Flashcards
Electrode potentials and cells
Cards in this deck (22)
- 1What is a half cell? What is a cell?When a metal is dipped into a solution containing its simple ions. An equilibrium is established between the metal ions and metal atoms.
2 half cells joined together - 2What can a salt bridge be of? What does a salt bridge contain to complete the circuit? Why is this particular compound used?1) Piece of filter paper soaked in solution of KCl or KNO3
2) KCl dissolved in agar gel and set in a U-tube
-Mobile ions
-This ensures no precipitation as chlorides/nitrates are usually soluble - 3What is the positive/negative electrode?Positive- where reduction occurs (cathode)
Negative- where oxidation occurs (anode)
*NEGATOX -NEGATive electrode is where OXidation occurs - 4Describe the movement of electrons in this cell1) Zinc atoms lose electrons and the electrons flow from the zinc metal externally in the circuit to the copper side
2) Copper ions in the solution gain electrons to form copper.
3) Copper forms on the copper electrode and increases the mass. Some of the zinc metal forms zinc ions and this decreases the mass of the zinc chloride
- 5What is used to measure potential difference across a (complete) cell?A high-resistance voltmeter that is connected in the external circuit. It maintains the concentration of the ions in solution by not allowing any current to flow.
The value shows the difference between the electrode on the left and the right. - 6What is used to measure the p.d. across a single half cell? What does it consist of? Conditions?The standard hydrogen electrode.
An electrode consisting of hydrogen gas in contact with hydrogen ions, H+ on a porous platinum surface (good conductor of electricity/inert + larger SA)
Ion concentration of 1.00 mol dm-3, gases under 100kPa pressure and whole cell is at 298K - 7How is the standard electrode potential measured?A cell is formed between a standard hydrogen electrode and another metal electrode.
When the standard hydrogen electrode is used, it must be the negative electrode (oxidation occurs- hydrogen gas to hydrogen ions).
This means a reduction occurs on the other half cell and the value is given for the reduction reaction. - 8Define standard electrode potentialThe electrode potential of a standard electrode with ion concentration of 1.00 mol dm-3 at 298K connected to a standard hydrogen electode (1.00 mol dm-3 H+ ions, 100kPa H2 gas at 298K) using a high-resistance voltmeter and a salt bridge
- 9Diagram of apparatus used to measure standard electrode potential
- 10Which electrode goes on the left/right?Left- oxidation/negative electrode (anode)
Right- reduction/positive (cathode)
The more negative electrode potential is on the LHS (oxidation) of the cell - 11What is electromotive force (EMF)? Calculation?The overall voltage measures on a cell.
EMF= right/positive - left/negative - 12What does the electrode potential show about feasibility? What does the EMF show about feasibility?The more positive the electrode potential, the more feasible the reduction reaction.
If the EMF is positive, the redox reaction is feasible - 13What can electrochemical cells be used for commercially? What does the EMF show?As a commercial source of electrical energy AKA cells/batteries
The EMF is the voltage of the cell/battery - 14Difference between primary and secondary cells?Primary= single use/disposable. The materials cannot be regenerated by recharging.
Secondary= rechargeable and original reactions in the cell can be regenerated. - 15Example of non-rechargeable cells Examples of rechargeable cellsAlkaline batteries
Dry cells
Nickel-cadmium cell
Lithium ion cell - 16Advantages of rechargeable cells-Can be reused
-Prevent waste
-Supplies of metal/reagents is not depleted as quickly
-Less energy used to extract metals - 17What can lithium ion cells be used for? How can they be dangerous?Used to provide electrical energy for cameras, laptops etc.
-Unstable at high temp
-Can ignite laptops/phones
-Li is very reactive (take care when recycling) - 18Reactions at: cathode anode overall? Cell notation?Li+ + CoO2 + e- --> Li+[CoO2]-
Li --> Li+ + e-
Li + CoO2 --> Li+[CoO2]-
Li|Li+||Li+, CoO2|LiCoO2|Pt - 19Define fuel cell examples?An electrical cell which converts the chemical energy of a redox reaction into electrical energy. The cell continues to function while fuel and oxygen are present. They do not need to be recharged.
Hydrogen/ethanol - 20How does it work?-Oxidation occurs at the anode and electrons released travel through a wire and into the external circuit
-Central electrolyte allows ions and molecules to move through it but not electrons.
-Ions react with another substance (reduction reaction)
-Oxidation/reduction reactions both catalysed. - 21Reactions for acidic hydrogen fuel cells at: cathode anode overall cell notationO2 (g) + 4H+ (aq) + 4e- --> 2H2O (l)
H2 (g) --> 2H+ (aq) + 2e-
2H2 (g) + O2 (g) --> 2H2O (l)
Pt|H2 (g)|H+ (g)||O2 (g)|H+ (aq), H2O (l)|Pt - 22Reactions for alkaline hydrogen fuel cells at: cathode anode overall cell notationO2 (g) + 2H2O (l) + 4e- --> 4OH- (aq)
H2 (g) + 2OH- (aq) --> 2H2O (l) + 2e-
2H2 (g) + O2 (g) --> 2H2O (l)
Pt|H2 (g)|OH- (aq), H2O (l)||O2 (g)|H2O (l),OH- (aq)|Pt
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- A2 Chemistry (Electrode potentials and cells) Flashcards on Electrode potentials and cells, created by Dolu Falowo on 30/12/2016.
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- Dolu Falowo
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