The Factors that Affect the Mass of Copper

The Factors that Affect the Mass of Copper
Electrolysis is the decomposition of a molten or aqueous compound by electricity. Electrolysis occurs only in liquids called electrolytes. Electrolytes are compounds, which conduct electricity when molten or dissolved in water, but not when they are in a solid state as the oppositely charged ions are held together by strong ionic bonds in a giant lattice and this means electricity cannot pass through it and the ions are unable to move. If electrolytes are molten or dissolved in water their ions are free to move, and the movement of ions in liquids is key in electrolysis. Electrolysis takes place in an electrolyte cell. The diagram below shows the apparatus used in the electrolysis of molten or aqueous ionic compounds. The electrodes (anode and cathode) are known as conducting rods. Normally they are made out of platinum or graphite as these substances are chemically unreactive and will not interfere with the experiment. They are inert electrodes. However in this experiment we are using copper electrodes. Copper electrodes are active electrodes and these metal electrodes take part in electrolysis. Copper electrodes are used in industry to obtain pure copper
The anode is the positive electrode, electrons flow from the anode to the battery. The anions, which are negatively charged non-metal ions (except for some complex transition metal ions) are attracted to the anode. The cathode is the negative electrode. Electrons flow into the cathode from the battery. The cations, which are positively charged metal ions (except for hydrogen ions and ammonium ions) are attracted to the cathode. In the diagram copper (11) sulphate solution is being electrolysed using graphite electrodes, one would expect the following to happen. At the cathode The ions Cu and H are both attracted to the cathode, but because copper is lower down in the reactivity series than hydrogen, copper ions migrate to the cathode forming a layer of copper at the cathode. Cu + 2e Þ Cu atom At the anode The ions OH (hydroxide ions) and So (sulphate ions) are attracted here. As So is not a halogen, OH ions give up electrons more readily and migrate to the anode forming oxygen there. OH ? 4e Þ 2H O + O Electrolysis involves both Oxidation and Reduction reactions at the electrodes. They are chemical opposites, oxidation is loss of electrons and reduction is the gain of electrons. At the cathode, cations gain electrons and are reduced and at the anode, anions lose electrons and are oxidised As we know there are two different types of electrolytes, aqueous and molten. I am now going to discuss what happens when the compounds are electrolysed. The electrolysis of molten electrolytes -?????????????????? When a molten ionic compound is used in electrolysis a metal is always formed at the cathode and a non-metal is always formed at the anode. There is only one exception to this and that is hydrogen, the only non-metal that forms at the cathode e.g. electrolysis of molten sodium chloride. The electrolysis of aqueous electrolytes -??????????????????- When an aqueous ionic compound is used in electrolysis the following occurs. Metals above hydrogen in the reactivity series are considered more reactive. At the cathode the more reactive the metal, the more eager it is to exist as ions and remain in the solution so we can say if you have a more reactive metal, the H+ ions accept electrons and hydrogen molecules are formed at the cathode and the metal stays in solution. The ions of less reactive metals (below hydrogen on the reactivity series) will accept electrons and form metal atoms at the cathode, leaving hydrogen ions in solution. At the anode the following occurs. If ions of a halogen are present (chlorine ions, bromine ions and iodine ions) they will give up electrons more eagerly than hydroxide ions (OH ) do. This means molecules of chlorine, bromine and iodine will form at the cathode. If a halogen is not present hydroxide ions will give up electrons more readily than other non-metal ions do and oxygen will form at the anode. Factors that affect the mass of copper deposited on the cathode:
Surface area of electrodes:
The greater the surface area of the electrodes, the greater the amount of Cu 2+ ions lost at the anode and gained at the cathode
Concentration of Copper (11) Sulphate Solution:
The greater the concentration of copper (11) sulphate solution, the more copper deposited at the cathode
Time
The more time the copper electrodes are left in the copper (11) sulphate solution, the more time there will be for cu 2+ ions to be deposited. ? Current If the current is larger, there will be more electrons flowing around the circuit and more copper will be deposited. ? Temperature The greater the temperature the more copper deposited at the cathode as particles will obtain more energy and collide more if placed in a warmer temperature. The factor I will investigate is current. This is because it is easy to obtain results and make predictions, calculating the theoretical value. Also using scientific knowledge I can make a qualitative prediction . The experiment will also be easy to set up and to achieve accurate results. Qualitative prediction In this investigation I am investigating the electrolysis of Copper (11) sulphate solution using copper electrodes. When this experiment is undertaken I predict that the anode will dissolve into the copper (11) sulphate solution and this is predicted because it?s atoms give up electrons to form ions in the solution Cu atom ? 2e Þ Cu ion I also predict that the opposite occurs at the cathode, the copper ions pick up electrons and become copper atoms Cu + 2e Þ Cu atom Here we can see that as copper ions leave the copper (11) sulphate solution to form copper atoms at the cathode, they are replaced in the solution at the anode. This means it can be predicted that the mass of copper gained at the cathode equals the mass of copper lost at the anode. This is what one expects to happen in the electrolysis of copper(11) sulphate solution using copper cathodes, now the factor which is going to be investigated, the current will be observed. It is predicted that the current will affect the amount of copper deposited on the cathode in the following ways. The larger the current the more copper will be deposited and so from this we can say if you double the current you double the amount of copper deposited at the cathode. This is because as the current increases, so does the amount of electrons flowing around the circuit, so in a given time (20 minutes) more ions will be formed at the anode by losing two electrons (oxidation) and therefore more copper atoms will be formed at the cathode as ions will gain two electrons (reduction). So as we can see the greater the amount of electrons (charge) flowing around the circuit, the greater the mass of copper deposited at the cathode. This means it can be predicted that the amount of copper deposited at the cathode is directly proportional to the size of the current. The currents that shall be used are 0.2A, 0.4A, 0.6A, 0.8A and 1A. I predict that as the current increases more copper will be deposited on the cathode and the amount of copper deposited on the cathode when using the current 0.2A will be half the amount of copper deposited on the copper cathode using the current 0.4A as 0.4A is twice 0.2A. This also applies to my other currents such as 0.4A and 0.8A. Quantitative Prediction Since how the current affects the mass of copper deposited on the copper cathode is being investigated it is sensible to pick five different readings, 0.2 Amps, 0.4 Amps, 0.6 Amps, 0.8 Amps and 1.0 Amps. This range and number of currents were chosen because they cover a wide scale and will therefore produce a broad range of results, which hopefully support my prediction. All the readings were left for a period of 20 minutes. I will now calculate the theoretical values for each reading in order to predict my results. The first reading: 0.2 amps Amount of electric charge = Current(A) x Time(S) 0.2 × 1200 = 240 C Number of moles of electrons transferred = 240 = 0.002487046632 96,500 At the cathode: Cu + 2e Þ Cu 1 mole of Cu ions requires 2 moles of electrons to form 1 mole of Cu atoms Number of moles of Cu = 0.002487046632 = 0.001243523316 2 Mass of copper deposited at the cathode = 0.001243523316 × 63.5 = 0.07896 g (5dp) = 0.08 g (2dp) The second reading: 0.4 Amps Amount of electric charge = 0.4 × 1200 = 480 C Number of moles of electrons transferred = 480 = 0.004974093264 96,500 Number of moles of Cu = 0.004974093264 = 0.002487046632 2 Mass of copper deposited at the cathode = 0.002487046632 × 63.5 = 0.158 g (3dp) = 0.16 g (2dp) The third reading: 0.6 Amps Amount of electric charge = 0.6 × 1200 = 720 C Number of moles of electrons transferred = 720 = 0.007461139896 96,500 Number of moles of Cu = 0.007461139896 = 0.003730569948 2 Mass of copper deposited at the cathode = 0.003730569948 × 63.5 = 0.236891191 g = 0.24 g (2dp) The fourth reading: 0.8 Amps Amount of electric charge = 0.8 × 1200 = 960 C Number of moles of electrons transferred = 960 = 0.009948186529 96,500 Number of moles of Cu = 0.009948186529 = 0.004974093264 2 Mass of copper deposited at the cathode = 0.004974093264 × 63.5 = 0.315854922 g = 0.32 g (2dp) The fifth reading: 1 Amp Amount of electric charge = 1 × 1200 = 1200 C Number of moles of electrons transferred = 1200 = 0.012435233 96,500 Number of moles = 0.012435233 = 0.00621761658 2 Mass of copper deposited at the cathode = 0.00621761658 × 63.5 = 0.394818652 g = 0.40g (2dp) Method Apparatus List Two strips of copper equal in size One Variable Resistor One Ammeter One beaker 200 ml of Copper (11) sulphate solution of a concentration of 1 mole A Power pack (or battery pack) Two red wires Two black wires A Stop clock Two crocodile clips One wire holder with crocodile clips An electronic balance Propanone Distilled water Ammonia Solution Tissue to wipe electrodes with A piece of emery paper A wooden mat DiagrMethod The apparatus was set up as shown in the diagram above. One of the two copper electrodes is cleaned with emery paper on a wooded mat to remove impurities such as oxide layers and grease and therefore to ensure that the copper cathode is pure. It is necessary to remove oxide layers as they might prevent current flowing and grease may prevent the new copper sticking well to the old copper. Next the cathode is wiped in a tissue soaked in ammonia solution, washed in distilled water and dried. This ensures that any further impurities are removed. The cathode is then weighed on an electronic balance and its mass is recorded. The electronic balance is used as it provides accurate readings of the mass to two decimal places, other methods of measuring the weight would not be as accurate as this, so it is essential the electronic balance is used. The anode is not cleaned as it is not necessary to weigh the anode. The cleaned cathode is then fixed onto the holder using a crocodile clip, which is not in contact with the Copper (11) sulphate solution, only the cathode, and is then connected to the negative terminal of the power pack. The same is repeated for the anode except it is connected to the positive terminal of the power supply. Both electrodes are immersed to a depth of 3cm in 1.0 mole dm Copper sulphate solution The Variable resistor is adjusted to give the desired current which could be read by looking at the ammeter. The variable resistor maintains a low and steady current. The power pack was then turned on for 20 minutes, the time was measured using a stop clock. When 20 minutes is passed the copper cathode is carefully removed from the copper sulphate solution. The cathode should (according to my prediction) be covered by a fresh layer of copper so it must be handled delicately. The copper is then gently washed with distilled water and the propanone and then the cathode is dried in the air, it is not rubbed. It is washed with the distilled water to remove the copper (11) sulphate solution and the propanone is used to rinse away the water, and because propanone is a volatile liquid it will quickly evaporate and form as gas. This will result in accurate measurement, as only the fresh copper will be left on the cathode and that is all that is being investigated. The cathode is then re-weighed and its mass is recorded and the amount of copper deposited at the cathode can then be calculated. This experiment should be carried out ten times. Each current 0.2A, 0.4A, 0.6A, 0.8A and 1.0A should be repeated once so the experiment gains in accuracy, so that if an anomalous result is acquired there will be another result to compare and confer to. Safe Test In the experiment propanone, copper sulphate and ammonia solution are used. It is therefore important that the dangers connected with these three substances are inquired about by referring to the hazcards in the chemistry laboratory. Propanone is extremely flammable, especially its vapour that will catch fire at temperatures above -20 c, its vapour also can cause dizziness and drowsiness. Also it is an irritant to the eyes and can degrease the skin. Copper sulphate is harmful if used internally, e.g. swallowed, and is irritating to both the eyes and the skin and is toxic to the aquatic environment. Ammonia solution can be corrosive if of a greater concentration than 6 moles. Ammonia of a concentration greater than 3 moles is an irritant and causes damage if used internally. The vapour is toxic. Solutions with a greater concentration than 14 moles are again, like copper sulphate, a danger to the aquatic environment. Ammonia solution is particularly dangerous when put in contact with chlorine, bromine, mercury, oxygen, silver and salts. Having paid attention to all these hazards the experiment may be carried out but safety glasses and a safety overall must be worn at all times. This is too ensure that if any solutions are spilt they will act as a barrier and prevent solutions getting in contact with your eyes and skin. The experiment should be carried out in the safe conditions of a laboratory, chairs should be tucked under tables, bags under desks and work should be put away. Also during the experiment all long hair should be tied up to avoid contact with the solutions. Fair Test In order for the experiment to be a fair test all variables that could be changed should be kept constant except the variable that is being investigated, and that is the current. So this means that the copper electrodes should have the same surface area, the electrolysis of the copper electrodes should always take place in 200 ml of copper (11) sulphate solution of the same concentration, the experiment should always be left out for the same amount of time, 20 minutes, and the experiments should be kept in equal temperatures. The experiment should be carried out in the uniform conditions of a laboratory and the same, accurate equipment should be used for each experiment, set up in exactly the same way each time. Also to ensure that the copper cathode is always pure the same cleaning method should be adopted each time. Accuracy To try and achieve very accurate results the cathode should be cleaned very thoroughly each time (to ensure the new copper will stick to the old copper), the ammeter should be carefully observed during the experiment so that if the current fluctuates it can be immediately put back using the variable resistor. Also the electronic balance should be carefully wiped between readings to ensure that copper (11) sulphate solution, water or any other substance is not left on the balance from previous readings as this will affect the reading. One must ensure that the cathode is properly dried before it is weighed so that we can obtain an accurate result. And finally one must make sure that the electrodes are exposed to the same amount of copper (11) sulphate solution so they must be immersed to the same depth and in an equal amount of copper (11) sulphate solution each time. Earlier Work A pilot experiment was carried out prior to the investigation to help practise setting up, carrying out and observing the experiment. A current of 0.3 amps was used. The same cleaning method was used as in the investigation and the cleaned cathode was weighed as a mass of 1.26g, and then connected to the negative terminal of the power pack. The anode was connected to the positive terminal. The copper cathode was immersed into at depth of 4 cm into the copper (11) sulphate solution, the power was switched on and the desired current set using the voltage and variable resistor. The experiment was left for twenty minutes and then carefully removed and cleaned using the same method as in the investigation. The cathode was then reweighed and a mass of 1.37g was recorded. Therefore it can be seen that a mass of 0.11g was deposited on the copper cathode when using a current of 0.3 amps. I then calculated the theoretical value, which was 0.12g (2dp), and this showed me that the experiment had been successful and therefore meant I was more prepared for my investigation. Also I had been given some secondary data to refer to which helped me in my planning. It helped me produce my qualitative prediction as the figures, when carefully observed showed how when the current increased so did the mass of copper deposited on the cathode, and that if you double the current you double the mass of copper deposited. Also the secondary data showed me that the current is directly proportional to the mass of copper deposited on the copper cathode. Bibliography: To help me in my planning the following sources were used: Chemistry class notes Chemistry for you (by Lawrie Ryan) Analysis From observing my results and graphs, the following pattern can be identified. On my results graph it can be seen that roughly if one doubles the current, the amount of copper deposited on the cathode will also be doubled, they are directionally proportional to one another as the line of best fit goes through the origin. In the experiment the following occurred. Using the current 0.2A, an average mass of 0.085g of copper was deposited on the cathode, which meant the cathode gained in mass. The copper ions gained electrons (reduction) and formed atoms and left the solution. At the anode copper atoms lost electrons (oxidation) and formed copper ions in solution. Hydrogen was prevented from forming at the cathode because copper is lower down in the reactivity series than hydrogen and so copper is less eager than hydrogen to exist as ions in the solution. Using the current 0.4A, an average mass of 0.17g of copper was deposited on the cathode which supports my prediction that the mass of copper would increase with the current and also that the mass of copper deposited on the copper cathode using the current 0.4A is double that deposited using 0.2A as the current, although these results are not identical to my theoretical values. The copper formed at the cathode for the same scientific reasons as previously stated. The mass of copper deposited at the cathode increased with the current because there were more electrons flowing around the circuit, due to the increase in current, so more copper atoms were lost at the anode and formed ions in solution and more copper ions were gained at the cathode and formed atoms. The results for the mass of copper deposited at the cathode using different currents increased with the size of the current, 0.6A caused an average mass of 0.24g of copper to be deposited on the copper cathode, 0.8A caused 0.29g and 1.0g caused 0.43g. Also for the same scientific reasons as stated when observing the result from the current 0.2A, copper forms at the cathode. From this we can draw the meaningful conclusion that the greater the current the greater the mass of copper deposited at the cathode. If one compares my prediction graph and my experimental results graph, they are extremely similar. In my prediction graph the mass of copper deposited at the cathode was directly proportional to the current because my line of best fit was a straight line that went though the origin. My experimental results formed a similar graph, as shown on the graph plotted showing both my theoretical values and my experimental results against one another. In fact when using the current 0.6A the average amount of copper deposited on the cathode was 0.24g, which is equal to my theoretical value. In contrast to this I also acquired some anomalous results, which means that with my graph of experimental results the straight line going though the origin is a line of best fit and does not go through all the points. This anomalous result was acquired when calculating the average gain in mass of the copper cathode using the current 0.8A. An average mass of 0.29g of copper was calculated. This inaccurate average was produced because the second experiment using 0.8A as the current provided a poor result, and this quite dramatically affected my average. Possible reasons for these anomalous results will be given in my evaluation. However having said this my quantitative prediction supports my results as my prediction graph and experimental results graph both have similar positive correlations and my qualitative prediction supports my conclusions drawn. Calculations It is important when producing my results to explain how they were acquired, using different calculations. The mass of copper deposited on the cathode was calculated by subtracting the mass of the copper cathode before the experiment from the mass of the copper cathode after the experiment and noting down the difference in mass to two decimal places. The average mass of copper deposited at the cathode was calculated by adding the mass of copper deposited at the current for the first experiment of each current to the mass of copper deposited at the cathode for the second experiment of each current. When these two figures had been added they were divided by two to calculate the average. Evaluation I was satisfied my experiment was reasonably successful. At the end I had acquired a set of results, which fitted my prediction quite well, not only the theoretical values but also the qualitative prediction. As I stated in my analysis one of my results was inconsistent with my prediction, it was an anomalous result. This was the 2nd result using the current 0.8A, where a mass of 0.26g was recorded as deposited on the cathode. The predicted amount of copper deposited on the cathode using the current was 0.32g, so as one can see there is quite a large difference between these two masses. Another result which was quite a long way from the predicted theoretical value and could be called anomalous was the 1st result using the current 1A, where a mass of 0.44g was deposited on the cathode. This second result did not appear an inconsistent result at first but when the average was calculated and plotted on the graph of experimental results, the result seemed to be quite a distance from the line of best fit, therefore leading me to believe it was a poor result. The anomalous results could have occurred for the following reasons. During the experiment the current seemed to be fluctuating quite frequently, especially when using higher currents and although most times the current was adjusted back to its previous amount using the ammeter as soon as possible, at times the experiment was left unattended for a minute or two and the current could have fluctuated then. Another reason for anomalous results is as follows. Towards the end of the experimental period I began to run out of time and because of this to save time and ensure I could finish all my experiments and therefore calculate the averages I began to replace only the cathode in between experiments, leaving the same anode and copper (11) sulphate solution to be used again. The repetition of using the same anode and copper (11) sulphate solution could have led to the anode becoming very thin and even falling apart and the copper (11) sulphate solution having excess amounts of copper floating around in it. This may well have had an affect on the amount of copper deposited on the cathode. The third reason for the anomalous result was that on one occasion the crocodile clip holder was knocked and fell into the solution and this may well have resulted in copper falling off the cathode, that had just been deposited on the cathode, which therefore results in a loss of mass of copper deposited at the end of the experiment. Also, when using high currents it?s important to realise that not all the ions stick to the cathode, some end up at the bottom of the solution. My method was a good way of carrying out the experiment as I achieved a good set of results and my method was easy and simple to carry out. I used accurate equipment such as an electronic balance, which gave reasonably accurate readings, a variable resistor which ensured a low and steady current and an analogue ammeter which meant I could easily read the current. I also did the experiment in the uniform conditions of a laboratory and kept all the variables the same during the experiment. However, there were certain errors and inaccuracies I encounterd and improvements I could make to my method. The first error was that the surface area of the copper electrodes used was not always the same which, as I have previously explained, affects the amount of copper deposited on the cathode. Also, I often found that some of the currents continually fluctuated (especially the higher currents), as I have said when talking about anomalous results. This will have caused an error as the size of the current flowing around the circuit will have been constantly changing and have caused disturbance to the experiment and thus the mass of copper deposited on the cathode. The experiment was inaccurate in the following ways. It was very difficult to know to what extent to clean the copper cathode, to ensure that the cathodes were in equal conditions in each experiment to allow new copper to stick to old copper. Also the electronic balance only gave masses to two decimal places, so the masses recorded may not have been as accurate as they could be. Another inaccuracy was that towards the end of the experiment the anode and copper sulphate solution were not changed between experiments (to save time) but after a few times the anode would become extremely thin and the copper(11) sulphate solution would become contaminated with flakes of copper floating around the solution, and this may have slightly affected the forming of copper atoms at the cathode. And finally another inaccuracy is that on one occasion, the crocodile clip holder slid into the solution, so the crocodile clip was exposed to the electrolyte. The following improvements could be made to limit the errors and inaccuracies in the method. Firstly identical sized copper electrodes should be used at all times. A power pack would not be shared, everyone would have their own so one can control the current fluctuating by changing the voltage to your experiment?s needs, and this may lower the fluctuation. Also it may be an improvement to use a digital ammeter rather than an analogue ammeter to ensure that the current is as desired, they are easier to read and more efficient. The analogue ammeter may well have been perfectly calibrated. Before each experiment each cathode should be carefully cleaned using the same technique each time and for the same amount of time. And finally the anode and copper (11) sulphate should preferably be changed every time, or every two experiments. After looking at the method and its errors it is then important to assess the reliability of my results in light of all the errors. Despite these errors I acquired a set of results that supported my prediction, particularly evident on the graph showing theoretical values and experimental results. Using the currents 0.2A, 0.4A, 0.6A, 0.8A and 1A, a wide set of results the average results of mass of copper deposited on the cathode were 0.085g, 0.17g, 0.24g,0.29g, 0.43g. The furthest these average results were from their theoretical values was 0.03g, which is not very much. This leads me to think my results were reliable. I am also led to think they are quite reliable because I took two sets of results and then calculated the average, so if an anomalous result was acquired, the other result would act as a second chance to try and get an accurate result. The results could have been improved in the following ways. Lower current values could have been used, and a wider range could have been used with smaller intervals because as the current increased it was more prone to fluctuation and with a higher current not all the ions stick to the cathode, some end up at the bottom of the electrolyte. Also I would do more repeats to obtain even more accurate results. As shown in my results when using the current 0.8A, the anomalous result heavily affected the average as there were only two readings. If there were more readings then poor results would not have such a heavy affect on the average and therefore more accurate results would be calculated. A Possible Extension A possible extension to the experiment could be to investigate how time affects the mass of copper deposited on the copper cathode during the electrolysis of copper (11) sulphate solution. As mentioned in my plan, time is one of the factors that affects the mass of copper deposited on the cathode, an experiment to investigate this factor could be as follows. The apparatus should be set up and used in the same way as when the current was being investigated only the amount of time the experiment is left should be changed each time, and the same current should be used for each experiment so all the variables are kept the same, except the variable being investigated, this makes the experiment fair. Therefore the method should be as follows. The copper cathode should be cleaned firstly using emery paper and then using ammonia solution, followed by distilled water. This is to remove layers of oxide and grease. The copper cathode should then be dried and weighed and placed in the electrolyte, and the power pack should be switched on. The current 0.2A should be used for every experiment, and ten experiments should be carried out. The experiments should be carried out using the times 10 minutes, 20 minutes, 30minutes, 40 minutes and 50 minutes, repeat each experiment once. When the copper cathode has been electrolysed for the designated amount of time it should then be removed from the electrolyte and washed with distilled water. The cathode should then be washed in propanone and air dried, not rubbed. The mass of the cathode should then be recorded using the electronic balance and I predict the results will be as follows. The longer the current flows the greater the mass of copper deposited at the cathode. This is predicted because the longer the time for the current to pass around the circuit, the greater the amount of time for the atoms to lose electrons (oxidation) become ions at the anode, and the greater the amount of time for the ions to gain electrons (reduction) and form atoms at the cathode. As we know from investigating current the mass of copper lost at the anode equals that gained at the cathode, so it can be said if you double the time you double the amount of copper deposited. Also I predict that the amount of copper deposited will be directly proportional to the time. It can be seem from this that I expect the greatest amount of copper deposited on the cathode to occur when using a time period of 50 minutes, and I expect the least amount of copper deposited on the cathode to occur when using a time period of 10 minutes.

The Factors that Affect the Mass of Copper 9.9 of 10 on the basis of 3402 Review.