3.2 Redox Rctns

Question 1

oxidising agent??

Answer 1

oxidising agent gains electrons from the species being oxidised, itself being reduced

Question 2

reducing agent??

Answer 2

reducing agent donates electrons to the species being reduced itself being oxidised

Question 3

half eqn??

Answer 3

an eqn that tells u what is happening at one of the electrodes during an electrochemical rctn

Question 4

half equn for reduction of Cr2O7^2- ions to Cr^3+ ions

Answer 4

Cr2O7^2- + 14H+ + 6e- -> 2Cr^3+ + 7H2O

Question 5

half eqn for reduction of MnO4- to Mn^2+ ions

Answer 5

MnO4- + 8H+ + 5e- -> Mn^2+ + 4H2O

Question 6

half eqn for oxidation of S2O3^2- to S4O6^2- ions

Answer 6

2S2O3^2- -> S4O6^2- + 2e-

Question 7

how do u combine two balanced half eqns?
Zn(s) -> Zn^2+(aq) + 2e-
2Fe^3+ (aq) + 2e- -> 2Fe^2+(aq)

Answer 7

combine eqns cancel out common electrons on both sides
overall eqn: Zn(s) + 2Fe^3+(aq) ->Zn^2+(aq) + 2Fe^2+(aq)

Question 8

redox titration??

Answer 8

a titration of a reducing agent by an oxidising agent or visa versa

Question 9

equip req to carry out a titration??

Answer 9

burette
pipette & pipette filler
conical flask
funnel
white tile
clamp & stand

Question 10

how dyou carry out a titration??

Answer 10

-pipette used to measure one rctnt into conical flask, fill burette w/ other rctnt recording initial vol of burette
-add few drops on indicator to conical flask
- open burette tap allowing rctnt to flow into conical flask, swirling to mix contents
-close burette tap once colour change occurs
-record final burette vol
-repeat until u get concordant results then calc a mean titre

Question 11

ionic eqn for the rctn bet acidified Fe^2+ & potassium manganate(VII)?

Answer 11

5Fe^2+ + MnO4- + 8H+ –> 5Fe^3+ + Mn^2+ + 4H2O

Question 12

describe the procedure of titrating potassium manganate(VII) w/ Fe^2+ ions in an unknown soln??

Answer 12

-add the potassium manganate(VII) soln into burette
-unknown soln containing Fe^2+ ions is acidified w/ dilute H2SO4 & measured into a conical flask
-record the initial vol in burette
- add potassium manganate(VII) soln slowly into the flask as it reacts it decolourises, when there is the first trace of a permanent pale pink soln close the burette tap
-record the final vol of burette

Question 13

what is potassium manganate(VII)?

Answer 13

strong oxidising agent

Question 14

explain what happens during the redox rctn bet Cu^2+ ions and I- ion??

Answer 14

in this rctn I- isn’t a strong enough reducing agent to completely reduce the Cu^2+ ions so they are only reduced to Cu+ ions

Question 15

chem eqn for the rctn bet Cu^2+ ions & I- ions?

Answer 15

2Cu^2+ + 4I- —> I2 + 2CuI

Question 16

what happens when iodine is titrated w/ thiosulfate ions?

Answer 16

iodine is reduced by the thiosulfate reducing agent
the thiosulfate ions are oxidised by the iodine oxidising agent

Question 17

chem eqn for the redox rctn that takes place bet iodine & thiosulfate ions??
I2 + 2e- –> 2I-
2S2O3^2- –> S4O6^2- + 2e-

Answer 17

cancel out electrons & combine the two half eqns:
I2 + 2S2O3^2- –> 2I- + S4O6^2-