46. Electrochemical measurements: the Daniell cell, concentration cell, redox and non-polarizable electrodes

Question 1

What does Oxidation mean?

Answer 1

the release of electrons

Question 2

What does reduction mean?

Answer 2

he uptake of one or more electron(s)

Question 3

The role of standard reduction potential

Answer 3

to decide in a given reaction, which substance is oxidized (reducing agent) and which is reduced (oxidizing agent).

Question 4

standard reduction potential of hydrogen

Answer 4

an arbitrary potential value of e° = 0 V

Question 5

The structure of Daniel cell

Answer 5

one half-cell consists of a zinc electrode immersed in a 1 mol / l ZnSO4 solution, the other half-cell is a copper plate in a 1 mol / l CuSO4 solution.

Question 6

What is Nernst-equation?

Answer 6

Question 7

Where does reduction take place in Daniel cell?

Answer 7

At the copper electrode (because its potential is higher) => this is cathode

Question 8

Where does oxidation take place in Daniel cell?

Answer 8

At the zinc electrode (because its potential is lower) => this is anode

Question 9

Write The half-cell reactions of Daniel cell.
Also write Short representation for it

Answer 9

Anode: oxidation: Zn -> Zn2+ + 2 e–
Cathode: reduction: Cu2+ + 2 e– -> Cu

Zn |1M Zn2+ || 1M Cu2+ | Cu

Question 10

Formula of the electromotive force

Answer 10

Question 11

The galvanic cell can only work if __

Answer 11

the two half-cells are connected by a salt bridge

Question 12

What are the 3 types of electrodes?

Answer 12

1. Normal electrode
2. Redox electrode
3. Non-polarized electrode

Question 13

What are the 3 types of normal electrodes?

Answer 13

1. Primary metal electrode
2. Gas electrode with cations
3. Gas electrode with anions

Question 14

Describe metal ion electrode

Answer 14

An element (e.g. zinc) is immersed in a solution, which contains the same ions (Zn2+).

Question 15

What is the half-cell reaction for primary metal electrode?

Give an example based on the following picture

Answer 15

Half reaction

Me^z+(aq) + ze- Me(s)

(direction depends on the partner)

Question 16

What is the half-cell reaction for gas electrodes with cations?

Give an example based on the following picture

Answer 16

Half reaction (direction depends on the partner)

2H+(aq) + 2e- → H2(g)

Question 17

Describe gas electrode with anions

Answer 17

In the case of a chlorine half-cell, the element is the oxidized form, thus c_ox = 1 mol / l und c_red is the electrolyte concentration that determines the potential value.

Question 18

What is the half-cell reaction for gas electrodes with anions?

Give an example based on the following picture

Answer 18

Half reaction (direction depends on the partner) Cl2(g) + 2e- 2Cl-(aq)

Question 19

Describe redox electrodes

Answer 19

Both oxidized and reduced forms are in solution

Question 20

Describe redox electrodes

Answer 20

Half reaction
(direction depends on the partner)

OX(aq) + ze- RED(aq)

Question 21

Describe non-polarizable electrode based on following picture

Answer 21

A metal plate (Ag) is immersed in a saturated, poorly soluble electrolyte solution that contains the same ions (Ag+) as well as precipitation (AgCl).

→ [Ag+] remains constant.

Question 22

In a normal half-cell, a ___ is immersed in a solution that contains the element’s ions.

Answer 22

water-insoluble element

Question 23

The activity of the element at standard pressure and temperature is ____

Answer 23

1

Question 24

What can a half cell be produce from?

Answer 24

A half-cell can be produced not only from metals but also from gases.

Question 25

In contrast, a half-cell with a constant potential value is required as a ___ electrode

=> These electrodes are called ___

Answer 25

reference

non-polarizable half-cells

Question 26

Can a galvanic cell be composed of two qualitatively identical half-cells?

Answer 26

Yes

Question 27

A galvanic cell can also be composed of two qualitatively identical half-cells, in this case the concen- tration of the two solutions must be different.

→ These galvanic elements are the ___ cells

Answer 27

concentration

Question 28

Describe the theoretical base of determining the pH using an electrochemical system

Answer 28

If a concentration cell consists of two hydrogen electrodes with a known and an unknown H+-concen- tration, respectively, after measuring the electromotive force, the unknown concentration can be calcu- lated.

Question 29

Materials for Daniel cell experiment

Answer 29

Zinc electrode, copper electrode, salt bridge, volt meter, cable, 2 beakers, measuring cylinder; 1 mol / l CuSO4 solution, 1 mol / l ZnSO4 solution