Electrochemistry – Inventing Better Batteries Essay Sample

Electrochemistry – Inventing Better Batteries Pages
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Ever since Alessandro Volta invented the first battery, the improvement of batteries has been phenomenal. The investigation was to explore three hypotheses that our group had designed to increase the voltage and/or current from the Daniell Cell to form a “Better Battery”. The group performed different procedures that catered for each hypothesis. Firstly the concentration of the electrolytes was changed, then the half cells and then the salt bridge. A current and voltage measurement was taken after each experiment was tested which formulated our data tables. The highest increases in voltage as the half cells are further away from each other on the Standard Reduction Potentials for Half-Reactions table was 192.78% and the current was increased by 159.1%. When the concentration was increased in the cathode and the concentration in the anode is decreased the percentage difference from the Daniell Cell was considerably higher with the current increasing by 127% and the voltage by 14.43%.

When using a porous pot as the salt bridge the percentage difference in voltage and current were as follows, 11.34% for voltage and 12172.73% for current which was an outstanding result. The Daniell Cell can be improved by implementing these three hypothesises into practice as the results show the current and voltage readings have increased dramatically. After applying these three hypotheses to our investigation it then formed the “Super Cell” which was the aim of the experiment. The results of the Super Cell were exceptional, with the voltage increasing by 216.91% and the current increasing by an amazing 53,990%. It is recommended that further research is be conducted into using higher concentrations in electrolytes, different types of salt bridges and stronger reducing and oxidizing agents to achieve more improved results that have come about after this investigation.

Aim

The aim of this extended experiment investigation is to formulate three valid hypotheses, based on relevant research that will improve the performance of the Daniell Cell. We aim to support the validity of each hypothesis through experimentation and evaluation in order to achieve the purpose of this investigation – creating better batteries

Hypothesis

1. In reference to the Nernst Equation and Le Ch�telier principle, our group believes that by having increased concentration in the cathode and a reduced concentration in the anode in each electrolyte will cause the voltage and current readings to increase and improve the Daniell Cell.

2. According to the Standard Reduction Potentials for Half-Reactions table, our group hypothesises that by changing the half cells so that their E0 values are a greater distance apart that the voltage and current will show an increase and improve the Daniell Cell.

3. After extensive research into different forms of salt bridges, our group believes that in using the porous pot salt bridge the decrease in resistance provided by the pot will increase the voltage and current readings of the original Daniell Cell.

Background

Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution using two metals and two different electrolytes which are described as half cells. The metals used are also named electron conductors and the ionic conductors (the electrolyte) are both involved in the electron transfer between the electrode and the electrolyte. The electrons released from the anode flow through both an internal and external circuit connected by a wire and a form of salt bridge or barrier as shown in figure 1.

Simple cells can be made from metals such as copper (Cu) and zinc (Zn) and the electrolyte being the metals sulfates which is called The Daniell Cell. In the process of the reaction, electrons can be transferred from the zinc metal to the copper metal through a resistor such as a light bulb or an ammeter in hope to produce a useful electric current. <Oxford University, 2004>

Zinc more willingly loses electrons compared to copper, so placing zinc and copper metal in solutions of their salts can cause electrons to flow through an external wire which connects the two metals together. The electrons flow from the anode (zinc) to the cathode (copper) causing the flow of electrons.

Here are the half equations of the Daniell Cell that show that electrons are transferred in this reaction.

Zn(s) –> Zn2+ (aq) + 2e-

Cu2+ (aq) + 2e- –> Cu(s)

This states that zinc goes from a solid (s) into an aqueous solution (aq) and vice versa for the copper. The zinc half reaction is classified as oxidation since it loses electrons. The terminal at which oxidation occurs is called the anode. For a cell, this is the negative terminal. The copper half reaction is classified as reduction since it gains electrons. The terminal at which reduction occurs is called the cathode. For a cell, this is the positive terminal. In order for a cell to continue to produce the flow of electrons, the solution in the salt bridge must flow into each solution to balance out any negative or positive charge in the electrolytes. <Bodner Research Web. 2007>

Electric Current and Voltage

The force motivating electrons to “flow” in a circuit is called voltage. Voltage is the measure of the potential energy that is always present between two points. Measured in volts, voltage is measured with a voltmeter and is properly named potential difference. When we speak of a certain amount of voltage in electrochemistry being present, we are referring to the measurement of how much potential energy exists between the anode and cathode. Alternatively, current is the flow of electrons through a circuit. Unlike voltage, it continues to flow throughout the circuit maintaining the same reading (depending on whether the resistance is kept the same). Current is measured in Amps (amperes) and is measured through an ammeter. The relationships present between these factors are shown in Ohm’s Law. Ohm’s Law deals with the relationship between voltage, current and a constant resistor. <Hyper Chemistry, 2004> This relationship states that when an ideal resistor is in place the voltage is increased and so is current and vice versa. The formula is, where V is the potential difference (voltage), R is resistance, and I is the current flowing through the resistance.

The amount of current in a circuit depends on the amount of voltage available to move the electrons, and also the amount of resistance in the circuit to oppose electron flow. Here are the standard units of measurement for electrical current, voltage, and resistance in Figure 2:

Hypothesis 1

In reference to the Nernst Equation and Le Ch�telier principle, our group believes that by having increased concentration in the cathode and a reduced concentration in the anode in each electrolyte will cause the voltage and current readings to increase and improve the Daniell Cell.

The general concentration of a Daniell Cell is presumed to be of 1 M (molar) for the theoretical E0 values to abide by the Standard Reduction Potentials for Half-Reduction table (Redox Table). Research and equations were used to identify the hypothesis, some of which were the Nernst Equation and Le Chatelier’s Principle both of which are involving the equilibrium between concentrations.

Electrochemistry deals with cell potential as well as energy of chemical reactions. The energy aspect is also related to the chemical equilibrium. All these relationships are tied together in the concept of Nernst equation. The maximum potential difference is called the electromotive force (EMF). The Nernst equation also indicates that you can build a battery simply by using the same material for both cells, but by using different concentrations. Cells of this type are called concentration cells. < All about Electrochemistry, by Stephen Lower, 2005>

Suppose, for example, that by reducing the concentration of Zn2+ in the Zn/Cu cell from its initial value of 1M to a much smaller value

Zn(s) | Zn2+ (aq, 0.1M) || Cu2+ (aq) | Cu(s)

This will then increase the E value for the cell reaction

Zn(s) + Cu2+ Zn2+ + Cu(s)

The Le Chatelier’s Principle can explain why reducing the concentration in the anode and increasing it in the cathode will improve the overall voltage of the cell. If a chemical system at equilibrium experiences a change in concentration, then the equilibrium shifts to counter-act the imposed change. Changing the concentration of the electrolyte will shift the equilibrium to the side that would reduce that change in concentration. <Chemistry Guide, 2003>. In the case of the Daniell Cell when the Copper sulfate concentration is increased, the equilibrium positioned is moved and more of the solution is used, and thus generates higher voltage. Likewise, increasing the concentration of the solution of the Zinc sulphate results in the reverse effect, where the equilibrium moves in the opposite way and less of the solution is used, thus generating lower voltage. In its most fundamental form the Nernst equation is written as: See Figure 3

Where RT is the room temperature, z is the charge number of the electrode reaction (which is the number of moles of electrons involved in the reaction), and F is the Faraday constant (96,500 C mole-1). <Science Waterloo, 2008> The notation ared represents the half cell which appears on the reduced side of the cell and the notation aox represents the half cell which appear on the oxidized side of the cell.

The concentration in the cathode should be increased since it speeds up the reaction of the anode forcing more electrons to flow through a resistor. By completing and testing this hypothesis our group believes that it will factor in the aim of increasing the voltage and current of our Daniell Cell.

Hypothesis 2

According to the Standard Reduction Potentials for Half-Reactions table, our group hypothesises that by changing the half cells so that their E0 values are a greater distance apart that the voltage and current will show an increase and improve the Daniell Cell.

The general make up of a Daniell Cell is two half cells, one with copper metal (Cu) and the other cell using zinc metal (Zn). The electrolyte then is both sulfates of each metal, CuSO4 and ZnSO4 making up the Cell. According to the Standard Reduction Potentials for Half-Reductions (SRPHR), Copper and Zinc is a good pair since Copper is a fairly strong oxidizing agent and Zinc is a very good reducing agent which gives a high voltage between these two half cells. <Corrosion Doctors, 2006>

The group has decided in changing one of these half cells to a better oxidizing agent or a reducing agent the voltage of our cell will increase and therefore support our hypothesis. Since this is a school experiment, it is very hard to access the best oxidizing agents, which has left us with Potassium Permanganate (KMnO4) as our best oxidizer and magnesium (Mg2+) as our best reducing agent.

When both ionic concentrations (the electrolyte) are at 1M and the room temperature is at 25oC you can calculate the voltage of what two half cells would be by using the given E0 value. Copper has an E0 of +0.34 volt and Zinc has an E0 of -0.76 volt and you subtract the oxidizer from the reducing agent which gives 1.10 V (volts). The calculations for the magnesium and potassium permanganate are as follows, potassium permanganate E0 value is 1.52 and the magnesium E0 value is -2.37 which gives 3.89 volts. Under these conditions the voltage should increase from 1.10 volts to 3.89 volts, in which will support our second hypothesis.

Hypothesis 3

After extensive research into different forms of salt bridges, our group believes that in using the porous pot salt bridge the decrease in resistance provided by the pot will increase the voltage and current readings of the original Daniell Cell.

A salt bridge, in chemistry, is a device used to connect the oxidation and reduction half-cells of an electrochemical cell. It is also apart of the internal circuit of the cell with the external circuit being the wire that connects the anode to the cathode. Salt bridge’s usually comes in two types: glass tube and filter paper with other portable options still available.

One type of salt bridges consists of U-shaped glass tubes filled with a relatively inert electrolyte, usually potassium nitrate. The conductivity of the glass tube bridges depends mostly on the concentration of the electrolyte solution. The other type of salt bridges consists of a filter paper, also soaked with a relatively inert electrolyte, usually potassium nitrate because it is chemically inert. Conductivity of this kind of salt bridges depends on a number of factors: the concentration of the electrolyte solution, the texture of the filter paper and the absorbing ability of the filter paper. Generally smoother texture and higher absorbency equates to higher conductivity. A porous pot or other porous barrier between the two half-cells may be used instead of a salt bridge; they give a much higher current flow since the resistance is much less which is ideal for this investigation. <Chemistry Virtual Textbook, 2006>

In the Daniell Cell the porous pot cell consists of a central zinc anode dipping into a porous pot containing the zinc sulfate solution. The porous pot is, in turn, immersed in a solution of copper sulfate contained in a large beaker, which acts as the cell’s cathode. The use of a porous barrier prevents the copper ions in the copper sulfate solution from reaching the zinc anode and undergoing reduction. This would render the cell ineffective by bringing the battery to equilibrium. Our group has hypothesised that using the Porous Pot as the salt bridge will bring upon an increase in voltage and current therefore making a “Better Battery”.

Balanced Chemical Equations and E0 values

Zn2+ (aq) + 2e- –> Zn(s) E0 = -0.76 V

Cu2+ (aq) + 2e- –> Cu(s) E0 = 0.34 V

Zn(s) –> Zn2+ (aq) + 2e-

Cu2+ (aq) + 2e- –> Cu(s)

Zn(s) + Cu2+ (aq) –> Zn2+ (aq) + Cu(s)

E0C = E0ox + E0red

= 0.76 + 0.34

E0C = 1.10 V

Mg2+ (aq) + 2e- –> Mg(s) E0 = -2.37 V

Cu2+ (aq) + 2e- –> Cu(s) E0 = 0.34 V

Mg(s) –> Mg2+ (aq) + 2e-

Cu2+ (aq) + 2e- –> Cu(s)

Mg(s) + Cu2+ (aq) –> Mg2+ (aq) + Cu(s)

E0C = E0ox + E0red

= 2.37 + 0.34

E0C = 2.71 V

5 Mg2+ (aq) + 10e- –> 5 Mg(s) E0 = -2.37 V

2 MnO4- (aq) + 16 H+ + 10e- –> 2 Mn2+ + 8 H20 (l) E0 = 1.52

5 Mg(s) –> 5 Mg2+ (aq) + 10e-

2 MnO4- (aq) + 16 H+ + 10e- –> 2 Mn2+ + 8 H20 (l)

5 Mg(s) + 2 MnO4-(aq) + 16 H+ –> 5 Mg2+ (aq) + 2 Mn2+ + 8H2O (l)

E0C = E0ox + E0red

= 2.37 + 1.52

E0C = 3.89

Method

Daniell Cell

1. Using two beakers place them close together and fill the beakers half way with the chosen electrolytes.

2. Place the Copper and Zinc metals in their respective salt solutions which are both 0.1 M in concentration

3. Connect the wires to each electrode (metal) and connect the wires though a voltmeter/ammeter

4. Saturate the salt bridge (filter paper) with Potassium Nitrate and insert each end into both half-cell solutions.

5. Record Results for both current and voltage

Hypothesis One

1. Setup the original Daniell Cell

2. After setting up and functioning the original Daniell Cell, change the concentration of the CuSO4 solution to 0.5M.

3. Record the results shown on the voltmeter and ammeter

4. After this, change the concentration of the CuSO4 solution to 1M

5. Record the results shown on the voltmeter and ammeter.

6. Repeat this with the zinc half cell, by changing the copper half cell back to 0.1M and increasing the zinc sulfate to 0.5M then 1M.

7. Record the results of the voltage and current for these two experiments.

Hypothesis Two (A)

1. Place two beakers side by side, filling them up half way with MgSO4 0.1M and CuSO4 0.1M.

2. Place the metals in their respective salts (sulfate solutions)

3. Connect the wires to each metal and plug the ends into the ammeter/voltmeter.

4. Now that the external circuit is present, saturate the salt bridge (in this case, filter paper) with Potassium Nitrate (KNO3) solution and place into each half cell.

5. Turn on the voltmeter/ammeter and record results.

Hypothesis Two (B)

1. Place two beakers side by side, filling them up half way with MgSO4 0.1M and MnO4 0.02M

2. Place the magnesium metal in its respective salt

3. Place an inert metal such as carbon in the MnSO4 solution

4. Connect the wires to each metal and plug the ends into the ammeter/voltmeter

5. Now that the external circuit is present, saturate the salt bridge (in this case, filter paper) with Potassium Nitrate (KNO3) solution and place into each half cell.

6. Turn on the voltmeter/ammeter and record results.

Hypothesis Three

1. Using a larger beaker, fill with the Cathode (Copper) electrolyte to around 1/2 full

2. Place the Porous Pot (which has been soaked in KNO3) in to the beaker and pour the other electrolyte (Zinc) inside.

3. Add the two electrodes to their distinguished salts.

4. Turn on the ammeter/voltmeter and record the results.

Super Cell

1. Repeat steps 1, 2 and 3 in hypothesis three.

2. Instead of using Copper and Zinc half cells, use MnO4 (Potassium Permanganate) and MgSO4 (Magnesium) with MgSO4 being the anode.

3. The concentrations for each half cells are as follows; KMnO4 0.02M and MgSO4 0.1M

4. Use an ammeter/voltmeter to receive the final data for the investigation.

Results Tables

Hypothesis One:

In reference to the Nernst Equation and Le Chtelier principle, our group believes that by having increased concentration in the cathode and a reduced concentration in the anode in each electrolyte will cause the voltage and current readings to increase and improve the Daniell Cell.

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