6543227
Description
Flashcards by Lesego Mabe, updated more than 1 year ago
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Created by Lesego Mabe
over 7 years ago
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| Question | Answer |
| Standard Hydrogen Electrode (Reference cell) | |
| What is the Standard Hydrogen Electrode (SHE) (Reference cell)? | The electrode (half-cell) to which every other electrode is compared. |
| Explain the role of the SHE as the "reference cell" | The electrode potential of the SHE is 0V and is used as a reference cell to determine the electrode potential of another electrode. |
| Explain the convention of the SHE and where oxidation and reduction takes place. | !) POSITIVE voltmeter reading: electrons flow from H-electrode (anode) the other electrode (cathode) 2) NEGATIVE voltmeter reading: electrons flow from the other electrode (cathode) to the H-electrode (anode) |
| The cell notation of the SHE. | 1) At ANODE: Pt | H2(g) | H+(aq) 2) At CATHODE: H+(aq) | H2(g) | Pt |
| Standard conditions to determine standard electrodes | 1) Concentrations of electrolyte solutions = 1 mol.dm3 2) Temperature of solutions = 25 degrees Celsius (298K) |
| How to write a cell notation (basic template) | - anode | anode electrolyte || cathode electrolyte | cathode + FOR Pt and C ELECTRODES: Pt | anode | anode electrolyte || cathode electrolyte | cathode | Pt |
| How can the standard electrode potentials be determined using the reference cell? | Another electrode (half cell A) is connected to a voltmeter in an external circuit with the reference cell (0v) and a salt bridge. The reading on the voltmeter will be the reading of the half cell A. |
| Use Table 5 to calculate the emf of a standard galvanic cell (E ) | E |
| What does the positive value of the standard emf indicate? | The reaction is spontaneous ∴ it is a GALVANIC cell |
| What is a GALVANIC cell? | |
| Describe the GALVANIC cell. | !) Spontaneous redox reaction to produce electrical energy (from chemical energy) 2) TOP (anode) to BOTTOM (cathode) on TABLE 5 3) ANODE is the NEGATIVE terminal 4) Salt bridge is present 5) POSITIVE standard emf 6) Used in torches and car batteries |
| Write the equations of the half-cells where reduction and oxidation take place, i.e. taking place at the anode/cathode (basic - how to); from TABLE 5 | OXIDATION-half reaction: anode (reducing agent) → anode electrolyte + no. electrons REDUCTION-half reaction: cathode electrolyte + no. electrons → cathode (oxidising agent) |
| Predicting the half-cell, half reaction in which oxidation/reduction take place | 1) Remember oxidation takes place at the anode; connected to the NEGATIVE terminal in a GALVANIC cell and reduction takes place at the cathode 2) Remember the convention regarding positive and negative values |
| Deducing the overall ionic cell equation | !) Find LCM of the oxidation-half and reduction-half reaction 2) Add (or subtract) the two half reactions: REMEMBER: anode (reducing agent) and cathode (oxidising agent) are always on the outside of the equation; the electrolytes are always on the inside of the equation |
| Identifying the reducing and oxidising agents for a redox reaction | 1) REDUCING agents: neutral metals & negatively charged non-metallic anions; on the RIGHT of equation (table) 2) OXIDISING agents: neutral non-metals & positively charged metal cations; on the LEFT of equation (table) |
| PERIODIC TABLE | |
| Purpose of salt bridge | 1) To complete the circuit 2) To maintain electric neutrality between the two 1/2-cell electrolytes |
| Equation of the GALVANIC cell | Zn(s) + Cu (aq) → Zn (aq) + Cu(s) Cell potential = +1,1 V (under standard conditions) |
| Effect of concentrations on the equilibrium of the GALVANIC cell in terms of Le Chatelier's principle | *Refer to equation of the cell* 1) INCREASED [reactants]: forward reaction favoured; cell potential increases 2) INCREASED [products]: reverse reaction favoured; cell potential decreases |
| How GALVANIC cell reaches equilibrium | START: [reactants] high and cell potential is at max DURING: [reactants] decrease, [products] increase, cell potential decrease AT EQUILIBRIUM: Cell potential = 0V |
| State the capacity of the Galvanic cell's equilibrium | It has the capacity to deliver current until the reaction reaches equilibrium or has run to completion |
| Explain, according to Le Chatelier's principle, how to cell potential reaches 0V. | Switch is closed. 1) [Cu-electrolyte] (reactant) high ∴ → reaction very fast and [Zn-electrolyte] (product} low ∴ ← reaction very slow 2) → reaction rate > ← reaction rate ∴ [Zn-electrolyte] gradually increases while [Cu-electrolyte] gradually decreases ∴ → reaction rate gradually decreases and ← reaction rate gradually increases 3) rates of reactions become equal, dynamic equilibrium is reached and the tendencies of the electrons to move from the left to the right and the right to the left are equal |
| What increases the cell's capacity to deliver current but does not affect the emf of the cell? | 1) An increased surface area increases the rate of the reaction 2) A wider, shorter and more conductive salt bridge lowers the internal resistance |
| Describe the movement of charges in an GALVANIC cell | Through the wire (external circuit) from the reducing agent (anode) to the oxidising agent (cathode) |
| Describe the movement of ions in a GALVANIC cell | Through the salt bridge (internal circuit). Positive ions move to the cathode half-cell and negative ions move to the anode half-cell. |
| Explain how electric neutrality is maintained. | 1) The neutral ZnSO4 solution becomes positively charged when Zn cations leave the surface of the Zn-electrode (Zn cations > SO4 anions) 2) The neutral CuSO4 solution becomes negatively charged when Cu cations leave the solution (SO4 anions > Cu cations) 3) Some of the Zn cations are attracted, through the salt bridge, to the CuSO4 solution and it is neutralised 4) Some of the SO4 anions are attracted, through the salt bridge, to the ZnSo4 solution and it is neutralised |
| Describe the electron flow in the external circuit of the GALVANIC cell (e.g. the zinc copper cell) | From the anode to the cathode (e.g. from the Zinc-anode to the Copper-cathode) |
| Describe the half reaction at the Zinc half cell (GALVANIC cell) | The Zn-atoms are released (oxidised) and enter into the solution ∴ the Zn-electrode is the anode since this is where oxidation happens. The solution becomes positively charged |
| Describe the half reaction at the Copper half cell (GALVANIC cell) | The electrons move from the Zn-electrode to the Cu-cathode because this where reduction happens: Cu-cations absorb Zn-anions and Cu-atoms move onto surface. Blue solution turns colourless. (RED CAT GETS FAT) |
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