Within a certain concentration range, the conductivity of a strong electrolyte increases as the concentration increases, and then decreases as the concentration increases; the conductivity of a weak electrolyte does not change significantly with concentration, because the degree of dissociation decreases as the concentration increases.

Image: κ-c

Strong electrolyte Λm = Λ∞m (1-β√c), that is, when the concentration is extremely dilute (below 0.001mol/L), the Λm of the strong electrolyte has a linear relationship with √c; the weak electrolyte has a linear relationship between Λm and √ under extremely dilute conditions. c is still not a linear relationship.

Image: Λm-√c

In an infinitely dilute solution, each ion moves independently, and the Λ∞m value of the electrolyte can be considered as the sum of the limiting molar conductivities of the two ions. 1-1 valence type electrolyte Λ∞m=Λ∞m ( ) Λ∞m (-); electrolytes of different valence types such as CaCl2, Λ∞m=Λ∞m (Ca2 ) 2Λ∞m (Cl-)

How to find the limit molar conductivity of weak electrolytes: Λ∞m (HAc) = Λ∞m (HCl) Λ∞m (NaAc) - Λ∞m (NaCl)

Type 1-1 strong electrolyte solution: t =Λm /Λm t∞ =Λ∞m /Λ∞m Λm=zuF (This formula applies to both the molar conductivity of positive and negative ions and the ultimate molar conductivity.

Test water purity

Calculate the degree of dissociation and dissociation constant of a weak electrolyte

Measuring the solubility of sparingly soluble salts

conductometric titration

I=0.5∑ (mB) (Z²B) B: All ions in the solution; ZB: The valence of the ion (Book 36 Example 8.10)

Take the one with positive ions in the center and negative ions in the periphery as an example. Under the action of an external electric field, the central positive ions move toward the cathode, and the equilibrium state of the peripheral ion atmosphere is damaged. However, due to the Coulomb force, the ions have to rebuild a new ion atmosphere, and at the same time the original ion atmosphere has to be dismantled. But whether it is establishing a new ion atmosphere or dismantling an old ion atmosphere, it takes a certain amount of time. This time is called relaxation time. Because the ions are always moving, the new ion atmosphere of the central ion has not been completely established, and the old ion atmosphere has not been completely dismantled, which forms an asymmetric ion atmosphere. This asymmetric ion atmosphere creates a resistance to the movement of the central ion in the electric field, often called a relaxation force. It reduces the movement rate of ions, thus reducing the molar conductivity.

Under the action of an external electric field, the central ion and its solvated molecules move in a certain direction at the same time, while the ion atmosphere with opposite charges moves in the opposite direction together with the solvated molecules, thereby increasing the viscosity and blocking the The movement of ions in a solution is called the electrophoretic effect. It reduces the rate of ion movement and thus the molar conductivity.

The minimum voltage that must be applied to enable continuous electrolysis of an electrolyte solution is called the theoretical decomposition voltage.

E (theoretical decomposition) = E (reversible)

Actual decomposition voltage > reversible decomposition voltage

Reason: Electrode polarization

When a current passes through an electrode, the electrode potential deviates from its reversible value.

Overpotential/overpotential

concentration polarization

resistive polarization

electrochemical polarization

electrolytic cell

Primary battery

The polarization curve of the negative electrode in the primary battery is the anode polarization curve.

Overpotential makes the anode electrode potential increase and the cathode electrode potential decrease

The more negative the cathode is, the more stable it is, and the more positive the anode is, the more stable it is.

Corrosion caused by electrochemical reaction due to the formation of micro-batteries when the metal surface is in contact with the medium.

Hydrogen evolution corrosion

Oxygen-absorbing corrosion

Non-metal protective layer

metal protective layer

Electrochemical protection

Add corrosion inhibitor protection

primary battery

secondary battery

fuel cell

cathode depolarizer

Anodic depolarizer