of acids even the number of hydrogen molecules played a role in affecting the conductivity of the solution.

In the case of distance between the electrodes and the area of electrodes the conductivity was decided by the path available for the ions to flow.

Contents:

Acknowledgements ..................................................................................................................... 6

Introduction ..................................................................................................................... 7

Theory …………………………………………………………………………...…8

Variables .......................................................................................................................12

Apparatus …………………………………………………………………………...…12

Chemicals Used .......................................................................................................................12

Procedure .......................................................................................................................13

Variable: Electrolyte ..........................................................................................13

Variable: Distance between electrodes ……………...………………………………………...…14

Variable: Area of electrodes ………..………………………………………………....15

Results .......................................................................................................................16

V-I Curves

Electrolyte:

Magnesium Chloride ……………………………………………….…...16

Calcium Chloride ………..…………………………………………..17

Sodium Chloride ………..…………………………………………..18

Hydrochloric Acid ………..…………………………………………..19

Sulphuric Acid ………..…………………………………………..20

Nitric Acid ………..…………………………………………..21

Distance:

3.5 cm ………..…………………………………………..22

7.5 cm ………..…………………………………………..23

9.5 cm ………..…………………………………………..24

Area:

2.4 cm2 ……..………………………………...…….……..25

19.2 cm2 ……..…………………………...……….………..26

117.6 cm2 ....……..……………………………….…………..27

240 cm2 ………..…………………………………………..28

Conclusion ........................................................................................................................29

Limitations ........................................................................................................................30

Unanswered questions ........................................................................................................................31

References and Bibliography.................................................................................................................32

Appendix ........................................................................................................................33

Acknowledgements:

I would like to thank the following people for their help in preparing my Extended Essay:

Mr. Ahmad Kamran, my Extended Essay Supervisor For helping me out in preparing my Extended Essay at various times

Mr. Sachin Durge, the school’s Lab assistant for providing me with the apparatuses I required and helping me prepare the setup.

My friend Aishni who helped me in taking my readings and also helped improve the experimental setup.

Introduction:

Stun Guns have a new working concept based on electrolytes. The use of copper wiring has decreased. While researching on this concept I realized how the importance of electrical properties in circuit devices has increased. So, I decided to investigate the electrical properties, mainly resistance, of different electrolytes and how altering different factors could give a low resistance increasing the power of a stun gun. Using liquids to conduct electricity is beneficial over using copper wires as it reduces the burden of the complicated wiring and saves the high costs that are spent on these wires. These are one of the many reasons why electrolytes are gaining popularity over copper wiring. Also the study of the conductivity of the electrolyte can contribute to the efficiency of the batteries used in portable devices such as laptop and mobile chargers.

Research Question:

To investigate the electrical resistance of different electrolytes/solutions.

The aim of this experiment is to find out how the electrical resistance of the electrolyte changes. A combination of the best three variables may be considered to be used in the working of a stun gun to provide an optimum result.

In this experiment different electrolytes will be used in a circuit. The most conductive electrolyte will be the most suitable in the circuit. However if an electrolyte tends to have very low resistance, it may not be used as it would conduct high amounts of current and possibly cause a lethal shock.

The other factors that can affect the resistance of electrolytes are the distance between the electrodes and the area of the electrodes immersed in the electrolyte.

Theory:

The experiment deals with the conduction of electric currents through different solutions/electrolytes. It deals with the factors affecting the electrical resistance of electrolytes.

The electrical resistance of a substance:

Conductor

The conductivity in case of metals is associated with the drift speed of electrons. In the study of conduction in metals the electrons present in the atoms are divided into two groups – core electrons which are close to the nucleus and are tightly bound, valance electrons which are in the outermost shells and are loosely bound to the nucleus. According to the band theory these loosely bound electrons are present in a valance band (group of energy levels). The next possible band is the conduction band in which the electrons flow during conduction with drift speed. In conductors the valance band overlaps with the conduction band and with the application of external fields the valance electrons start to move in the direction opposite to the field, as the negative charge moves opposite to the direction of the field.

The resistance of a conductor is the reciprocal of its electrical conductance.

The resistance of a conducting wire is dependent on:

The length of the wire,

The cross section area of the wire and

The temperature of wire.

According to the Ohm’s law the electrical resistance of a conductor is independent of the potential difference (V) applied across the conductor and the amount of current (I) flowing through it. The length and temperature are directly proportional to the resistance and the cross section area is indirectly proportional to the resistance.

Semi-Conductor

According to the band theory there is a gap of around 1eV or more between the valance band and the conduction band. At room temperature most of the semi-conductors conduct electricity as the electrons in the valance band receive energy in the form of heat to move to the valance band and also the breaking of the covalent bonds increases the concentration of charge carriers in the valance band. Even the conductivity of the semi-conductor can be increased by adding certain impurities to it which will increase the concentration of charge carriers.

The resistance of a semi-conductor is dependent on:

The temperature of the semi-conductor and

The amount of impurities or doping in the semi conductor.

Electrolyte (conduction in Liquids)

In case of liquids electricity is conducted not only by electrons but also by positive ions. Hence the conduction in liquids depends upon the mobility/drift speed of positive and negative ions. Also when salt is taken in form of solution the electrostatic force between the ions decreases sue to increase in the permittivity of thee medium. When two electrodes are placed in a liquid and a potential difference is applied, a current flows through the electrolyte or liquid. The electrical conductivity of the electrolyte will depend upon the number positive and negative ions produced, the amount of negative and positive ions and their respective drift velocities.

Since the resistance is the reciprocal of electrical conductance it will decrease as the electrical conductivity increases.

The resistance of the electrolyte depends upon:

The type of electrolyte

The concentration of the electrolyte,

The distance between the electrodes,

The area of the electrodes and

Temperature.

Electrolytes can be Ohmic or Non-Ohmic conductors. An Ohmic conductor is one that obeys the Ohm’s Law i.e. the Voltage – Current ratio is constant. The Voltage – Current graph for an Ohmic conductor would be as follows:

Here the graph is linear and the gradient of the slope is a constant which means that the resistance and hence the Voltage – Current ratio is constant.

Non-Ohmic conductors are those which do not obey the Ohm’s Law. Their Voltage – Current ratio will not be a constant.

Concentration of electrolytes:

The resistance of the electrolyte decreases with an increase in the concentration. As the concentration of the electrolyte increases the number of ions in the electrolyte increases which will decrease the resistance.

Distance between Electrodes:

The distance between the electrodes and the resistance are directly proportional. As the distance between the electrodes decreases the resistance decreases. This is because as the electrodes are brought closer the resistive particles in the electrolyte between the electrodes are reduced. Thus the resistance is less.

In the experiment the distance between the electrodes will be changed and the resistance will be measured by measuring the current the potential difference and the current.

Area of Electrodes:

The area of the electrode immersed in water is inversely proportional to resistance. As the area of the electrode immersed in the electrolyte increases the resistance decreases. As the area increases the number of electrons being able to flow through the electrode will increase. This means that more current flows the circuit and so resistance decreases.

Temperature of electrolyte:

Temperature and Resistance are inversely related. As the temperature increases of an electrolyte, its resistance decreases.

The purpose of the investigation is to find out the resistance of different electrolytes. There are two possible methods of finding out the resistance of an electrolyte. The first method is the Wheatstone bridge method. A Wheatstone Bridge is a type of an electrical circuit where an unknown electrical resistance can be found out. The Wheatstone bridge looks as follows:

The unknown resistance Rx is found using the other three known resistors. The galvanometer in the centre is used to detect the flow of current. To find out the unknown resistance the ratio of R2/R1 and Rx/R3 are used. When these ratios are equal the reading on the galvanometer becomes zero. Thus R2 can be adjusted in order to find Rx as the ratios have to be equal.

The other method to find the resistance of the electrolyte is by finding the voltage and current of the circuit at different resistances of the circuit. The resistance of the circuit is altered by using a resistance box. This method will involve using an analogue voltmeter to find the potential difference of the circuit and a digital multimeter as an ammeter to find the current. The resistance will then be found out using ohm’s law. To find out the resistance ‘R’ through ohm’s law the following formula will be used:’ where ‘V’ is the voltage or potential difference and ‘I’ is the current. These readings can be plotted on a graph to find the resistance.

Variables:

Independent Variables:

Electrolytes

Concentration of electrolyte

Distance between electrodes

Are of electrodes

Temperature

Dependent Variables:

Resistance of electrolyte.

Controlled Variable:

Concentration of electrolyte

Electrolyte

Apparatus required:

Voltmeter (range: 0-5V) (least count: 0.1V)

Multimeter (for the measurement of current) (least count: 0.001 mA) (0-200mA)

Connecting wires(Copper)

Crocodile clips

Cardboard to keep the distance between electrodes.

Beakers: Capacity 250 ml, 1000ml (±0.5cm3)

Resistance box (range: 0-500Ω)

Power Supply (range : 2-10V)

Electrodes (Copper)

Electronic balance (least count: 0.01gm )

Chemicals Required:

Sulphuric Acid

Hydrochloric acid

Nitric Acid

Calcium chloride

Magnesium chloride

Sodium chloride

Procedure:

RB – Resistance Box (0-500Ω)

K – Plug Key

A – Multimeter (Ammeter)

R – Electrolyte

V - Voltmeter

Variable: Electrolyte

Part 1 (Salts):

The circuit is to set up as shown in the figure above.

The electrolyte was prepared by adding 3g of Calcium Chloride to 200cm3 of water in a 250ml beaker. The solution of the salt is stirred to completely dissolve the salt.

The electrodes were placed inside the beaker. To keep the distance between the electrodes constant they were made to pass through a cardboard disc.

The potential difference across the electrolyte (R) was measure by connecting the voltmeter (V) across the electrolyte. The corresponding value of current was recorded by using the multimeter (A).

The resistance of the resistance box was fixed at 10Ω. The power supply was switched on and the readings on the Voltmeter and the Multimeter were recorded. After recording open the switch so that the current stops flowing and heating of the circuit can be avoided.

The above steps were repeated by varying the resistance to 20Ω, 30Ω, 40Ω and 50Ω on the resistance box. The voltmeter and Multimeter readings were recorded each time the resistance was varied.

The V-I graph was plotted for the above reading and the resistance was measured from the gradient of the V-I graph.

The electrical resistance of salts Sodium Chloride and Magnesium Chloride were also measured in the same manner following steps 1-7.

Part 2 (Acids):

The resistance of Sulphuric acid, Hydrochloric acid and Nitric acid were measured using a similar circuit setup and by adopting a similar procedure of plotting the V-I curve and calculating its gradient to measure the resistance.

The acids added were of concentration 0.1moldm-3.

Variable: Distance between electrodes

RB – Resistance Box (0-500Ω)

K – Plug Key

A – Multimeter (Ammeter)

R – Electrolyte

V - Voltmeter

Here the distance between the electrodes are to be altered

The circuit was setup as shown in the circuit diagram above.

9g of NaCl in 700cm3 of water was used as a constant electrolyte. (700cm3 was used to increase the height of the water in the beaker.)

The experiment was carried out as before with the distance between the electrodes at 7.5cm.

The readings were recorded for 7.5cm.

The experiment was repeated with the electrodes at 3.5cm and 9.5cm. The readings were recorded for these experiments.

Variable: Area of the electrodes submerged

RB – Resistance Box (0-500Ω)

K – Plug Key

A – Multimeter (Ammeter)

R – Electrolyte

V - Voltmeter

The area of the electrodes submerged is altered.

The area of the electrodes submerged is measured using a ruler. The area is doubled as there are two sides to the electrode.

The experiment is carried out as before with the area of the electrode bring 2.4cm2.

The readings are recorded.

The experiment is repeated with the area as 19.2cm2, 117.6cm2 and 240cm2. The readings are recorded and tabled.

Results:

Variable: Electrolyte

Magnesium Chloride:

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

3.2

0.075

3.1

0.071

3.15

0.073

2.8

0.060

2.6

0.058

2.7

0.059

2.4

0.050

2.4

0.051

2.4

0.0505

2.2

0.040

2.1

0.043

2.15

0.0415

2

0.030

1.8

0.026

1.9

0.028

The current flowing through the electrolyte Magnesium Chloride was varied by varying the resistance in the resistance box from 0.026A to 0.075A. The uncertainty in the measurement of the current is of the order of 0.001A which is the reading error of the measuring instrument. The variation in the potential difference was from 1.8V to 3.2V. The uncertainty in the measurement of voltage was 0.1V. The resistance of Magnesium Chloride solution is calculated from the slope of the V-I graph which came out to be 28.3Ω.

Calcium Chloride

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

4.2

0.120

4.2

0.120

4.2

0.12

3.6

0.090

3.6

0.090

3.6

0.09

3.1

0.080

3.1

0.080

3.1

0.08

2.9

0.070

2.9

0.070

2.9

0.07

2.6

0.055

2.6

0.055

2.6

0.055

In the case of Calcium Chloride the current was varied from 0.055A to 0.120A and the respective voltage across the solution of Calcium Chloride varied from 2.6V to 4.2V. Plotting the graph between the potential difference and the current the resistance of the solution was found to be 25.6Ω.

Sodium Chloride:

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

2.6

0.09

2.6

0.09

2.6

0.09

2.15

0.065

2.15

0.065

2.15

0.065

2

0.05

2

0.05

2

0.05

1.9

0.04

1.9

0.04

1.9

0.04

1.3

0.02

1.3

0.02

1.3

0.02

In the case of Sodium Chloride the current was varied from 0.020A to 0.090A and the respective voltage across the solution of Sodium Chloride varied from 1.6V to 2.6V. Plotting the graph between the potential difference and the current the resistance of the solution was found to be 17.4Ω.

Amongst the Salts, the resistance of Sodium Chloride came out to be the least where as Magnesium Chloride has the highest resistance. This shows that the electrical conductivity of Sodium Chloride is marginally more than that of Calcium Chloride and Magnesium Chloride. The reason for the higher value of conductivity in Sodium Chloride may be because of higher drift velocity of Sodium ions and also due to the lower mass of these ions. The decrease in the electrostatic force between the positive and the negative ions will be same in all the three cases. Thus the effect of permittivity related with the dissociation of ions will be same in all the three cases.

Resistance of Acids:

Hydrochloric Acid

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.4

23.9

1.4

0.0241

1.4

0.024

1.3

21

1.3

0.021

1.3

0.021

1.2

18.8

1.2

0.0179

1.2

0.01835

1.1

17.7

1.1

0.0174

1.1

0.01755

1

16.5

1

0.0165

1

0.0165

The current through Hydrochloric Acid solution varied between 0.0165A to 0.0241A and its respective voltage varied between 1V to 1.4V. The resistance of the solution was found by plotting the readings in a Voltage against Current graph and this resistance was 50.4Ω. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the uncertainties caused due to readings errors of the instrument.

Sulphuric Acid:

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.1

0.0456

1.1

0.0456

1.1

0.0456

1

0.0354

1

0.0354

1

0.0354

0.9

0.0304

0.9

0.0304

0.9

0.0304

0.8

0.0261

0.8

0.0261

0.8

0.0261

0.7

0.0235

0.7

0.0235

0.7

0.0235

The current through Sulphuric Acid solution varied between 0.0235A to 0.0456A and its respective voltage varied between 0.7V to 1.1V. The resistance of the solution was found by plotting the readings in a Voltage against Current graph and this resistance was 17.5Ω. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

Nitric Acid:

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

0.9

0.062

0.9

0.062

0.9

0.062

0.7

0.0511

0.7

0.0522

0.7

0.05165

0.5

0.0415

0.5

0.0411

0.5

0.0413

0.4

0.035

0.4

0.035

0.4

0.035

0.3

0.0299

0.3

0.0299

0.3

0.0299

The current through Nitric Acid solution varied between 0.0299A to 0.062A and its respective voltage varied between 0.3V to 0.9V. The resistance of the solution was found by plotting the readings in a Voltage against Current graph and this resistance was 18.6Ω. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

Amongst the acids the resistance of Sulphuric Acid was the least at 17.5Ω and that of Hydrochloric Acid was highest at 50.4Ω. The resistance in the case of Hydrochloric Acid was quite high as compared to the other two acids. This trend does not support the expected value of resistance for Hydrochloric Acid. The concentration in case of the three acids was kept the same. Therefore the rate of dissociation of ions should be same in the three cases. The variation in the resistance maybe because of the mobility of the ions and the mass the ions in the three cases.

Variable: Distance between electrolytes

Distance: 3.5cm

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.8

0.125

1.8

0.125

1.8

0.125

1.7

0.116

1.7

0.116

1.7

0.116

1.6

0.106

1.6

0.106

1.6

0.106

1.5

0.097

1.5

0.097

1.5

0.097

1.4

0.090

1.4

0.088

1.4

0.089

The resistance of the electrolyte when the electrodes are at a distance of 3.5cm is 11.0Ω. The current through the electrolyte was varied from 0.088A to 0.125A by changing the value of the resistance of the resistance box. The Potential Difference varied in the current from 1.4V to 1.8V. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

Distance: 7.5cm

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.8

0.094

1.8

0.094

1.8

0.094

1.7

0.083

1.7

0.083

1.7

0.083

1.55

0.071

1.55

0.071

1.55

0.071

1.4

0.061

1.4

0.065

1.4

0.063

1.3

0.054

1.2

0.055

1.25

0.0545

The resistance of the electrolyte when the electrodes are at a distance of 7.5cm is 14.0Ω. The current through the electrolyte was varied from 0.054A to 0.094A by changing the value of the resistance of the resistance box. The Potential Difference varied in the current from 1.2V to 1.8V. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

Distance: 9.5cm

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.8

0.083

1.8

0.083

1.8

0.083

1.5

0.061

1.5

0.061

1.5

0.061

1.45

0.058

1.45

0.058

1.45

0.058

1.4

0.055

1.4

0.055

1.4

0.055

1.2

0.051

1.2

0.051

1.2

0.051

The resistance of the electrolyte when the electrodes are at a distance of 9.5cm is 16.7Ω. The current through the electrolyte was varied from 0.051A to 0.083A by changing the value of the resistance of the resistance box. The Potential Difference varied in the current from 1.2V to 1.8V. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

The resistance of the Sodium Chloride Electrolyte increased as the distance between the electrodes was increased. With the increase in the distance the path between the electrodes increase which in turn increases the energy loss in form of heat.

Variable: Area of electrodes

Area: 2.4cm2

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.4

0.18

1.5

0.19

1.45

18.5

1.4

0.156

1.4

0.175

1.4

16.55

1.3

0.146

1.4

0.146

1.35

14.6

1.3

0.11

1.3

0.122

1.3

11.6

1.2

0.095

1.3

0.101

1.25

9.8

The resistance of the electrolyte when 2.4cm2 of the electrode is immersed in the electrolyte is 2.22Ω. The current through the electrolyte was varied from 0.095A to 0.190A by changing the value of the resistance of the resistance box. The Potential Difference varied in the current from 1.2V to 1.5V. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

Area: 19.2cm2

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.4

0.304

1.4

0.315

1.4

0.3095

1.3

0.224

1.3

0.231

1.3

0.2275

1.3

0.18

1.3

0.183

1.3

0.1815

1.2

0.151

1.2

0.151

1.2

0.151

1.1

0.13

1.1

0.13

1.1

0.13

The resistance of the electrolyte when 19.2cm2 of the electrode is immersed in the electrolyte is 1.46Ω. The current through the electrolyte was varied from 0.13A to 0.315A by changing the value of the resistance of the resistance box. The Potential Difference varied in the current from 1.1V to 1.8V. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

Area: 117.6cm2

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.4

0.382

1.3

0.394

1.3

0.388

1.3

0.269

1.3

0.272

1.3

0.2705

1.2

0.204

1.2

0.205

1.2

0.2045

1.1

0.17

1.15

0.173

1.15

0.1715

1.1

0.145

1.1

0.147

1.1

0.146

The resistance of the electrolyte when 117.6cm2 of the electrode is immersed in the electrolyte is 1.07Ω. The current through the electrolyte was varied from 0.145A to 0.394A by changing the value of the resistance of the resistance box. The Potential Difference varied in the current from 1.1V to 1.4V. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

Area: 240cm2

Trial 1

Trial 2

Average

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (A) (±0.001A)

Potential Difference (V)

(±0.05V)

Current (I) (±0.001A)

1.3

0.401

1.3

0.401

1.3

0.3975

1.2

0.274

1.2

0.274

1.2

0.273

1.2

0.211

1.2

0.211

1.2

0.2095

1.15

0.175

1.15

0.175

1.15

0.173

1.1

0.143

1.1

0.143

1.1

0.1435

The resistance of the electrolyte when 117.6cm2 of the electrode is immersed in the electrolyte is 0.706Ω. The current through the electrolyte was varied from 0.143A to 0.401A by changing the value of the resistance of the resistance box. The Potential Difference varied in the current from 1.1V to 1.3V. The uncertainty of the voltage is 0.1V and of the current is 0.001A which are the readings errors of the instrument.

As expected the resistances of the Sodium Chloride electrolyte decreased with an increase in the area of the electrode submerged. This decrease in the resistance is due to the increase in the amount of ions that pass through the electrodes in the same amount of time.

Conclusion:

In my experiment the resistance for Sodium Chloride amongst Magnesium Chloride and Calcium Chloride was the least which indicates that the conductivity is best due to the ions speed and mass. In comparison, the speed was marginally more than the other ions. The mass was marginally less as compared to the other two ions. The chloride ions were common in all the three salts which suggests that the difference in the conductivity was due to the difference in the speed and mass of Sodium with respect to Magnesium and Calcium. The effect of permittivity of water on the electrostatic force would have been same in all the three cases as similar solutions were used. Since the conductivity also depends upon the number of ions per unit volume this factor was difficult to control. This factor would have been taken care of if solution of same moles were used.

In the case of acids, the resistance for Sulphuric Acid was least and Hydrochloric Acid was the highest. The higher conductivity in case of Sulphuric Acid is due to the higher mobility of Sulphate ions. If we go according to the masses of chlorides and sulphates then the mobility of chloride ions should be more. However since there are more number of hydrogen ions in sulfuric acid as compared to hydrochloric acid which increases its conductivity.

In the case of the distance between the electrodes and the area of the electrodes the trends were very much in accordance with the theory. As the distance between the electrodes were increased the resistance of the electrolyte increased. This was due to the increase in the path traveled by the ions between the electrodes

As the area of the immersed electrodes increased the amount of ions moving from one electrode to the other increased and this resulted in the decrease of the resistance.

The resistance of the electrolyte decreases with an increase in temperature as the attractive force between the ions decreases. Since the temperature at which the rate of dissociation is optimum is low, there is no point in changing the temperature to obtain the variation in resistance. Even then heating was controlled by keeping the duration of the flow current short.

Limitations:

In certain cases the electric field applied across the electrolyte was not same which resulted in the variation of ions produced by dissociation. If the Wheatstone Bridge Method would have been used to measure the resistance, this problem would have not arisen.

In most of the measurements the reading errors higher than the variation in the readings of Potential Difference and current.

For the measurements of potential difference and current circuit was switched on for very short duration of time in order to avoid heating of the electrolyte. This may have affected the dissociation of ions by the application of electric field.

The distance between the electrodes was kept constant by inserting the electrodes through a cardboard kept at the top of the beaker. However during the experiment the electrodes may have shifted/tilted causing an error by altering the distance.

The area of the electrodes immersed in the electrolyte was kept constant by fixing it inside the cardboard placed in top of the beaker. During the course of the experiment the area immersed might have changed due to the shifting of the electrodes or even by change in the level electrolyte in the beaker.

Unanswered Questions for further research:

The electrical conductivity of an electrolyte depends upon the number of ions per unit volume. In my experiment, instead of keeping the amount of salt in water same it would have been better if the molarity of the salts were kept constant.

In the case of acids the conductivity of heavier ions came out to be more than the lighter ones. Here it was not clear whether the conductivity was more because of the mass of the ions or because of the number of Hydrogen molecules present.

In the course of the experiment the conductivity of the electrolyte which depends upon the rate of dissociation of ions might also have a relation with the nature of the electrodes used. This can be analyzed by taking into consideration the reactivity of electrodes with the solution/electrolyte.

Generally in the case of acids the dilution affects the rate of dissociation of ions which is not same in the case of strong acids.

References:

Books:

Giancoli, Douglas C., Physics for Scientists and Engineers with Modern Physics, 4th Edition, Pearson Education Limited, ISBN – 13:978-0-13-149508-1.

Nelkon, M., and Parker, P., Advanced level Physics, London, Heinemann Educational Books Limited, ISBN 0-435-68636-4

Websites:

http://www.physics.uoguelph.ca/tutorials/ohm/Q.ohm.intro.html

http://en.wikipedia.org/wiki/Ohm's_law

http://www.antonine-education.co.uk/Image_library/Physics_1/Electricity/graph_1.gif

http://en.wikipedia.org/wiki/Wheatstone_bridge

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1163&context=physicskatz

Appendix 1:

Pictures of Experimental Setup:

C:\Users\Rushabh\Documents\Youcam\Snapshot_20121130_1.JPG

C:\Users\Rushabh\Documents\Youcam\Snapshot_20121130_2.JPG

C:\Users\Rushabh\Documents\Youcam\Snapshot_20121130_3.JPG

Appendix 1:

Graphs