redox and electrode potentials

Question 1

whats special about an ion/ion half cell? eg: fe (3+) + e- —> fe ( 2+ )

Answer 1

the electrode used is a INTERT PLATINUM electrode ! since there is no metal present to transport electrons in or out of the cell AND the solution is made of 1 moldm3 of FE (3+) AND 1 moldm3 of FE(2+)

Question 2

how would you work out the sign of an electrode ?

Answer 2

look at whether its the more postive or more negative electrode in the system : if its the more positie electrode, eg ( -0.25> -0.7), then its the POSITIVE ELCTRODE LARGER CHARGE ELECTRODE= POSITIVE SMALLER CHARGE ELECTRODE= NEGATIVE (this was from the nickel question) (when taking away more negative terminal from more positive terminal, you have already identified negative and positvie electrodes; the more negative one is negative and the more positive one is positive )

Question 3

in cell A , the nickel electrode lost mass. in cell B, the nickel electrode gained mass . in both cells, the measured potential slowly changed explain observations AND INCLUDE EQUATIONS (3) NOTE: READ THE GODDAMN QUESTION CAREFULLY SO YOU KNOW WHERE TO GET THE MARKS. i didnt read this question properly so i didnt include any equations when the two marks *were* for the equations and one was for the explanation

Answer 3

1. include the equations cell A–> ni + 2fe(3+) -ni(2+) + 2fe(3+) (1 mark) cell B– 2cr + 3Ni (2+) –>> 2cr (3+) + 3Ni (1 mark) ( as you can see 2 marks have been gained for each equation) concentrations of ions in each cell change ( 1 mark) MARK SCHEME SAYS: “ allow any statement that concentration is changing”

Question 4

What are some alternatives other than absorption ( absorbing hydrogen as metal hydride using a nickel metal hydride cell) for storing hydrogen for use in fuel as cars ? (1)

Answer 4

ADSORPTION on to solid ( 1) OR store as liquid under pressure !

Question 5

if a question asks you to draw a diagram to measure STANDARD ELECTRODE POTENTIAL OF A half CELL, what do you draw ?

Answer 5

if its an ion/ion half cell, draw the ion/ion half cell with platinum electrode connected to a h2/H+ half cell with platinum electrode aswell if its an ion/metal half cell, draw the ion/metal half cell with a metal electrode of the ionic solution connected to the a h2/H+ half cell with a platinum electrode NOTE; make sure to put hydrogen gas coming through the tube and HCL solution as the ionic solution in hydrogen electrode

Question 6

what is an important efautre you have to label on an e electrochemical cell diagram ?

Answer 6

that the solutions are 1 MOL/DM3 !!!!!!!!!!!!!!! ( if its ion/ ion half cell, make sure to show TWO ionic solutions at 1 moldm3) !

Question 7

what are standard conditions?

Answer 7

1 moldm-3 .298 K .100 KPA

Question 8

what are the causes of reactions not seeming to take place in electrochemical cells ? (2)

Answer 8

mark scheme answer: slow rate/high activation energy (1) AND concentrations NOT 1 moldm-3 (1) textbook explanation : even though a reaction might have a negative (delta G) , the activation energy may be very large causing very slow rate

Question 9

what to do before finding the missing half cell equation ?

Answer 9

you BALANCE the first equation out so that it matches what you see in the overall equation eg if the first equation has “O2” and the overall has “3/2 O2” , THEN MULTIPLY THE FIRST EQUATION BY “3/2”

Question 10

What are the advantages of using fuel cells rather than combustion of fossi fuels ?

Answer 10

fuel cells use less CO2/ greenhouse gases (1) AND are more efficient (1)

Question 11

advantages of using methanol rather than hydrogen fuel cells ? (2)

Answer 11

can be stored as liquid (1) thus easier to store and transport (1)

Question 12

how would you find the equation recharging a cell ?

Answer 12

reverse the overall equation for charging it or reverse both half equations involved in charging and then add them up!

Question 13

fuel cells are a type of electrochemical cell being developed as a potential source of energy in the future, state one important difference between fuel cell and conventional electrochemcial cell. write equation for overall reaction that takes place in a hydrogen fuel cell. state two ways that hydrogen might be stored as fuel for cars. suggest why some people consider that the use of hydrogen as a fuel for cars consumes more energy that using fossil fuels

Answer 13

A fuel cell converts energy from reaction of a fuel with oxygen into a voltage/electrical energy

2H2 + O2 –> 2H2O

 Two from:  under pressure OR at low temperature OR as a liquid  adsorbed on solid  absorbed within solid Energy is needed to make the hydrogen OR energy is needed to make fuel cell 

Question 14

effect on change in PH on equillibrium….

Answer 14

Question 15

causses for uncertain E values?

Answer 15

.high activation ernergy/slow rate

non standard conditions

Question 16

in ACIDIC conditions , sn 2+ ions react with Io3- ions, construct equation

Answer 16

5Sn2+ + 2IO3– + 12H+  I2 + 5Sn4+ + 6H2O

lesson learnt: go with your gut! ; i was about to put this answer but had trouble balancing and just gave up

Question 17

note for drawing diagrams

Answer 17

dont forget to put the concentration in (1 moldm3) for OTH OF THE HALF CELLS

Question 18

how do you select the strongest oxidising agent from a table of E values ?

Answer 18

LOOK FOR HIGHEST E CELL POTENTIAL.

oxidising agents are the most likely to be reduced so look for the equation with the highest E/V. the reactant(s) of this reaction will be the strongest oxidising agent

Question 19

if a question asks you to construct an equationfor a reaction between two chemicals , what do oyu look for in the half equations ?

Answer 19

the reactants have to be on the same side of each equation after the more negative E/V has been swapped around

Question 20

A student added some chromium metal to an acidified solution containing copper(II) ions. A reaction took place. The student concluded that ‘chromium is more reactive than copper’.

(i) Explain, in terms of their electrode potentials, why ‘chromium is more reactive than copper’ in this reaction.

Answer 20

E(o) for chromium (redox system) is more negative/lower/less (than copper redox system)

chromium system shifts to the left / Cr(s) –>Cr3+(aq) + 3e– AND copper system shifts to the right / Cu2+(aq) + 2e–> cu(s)

note always include equations as to what is occuring

Question 21

bubbles of gas were observed, why ?

Answer 21

metal ion reacted with H+ ions which released H2 in the process (hydrogen gas )

Question 22

advantages of using methanol rather than hydrogen

Answer 22

methanol= liquid thus easier to store

hydrogen=more flammable

methanol has more political acceptance as a fuel

Question 23

Two transporters on current in a cell ?

Answer 23

electrons and ions

Question 24

how to identify the strongest reducing agent ?

Answer 24

reducing agents get oxidised so look for LOWEEST E/V and then switch the equation and the reactants are the reducing agents

Question 25

NOTE ; LOOK BACK AT REDOX PAPER 2 PMT LAST QUESTION; MADE MAJOR MISTAKES WHILST CALCULATING CONCENTRATION OF DILUTION

Answer 25

BLANK

Question 26

jnj

Answer 26

b

Question 27

test card

Answer 27

it saved