The Effect of Salt Bridge Media Types on Galvanic Cell Voltage

Study Case The Effect of Salt Bridge Media Types on Galvanic Cell Voltage Michael Kurniawan (2018123456) University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45221, United States kurniaml@mail.uc.edu Abstract This practicum aims to study the construction of a Galvanic Cell circuit, measure the electrical voltage produced, and compare the effectiveness of various materials as salt bridges. A Galvanic Cell is an experiment that converts chemical energy into electrical energy through spontaneous redox reactions. This phenomenon was first observed by Luigi Galvani and Alessandro Volta. In this experiment, various fruits were used as salt bridge media; each fruit was cut and dipped into a CuSO₄ and ZnSO₄ solution, connected via copper and zinc electrodes to a multimeter. The measurement results showed that the agar salt bridge produced the highest voltage, while the mango salt bridge produced the lowest voltage. Keywords: Salt Bridge Material INTRODUCTION Electrochemistry is a branch of chemistry that studies the interconversion of electrical energy and chemical energy. Electrochemical processes involve redox (oxidation-reduction) reactions, in which the energy released by spontaneous reactions can be converted into electricity, or electrical energy is used to cause nonspontaneous reactions to occur [1]. An electrochemical cell is a device that allows oxidation and reduction reactions to occur in the form of separate half-reactions [2]. A Galvanic cell is a type of electrochemical cell that converts the free energy of a chemical reaction into electrical energy. The relationship between the free energy of a chemical reaction and cell voltage can be expressed by the equation: MICHAEL KURNIAWAN 1 Study Case Δ𝐺 = −𝑛𝐹𝐸 where ΔG is the change in free energy (J), n is the number of moles of electrons involved in the reaction, F is Faraday's constant (96485" C/mol), and E is the electromotive force (emf) of the cell in volts [3]. Galvanic cells or voltaic cells are named after Luigi Galvani and Alessandro Volta, who created early versions of this device. A zinc rod is immersed in a ZnSO₄ solution and a copper rod is immersed in a CuSO₄ solution. The cell works based on the principle that the oxidation of Zn to Zn²⁺ and the reduction of Cu²⁺ to Cu can occur simultaneously in separate locations, with the transfer of electrons through an external wire. The zinc and copper rods are called electrodes, and the combination of electrodes and solutions is called a Daniell cell [2,4]. In a Galvani cell, the anode is the electrode where oxidation occurs and is negatively charged because it releases electrons. The cathode is the electrode where reduction occurs and is positively charged when connected to the anode. Positive ions move to the cathode to be reduced by electrons from the anode [3]. Galvani cells can be used as a source of electricity for lighting, heating, or powering motors. Chemical cells can be divided into: 1. Transference Chemical Cells An example is the Daniell cell. This cell consists of a Zn rod in a ZnSO₄ solution and a Cu rod in a CuSO₄ solution, which are connected via a salt bridge or liquid junction. When the Zn and Cu electrodes are connected, an electric current flows due to the oxidation of Zn and the reduction of Cu²⁺ ions in the solution. 2. Chemical Cells without Transference Examples of chemical cells without transference include accumulator cells, Leclanché cells (dry cells), and fuel cells: 1. Accumulator Cells The negative pole is a Pb solution, the positive pole is Pb metal coated with PbO₂, and the electrolyte is H₂SO₄. 2. Leclanché Cells (Dry Cell) In a typical battery, the negative electrode is zinc metal, the positive electrode is a graphite (C) rod coated with MnO₂, and the electrolyte is a paste of NH₄Cl and ZnCl₂. 3. Fuel Cell Fuel cells typically use oxygen at the cathode and an oxidizable gas at the MICHAEL KURNIAWAN 2 Study Case anode, usually hydrogen [5]. MATERIALS AND METHODS Apparatus 1. Empty water glasses (2 pcs) 2. Connecting wires (as needed) 3. Multimeter (1 pc) 4. Dropper pipettes (2 pcs) 5. 25 mL graduated cylinder (1 pc) 6. U-shaped tube (1 pc) 7. Sandpaper (as needed) 8. Ohaus balance (1 pc) Materials 1. Zinc electrode rod (1 pc) 2. Copper electrode rod (1 pc) 3. 15 mL ZnSO₄ solution 4. 15 mL CuSO₄ solution 5. Salt bridge materials: • Agar + KCl (as needed) • Melon (as needed) • Mango (as needed) • Jicama (as needed) • Papaya (as needed) Experimental Procedures 1. Clean the Cu and Zn electrode rods using sandpaper. 2. Prepare 15 mL of ZnSO₄ solution and 15 mL of CuSO₄ solution in separate containers. 3. Cook the agar-agar and mix it with NaCl, then pour it into a U-tube as a salt bridge. 4. Connect the Zn and Cu electrodes with a cable, then connect the cable to a multimeter to form a complete circuit. 5. Dip the Zn electrode into the ZnSO₄ solution and the Cu electrode into the CuSO₄ solution. MICHAEL KURNIAWAN 3 Study Case 6. Connect the two solutions through the agar-agar salt bridge, and observe the voltage that appears on the multimeter. The results show a voltage of 1.06 V after 3 minutes; there is no color change on the electrodes. 7. Repeat the above steps by replacing the agar-agar with fruits as the salt bridge: • Melon: The voltage recorded is 1.05 V after 3 minutes; the electrodes remain unchanged in color. • Papaya: The voltage recorded was 0.99 V after 3 minutes; the electrodes remained stable. • Jicama: The voltage recorded was 0.88 V after 3 minutes; the electrodes remained unchanged. • Mango: The voltage recorded was 0.61 V after 3 minutes; the electrodes remained unchanged. RESULTS AND DISCUSSION In this Galvanic Cell experiment, ZnSO₄ and CuSO₄ solutions were placed in separate containers. Materials such as agar + KCl, melon, papaya, jicama, and mango were used as salt bridges. The function of these materials as electrolytes is to allow the flow of ions without undergoing significant chemical changes. The voltage measurement results showed that agar + KCl produced the highest voltage, while mango produced the lowest voltage. This indicates that the composition and conductivity of the salt bridge material affect the efficiency of electron transfer in the Galvani cell. The Zn and Cu rods functioned as electrodes. The Zn electrode acted as a reducer because it underwent oxidation, while the Cu electrode acted as an oxidizer because it underwent reduction. Electrons flow from Zn atoms in the ZnSO₄ solution, forming Zn²⁺ ions that diffuse away from the Zn electrode into the solution. Meanwhile, negative ions from the CuSO₄ solution move through the salt bridge toward the Zn electrode. The electrons released by Zn flow through the external cable and collect on the surface of the Cu electrode. These electrons then react with Cu²⁺ ions to form Cu atoms. During the reaction, negative ions move toward the Zn electrode, while positive Zn ions move toward the Cu electrode, forming two electron flow paths: 1. Internal circuit – ion flow through the salt bridge medium toward the Zn and MICHAEL KURNIAWAN 4 Study Case Cu electrodes. 2. External circuit – electron flow through a cable whose electrical voltage can be measured. Electric current in a Galvanic cell occurs due to a difference in electrical potential between two points in the circuit, similar to the difference in height that causes water to flow on the earth's surface. The voltage measurement results vary depending on the type of salt bridge used. Table 1. Voltage Produced by Various Salt Bridge Media Observations show that agar + KCl media produces the highest voltage, while mango media produces the lowest voltage. This difference is due to the type of substance and distribution of ions in each medium. In agar + KCl, K⁺ and Cl⁻ ions are strong electrolytes that distribute quickly, with K⁺ moving to the anode to prevent charge accumulation. Fruits also contain ions that neutralize cells, but their distribution is much lower than in agar + KCl, resulting in a lower voltage. CONCLUSION Based on the experiment, it can be concluded that: 1. Galvanic cells or Voltaic cells are electrochemical cells that generate electric current through spontaneous redox reactions. 2. A salt bridge medium made of agar + KCl produces a higher voltage than a medium made of fruits (melon, papaya, jicama, mango). 3. The salt bridge functions to neutralize the electric charge on the electrodes through ion diffusion, so that the two solutions remain separate and do not mix directly. MICHAEL KURNIAWAN 5 Study Case REFERENCE MICHAEL KURNIAWAN 6