Flashcards
Electochem & redox equilibrium
Cards in this deck (51)
- 1Define the term oxidation numberThe combining power of an atom, element or compound.
- 2Define oxidation and reduction in terms of oxidation number•When the oxidation number is more positive, it is oxidation.
•When the reduction number is less positive, it is reduction. - 3What is redox equilibrium?•A balanced position where the oxidant is reduced by accepting electrons and the reductant is oxidized by losing electrons.
•The oxidation and reduction occurs under the same conditions
•The rates of oxidation and reduction are equal to each other. - 4How can redox equilibrium be achieved in a simple laboratory experiment?•By immersing a salt in an aqueous solution of its salt.
- 5What is an electrode potential?•The power of potential of an aqueous species to oxidize or reduce.
- 6What is a another name given to electrode potential?•Reduction potential
- 7How is an electrode potential formed when a metal is immersed in an aqueous solution?•The metal ion loses electrons.
•Electrons will form a layer of electrons on the surface of the metal.
•Metal cations surround the electrons forming an electric double layer.
•The double layer results in an electric potential on the surface of the metal. - 8State the factors which affect electrode potential•The nature of the metal.
•Temperature.
•Concentration & pressure. - 9Explain how the nature of a metal affects the electrode potential•More reactive metal ionize faster compared to less reactive metals.
•As the ionization increases, electrode potential increases as well. - 10Explain how temperature affects the electrode potential•Depending if the reaction is exothermic or endothermic
•the change in temperature will affect the electrode potential accordingly. - 11Explain how concentration and pressure affect the electrode potential•Increased concentration or pressure will decrease the ionization of the metal to metal ions.
•Therefore, the electrode potential will decrease with increased concentration and pressure. - 12In terms of equilibrium, explain the effects of increased concentration•Conc of left side species increases, equilibrium shifts to right
•consequently, the electrode potential will increase. - 13Therefore, explain the effects of conc of right side species?•equilibrium shifts to the left.
•consequently, the electrode potential will decrease. - 14How can electrode potential be measured?•At constant pressure, temp and concentration, the only factor which affects the electrode potential will be the nature of the metal.
- 15Why cant the electrode potential of a single electrode be measured?•There is no instrument available to measure the electric potential of a single electrode.
•However, there are instruments to measure the potential difference. - 16Outline the details of the experiment to show evidence of electric potential when a metal is dipped in a solution of its salt.•Two metals of different reactivity are connected to a voltmeter and a salt bridge.
•The metals are immersed in aqueous solutions of their salts. - 17Why is it important that the voltmeter has high resistance?•To ensure that the voltmeter itself draws up very little current.
•Consequently, the voltage which is measured doesnt drop. - 18What are the two reasons on as to why we use a salt bridge?1) It allows the movement of ions from one cell to another by completing the circuit.
2) It also provides cations and anions to replace those consumed at the electrodes and so it will balances the charges. - 19What are the names given to the terminals of oxidation and reduction?•Oxidation - Anode
•Reduction - Cathode - 20What is another name given to salt bridge?•Solution junction
- 21What is the salt bridge composed of?•A filter paper dipped in a salt of KNO3.
- 22Why do we say that electrolysis is opposite to that of the electrical cell?•Electrolysis uses chemical energy to be transferred to electrical energy
•An electrical cell transfers electrical energy to chemical energy. - 23Define the term electromotive force (e.m.f.)•The maximum potential difference produced by an electrical cell.
•It is given with respect to metals. - 24What can be visibly seen at the anode and cathode?•At the anode, the electrode erodes.
•At the cathode, a deposit forms at the electrode. - 25What is the standard hydrogen electrode? (S.H.E.)•It is 0.00V
- 26Why is the S.H.E. important?•It is impossible to measure the electrode potential of a single cell.
•However, the electrode potential can be measured with respect to another element.
•This element is Hydrogen. - 27Why do we use a Pt electrode in S.H.E?•Pt does not ionize itself. Therefore, it acts as an inert metal connection to the H2.
•Pt allows H2 gas to be absorbed on its surfance.
•Increases the surface area - 28What is the importance of increasing the surface area for the Pt electrode?•The equilibrium between H2 and H+ can be established faster.
- 29Define the term standard electrode potential or standard electrode potential•The emf of an electrode measured with respect to SHE.
•The concentrations of all solutions are 1M.
•Pressure of all gases are atm.
•Temperature is 298K. - 30How can the standard electrode potential be measured?•Immersing the metal in its metal ions and connecting it to an SHE using a salt bridge.
•A voltmeter is used to measure the pd which arises due to the movement of ions. - 31What are the three main types of half cells used in the calculation of standard electrode potentials?•metal - metal ion (MMI)
•non metal - non metal (NMNM)
•ion - ion (II) - 32What do we use an Ion - Ion half cell?•When the half cell consists of ions of the same element in different oxidation states.
- 33When do we use a Pt electrode?•Non metal - non metal ion half cell.
•Ion - Ion half cell. - 34What is the difference between the Pt electrode in the Non metal - non metal ion half cell and an ion - ion half cell?•In the non metal - non metal ion half cell, the electrode is partially immersed.
•In the ion - ion half cell. the electrode is fully immersed. - 35Why is the electrode partially immersed in the non metal non metal ion half cell but not in the ion ion half cell?•In the non metal non metal ion half cell, we use a gas that needs to establish redox equilibrium.
•Redox equilibrium is achieved at the surface of the electrode.
•In the ion ion half cell, we do not use a gas, - 36What can standard electrode potentials be used for?•They give a direct measure of the relative oxidizing and reducing power of species.
- 37What occurs to the metal with the small reduction potential?•Smallest is oxidized.
•Therefore, the smallest reduction potential acts as the reducing ahent. - 38What occurs to the metal with the largest reduction potential?•It is reduced.
•Therefore, it acts as an oxidizing agent. - 39What are the three breath analysers used?•Dichromate (VI)
•Fuel cell
•Infrared - 40How does a Dichromate (VI) breath analyzer work?•The suspect breathes into a tube containing K2Cr2O7.
•Ethanol in the breath is oxidized to ethanoic acid. - 41What will be the observation in a Dichromate(VI) breath analyzer?•A colour change from orange to green.
•This is due to the formation Cr3+ ions. - 42How can the amount of alcohol be measured using a Dichromate (VI) breath analyzer?•The extent of greening OR extent of electrical current shows on the ammter
- 43What are the disadvantages of the Dichromate(VI) breath analyzer?]•The breath analyzer cant be reused since Cr3+ cant be converted back.
•The method is inaccurate. - 44How does a fuel cell breath analyzer work?•A Pt catalyst (anode) is used to oxidize the alcohol to ethanoic acid.
•At the cathode, oxygen is reduced.
•H ions and electrons are produced.
•The external circuit measures the amount of electricity produced. - 45What is the relationship between the quantity of electricity produced and the amount of ethanol in the breath?•They are directly proportional.
- 46Why can't a fuel cell breath analyzer be used in courts?•This method contains many errors.
- 47How does an Infrared breath analyzer work?•IR Radiation is passed through the exhaled air.
•The wavelengths of certain bands will be absorbed.
•The IR absorptions in the fingerprint region of ethanol is measured - 48What are the bands which will be absorbed?•C-O
•O-H
•C-H
•C-C - 49How can the concentration of ethanol be measured?•Using a microprocessor and the fingerprint region of ethanol.
- 50What are the advantages and disadvantages of a infrared breath analyzer?•Gives very accurate results
•Not portable.
•The peak height does not depend on the concentration of ethanol. - 51—
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- A-Level Chemistry Flashcards on Electochem & redox equilibrium, created by Jio Jenassi on 12/02/2016.
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