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Electrode Potentials
AQA A Level Chemistry
| Question | Answer |
|---|---|
| Write the balanced redox half equation for the oxidation of iron(ii) to iron(iii) | Fe2+ ——> Fe3+ + e¯ |
| "Write the balanced redox half equation for the MnO4¯ being reduced to Mn2+ in acidic solution | " MnO4¯ + 5e¯ + 8H+ ———> Mn2+ + 4H2O |
| "Write the balanced redox half equation for Cr2O72- being reduced to Cr3+ in acidic solution | " Cr2O72- + 6e¯ + 14H+ ——> 2Cr3+ + 7H2O |
| "Fill in the gaps in this phrase: Each electrode / electrolyte combination has its own half-reaction which sets up a ---------- ---------- because different cells have a different tendency to donate or accept ---------. | " "Each electrode / electrolyte combination has its own half-reaction which sets up a potential difference because different cells have a different tendency to donate or accept electrons. |
| " On what variables does Electrode Potential depend? | "TEMPERATURE, PRESSURE OF ANY GASES, SOLUTION CONCENTRATION |
| " Define Standard Electrode Potential | "The definition of standard electrode potential E° of a half cell is the voltage of that half cell relative to a standard hydrogen electrode when all solutions have a concentration of 1 moldm-3 all gases are at 1 atmosphere and the temperature is 298K |
| " What is the Standard Electrode Potential of a standard hydrogen half cell defined as? | 0.00V |
| What is the purpose of a salt bridge between two half cells? | it completes the circuit by allowing the transfer of ions. |
| How does one make a salt bridge? | Soak filter papers in a saturated solution of potassium nitrate. |
| By convention how are all half equations written for each standard electrode potential? | All equations are written as reduction processes |
| If two half equations are combined how do you know what the overall reaction will be? | "A species with a higher E° value oxidise (reverses) one with a lower value |
| " Write an acronym to remember how to write a combination of cells in standard cell notation. | Reduced Oxidised Oxidised Reduced. ROOR |
| Write a formula to work out Ecell for a cell written in cell notation. | "Ecell= E°RHS-E°LHS |
| " Write a formula to work out Ecell for a redox reaction. | "Ecell= E° half equation for the Reduction reaction - E° half equation for the oxidation half equation. |
| " Write down the 7 rules for writing a cell in cell notation. | ROOR, Add State Symbols, Species in the same state in the same half cell are separated by a comma, Species in different states are separated by a solid vertical line, If there is not solid species in the half cell you must add a Platinum Electrode, If the |
| " Write the oxidation and reduction reactions occurring, and then write the overall reaction occurring in each cell for the Ag/Zn electrode pair. | "Zn(s) → Zn2+ (aq) + 2e- and Ag+(aq) + e- → Ag(s) so overall: Zn(s) + 2Ag+ (aq) → Zn2+ (aq) + 2Ag(s) |
| " Calculate the standard electrode potential of the Na+/Na electrode given that when it was joined to the standard hydrogen electrode, the cell emf was –2.71 volts. | -2.71 |
| Calculate the emf of a cell with the standard AgCl/Ag electrode (Eº = +0.22 V) as the left hand electrode and the Fe2+/Fe (Eº = –0.44 V) electrode as the right hand one. | emf = –0.44 – +0.22 = –0.66 V |
| Calculate Eºcell of the following cells using the Eº values from a data sheet: Ni2+/Ni Sn4+/Sn | 0.44 |
| Calculate Eºcell of the following cells using the Eº values from a data sheet: 2I-/I2, Ag+/Ag | 0.26 |
| "How can E° values be used to predict the feasibility of redox and cell reactions? | " "In theory ANY REDOX REACTION WITH A POSITIVE ECELL VALUE WILL WORK, A half equation with a more positive E° value reverse a less positive one |
| " Give two reasons why a redox reaction that is predicted to be feasible might not occur | Its activation energy might be too high, it might not be occurring under standard conditions. |
| How do the redox half equations that are set up in a rechargeable battery when the battery is being recharged compare to when it is being charged | They are reversed by an external current. |
| What are the pros and cons of non rechargeable batteries. | Pros cheap, small Cons waste issues due to very limited lifetime |
| What are the pros and cons of rechargeable batteries. | "pros: less waste, cheaper in long run, Cons time to recharge, still some waste issues because lifetime is still limited |
| " State three essential conditions in order for a cell to operate under standard conditions | "1 298K 2 All solutions 1moldm-3 3 All gases at 1 atmosphere pressure. |
| " What is the role of the platinum electrode in a standard hydrogen electrode | To provide a surface for electron transfer. |
| If the concentration of Zn2+ ions in an Zn2+/Zn half cell was halved how would this affect the electrode potential of the cell. Explain your answer. | Zn2+/Zn equilibrium moves left releasing more electrons so making Zn2+/Zn potential more negative |
| What is the EMF of the cell created from these two half cells Zn2+(aq) + 2e– ⇌ Zn(s) E° = –0.76 V, Fe3+(aq) + e– ⇌ Fe2+(aq) E° = +0.77 V | +1.53V |
| Write the cell created by these two half cells in standard cell notation Zn2+(aq) + 2e– ⇌ Zn(s) E° = –0.76 V, Fe3+(aq) + e– ⇌ Fe2+(aq) E° = +0.77 V | Zn(s) I Zn2+(aq) II Fe3+(aq), Fe2+(aq) I Pt(s) |
| "The Fe3+/Fe2+ half cell contained a mixture of iron(III) sulfate and iron(II) sulfate. Give the concentration of each reagent in the mixture for this to be done under standard conditions. | " "iron(III) sulfate 0.5 mol dm–3 Fe2(SO4)3 iron(II) sulfate 1.0 mol dm–3 FeSO4 |
| The electrode potential of the Zn2+/Zn half cell was measured against the standard hydrogen electrode (SHE). In this cell, the SHE was placed on the left, and an emf of –0.76 V was recorded. Write the standard cell notation for this cell. | " Pt(s) I H2(g) I H+(aq) II Zn2+(aq) I Zn(s) |
| "The electrode potential of the Zn2+/Zn half cell was measured against the standard hydrogen electrode (SHE). In this cell, the SHE was placed on the left, and an emf of –0.76 V was recorded. Calculate the standard electrode potential of the cell. | " -0.76V |
| "The electrode potential of the Zn2+/Zn half cell was measured against the standard hydrogen electrode, the SHE was placed on the left, and an emf of –0.76 V was recorded. Write a balanced equations for the reaction that takes place in this cell. | " Zn + 2H+ → Zn2+ + H2 |
| "Half cells for the following redox half equations were connected using a wire and salt bridge. Cu2+ + 2e– ⇌ Cu E° = +0.34 V Fe2+ + 2e– ⇌ Fe E° = –0.41 V Write the standard cell notation (cell representation) for this cell. | " Fe(s) I Fe2+(aq) II Cu2+(aq) I Cu(s) |
| "Half cells for the following redox half equations were connected using a wire and salt bridge. Cu2+ + 2e– ⇌ Cu E° = +0.34 V Fe2+ + 2e– ⇌ Fe E° = –0.41 V Calculate the emf of this cell | " 0.75V |
| Use a redox potential table to decide if the following reaction is feasible 3Ca2+ (aq) + 2Al (s) --> 3Ca(s) + 2Al3+ (aq) | Yes E cell = 1.38V |
| Use a redox potential table to decide if the following reaction is feasible 2Na+ (aq) + Mg (s) --> 2Na(s) + 2Mg2+ (aq) | No. Ecell = -0.34V |
| Use a redox potential table to decide if the following reaction is feasible 2Br-(aq) + Cl 2(g) --> Br 2(l) + 2Cl- (aq) | Yes E cell = 0.29V |
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davenantchemistry
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