# What is the need for oxidation number

## Course

hours

Lesson course

Hints

15-16

Redox potentials

Standard hydrogen half-cell
LV: Measurement of standard potentials

evaluation

• Inert electrodes
• Voltage series

Ü: Calculation of cell voltages of any galvanic cells (under standard conditions)

Zn / Zn 2+ , Cu / Cu 2+ , Ag / Ag + , Fe 2+ / Fe 3+ , 2I - / I 2
Alt: P Voltage measurement (petri dish tests)
E 163 AB Experimental sketch of a measuring arrangement, With Standard hydrogen half-cell E 163 LI
Old: Virtual experiments:
Classification of further redox pairs in the voltage series → / u> < http://www.chemie-interaktiv.net/html_flash/redox.swf="">

17-18

Prediction of pH-independent redox reactions

LV: Cl-, Br-, I- + chlorine or bromine water (or iodine water) as confirmation tests

or P: Cl-, Br-, I- + chlorine

Ü: Direction of redox reactions

E 170 LI "Redox series of halogens"
Standard potential table

Old: P: E 171 LI (with AB)

What reacts with what? E.g .: Fe + Cu 2+ or Fe 2+ + H 2 or Cu 2+ + Ag + ?
Exercises LB or AB

19

Dependence of the redox potential on the ion concentration in the half-cell

• Presentation of the experimental project
• Building hypotheses
• Experimental review

Qualitative:
LV: H 2 (Pt) / 2 H + // Ag + / Ag
Shift in equilibrium when the electrolyte concentration changes (solution pressure and deposition tendency)

Dilution series:
c (Ag + ) = 1 / 0.1 / 0.01 / 0.001 mol ∙ L -1
Application of the Le Chatelier principle

(1)

Quantitatively:
Determination of the proportionality factor 0.059 V

• As a further test evaluation
• Optional if Nernst equation is to be treated

20-22

P. : Concentration cell in petri dish

E 180 AB / < e="" 180="" li="">
Old: LV Ag / Ag + Concentration cell

Behavior of metals towards water and dilute hydrochloric acid

LV o. P: Metals + water /
Metals + hydrochloric acid

Metals: Al, Ca, Cu, Fe, Li, Zn
E. (H 2 +2 OH - / 2 H 2 O) pH = 7 = - 0.41 V

P. "Who identifies the metals?"
Old 1: E 190 AB / E 190 LI
Alt 2: E 192 AB / E 192 LI

(2)

seriously -Equation and applications e.g. pH-dependent redox reactions

Optional

Diagnosis 2

Diagnostic sheet E 200 AB