Research Question: How does the independent variable of the experiment - the concentration of the Copper Sulphate electrolyte (M) affect the dependent variable of the experiment- the change in mean electrical resistance (Ω) and ultimately help in determining whether the Copper Sulphate electrolyte is an ohmic or non-ohmic conductor?
Aim
The aim of the ‘Investigating Resistance’ lab is to investigate the relationship between the independent variable of the experiment, the concentration of Copper Sulphate electrolyte, and the dependent variable of the experiment, the change in mean resistance, and how this relationship determines whether the Copper Sulphate electrolyte is an ohmic or non-ohmic conductor. The aim of this investigation will be achieved by manipulating the independent variable - the concentration of Copper Sulphate ionic solutions, this will be done by using 6 different concentrations of Copper Sulphate ionic solution, specifically - 0.0M, 0.2M, 0.4M, 0.6M, 0.8M and 1.0M and measuring the current and voltage using an ammeter and voltmeter respectively and then calculating the resistance using Goerg Simon’s Law. In this experiment, the 0.0M of Copper Sulphate will contain zero molar value of Copper Sulphate/ lowest molar value of Copper Sulphate, meanwhile, the solution containing 1M of Copper Sulphate will contain the highest mole value of Copper Sulphate.
Hypothesis
It is understood that electrolysis is the “process by which electric current is passed through a substance to effect a chemical change. The chemical change is one in which the substance loses or gains an electron (oxidation or reduction)” (“Electrolysis | Definition, Uses, & Facts | Britannica”). It is also understood that in order to achieve the process of electrolysis, three main components are required - an external power source, electrodes and an electrolyte (“Electrolysis - Definition, Process, Applications, Electrolysis of Water.”).
An external power source is a “used to convert electric current into DC current or lower-voltage AC current”(“Definition: External Power Supply from 42 USC § 6291(36) | LII / Legal Information Institute”).In this experiment a battery pack will be used in order to supply current for electrolysis. An electrode is simply a conductor (Dingle,2021).In this experiment the two identical copper strips will be used in order to conduct the process of electrolysis. Two electrodes are needed as one will be the cathode “the negative electrode of an electrolysis cell” and the other will be the anode - “the positive electrode of the electrolysis cell” (“Electrolysis Principles (4.1.1) | CIE IGCSE Chemistry Revision Notes 2023 Membership”).
An electrolyte can be defined as “a substance that conducts electricity when dissolved in water” (Felmen, 2021) and “a chemical whose atoms are tightly bonded together, by ionic bonds but when we dissolve it in water, its molecules split up into positive, and negative ions” (“Principle of Electrolysis of Copper Sulfate Electrolyte“).In this experiment, the electrolyte being used in Copper Sulphate. Copper Sulphate is an inorganic chemical compound which is found naturally in a solid state of matter (Felmen, 2021)However, since Copper Sulphate is not a conductor in its solid state, it needs to be liquified in order to conduct electricity. In Copper Sulphate.
During the process of electrolysis, the power pack will supply the cathode with electrons causing it to become negatively charged. The cations present in the electrolyte, which in this case are the Cu2+ cations will then move towards the cathode because of Coulomb's law stating that opposite charges attract. This causes the cations to gain electrons. The anions which in this experiment is the S042- present in the electrolyte will then move towards the anode which is positive, where the anions will lose electrons. The electrons will then move towards the power supply from the anode.
After conducting adequate research, it can be hypothesized that the ionic solution containing the lowest molar value of Copper Sulphate will have the highest resistance. Therefore it is predicted that the ionic solution containing 0.0M concentration of Copper Sulphate will have the highest resistance. The scientific explanation for the following would be that - The solution containing 0.0M of Copper Sulphate does not contain any Copper Sulphate as the solution is pure and only contains distilled water. Distilled water is “deionized water meaning it does not contain any ions”, due to the lack of ions, distilled water cannot conduct electricity (Toppr). Therefore when current is supplied to the identical copper electrodes, no current is generated as electricity is unable to travel through the medium (i.e distilled water).Since current flowing through the circuit is 0, this means that the resistance will be infinite. The scientific explanation for the following would be that - Ohm’s Law states that Resistance = Voltage/ Current. Therefore regardless of the voltage generated, x divided by 0 will be undefined (Banerjee),meaning there is infinite resistance. Since current and resistance are inversely proportional to one another, 0 current means that resistance is extremely high (Banerjee)).Therefore on the predicted graph, at 0.0M, the gradient is touching the y-intercept of the graph.
It can be hypothesized that the range of Copper Sulphate solutions containing a lower molar value of Copper Sulphate will have a high resistance compared to solutions containing a high molar value of Copper Sulphate, however, these solutions will have a lower resistance compared to the Copper Sulphate solution with a concentration of 0.0M . Therefore it is predicted that the solutions containing 0.2M, 0.4M and 0.6 of Copper Sulphate will have a higher resistance compared to the Copper Sulphate solutions with the concentration of 0.8M and 1.0M. The scientific explanation for the following would be that as the concentration of the Copper Sulphate increases, the concentration of cations and anions moving freely in the solution increases, and according to the Atlas-Scientific “as the concentration of ions increases, the conductivity also increases” ((“How Do Ions Increase Conductivity? | Atlas Scientific”)). This is because electrical current is carried by the ions present in the ionic solution (Chemistry Stack exchange). And since the Ohm’s Law states that current is inversely proportional to resistance, the increase in current will result in a decrease in resistance. Therefore it is predicted that as the concentration of the Copper Sulphate increases, the resistance will decrease. So it is assumed that the solutions containing 0.2M, 0.4 and 0.6M - as the concentration increases the resistance will decrease as more current is able to flow through.
It can be hypothesized that in solutions having the Copper Sulphate concentration of 0.8M and 1.0M, the resistance will be the lowest as the ratio of Copper Sulphate to Distilled water increases significantly allowing for more current to flow to be generated, resulting in am extremely low resistance.
The predicted graph shows that the concentration of Copper Sulphate is inversely proportional to the mean resistance, creating a steep downward trend.
Variable
Independent Variable (IV)
“The independent variable is the variable the experimenter manipulates or changes, and is assumed to have a direct effect on the dependent variable” (McLeod, 2019). In this experiment, the independent variable is the concentration of the Copper Sulphate Solution (electrolyte) which is assumed to affect the resistance of the copper electrodes. A range of 6 different Copper Sulphate solutions will be used - 0.0M, 0.2M, 0.4M, 0.6M, 0.8M and 1M.The unit ‘M’ can also be written as mol/ dm³ is used to to represent the unit of Molar. “Molar refers to the unit of concentration molarity, which is equal to the number of moles per litre of a solution” (Helmenstine Ph.D). The lowest molar value of 0.0M has a zero molar value of copper sulphate, hence distilled water will be used as it lacks copper sulphate and any other impurities which may hinder the data collected. Since only 1M of copper sulphate is available, the 1M copper sulphate will be diluted for other concentrations by also using distilled water.
Dependent Variable (DV)
“The dependent variable is the variable that is being tested and measured in an experiment” (McLeod, 2019).In this experiment the dependent variable is the change in resistance (Ω) of the copper electrode. The resistance cannot be measured directly, therefore, a voltmeter and ammeter will be plugged to each of the copper electrodes which is suspended halfway in the ionic solution in the beaker using crocodile clips. The reading from both the voltmeter and ammeter will be noted down after a set time period, then using the Ohm’s Law created by the physicist Georg Simon Ohm which shows the relationship between current and voltage as V=IR, the equation will be rearranged to R=V/I in order to calculate the resistance (“Ohm’s Law | Physics | Britannica”).The average resistance of all three trials will be conducted by adding the sum of all three resistances calculated and then dividing it by 3 to find the average. Only positive values are expected as negative resistance cannot be gotten.
Controlled Variables
“A control variable is any factor that is controlled or held constant during an experiment, control variables aren’t a part of the experiment, but they are important because they could affect the outcome.” (Anne Helmenstine, 2020). In this experiment there are 7 main control variables that need to be held constant-
The volume of the 6 different concentrations of Copper Sulphate ionic solution The volume of the 6 different solutions will be kept constant by using a graduated cylinder which has the sensitivity of 10 mL.This will allow us to measure the ionic solutions of 150mL volume of the liquid more accurately. The graduated cylinder will then be viewed at eye level in order to reduce parallax errors which usually increase the probability of systematic errors and random errors (Mini Physics, 2020) which could negatively affect the data collected. The following CV needs to be kept constant in order to ensure that the change in mean resistance is caused by an increase/decrease in the concentrations of Copper Sulphate solutions and not because of difference volumes of the ionic solution.
Type of electrode The type of electrodes will be kept constant by using two identical reactive electrodes of the same metal. This means that the same ions will make up the metals, allowing for the same amount of ions to carry charge and conduct electricity during electrolysis. The following CV needs to be kept constant this is because if two different types of metals are used for example one reactive and one inert electrode is used this means that the current will only pass through one of them not allowing the process of electrolysis to take place..
The size and length of the copper electrodes The following CV will be kept constant by using a vernier calliper to ensure that the both the length and thickness of the copper electrodes are as identical as possible.The following CV needs to be kept constant this is because the cross sectional area of a conductor affects resistance and “with increasing the electrode area, the ratios of voltage and current decrease nonlinearly while the ratios of charge and voltage also decrease non-linearly. This can affect the results of the experiment as it can completely disprove whether or not Copper Sulphate solution is an ohmic or non-ohmic conductor.
Water used when diluting the concentration of the copper sulphate electrolyte
The following CV will be kept constant by always using distilled water when diluting the copper sulphate solutions. The following CV needs to be kept constant as Tap water contains ions, metals, salts etc which may hinder the results of this investigation as all the things present in tap water can increase conductivity affecting the final results (“Solutions and Dilutions Template”)
Equipment
Copper Sulphate electrolyte solution with concentration of 1M (300ml)
Distilled water (300ml)
Beaker with sensitivity of +/- 50ml (1)
Measuring cylinder with a sensitivity of +/- 10ml (2)
Crocodile clips ( 4- 2 each of red and black)
Power pack
Identical copper electrodes (2)
Ammeter (1)
Voltmeter (1)
Red wire (2)
Black wire (2)
Connecting leads (2)
Banana Connectors (2)
Timer (1)
Thermometer (1)
Safety precautions
Copper Sulphate electrolyte is a hazard as it can cause serious eye and skin irritation. In order to avoid this possible harm, wearing gloves and safety goggles is essential to protect the skin and eyes throughout this experiment.
Power pack is a hazard as it can cause an electric shock, in order to avoid this possible harm, the power pack must be switched off before touching and ensure that electrodes do not come in contact with one another.
Method
Use a measuring cylinder with a sensitivity of +/- 10ml and pour a 150ml of Copper Sulphate electrolyte which has a concentration of 1.0M into the measuring cylinder.
Ensure the measurement is viewed at eye level in order to reduce parallax error.
Pour the electrolyte into a beaker which has a sensitivity of +/- 50ml.
Use a thermometer to measure the temperature of the electrolyte and make sure that it is within the window of +/- 3 degrees for the most accurate results.
Clip each electrode to the mouth of the beaker using a crocodile clip and ensure that the electrode is submerged halfway.
Attach one electrode to the negative terminal of the power pack and the other electrode to the positive terminal of the power pack using the connecting leads.
Connect one red wire to the ammeter and one black wire to the voltmeter and repeat the same action for the other electrode.
Switch on the power pack and set a timer for 30 seconds.
After 30 seconds make note of the current displayed on the ammeter and the voltage displayed on the voltmeter as well as any observations.
Steps 1-9 will need to be repeated for the other concentrations, however this time the volume of copper sulphate electrolyte and distilled water need to be measured using separate measuring cylinders as the solution will need to be diluted.
Table 1 shows the set volumes of Copper Sulphate and distilled water needed to dilute the Copper Sulphate concentration to 0.0M, 0.2M, 0.4M, 0.6M and 0.8M.
Results
Table 2 - The following table illustrates how manipulating the concentration of copper sulphate causes a change in current. When inputting data into the table 3 anomalies were spotted. When calculating the mean average of current these three anomalies have been ignored and instead the other two values have been used to calculate the mean current. In the table, it can be observed that as the concentration of copper sulphate electrolyte increased, the current also increased- showing that the concentration and current are directly proportional as predicted in the hypothesis.
Table 3 – The following data table illustrates how manipulating the concentration of the copper sulphate electrolyte causes a change in the voltage observed. When inputting the data into the data table, no anomalies were spotted, however, no trend/ relationship can be spotted between the concentration of copper sulphate electrolyte and mean voltage.
Table 4 - The following data table illustrates how manipulating the independent variable of the experiment - the concentration of copper sulphate electrolyte affects the mean resistance. The resistance was calculated by using Ohm’s Law which states that
Resistance = Voltage/ Current. It can be observed that there is no trend/ relationship between the Concentration of Copper Sulphate and Mean Resistance as the mean resistance doesn’t seem to decrease as the concentration of copper sulphate electrolyte increases as predicted in the hypothesis.
Observations
The left electrode - the cathode seems to have become thinner as the copper has dissolved from the electrode. This may have resulted in an increased resistance. Meanwhile, the anode bits of copper have seen to be gathered causing the anode to become fatter. This may have led to a decrease in resistance. This may have disrupted the pattern of the voltage in Table 3.
Conclusion
The final graph illustrates an upward trend as per the line of best fit which shows values of the mean resistance increasing from 3.92 to 4.38. The blue trendline does not show a strong negative correlation as predicted in the hypothesis, instead the trendline shows a weak positive correlation between the independent and dependent variables. However the following incorrect correlation is observed because there was an anomalous data for the final data point which shows a sudden increase in resistance. However, ignoring the anomalous data point a pattern can be observed of the mean resistance decreasing disproportionately as the concentration of the copper sulphate electrolyte increases. The relationship of the graph can be categorised as being inversely related ( ignoring the anomalous data) this is because as the concentration of the Copper Sulphate electrolyte increases the mean resistance decreases.
However the relationship cannot be categorised as inversely proportional like predicted in the hypothesis, this is because inversely proportional refers to when the independent variable increases and dependent variable decreases by the same proportion/value and vice versa and since the two variables are not increasing by the same value their relationship cannot be termed as inversely proportional. Therefore the general formula to cannot be derived by substituting the x and y values from the graph and into the formula y = k/x and then re-arranging it so that k= y*x , to find the value of the constant and therefore finding the general formula.
To conclude, it can be stated that at the y-intercept the resistance is the greatest. The scientific explanation for the following - because the solution has zero concentration of Copper Sulphate electrolyte which is the main conductor of this experiment which and Distilled water is “deionized water meaning it does not contain any ions”, due to the lack of ions, distilled water cannot conduct electricity (Toppr), meaning current cannot flow through the distilled water causing the current to be zero, using ohm's law to calculate resistance will Resistance = Voltage/ Current. Therefore regardless of the voltage generated, x divided by 0 will be undefined (Banerjee)). Since current and resistance are inversely proportional to one another, 0 current means that resistance is extremely high (Banerjee). In short the as the concentration of the copper sulphate electrolyte increases the higher the resistance. This is because an increasing concentration of copper sulphate means an increasing concentration of ions which are used to carry charge to carry current to conduct electricity (Chemistry Stack eXCHANGE). Since more current is being generated- automatically resistance will go down as both values are inversely proportional to one another(“How Do Ions Increase Conductivity? | Atlas Scientific”)
After interpreting the data using the graph and conducting research, it can be concluded that there is a similarity between the hypothesis and the final graph. This is because in the hypothesis it was predicted that the mean resistance would be the highest at the Copper Sulphate concentration of 0.0M as no current cannot flow through distilled water as it's not a conductor and since current flowing is 0, an extremely low value, the resistance would be at its highest as both current and resistance and inversely proportional to one another.the final graph also shows the data point for 0.0M to be the highest as it touches the y-intercept. It was also predicted that as the concentration of copper sulphate electrolyte increases the resistance will decrease as copper sulphate is a conductor and if a higher concentration is present it also means that more cations and anions are present resulting in a greater flow of current, And since current and resistance are inversely proportional to one another this means that the resistance will decrease. Therefore , overall the graph follows the principles of the hypothesis but without proportionality (if the anomaly is ignored).However in the hypothesis it was predicted that the independent and dependent variables were inversely proportional to one another which was not the case.
There was one anomalous data point on the graph which resulted in the trajectory of the line of best fit changing, the data point for 1.0M concentration of Copper Sulphate. The data might be anomalous because the controlled variables weren’t carefully kept constant. I believe that the following factors all contributed to the data being anomalous- Firstly, even though my team members and I tried to keep the volume of the 6 solutions constant, parallax error may have occurred as different people checked for parallax error for each trial, therefore there may have been a slight increase or decrease in the volume of the 6 constraints when conducting the experiment, as mentioned in the observations, the thickness of cathode and anode increased and decreased respectively, and since the cross-sectional area is one of the factors that affect resistance, the increase and decrease in area may have hindered the mean resistance, as according to ruf.rice.edu increasing the electrode area, the ratios of voltage and current decrease nonlinearly which is what was observed in the final graph. My team members and I also forgot to use distilled water, this may have resulted in impurities and ions present in tap water to affect the results.
Evaluation
Evaluation of the validity of the hypothesis based on the outcome of the investigation
The principles in my hypothesis seemed to be right, the incorrect thing hypothesized was that the relationship as an inversely proportional relationship was predicted but it trend out to be an inversely related relationship between the independent and dependent variable.
Evaluation of the validity of the method and improvements s of the method that would benefit the investigation
The method was well conducted, however, the main improvement that would benefit the investigation pertain to better controlling the control variables When trying to measure the volume of the 6 different Copper Sulfate concentrations two mistakes were made, firstly measuring cylinders of two different sensitivities were used - firstly being +/- 10ml which made sense as the volume was being measured in divisions of 10. However the second measuring cylinder had the sensitivity of +/- 5 ml which may have resulted in incorrect readings being taken due to parallax errors, parallax errors may have also occurred in another way as the team members were in charge of measuring the volume of the different solutions for different trials, making it incohesive, which may have hindered our data.Therefore, if I were to conduct this experiment again, I would use all equipment with the same sensitivity as well as have only one team member in charge for doing a task for all the constraints and trials of the experiment. As mentioned in the observations, some of the copper particles were either dissolved from the copper anode and some of the particles were deposited at the cathode, this resulted in the cross sectional area of the anode decreasing and the cathode increasing. Since cross sectional areas are one of the factors that affect resistance, the following may have hindered the results as they were no longer uniform and identical. Therefore, if I were to conduct the following experiment again, I would use a new pair of identical copper electrodes for each concentration of each trial of the experiment.
Extensions to the investigation
If I had the opportunity to conduct the Investigating resistance investigation again, I would want to do electrolysis again, however instead of using identical reactive copper electrodes, I would use inert electrodes such as graphite or platinum in order to observe how this may result it ions being discharged and a gas being formed. I would follow a similar methodlie the one conducted for this experiment, however, I would make sure to work on better controlling the control variables.
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