46. Electrochemical measurements: the Daniell cell, concentration cell, redox and non-polarizable electrodes Flashcards
What does Oxidation mean?
the release of electrons
What does reduction mean?
he uptake of one or more electron(s)
The role of standard reduction potential
to decide in a given reaction, which substance is oxidized (reducing agent) and which is reduced (oxidizing agent).
standard reduction potential of hydrogen
an arbitrary potential value of e° = 0 V
The structure of Daniel cell
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.
What is Nernst-equation?
Where does reduction take place in Daniel cell?
At the copper electrode (because its potential is higher) => this is cathode
Where does oxidation take place in Daniel cell?
At the zinc electrode (because its potential is lower) => this is anode
Write The half-cell reactions of Daniel cell.
Also write Short representation for it
Anode: oxidation: Zn -> Zn2+ + 2 e–
Cathode: reduction: Cu2+ + 2 e– -> Cu
Zn |1M Zn2+ || 1M Cu2+ | Cu
Formula of the electromotive force
The galvanic cell can only work if __
the two half-cells are connected by a salt bridge
What are the 3 types of electrodes?
- Normal electrode
- Redox electrode
- Non-polarized electrode
What are the 3 types of normal electrodes?
- Primary metal electrode
- Gas electrode with cations
- Gas electrode with anions
Describe metal ion electrode
An element (e.g. zinc) is immersed in a solution, which contains the same ions (Zn2+).
What is the half-cell reaction for primary metal electrode?
Give an example based on the following picture
Half reaction
Mez+(aq) + ze- Me(s)
(direction depends on the partner)
What is the half-cell reaction for gas electrodes with cations?
Give an example based on the following picture
Half reaction (direction depends on the partner)
2H+(aq) + 2e- → H2(g)
Describe gas electrode with anions
In the case of a chlorine half-cell, the element is the oxidized form, thus cox = 1 mol / l und cred is the electrolyte concentration that determines the potential value.
What is the half-cell reaction for gas electrodes with anions?
Give an example based on the following picture
Half reaction (direction depends on the partner) Cl2(g) + 2e- 2Cl-(aq)
Describe redox electrodes
Both oxidized and reduced forms are in solution
Describe redox electrodes
Half reaction
(direction depends on the partner)
OX(aq) + ze- RED(aq)
Describe non-polarizable electrode based on following picture
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.
In a normal half-cell, a ___ is immersed in a solution that contains the element’s ions.
water-insoluble element
The activity of the element at standard pressure and temperature is ____
1
What can a half cell be produce from?
A half-cell can be produced not only from metals but also from gases.
In contrast, a half-cell with a constant potential value is required as a ___ electrode
=> These electrodes are called ___
reference
non-polarizable half-cells
Can a galvanic cell be composed of two qualitatively identical half-cells?
Yes
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
concentration
Describe the theoretical base of determining the pH using an electrochemical system
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.
Materials for Daniel cell experiment
Zinc electrode, copper electrode, salt bridge, volt meter, cable, 2 beakers, measuring cylinder; 1 mol / l CuSO4 solution, 1 mol / l ZnSO4 solution
