Please enable JavaScript.
Coggle requires JavaScript to display documents.
Designing an electrochemical cell that produces an optimal energy output. …
Designing an electrochemical cell that produces an optimal energy output.
Factors determining energy output
Electrolyte concentration
Increasing concentration increases the particles present for collision, increasing reaction rate and theoretically increasing energy output.
According to the Nernst equation, the induced cell potential difference is dependent on the ratio of concentrations between the two electrolytes.
When the concentration of the cathode electrolyte increases, the induced cell potential difference will increase.
Increasing the concentration of copper sulfate solution will therefore theoretically increase the energy output.
The relationship between concentration and induced cell potential difference is logarithmic, therefore such a relationship is expected.
The concentration of the copper sulfate electrolyte solution will be investigated as the independent experimental variable.
Temperature
Temperature determines the movement of particles, therefore dictating collisions and reaction rate.
Temperature is a consideration in the Nernst equation, therefore predictions can be compared with data.
Reliably controlling temperature may be difficult using the available apparatus.
Pressure
Pressure can increase the rate of reactions involving gases, however since all reactants will be in solution or solid, this will not be a factor.
Pressure cannot practically be controlled using the available apparatus.
Salt bridge
Material
Different materials my be used to absorb the salt bridge solution which may affect the rate of diffusion
Solution
Type
Concentration
Altering concentration may alter the rate of diffusion.
Catalyst
Catalysts provide an alternate reaction pathway with lower activation energy, thus increasing reaction rate and theoretically increasing energy output.
Type of conductor
Different conductors will have different resistance. Resistance is inversely proportional to current (Ohm's Law). Using a current with lower resistance will increase current.
Although relevant, this factor is more physics focused rather than chemistry.
Electrode metal
Half cell standard reduction potential
Standard reduction potential is a consideration in the Nernst equation, therefore predictions can be compared with data.
Metal electrodes may be used in different combinations resulting in a greater number of total standard reduction potentials
Due to the nature of provided materials, it may not be possible to control the surface areas of electrodes between trials with different metals.
Electrode surface area
Surface area is not a consideration in the Nernst equation, therefore comparisons between predicted values and experimental data cannot be made.
Increasing electrode surface area increases the available surface for reactions to occur. This increases reaction rate, theoretically increasing the current.
Electrochemical Cells
Galvanic Cells
Converts chemical energy into electrical energy through redox reactions.
Components
Electrodes
Solid metal component which contains metal cations and electrons. Solid metal electrode will either gain or lose electrodes, resulting in metal ions either entering or coming out of solution in a redox reaction. The anode and cathode each are each known as half cells.
Cathode
The cathode is the less reactive metal and has a positive charge in a galvanic cell.
An oxidation reaction occurs at the cathode where the electrode gains electrons, resulting in the metal atoms coming out of solution, therefore causing metal build up.
Half Reaction: Cu {2+} + 2e {-} → Cu
Anode
The anode is the more reactive metal and has a negative charge in a galvanic cell.
A reduction reaction occurs at the anode where the electrode loses electrons, resulting in the metal atoms entering solution, therefore causing corrosion.
Half Reaction: Zn → Zn {2+} + 2e {-}
Metal Types
Half cell standard reduction potential
The standard reduction potential of a given element is based on its reactivity, specifically the likelihood it will be reduced.
Copper and zinc have half cell reduction potentials of 0.34 V and 0.76 V respectively, therefore the overall standard cell potential is 1.10 V.
Each element will have a standard reduction potential.
Copper is chosen as the cathode metal and zinc is chosen as the anode metal.
Overall Reaction: Zn + Cu {2+} → Zn {2+} + Cu
Electrolytes
Electrolytes are solutions of ionic compounds in which the electrodes are submerged.
The electrolyte must match the metal of the electrodes, therefore copper and zinc compounds must be used.
Zinc compound examples:
Zinc Nitrate (Zn(NO3)2)
Zinc Sulfate (ZnSO4)
Zinc Chloride (ZnCl2)
Copper compound examples
Copper Sulfate (CuSO4)
Copper Chloride (CuCl2)
Copper Nitrate (Cu(NO3)2)
The ratio of the concentration of the electrolytes alters the induced cell potential difference as described by the Nernst equation.
Increasing the concentration of the copper sulfate electrolyte increases the rate of reaction, theoretically increasing the energy output.
The electrolyte is a liquid medium through which the charge flows. The electrolyte provides electrons and metal ions, enabling redox reactions to occur.
Salt bridge
As the reaction progresses, the net charge in the electrolyte solution will change. The salt bridge provides spectator ions which maintain neutrality of electric charge in each of the electrolytes.
Solution
Must be generally unreactive with the electrolyte solutions and the metal electrodes.
Examples
Potassium Chloride (KCl)
Sodium Chloride (NaCl)
Potassium Nitrate (KNO3)
Medium
Filter Paper
A porous medium such a filter paper is soaked in salt bridge solution. The absorbed solution will diffuse into the two electrolyte solutions.
Is easily accessible however must be regularly replaced.
Glass
A U-shaped tube filled with salt bridge solution. The two ends of the tube diffuse ions into the two electrolyte solutions.
Necessary materials are unavailable
Conducting Wire
Carries an electron current between the two electrodes
Nernst equation
Predicts the induced cell potential difference of a galvanic cell based on electrode half cell reduction potential, temperature, ion charge and electrolyte concentrations.
Predicts that when concentration of copper sulfate electrolyte increases, the induced cell potential difference will also increase.
Electrolytic Cells
Used to conduct electrolysis; to pass an electric current through a substance to cause a chemical reaction.
Can be used to explore the relationship between electric circuits and chemical reactions, however it does not produce its own current, rather uses an external one.
Therefore will not be used for this experiment.
Experiment
Method
Dilution
Serial dilutions can be used to reuse solutions diluting each electrolyte further and further.
Individual dilutions can be used where a new copper sulfate is diluted from scratch for each trial.
Galvanic Cell
The electrolytes will be transferred to two beakers. The zinc and copper electrodes will be placed in their respective electrolytes. The two electrolytes will be connected via a filter paper salt bridge soaked in solution. Each of the the electrodes will be connected via wire conducted which attach to a voltmeter which measured the induced cell potential difference.
Trials
Two trails will be conducted for each concentration, using new solutions, salt bridges and electrodes each time. Trials will be conducted for solutions with concentrations 1, 0.8, 0.6, 0.4 and 0.2 mol/L.
Hypothesis
When the concentration of the copper sulfate electrolyte solution increases, the induced cell potential difference will increase.
Variables
Independent
Concentration of copper sulfate electrolyte solution.
Dependent
Energy output of galvanic cell
Current
Rate of flow of electric charge, energy output.
Can be measured using ammeter.
Is dependent on external factors such as resistance in electric circuit.
Induced cell potential difference
Difference in potential energy per unit of charge between anode and cathode.
Proportional to current according to Ohm's Law (V=IR)
Can be measured using voltmeter.
Can be predicted using Nernst equation.
Will be used as dependent variable.
Controlled
Type of electrode
Electrode Surface Area
Salt bridge type and concentration
Electrolyte volume
Electrolyte solution type
Materials
alligator clips, wires, voltmeter, beakers, measuring cylinders, cutting pliers, filter paper, zinc strips, copper strips, zinc sulfate solution, copper sulfate solution, potassium chloride solution, distilled water
Optimal Energy Output
Energy Output
A higher induced cell potential difference means a greater energy output. Despite having a greater energy output, the cell may not be considered optimal due to further considerations.
Due to the logarithmic nature of the Nernst equation, it is expected that a lower concentration will be the most optimal.
Environmental Factors
Materials usage
Wastage
Economic Factors
Concentration to voltage ratio
Cost of metals and ionic compounds.
Other
Battery life: duration
Total energy produced
Recharging (reversing reaction)
Durability