Redox equations and titrations

Question 1

oxidising agent

Answer 1

an electron acceptor

Question 2

reducing agent

Answer 2

electron donor

Question 3

voltaic cell

Answer 3

a cell that converts chemical energy into electrical energy.

Question 4

simple half cells consist of , and what do they produce?

Answer 4

metals or non-metals in contact with their ions in aqueous solution, creating a small voltage if connected into a circuit, creating a voltaic cell.

Question 5

standard electrode potential

Answer 5

The e.m.f of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentrations of 1 mol dm^-3 and a gas pressure of 100kPa (1 atmosphere).

Question 6

what does e.m.f stand for?

Answer 6

the electromotive force (EMF) is the maximum potential difference between two electrodes of a voltaic cell

Question 7

why is an inert metal (Pt) electrode is used in a standard electrode. Why?

Answer 7

to allow electrons into and out of the half cell because there is no metal to transport electrons either into or out of the half cell.

Question 8

by definition the standard electrode potential of a standard hdyrogen electrode is what and why is it used as the standard ?

Answer 8

exactly 0v

- allows for use as a standard reference for when calculating other electrodes.

Question 9

what is the purpose of using two electrodes and a salt bridge when measuring a standard electrode potential?

Answer 9

two electrodes; allow a controlled flow of electrons

salt bridge; allows ions to flow

Question 10

give an example of a salt bridge ?

Answer 10

a strip of filter paper containing a concentrated solution of an electrolyte that does not react with either solution ,

dipped in aqueous KNO3

Question 11

distinguish between the anode and the cathode?

Answer 11

anode = - electrode 
cathode= +electrode.

Question 12

limitation of using E° value associated with reaction rate?

Answer 12

• electrode potentials indicated thermodynamic feasibility of a creation but not the rate of reaction
• when trying to predict feasibility, a reaction may require a large Ea and therefore has very slow rate this is not picked up by the voltmeter

Question 13

limitation of using E° value associated concentration?

Answer 13

increasing conc of reactants above 1 moldm^-3 would shift eq to the right, removing electrons from the anode, increase the emf and making electrode potential less negative. therefore affect the overall E° cell value. therefore all solutions need to be 1 moldm^-3

Question 14

what are the factors other than concentration and rate, that can limit the predictions for feasibility using E° values.

Answer 14

• actual conditions may be different from the standard conditions used to record the E° values.
• state; needs to be in an aqueous equilibria, many reactions that are not aqueous take place

Question 15

storage and fuel cells;

primary cells electrical energy without a reaction being in equilibrium why?

Answer 15

forward reaction is not reversible.

Question 16

What does a fuel cell do?

Answer 16

uses energy from the reaction of a fuel with oxygen to create a voltage.

Question 17

key features of a fuel cell?

Answer 17

• energy produced remains constant because of constant input of oxygen and hydrogen
• fuel cells do not have to be recharged.

Question 18

state two advantages of vehicles using fuel cells instead of combustion of conventional fossil fuels?

Answer 18

• less CO2/no CO2 produced in fuel cells

- greater efficiency

Question 19

what is an advantage of using methanol in hydrogen fuel cells rather than hydrogen?

Answer 19

methanol is liquid therefore easier to transport.

Question 20

define standard electrode potential ?

Answer 20

the potential difference of an electrochemical cell comprising of a half cell combined with a standard hydrogen electrode . conditions of 1atm , 1moldm^3 , 298k