Experiment- Galvanic Cells PDF

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A scientific report on galvanic cells. (Production of Materials)....

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Erica Howell- 2017

EXPERIMENT: GALVANIC CELLS Aim: To investigate and measure the differences in voltage when different combinations of metals are used in constructing a galvanic cell Hypothesis: Two metals which are further apart in the activity series will be more reactive than two metals close together in the activity series Equipment: • 2x 100mL beakers (2 per group) • Watch glass and pipette • Tweezers • Digital multimeter • Sandpaper • Strips of: zinc; copper; iron; lead; nickel • Strips of filter paper (10cm by 1cm)

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0.1 mol/L zinc nitrate (Zn(NO3)2) 0.1 mol/L copper nitrate (Cu(NO3)2) 0.1 mol/L lead nitrate (Pb(NO 3)2) 0.1 mol/L iron (II) sulfate (FeSO4) 0.1 nickel nitrate (Ni(SO 4)2) saturated potassium nitrate (KNO3) solution

Diagram:

Method: 1. The class was split into 10 groups and each group was assigned one metal combination 2. The metal strips were cleaned with sandpaper or steel wool 3. The filter paper was placed on a watch glass and a pipette was used to soak the potassium nitrate into the filter paper 4. The equipment was set up as per the diagram ensuring the metals did not touch the salt bridge (filter paper) and the filter paper ends were in each of the solutions 5. The multimeter was used to measure the magnitude of voltage produced and it was recorded in a table, noting the anode and cathode 6. Step 5 was repeated 3 times with a new filter paper 7. Each group repeated steps 2-6 with each of the metal combinations

Erica Howell- 2017 Safety: Hazard Zinc nitrate (Zn(NO 3)2)

Risk of Injury - Harmful if swallowed - Causes skin and eye irritation - May cause respiratory irritation

Copper nitrate (Cu(NO3)2)

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Lead nitrate (Pb(NO3)2)

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Iron (II) sulfate (FeSO 4)

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Nickel nitrate (Ni(SO4)2

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Saturated potassium nitrate (KNO 3) solution

Results: Raw Data Metals Tested

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Prevention/Treatment - Wear safety goggles - Wash hands if contact with skin - Open ventilation Harmful if swallowed. - Wear safety goggles Irritating to eyes and skin - Wash hands if contact with skin May be harmful in contact with skin. - Wear safety goggles Harmful if swallowed. Ingestion - Wash hands if contact with may cause gastrointestinal irritation, skin nausea, vomiting and diarrhoea. - Dispose of waste responsibly Harmful if swallowed. - Wear safety goggles Irritating to eyes and skin - Wash hands if contact with skin Very hazardous if ingested, or - Wear safety goggles inhaled. - Wash hands if contact with Causes skin and eye irritation skin Harmful if swallowed - Wear safety goggles Causes skin and eye irritation - Wash hands if contact with skin

Beaker 1/Beaker 2

Experimental Voltage (V) Trials 2 3 Average 1.07 1.07 1.07 1.07 0.0014 0.0086 0.12 0.04 0.59 0.57 0.58 0.58 0.22 0.22 0.23 0.22 0.57 0.57 0.57 0.57 0.26 0.26 0.28 0.27 0.11 0.18 0.17 0.15 0.21 0.24 0.25 0.23 0.2 0.13 0.12 0.15 0.46 0.47 0.46 0.46 1

Zinc/Copper Zinc/Iron Zinc/Nickel Zinc/Lead Iron/Copper Iron/Nickel Iron/Lead Lead/Nickel Nickel/Copper Copper/Lead

Zn|Zn2+ ||Cu|Cu2+ Zn|Zn2+ ||Fe|Fe2+ Zn|Zn2+ || Ni|Ni2+ Zn|Zn2+ ||Pb|Pb2+ Fe|Fe2+ ||Cu|Cu2+ Fe|Fe2+ || Ni|Ni2+ Fe|Fe2+ ||Pb|Pb2+ Pb|Pb2+||Ni|Ni2+ Ni|Ni2+ ||Cu|Cu2+ Cu|Cu2+||Pb|Pb2+

Calculating Eo Potentials Metal Anode Reaction Zinc/Copper Zn(s) → Zn2+(aq) + 2eZinc/Iron Zn(s) → Zn2+(aq) + 2eZinc/Nickel Zn(s) → Zn2+(aq) + 2eZinc/Lead Zn(s) → Zn2+(aq) + 2eIron/Copper Fe(s) → Fe2+(aq) + 2eIron/Nickel Fe(s) → Fe2+(aq) + 2eIron/Lead Fe(s) → Fe2+(aq) + 2eLead/Nickel Ni(s) → Ni2+(aq) + 2eNickel/Copper Cu(s) → Cu2+(aq) + 2eCopper/Lead Cu(s) → Cu2+(aq) + 2e-

Cathode Reaction Cu2+(aq) + 2e- → Cu(s) Fe 2+(aq) + 2e- → Fe(s) Ni2+(aq) + 2e- → Ni(s) Pb2+(aq) + 2e- → Pb(s) Cu2+(aq) + 2e- → Cu(s) Ni2+(aq) + 2e- → Ni(s) Pb2+(aq) + 2e- → Pb(s) Pb2+(aq) + 2e- → Pb(s) Ni2+(aq) + 2e- → Ni(s) Pb2+(aq) + 2e- → Pb(s)

E0 Potential 1.10 0.32 0.52 0.63 0.78 0.2 0.31 0.11 0.58 0.47

Erica Howell- 2017 Results Analysis: Beaker 1/Beaker 2 Zn|Zn2+ ||Cu|Cu2+ Zn|Zn2+ ||Fe|Fe2+ Zn|Zn2+ || Ni|Ni2+ Zn|Zn2+ ||Pb|Pb2+ Fe|Fe2+ ||Cu|Cu2+ Fe|Fe2+ || Ni|Ni2+ Fe|Fe2+ ||Pb|Pb2+ Pb|Pb2+||Ni|Ni2+ Ni|Ni2+ ||Cu|Cu2+ Cu|Cu2+||Pb|Pb2+

Experimental Voltage (V) 1.07 0.43 0.58 0.22 0.57 0.27 0.15 0.23 0.15 0.46

Expected Voltage (V) 1.10 0.32 0.52 0.63 0.78 0.20 0.31 0.11 0.58 0.47

Experimental Percentage Error 2.7% 34.4% 11.5% 65.1% 26.9% 35.0% 51.6% 109.1% 74.1% 2.12%

Discussion: Errors: Some data collected does not reflect secondary data collected, being as high as 109.1% experimental percentage error. This may have been caused by inexperience, a faulty multimeter or residual oxide left on the metal which may have obstructed the reaction Accuracy: The accuracy of the experiment was improved by using a digital multimeter correct to 2 decimal places rather than a conventional voltmeter. Other variables had no need to be very accurate, hence, the reason why 30mL of solution was measured using a beaker, rather than a pipette. Reliability: Each experiment was repeated 3 times to ensure reliability. The data was also compared to secondary data, which proved some of the results to be reliable. To improve reliability, more trails are needed and by separate people to ensure the method followed was exactly the one written. Validity: The experiment contained only 1 independent variable, type of metal, and measured one dependant variable, the voltage produced. The same beaker size and molarity was kept consistent through all the trials, to ensure a valid result. Other variables, for example amount of solution, was kept consistent by measuring to a 30mL line, which was not as important to keep exactly the same (to the mL). This would classify the experiment as a fair test. Safety: Goggles were worn by each member of every group, hair was tied back and black leather shoes were worn by each individual. To improve safety, opening windows would be recommended for ventilation as many chemicals are being used. Results: How to Calculate E0 Values Example: Zinc/Copper 1. Write down the reactions at the cathode and anode Cathode: Cu2+(aq) + 2e- → Cu(s) Anode: Zn(s) → Zn2+(aq) + 2e2. Recognise which reactions are reductions and which are oxidations This can be remembered by “Red Cat” for reduction reaction at cathode and “An Ox” for the oxidation reaction at the anode. 3. Use the standard potentials table and identify the corresponding reactions Zinc: Zn2+(aq) + 2e- → Zn(s) = -0.76V Copper: Cu2+(aq) + 2e- → Cu(s) = 0.34V 4. Flip the sign of the oxidation reaction to reverse it Zn(s) → Zn2+(aq) + 2e- = 0.76V 5. Add the potentials together E0 = Eoxidation + Ereduction E0 = 0.76 + 0.34 E0 = 1.1V

Erica Howell- 2017 The results found that the further apart the metals were in the activity series of metals, the amount of voltage produced was higher. This is supported by secondary data from textbooks. The Eo values were calculated for each cell and the values obtained were not the same. The majority of the results were found to be lower than expected. This may have occurred as standard conditions for potentials were not followed, opting for a 0.1mol/L solution instead of a 1mol/L solution. Many results were much higher than expected. This may be due to faulty multimeters. To minimise this risk, the measurement should be taken with more than one multimeter to ensure the result is accurate Theory: This experiment shows a galvanic cell. In a galvanic cell, redox reactions occur; an oxidation reaction at the anode and a reduction reaction at the cathode. The more reactive metal becomes the reducing agent, undergoing oxidation itself and causing reduction at the cathode. The flow of electrons goes from the anode to the cathode and back through the salt bridge to create a circuit. A salt bridge is necessary to create the circuit as the cations and anions are separated from each other and allow a flow of electrons. Society: The galvanic cells lead to the development of the modern dry cell battery, that is, Leclanché dry cell and button batteries. These batteries have made many portable devices possible, e.g. cell phone, flashlight, radio, and helped improve medicine, e.g. pacemakers. Conclusion: The further apart two metals are in the activity series, the higher will produce a higher voltage than metals close together. This supports the hypothesis. Bibliography: - https://chem.libretexts.org/Core/Analytical_Chemistry/Electrochemistry/Case_Studies/Commerci al_Galvanic_Cells...