Electrochemistry

Question 1

What does more positive E mean

Answer 1

More spontaneous/more favoured

Question 2

Standard cell potential equation
And R constant

Answer 2

Slide 2

Question 3

Reduction happens where

Answer 3

Gain of electrons

Cathode

Red cat

Question 4

Oxidation happens where

Answer 4

Loss of electrons

Anode

An ox

Question 5

Q= I x t

Q is what
I
t

Answer 5

Charge in coloumbs

Current in Amps (C/second)

Time (in seconds)

Question 6

What is current

Answer 6

The flow of electrons

Question 7

Connection of current to moles of electrons moved

Answer 7

Slide 3

Question 8

Explain how we can control a reductions reaction based on controlling the potential of the electrode

Answer 8

If my electrode has one electron and wants to transfer it to solution A

It would transfer it to the LUMO of A which is higher in energy the the electrode right now, This is unfavourable

We put more energy into the electrode (give it more negative potential and more electrons) and make it higher than the LUMO in energy

now the electron can transfer to LUMO favourably and go down in energy after the transfer

Question 9

Explain how we can control a oxidation reaction based on controlling the potential of the electrode

Answer 9

We want an electron from A to move to the orbital of the anode

But the anode is higher in energy than A

So we add more postive potential to the electrode to make it lower in energy

Then A can transfer an electron to the lower energy electrode

Question 10

What is fermi

Answer 10

The highest natural energy of the electrode

Question 11

Explain how a current graph works

Answer 11

At the level where the line is straight on the x axis, not redox reaction happen

As the current and voltage (potential) goes (positive) the energy level of electrode goes down, and oxidation reaction happen

As current goes negative, the energy level of the electrode goes up and reduction happens

Question 12

If a reduction is happing what type of potential is it

Answer 12

Cathodic potential

Question 13

What is over potential

Thermodynamics potential

Answer 13

The extra voltage always needed to overcome the activation energy of the electron transfer (to let the reaction fully Likely happen)

The Nernst E is the thermodynamic potential which is the minimum energy need to make the reaction favourable

Question 14

Why do we need overpotential

Answer 14

To overcome the activation energy of a in solution reaction

To overcome the activation energy of a counter reaction (there always reduction and oxidation, two reactions, so there no charge buildup)

To nucleate bubbles when gas forms (smooth need higher overpotential vs rough electrodes)

To overcome electrical resistance of the solution (V=IR)

Question 15

What are the counter reactions that happen

Answer 15

Oxygen reduction or h2 oxidation

Also a voltage (V=IR) drop due to voltage being lost over a distance

Question 16

What is an electrical double layer

Answer 16

This it at the surface of the electrode where the electrodes negatively charged surface attracts postive charges in the solution

This caused a double layer of - + charge

The other ions spread out through the rest of the solution

Question 17

What is E when far from the electrode

Answer 17

0

Question 18

What is the three electrode cell

Answer 18

Usually there’s the ref electrode and the working electrode

We don’t touch the ref electrode

A counter electrode is added to avoid passing current through the RE and changing its concentrations/potential

This counter electrode has high surface area and is inert to prevent unwanted reactions on the ref electrode

Question 19

What is electrolysis

Answer 19

Using a potentiostat to drive a less favourable reaction forward

to usually deposit a solid product

Question 20

What is a potentio stat

Answer 20

A thing used to control and measure both potential and current

Question 21

What happens during an electrolysis

Answer 21

The concentration of the analyte goes down which makes the E go down too

(Nernst potential needed to reduce analyte is more negative (1/[]))

This change makes interferents in the solution start to react, and water starts to break down

Question 22

What do we do to counter the effects of electrolysis

Answer 22

We need to change the E (potential) at the CATHODE

adjusts for the drop in cu concentration and keeps the overall E constant

Question 23

If potential goes too negative what happens

Too postive

Answer 23

Too negative, H2 is made

Too +, O2 is made

All by breaking down water

Question 24

Slide 11 equations

Answer 24

Put in sheet

Question 25

What is electrogravimetric analysis

What does the graph tell is

Answer 25

Depositing all of the metal from the solution into a mesh with large surface area at the cathode when reduced

The start of the graph is the overpotential then the reduction occurs as potential gets more negative

More -V means more -I (current), as v gets more negative the reduction of h20 to h2 happens (two reaction begin to happens)

Question 26

In a mix of na cl and h20 how do you know what I’ll reduce and be oxidized

Answer 26

By the potentials in the equations redox equations.

Cl2 reduction has postive E so it won’t reduce

IDK LOOK UP

Question 27

What is coloumetry

What is kept constant

Answer 27

Measuring the coloumbs (charge transferred) in a reaction to see for far the reaction goes

Also called chronocoulometry since current and time are being measured

Only one of either the current or potential is held constant, and the other changes

Question 28

In coloumetry, what gives the total charge (I) in relation to mols of the thing that reacted

Answer 28

The area under the curve of the graph

Question 29

In coloumetry, why does the current drop off over time (decrease)

Answer 29

The reactant concentration decreases over time and the reaction goes more slowly

A small amount of capacitave current is needed to rearrange the ions in the double layer