375188 F 2CHM20 AT2 Design Experiment PDF

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SACE ID: 375188F

Factors of electroplating determine the mass of copper deposited at the cathode DECONSTRUCTION OF PROBLEM/ EXPERIMENTAL DESIGN The problem to be deconstructed states that during an electroplating process, metal is deposited on the surface of the cathode and the factors that affect the mass of metal deposited at the cathode must be determined. In order to identify these factors, thorough research on the electroplating process and electrolytic cells must be conducted. Electroplating is a plating process involving electrolytic cells in which a thin layer of metal is deposited onto an electrically conductive surface. In an electrolytic cell, shown in figure 1, two electrodes (anode and cathode) are immersed in an electrolyte and are connected to an external energy source, typically a power pack. Electrolytic cells convert electrical energy into chemical energy when a current is passed through the electrolyte. This process is referred to as electrolysis. An electrolyte solution, a chemical solution or molten salt conducts an electrical current through ion migration. Negatively and positively charged ions respectively migrate towards the cathode and anode terminals of the electric circuit. The anions (negatively charged ions), flow towards the anode (positively charged electrode). Once the ions reach the anode, electrons are removed from the valence shell of anions and transferred to the positive anode, losing their negative charge. Conversely, cations (positively charged ion) flow towards the cathode (negatively charged electrode). Once they reach, they combine with electrons and lose their positive charge. The cations gain electrons at the surface of the cathode.

Figure 1: Diagram of an electrolytic cell

At the anode, the metal ions are oxidized and enter the electrolyte as mobile ions: Z-(s) → Z+ + e-. The anode will disintegrate in this time as the metal atoms, M(s), are converted to metal ions, M+. At the cathode (negative electrode), metal ions from the electrolyte are reduced: Y+ + e- → Y(s). Solid metal, M(s), is deposited on the cathode. The overall cell equation is Y+ + Z → Y + Z An example of this is when copper is electroplated onto the anode (magnesium). The copper ions gain electrons in the cathode hence reduction occurs: Cu2+ + 2e- à Cu. The magnesium ions lose electrons in the anode; hence oxidation occurs: Mg à Mg2+ + 2e-

BENEFITS OF ELECTROPLATING There are multiple benefits of electroplating as it aids to improve the overall quality of substrates. Many electroplating processes create a barrier on substates and protect them against atmospheric conditions, including corrosion. This allows metals to last longer under extreme conditions and hence allows industries to save money significantly. Electroplating also allows manufactures to cost-effectively produce aesthetically appealing products. This process is often used for jewellery, which involves a thin plate of precious metal to allow the jewellery to appear more lustrous and attractive.

BRAINSTORMING Table 1: Determining which electrode is appropriate for the practical Figure 2: Metal reactivity series demonstrating the reactivity of metals in order of highest to lowest

Potassium

Zinc

Lead

Aluminium

Magnesium

Pure potassium is highly reactive. When exposed to water it may explode, hence is dangerous to utilise in a school environment and is not readily available in a school environment. Zinc is a better reducing agent compared to copper because its less electronegative. Accessible at school, however not as reactive compared to magnesium. Lead readily oxidises when exposed to air. This can cause imprecise results if the metal is inconsistently left out for all trials. Lead is also positioned very close to copper; therefore, an effective reaction may not occur. Aluminium is located much higher on the metal reactivity scales; hence it is very reactive. However, similar to lead It readily oxides when exposed to air, influencing imprecise results if the metal is left out in the air. Magnesium is placed significantly higher in the metal reactivity series, suggesting that it is more reactive compared to copper; hence it can readily displace copper from a copper sulphate solution. Considering magnesium will easily displace copper and is easily accessible at school, it will be chosen for the final design.

SACE ID: 375188F Table 2: Determining which electrolyte is appropriate for the practical Copper sulphate

Magnesium sulphate

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Available at school Can cause severe eye and skin irritation Utilised in the experimental trial and worked well when reacting with the copper and magnesium electrodes This solution will be used in the final with a concentration of 0.1M Highly reactive Available at school Not at dangerous compared to copper sulphate, however, can cause respiratory irritation in consumed. The concentration of the electrolyte will be 0.1M if chosen in the final design

Table 3: Possible factors affecting the mass of metal deposited at the cathode. Surface area of electrode

Type of electrode (cathode) Concentration of electrolyte Time taken to deposit copper onto cathode

Temperature of electrolyte

Voltage of battery

Space between electrodes

An increase in the surface area of cooper will influence more area to be proportional to the electrolyte according to the faradays law of electrolysis. This suggests that the electrolyte will have an increased chance of touching with the copper metal, hence more electrons will be transferred to the cathode. This overall will increase the amount of copper transferred in the reaction. This test can be conducted through the utilisation of the metal reactivity series. Determining how the reactivity between the cathode and copper influences the rate of reaction. This test can be easily conducted as the materials can be obtained. With a concentrated electrolyte. The plated metal amount is expected be greater When the concentration of the electrolyte is increased. This experiment can be easily tested with if different concentrations of electrolyte are available. Time is directly proportional with the amount of coated metal. This suggests that during a certain time period, a certain amount of mass is deposited onto the cathode. This experiment can be easily conducted, using time as an independent variable and choosing appropriate time periods; e.g. 2mins, 4mins, 6mins, 8mins and 10mins Temperature can impact the rate at which copper is deposited at the cathode since it affects the rate of reactions at the electrodes. Referring to rates of reaction, an increase in temperature suggests an increase in kinetic energy, hence a greater proportion of molecules to create a successful reaction. This experiment can be conducted using temperature as an independent variable and utilising an appropriate range of temperatures: e.g. 60°, 70°,80°, 90° and 100°/ Voltage is typically a force that drives a current though a circuit. Increasing the voltage will lead to an increase in the rate of electroplating the metal as more current will flow throughout the circuit. Within the experiment, a change in voltage can be used as the independent variable. This can be done by increasing or decreasing the dial on the power supply. This factor will be chosen to be investigated during the final experiment design with voltages of 4V, 6V, 8V, 10V and 12V. If the space between both electrodes is increased, then the amount of copper deposited onto the other electrode would decrease. This is because more current is needed to transfer between a larger distance. It will be too difficult to place both electrodes in the same position and change then distance, however the materials are readily accessible. If distance is chosen to be the independent variable then possible spaces between electrodes could be 1cm, 3cm, 5cm and 7cm.

Table 4: Possible methods of calculating the mass of copper deposited at the cathode. There are two possible methods the mass of electrodeposition can be measured: The first method is weighing both metals before and after the experiment and then determining the mass difference. This method has the possibility of multiple errors. The second method can be through the use of mathematical equations/ calculations. This method may result in more precise results and may limit the occurrence of random errors from effecting the results. However, mathematical errors may occur. Faradays law is a potential mathematical method that can be used to determine the mass of copper deposited at the cathode. There are multiple steps involved when using faradays law: 1. Charge (C) = Current (A) x Time (s) 2. Moles of Electrons or Faradays = Charge (C) / 96500 (faradays constant) 3. Moles of Copper = Moles of electrons or Faradays / ratio 4. Mass (g) = moles x relative atomic mass Although this method can produce precise results, the current travelling through the electrolytic cell is small, hence it will be difficult to accurately calculate the mass.

SACE ID: 375188F Table 5: Experimentation of electrolytic set up Figure 1: A test experiment showing the dissociation of copper onto magnesium. The trial was conducted over two minutes with a voltage of 4V.

Figure 2: A test experiment utilising magnesium as the cathode and copper sulphate as the electrolyte.

In the experimental trial, a beaker 100ml beaker was filled up with 50mL of copper sulphate, however, 50mL was not enough as the electrodes did not submerge into the electrolyte effectively. Hence the quantity was changed to 80mL. Additionally, two minutes was not enough time for the copper to effectively deposit onto the magnesium. Hence the time was changed to 5 minutes.

PRACTICAL DESIGN Research question development: Conducting an experimental trial allowed the flaws of the original design to be identified and hence improved the overall quality and precision of the experiment. The chosen experiment consists of a magnesium cathode and a copper anode with a copper sulphate electrolyte. The variable chosen to be changed is the voltage, which will be changed between 4V, 6V, 8V and 10V. Hence the research question is: Does the voltage of an electrolytic cell determine the rate at which copper from the anode is deposited on magnesium the cathode? Aim: A problem determining factors that affect rate of copper deposition was deconstructed and an experimental design was produced. The aim of this investigation is to determine how voltage affects the mass of copper electroplated onto the cathode (magnesium). Hypothesis: If the voltage in an electrolytic cell is increased to 12V, then the mass of copper deposited onto magnesium will increase by 0.4g. Variables - Independent – The independent variable is the voltage (V) flowing through the electrolytic cell. The arbitrary voltage values chosen to be used within the experiment are: (4V, 6V, 8V, 10V, 12V) Increasing/ decreasing the voltages on the power supply using a dial will allow the voltage values above to be obtained. -

Dependent – The dependent variable is the mass in grams of copper (Cu) metal deposited onto magnesium (Mg). This change in mass will be measured by calculating the difference between the initial and final mass of both the anode and cathode in grams.

Table 5: Controlled variables and how they will be kept constant Controlled variable Type, molarity (M) and volume of electrolyte solution (80mL) Time of reaction (5 minutes) Size of both electrodes Space between electrodes Type of electrodes (magnesium and copper)

How it will be controlled To ensure the consistency in each trial, the trials were all undertaken using the same quantity of 1.0M copper sulphate solution (80mL). In order to keep time a constant factor through the experiment, a stopwatch will be utilised to determine the 5-minute mark. Each electrode will be measured before using in the experiment to ensure the precision of each trial. Attaching both electrodes to the side of the beaker using alligator clip. This variable will be difficult to keep constant. Magnesium and copper will be utilised as the electrodes in every trial for each experiment.

Table 6: Safety and ethical considerations Harmful and corrosive chemical Power supply

Copper sulphate is a corrosive solution which can cause sever skin and eye irritation, hence gloves and eye protection must be worn. Similarly, a lab coat must be worn to prevent damage to clothes. The utilisation of a power supply has the potential risk of electrocution. Hence, cation must be implemented when connecting the electrodes to the power supply. The power supply was turned off before attaching the electrode.

SACE ID: 375188F Glassware Covid-19

Waste of chemicals and materials

Caution must be taken when handling glassware to ensure it is not broken and the safety of students is maintained. If glassware is broken, then approaching a teacher will be an ideal solution. Considering the current circumstances of covid-19, appropriate distance between students and teachers must be maintained. equipment must be washed, and benches must be wiped before and after conducting the experiment. Considering the chemicals used hazardous and dangerous, depositing them into the bin can result in environmental and ethical risks. Hence the chemicals must be deposited in a waste bucket, so they can be filtrated and evaporated in order to reduce its dangers.

Note: This practical was conducted in pairs, hence the apparatus is divided between both members of the group Apparatus - 25x copper (Cu) strips - 1x 100ml beaker - 25x magnesium (Mg) strips - 1x 100ml measuring cylinder - 1x Timer - 1600ml of copper (II) sulphate (CuSO4) solution (1.0M) - 1x electronic balance scale - 1x Power supply - 1x tweezers - 2x alligator clips and wires (positive and - Distilled water negative) Procedure 1. Put on safety gear including glasses, lab coat and gloves to ensure the safety of the experiment. 2. Gather all equipment required and rinse all the glassware with distilled water in order to remove any reagents from previous practicals. 3. Using a measuring cylinder measure 80mL of 1.0M copper sulphate (CuSO4) solution and pour into a 100mL beaker. 4. Using sandpaper, sand both electrodes to ensure there is no corrosion from previous experiments. 5. One at a time, place the electrodes on an electronic scale to determine its initial mass. Record the initial mass of both electrodes in the results table. 6. Attach one end of the positive alligator clip to the cathode (copper) with one side of the beaker and the other end to the power supply. Similarly attach one end of the negative wire to the anode (magnesium) with the opposite end of the beaker and the other alligator clip to the power supply. Ensure both electrodes are placed in the electrolyte solution while attaching them to the power supply the distance between both electrodes must be consistent. 7. The initial voltage is set to 2V. The experiment is conducted over 5 minutes. Note that the experiment begins when the power supply is turned on at the beginning of the 5 minutes and finishes when power supply is turned off, hence the power supply must be immediately turned off at the 5-minute mark. 8. Remove the electrodes from the solution and individually place the electrodes onto the electronic scale and determine the final mass. Calculate the mass deposited onto the magnesium. 9. Repeat steps 3 to 8 with voltages of 4V, 6V, 8V, 10V and 12V with each experiment conducted over 4 trials to ensure the precision of the results. Record the final mass of the electrodes in the results table.

Table 7: design for results table Initial mass of Cu (g) Voltage (V):

Mass of Cu after (g)

Change mass of Cu (g)

Initial mass of Mg (g)

Mass of Mg after (g)

Change mass of Mg (g)

Trial 1 Trial 2 Trial 3 Trial 4 The average change in mass of copper:

The average change in mass of magnesium:

This design for the results table will be utilised for every experimental trial. The table will be used for 4V, 6V, 8V, 10V and 12V. The table demonstrates the mass of anode deposited at the cathode.

SACE ID: 375188F

FACTORS EFFECTING THE RATE OF COPPER ELECTROPLATING BACKGROUND THEORY: Corrosion is the deterioration of a metal as a result of chemical reactions between it and the surrounding environment. The main purposes of electroplating is to improve the appearance of the material and provide protection against corrosion. Electroplating is generally carried out in order to improve the appearance or corrosion resistance of the surface of a metal (or any other conductor, e.g., graphite) by electrodepositing a thin layer of some desired metal on it. Electroplating involves the change of electrical energy (supply of electrons) into chemical energy, by producing new chemicals as a result of the passage of an electric current through an electrolyte. Chemical decomposition occurs in order to transfer the electrons to the cathode (negatively charged) from the anode (positively charged). The anode is positively charged since electrons are being removed and the cathode is negatively charged because electrons are being added. There is an excess of electrons at the cathode, hence a reduction occurs. Electrons are removed at the anode; hence oxidation occurs.

As shown in table 8, when copper is electroplated onto the anode (magnesium), the magnesium atoms undergo oxidation when placed in the electrolyte solution: Mg à Mg2+ + 2e-. The copper ions gain electrons in the cathode hence reduction occurs: Cu2+ + 2e- à Cu. The overall redox reaction is: Mg(s) + Cu2+ (aq) Mg2+ (aq) + Cu(s)

Figure 3: diagram of an electrolytic cell

AIM OF EXPERIMENT: A problem determining factors that affect rate of copper deposition was given to deconstruct. The problem stated that during an electroplating process, metal is deposited on the surface of the cathode and the factors that affect the mass of metal deposited at the cathode must be determined. Research on the electroplating process assisted in the development of the experimental design. The aim of this investigation is to determine how voltage produced by the power supply affects the mass of copper electroplated onto the cathode (magnesium) in an electrolytic cell.

SACE ID: 375188F

TESTABLE HYPOTHE HYPOTHESIS SIS : If the voltage in an electrolytic cell is increased to 12V, then the mass of copper deposited onto magnesium will increase by 0.4g.

VARIABLES -

Independent – The independent variable is the voltage (V) flowing through the electrolytic cell. The voltage will be changed between 4V, 6V, 8V, 10V and 12V.

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Dependent – The dependent variable is the mass of copper (Cu) metal deposited onto magnesium (g). This change in mass will be measured by calculating the difference between the initial and final mass of both the anode (copper) and cathode (magnesium).

Table 8: Controlled variables and how they will be kept constant Controlled variable Type, molarity (M) and volume of electrolyte solution (80mL) Time of reaction (5 minutes) Size of both electrodes Space between electrodes Type of electrodes (magnesium and copper)

How it will be controlled To ensure the consistency in each trial, the trials were all undertaken using the same quantity of 1.0M copper sulphate solution (80mL). In order to keep time a constant factor through the experiment, a stopwatch will be utilised to determine the 5-minute mark. Each electrode will be measured before using in the experiment to ensure the precision of each trial. Attaching both electrodes to the side of the beaker using alligator clip. This variable will be difficult to keep constant. Magnesium and copper will be utilised as the electrodes in every trial for each experiment.

SAFETY CONSIDERATIONS Table 9: Safety and ethical cons...