Electrical Resistance of Different Liquids | Experiment

After the invention of electricity by Michael faraday many scientists studied the ways of conducting electricity. It was in the middle of 18th century scientists thought about using liquid as a medium of conducting electricity. In 1808 Sir Humphrey Davy conducted electricity using potassium solutions in ammonia. The experiments were to show the electrical conductivity of liquids, but the reason for this was not explained in his experiments.

In 1879 F.Kahlrausch proposed that ions are responsible for the conductivity of liquids. Ions are the building blocks of each molecule defined by its electron number. Ions which formed by the decomposition of minerals and other impurities carry current across the liquid and this is directly proportional to the ionic velocities. These findings were scientifically proven by M.M.Wrobleewisky and Olszweski in 1883 by liquefaction of nitrogen and other minerals from a solution under a pressure of 50 atmospheres showing the presence of ions in solute.

The experiments conducted by WG Scaife in 1973 on the natural conductivity of liquids showed that at higher pressures of 2500 bars and above the electrical conductivity of polar solutions decreases rapidly. Even though there is a decrease at low pressures which are not practically measurable. Polar compounds like castor oil, sebacate etc. were used for these experiments and were discovered that the double layer formed at the tip of electrodes was the reason behind the reducing nature of electrical conductivity. While experiments on ionic solutions like Diethyl ether, carbon disulphide, benzene etc showed an increasing trend of electrical conductivity with pressure. This was due to the triple ions formed during the experiment. [1]

In the experiments conducted by Alexander, Stoppa, Johannes Hunger, and Richard Buchner in 2009, it was found that the electrical conductivity of ionic solutions is higher than a mixture of ionic and polar mixture solutions. The experiment used potassium chloride (ionic) and non soluble oil base (polar) and the experiments were conducted under constant temperature and pressure conditions. The experiment showed a decrease in resistivity of nearly 1 ohm with an addition 5 wt % ionic compound. This experiment proved that the electrical conductivity depends on the charge density (number of ions) and the resistance to the movement of ions known as viscosity of a liquid [Stokes-Einstein, 1906]. The experiment compared the conductivities by increasing the percentage of ionic molecules in the solution. [2]

Experiments were conducted by Aresatz Usobiaga, Alberto De Diego, and Juan Manuel Madariaga 1n 1999 to relate temperature with the electrical conductivity in solutions. HCL Solution (ionic solution) was used for the experiments. Under different temperatures close to the room temperature (292-315K) the solution exhibited an inverse proportionality relation to the conductivity. This correlated to the findings of A I Zhakin in 1995 were KCL which is less ionic compared to HCL was used. The experiment with HCL pointed out that at near to room temperatures resistivity was increased by 5-10% with every increase of 5K. The reason for this behaviour was the increase of viscous properties of the solution and viscosity decreases electrical conductivity. [3]

In 2006 J. Vilaa, P. Ginésa, E. Riloa, O. Cabezaa and L.M. Varelab conducted experiments on the electrical conductivities of solutions of aluminium chloride, aluminium bromide, aluminium sulphate and aluminium chromide. These compounds are ionic in nature. The experiments were carried out under constant temperature and pressure conditions. Experiments conducted by increasing the density of solutions showed an increasing trend of electrical conductivity by 10 % on each increase of density. Density was increased by adding 5 wt % aluminium salt into the solution. These increasing trends went until the solution is 50% saturated. The reason for the rise in conductivity was explained to be the increase in ion concentration. The more the ionic compounds present the more the conductivity would be. The results also showed that aluminium chloride which is more ionic than other samples will conduct more electricity at any concentration. But for polar compounds the increase in density resulted in a decrease of conductivity. [4]

J. Vilaa, P. Ginésa, J.M. Picoa, C. Franjoa, E. Jiméneza, L.M. Varelab and O. Cabeza in 2005 conducted experiments on aluminium chloride and aluminium bromide for the binary relation on electrical conductivity with varying temperature and density. The experiment used 30% and 60 % concentrated solutions over a temperature range of 250-430K. The electrical conductivity increases with temperature, up to 400 times for aluminium chloride and 52 times in aluminium bromide solutions. But the conductivity decreases inconsistently with the increase in concentration. The probable reason for this controversial result could be the change in the properties of compounds with temperature. This showed that temperature had a greater influence on conductivity than density. [5]

METHODS AND MATERIALS

Overview of the experiment

In order to contrast the electrical resistance of different liquids to expose their ionic or covalent characteristics, the following measures were carried out.

Description of the procedural steps

Firstly the electrical resistance measurement was set up. Then hundred and fifty milliliters of desired liquid was measured and poured in to a clean beaker. After the power supply was switched on, using the multimeter, circuit’s current was measured. Then at five minutes interval reading was traced again for three times. After this the average of three recordings was determined. Once the current was computed resistance of liquid was found out using Ohm’s law. Next the steps were repeated for all selected liquids. Subsequently all the selected liquids were cooled to 18°C. Finally the above steps were followed for the refrigerated liquids.

Materials

Overview of mechanism

The materials used for the experiment are listed below.

• Digital Multimeter
• DC Power supply,
• 250 ml glass beaker
• Sample solution of 150 ml Orange juice, 0.01% salt solution, 1% salt solution, 2% milk, and mineral water.
• Table salt

Description of principal parts

Digital multimeter

Multimeter is an electronic tool which can be used for the measurement of voltage, current and resistance. There are two types of multimeters available. Multimeter which comes with digital display is commonly known as DMM (Digital Multimeter).Main parts of a digital multimeter are measuring probes, adjusting knob and digital display.

Firstly the probes are used to get connection between points where we need to measure electrical property. One multimeter got two probes for achieving the connection between two selected points. Secondly the adjusting knob is used to select which property need to measure. It is also used to select the range of values of the results. The digital display helps the user to get accurate readings. It also provides information about different settings used for measurement.

The multimeter can be switched on by turning the adjusting knob to desired property to measure. The display will provide us the relevant information. To test the DMM, turn the knob to resistance measuring mode and then touch each end of a copper wire to probe tips. Then the display will show resistance which should be almost zero.

Results and Discussion

The resistances of different liquid solutions prepared for the research were calculated using the Ohm’s law equation at room temperature. Observations show the average resistance of different liquid ranged from 26.1 kilo Ω to 1728 kilo Ω. Among the liquids, orange juice was best conductor (26.1 kilo Ω) and distilled water (1728 kilo Ω) was the worst. The two salt solutions showed almost the same resistances even though higher concentrated gave us a slightly lower resistance.

Orange juice

The figure 8 chart shows that orange juice is the best conductor of electricity. The resistance for orange juice was found out to be the least during the experiment. We had an assumption that acids are the best conductors because they are ionic in nature. Acids separate into ions when mixed with water and ions are charge carriers. The electrical resistance computed was 26.1 kilo Ω at room temperature. We had also made another assumption that when refrigerated; the conductivity will increase as the ions move slower related to normal room temperature liquid. After refrigeration, the resistance increased slightly to a value of 26.4 kilo Ω. Even though there was only a small decrease in the resistance value from that of the room temperature, our assumption regarding the refrigerated liquids came true. As studies and experiment done by Aresatz Usobiaga, Alberto De Diego, and Juan Manuel Madariaga in 1999 to relate temperature with the electrical conductivity in solutions [3] supports our results in this section.

Salt solution

The second best conductor is the salt solution. For the salt solution, the experiments were carried out with a concentration of 0.01% and 0.1% salt. The salt crystals in solid state won’t conduct electricity because anions (chloride ions) and cations (sodium ions) are held together. But in a salt solution they are free to move around and thus conduct electricity. The main reason behind conducting this research experiment on different concentration of salt is to study whether it is the density or temperature of the solution that affects the electrical conductivity more. We hypothesized that the density of solution would decrease the electrical conductivity. The 0.01% and 0.1% concentrated salt solution exhibited almost the same resistance value of 35.6 kilo Ω. But the higher concentrated solution gave slightly less resistance value of 35.3 kilo Ω as compared to the other solution. The resistance value of refrigerated salt solution of 0.01% and 0.1% are 115.2 kilo Ω and 114.1 kilo Ω respectively. As per the assumptions the higher concentrated solution gave slightly less resistance and the refrigerated solution showed great resistance as compared to the room temperature values. This showed that temperature had a greater influence on conductivity than density. [5]

Milk

The third liquid tested was 2% milk solution. Milk also conducts electricity but only in a small amount as compared to orange juice and the salt solutions. Electrical resistance of the milk solution was worked out to be 210.3 kilo Ω during the experiment at room temperature. Viscosity and density are the other factors that contribute to the poor conductivity of electricity as compared to the above mentioned liquids. The refrigerated resistance value of the milk solution calculated is 211.1 kilo Ω. While cooling, the viscosity increases due to the higher voluminosity of fatty acids, proteins, etc. [Website reference: http://www.dairy-science.org/cgi/reprint/80/4/628.pdf]. Thus we came to the conclusion that milk conducts electricity due to their typical covalent bond structure and the presence of fatty acids.

Distilled Water

Figure 8 shows that distilled water is a worst conductor of electricity. During the research experiment, distilled water showed a resistance value of 1728 kilo Ω. The reason why liquid conducts electricity is due to the free movement of cations and anions in between the electrodes. For example, in our salt solution test electricity was conducted as the salt readily ionizes to sodium cations and chloride anions which can move freely around in the solution thereby transporting electric charges. In the distillation process water is boiled to steam and the steam is again condensed to water. Nearly all the salts present in the water is thus left out during the distillation process. Thus distilled water is pure H2O. Although pure H2O (distilled water) can dissociate into H+ and OH- ions like salt, it ionizes very rarely therefore exhibiting the property of an insulator. [Citation may or may not be given for the above statements made]

Thus from the research experiment carried out we concluded that among the liquid solutions chosen, orange juice is the best electrical conductor and distilled water is the worst. From this we understood that orange juice has more ions present than distilled water (pure H2O). Therefore our assumption regarding acidic solution has high electrical conductivity is correct. Adding to the above results, the density and temperature also affects the electrical conductivity. The more salt added to the solution i.e. more ions added, the lesser the electrical resistance. The assumption regarding temperature as a factor affecting electrical conductivity was correct in some measure as some liquid solutions show higher resistance whereas some show almost the same resistance value with the room temperature values.