E1 Group 2 2CHEM2 FR - Physics PDF

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Determination of Metal Ion Concentration using Potentiometric Methods Juzef B. Barro, Nicole Andrea B. Bacabac, Angelo Ezekiel Agustine L. Batayon and Mark Patrick P. Castillo Group #2, 2Chem2, Department of Chemistry, College of Science, University of Santo Tomas, España, Manila 1015 (Affiliation, size 10, italicized, single-spaced)

Abstract This experiment focuses on determining the correlation of cell potential and concentration, as well as to determine the metal ion concentration of an unknown sample. Importantly, the data gathered from the experiment was used for statistical analysis which is essential in finding results and coming up to the conclusion. To simulate the experiment, a virtual simulation of electrochemical cells was used. This comprised of a voltmeter, two beakers, a salt bridge and chemicals such as Cadmium nitrate, Nickel nitrate, Copper nitrate, Iron nitrate, Lead nitrate, Silver nitrate, Hydrogen, Platinum, Nitric acid, and Sodium nitrate that complete the reactions. Upon conducting the experiment, the results showed the expected dependency of cell potential on the varying concentrations.

1. Introduction Batteries are made up of two or more electrochemical cells - which contains two metal electrodes and a solution that contains ions that can conduct electricity. Batteries operate through electrochemical reactions called redox reactions (oxidation-reduction reactions). Such reactions require electron exchange among chemical species. Oxidation occurs when a chemical species loses electrons. On the other hand, reduction occurs when a chemical species gains electrons.

2 Mg (s) + O2 (g) ➡ 2MgO (s) Example 1: The formation of magnesium oxides from the reaction between magnesium metal and oxygen which involves the oxidation of magnesium. MgO (s) + C (s) ➡ Mg (s) + CO (g)

Example 2: The formation of magnesium metal and carbon monoxide from the reaction of magnesium oxide and carbon at 2000C, an example of the reduction of magnesium oxide to magnesium metal.

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In this experiment, cells with different electrodes and concentrations are prepared in order to measure their voltages in a galvanic cell setup. A galvanic cell is a device in which concurrent oxidation and reduction reaction takes place, used in the conversion of chemical energy into electrical energy. Galvanic cell utilizes the capacity to separate the stream of electrons within the process of oxidation and reduction reactions, causing a half reaction. This stream of electrons is basically called a current.

In order to make a galvanic cell, one would need a setup of two electrodes. One of these electrodes, the cathode, should be a positively charged electrode where the reduction takes place. On the other hand, the oxidation half-reaction takes place at the anode, the negatively charged electrode. Since the two metals will be put in two isolated containers, connected by a conducting wire, an electric current would be formed, which would transfer all electrons from one metal to another. At the same time, the two metals are submerged in a salt solution. In this case, the two arrangements are not directly mixed but can be joined using a bridge or a medium, which keeps the electrical neutrality within the circuit. This medium should be responsible for the transferring of ions but moreover, make sure that the one solution won’t mix with the other.

During the course of the experiment, the students will be tasked to determine the correlation of cell potential and concentration and how the two are related to each other. Secondly, the students will also be able to determine the metal ion concentration of an unknown sample based on the data gathered from the experiment. By performing statistical analysis on the data collected, the students will be able to evaluate and interpret the results and come up with an effective conclusion.

2. Experimental 2.1 Materials and Instruments used The

experiment

was

done

by

simulation

through

website

http://web.mst.edu/~gbert/Electro/Electrochem.html from Gary L. Bertrand, University of Missouri-Rolla. The electrode was immersed in a solution of its nitrate salt. Various cells were constructed and the expected voltage of a cell was displayed. The instrument used was a voltmeter with two beakers and salt bridge included.. The chemicals that were used are as follows: cadmium, nickel, copper, iron, lead, silver, cadmium nitrate, nickel nitrate, copper nitrate, iron nitrate, lead nitrate, silver nitrate, hydrogen, platinum, nitric acid, and sodium nitrate.

2.2 Sample preparation

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The amount of salt indicated to prepare 100.0 mL of concentrations of cadmium nitrate and metal solution assigned were arranged in a table such as shown below. Additionally, the cell potential of the other metals were measured and plotted in a separate table. Concentration (M)

Cd(NO3)2

Assigned Metal

0.0001 0.0010 0.0100 0.1000 0.1500 1.0000 1.5000 2.0000 2.3 Instrument parameters The SHE electrode in nitric acid solution was used as the constant reference electrode in the beaker. In the other beaker, the assigned metal electrode with its nitrate salt solution was used. The two beakers were connected through a salt bridge with 2.00 M sodium nitrate solution. Level was set to 0. Negative terminal of the voltmeter was connected to the SHE electrode, while the positive terminal was connected to the metallic indicator electrode.

3. Results and Discussion

Concentration

Cd2+

Ni2+

Cu2+

Fe2+

Pb2+

Ag+

0.0001

-0.513

-0.361

0.228

-0.551

-0.237

0.570

0.0010

-0.484

-0.332

0.257

-0.522

-0.208

0.629

0.0100

-0.457

-0.305

0.284

-0.495

-0.182

0.686

0.1000

-0.432

-0.280

0.309

-0.470

-0.159

0.740

0.1500

-0.428

-0.275

0.313

-0.466

-0.156

0.749

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1.0000

-0.404

-0.249

0.337

-0.440

-0.143

0.786

1.5000

-0.398

-0.240

0.345

-0.432

-0.140

0.792

2.0000

-0.392

-0.232

0.351

-0.425

-0.139

0.796

Table 1. Concentration and Cell Potential

Graph 1. Cell Potential vs [Cd2+  ]

Graph 2. Cell Potential vs log[Cd2+  ]

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Graph 3. Cell Potential vs [Cu2+  ]

Graph 4. Cell Potential vs [Ni2+  ]

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Graph 5. Cell Potential vs [Fe2+  ]

Graph 6. Cell Potential vs [Pb2+  ]

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Graph 7. Cell Potential vs [Ag2+  ] Metal

Sensitivity

Cd2+

0.428

Ni2+

0.0426

Cu2+

0.0438

Fe2+

0.0453

Pb2+

0.0313

Ag+

0.0762 Table 2. Sensitivity values of different metal ions.

Metal

Correlation

Cd2+

0.9985

Ni2+

0.6624

Cu2+

0.7479

Fe2+

0.6501

Pb2+

0.4864

Ag+

0.5330 Table 3. Correlation values of different metal ions.

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E cell = E ind − E ref + E junction E = E° −

RT nF lnQc

(1)

When the concentrations of the chemicals are increased, the cell potential of the chemicals also increases. It means that when the concentration is higher the more electrons electrons are moving in the cell. Cu2+  and Ag+ both exhibit positive cell potential in the cell which means electrons flow more in those 2 metal ions. The highest sensitivity in the metal ions is Ag+ with an ion sensitivity of 0.0762. Cd2+  has the best exhibited correlation among the metals. The true value is 2.0 M which gives a relative error of 1.208 x 1026.  , which is really far from the true value. it means that the error is great and there could be something wrong with the virtual experiment. The method used throughout the experiment required a virtual set-up of a galvanic cell. With the utilization of this, the experiment was conducted with ease. Sources of error may come from miscalculations of the researcher in their data.

4. Conclusion and Recommendation Cell potential and concentration has a directly proportional relationship. The more the concentration is the more the electrons move. Ag+ and Cu2+  both exhibit positive cell potential which is why they are used in wires more often. Silver had the highest ion sensitivity and Cadmium showed the best correlation among the metals. The things that can be done in this experiment, since this is made virtually, is that the researcher must find a better method of calculating it. The miscalculations are the ones that might have ruined the measurements during the experiment.

5. References Bertrand, G. (n.d.). Electrochemical Cells. Missouri S&T. Retrieved October 16, 2020, from http://web.mst.edu/~gbert/Electro/battery.html Chemistry Libretexts. (n.d.). Dependence of Cell Potential on Concentration. Retrieved October 17, 2020, fromhttps://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_(Zumdahl _and_Decoste)/11%3A_Electrochemistry/11.4%3A_Dependence_of_Cell_Potential_on_Concent ration

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Galvanic Cells. (n.d.). Toppr. Retrieved October 16, 2020, from https://www.toppr.com/guides/chemistry/electrochemistry/galvanic-cells/

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