Redox And Electrode Potentials

Front 1

What is an oxidising agent

Back 1

It is a substance that takes electrons away from the atom that is being oxidised . it contains the atom that is reduced

Front 2

What is a reducing agent

Back 2

Any truth in aging is a substance that add electrons to the atom that is reduced and it contains the atom that is oxidised

Front 3

Manganate réduction équation

Back 3

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

Front 4

What is acidified manganate

Back 4

It is an oxidising agent meaning that it is reduced

Front 5

What colour is potassium manganate

Back 5

It is purple

Front 6

During titration with manganate redox titration what goes in the burette

Back 6

The potassium manganate which is a purple colour goes into the burette

Front 7

What is the Endpoint of a manganate redox titration

Back 7

At the Endpoint the solution changes from colourless to a permanent pink colour. the reaction self indicating

Front 8

Oxidation of Iron half equation

Back 8

Fe^2+ ----> Fe^3+ + e-

Front 9

Why is dilute sulfuric acid added into potassium manganate titration

Back 9

To supply the H+ ions

Front 10

What is the first stage of an iodine thiosulfate redox reaction

Back 10

The oxidizing agent is first reacted with an excess iodine ions. Iodine ions are oxidised to iodine

Front 11

What is the second stage of an iodine thiosulfate redox reaction

Back 11

The iodine generated is then titrated with thiosulfate ions. Thiosulfate ions are oxidised in iodine is reduced to iodide

Front 12

What's the half equation for the oxidation of thiosulfate ions

Back 12

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

Front 13

What happens during the sodium thiosulfate reaction?

Back 13

1. A standard solution of sodium thiosulfate is added to the burette

2. Excess KI and oxidising agent are added to the conical flask

3. The oxidising agent reacts with iodide ions to form iodine... turning the solution a yellow-brown colour

4. Burette tap is opened, and sodium thiosulfate added

5. As the end point approaches, colour changes from yellow brown to pale straw colour

6. Starch indicator added, forming a deep blue black

And at the end point, the colour changes from blue black to colourless, indicating all the iodine has reacted

Front 14

What are the main colour changes in a sodium thiosulfate réaction?

Back 14

Yellow brown to pale straw.

Then to blue black and then to colourless

Front 15

What happens when iodine thiosulfate titrations are used to analyse copper ions

Back 15

The copper ions are reduced by the iodine to form a white precipitate of copper iodide.

The iodide ions are oxidised to form a yellow brown solution of iodine

Then the iodine is titrated with sodium thiosulfate

Front 16

What is the molar ratio of copper to thiosulphate ions

Back 16

1:1

Front 17

What is brass an alloy of

Back 17

Zinc and copper

Front 18

What does a half cell contain

Back 18

It contains the chemical species present in a redox half equation

Front 19

What is electrode potential

Back 19

Electrode potential is the tendency for electrons to be gained and for reduction to take place in a half cell

Front 20

What metal is used in a half cell based on ions of the same element in different oxidation states

Back 20

Platinum is used since it is unreactive

Front 21

What does the electrode do

Back 21

The electrode transport electrons into out of the half cell

Front 22

What is the standard electrode potential

Back 22

It is the electromotive force of a half cell connected to the standard hydrogen half cell under standard conditions

Front 23

What is the standard electrode potential of a standard hydrogen electrode

Back 23

It is 0 volts

Front 24

What makes up a standard hydrogen half cell

Back 24

Look at this diagram

Front 25

How is standard electrode potential measured

Back 25

It is measured through a half cell connected to a standard hydrogen electrode

Front 26

What is the purpose of a salt bridge

Back 26

It allows ions to flow

Front 27

What makes up the salt bridge

Back 27

The salt bridge contains the concentrated solution of an electrolyte that does not react with either solution

Front 28

What does a more negative electrode potential value mean

Back 28

It means that there's a greater tendency to lose electrons and undergo oxidation

Front 29

What is the negative electrode

Back 29

The negative electrode is the anode and it belongs to the element with the most negative electrode potential

Front 30

How do you work out standard cell potential

Back 30

More positive - more negative electrode potential

Front 31

What is the first limitation of feasibility predictions

Back 31

Reaction rate. I Predict a reaction may have a large activation energy resulting in a very slow rate

Front 32

What is the second limitation of a feasibility prediction

Back 32

Concentration. Predictions are based on standard electrode potentials measured using concentrations of 1moldm^-3. For concentrations that aren't 1moldm^-3 then the electrode potential is different

Front 33

Give me a description of a primary cell and an example

Back 33

A primary cell is one use only meaning that it can only be used until the chemicals have reacted. This cell is not rechargeable and an example of this would be the Zinc copper cell

Front 34

What is a secondary cell

Back 34

A secondary cell can be recharged. d

During recharging the reaction that discharges the cell is reversed.

Front 35

What is a fuel cell

Back 35

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

Front 36

In a fuel cell where is oxygen

Back 36

Oxygen is at the positive electrode where reduction place

Front 37

Do Fuel Cells need recharging?

Back 37

Nope. They function all the time as long as they have a continuous supply of oxygen and fuel

Front 38

Colour change for reduction of manganate with Iron

Back 38

Purple to colourless

Front 39

Colour change for the reduction of Fe²+

Back 39

Orange brown to pale green

Front 40

Give the equation for when acidicfied Cr2O7²- are reduced to Cr³+ by addition of zinc

Back 40

Front 41

What's the colour change for when acidified dichromate ions are reduced?

Back 41

Orange to green

Hint 41

Cr2O7²-

Front 42

When zinc is in excess what can happen to chromium (III) ions

Back 42

They can be reduced further to form chromium (II) ions which is pale blue

Front 43

What can hot alkaline H2O2 (hydrogen peroxide) be used?

Back 43

Since it's a strong oxidising agent it can be used to oxidise chromium (III) to chromium (VI) in CrO4²-

Front 44

What's the overall reaction for the oxidation of chromium (III)

Back 44

3H2O2 + 2Cr³+ + 10OH- ---> 2CrO4²- + 8H2O

Front 45

What's the equation for when Cu²+ reacts with excess I ions

Back 45

Hint 45

Pale blue to white precipitate in brown solution