Hydrolysis Constant — Definition, Formula, Properties & Uses | AllChemicals | AllChemicals

Q: What is the formula for Hydrolysis Constant?

The formula or notation for Hydrolysis Constant is: Kh = [H⁺][A⁻]/[HA]; related to Ka and Kw: Kh = Kw/Ka (for anion hydrolysis)

Formula / Notation	Kh = [H⁺][A⁻]/[HA]; related to Ka and Kw: Kh = Kw/Ka (for anion hydrolysis)
Also Known As	Hydrolysis constant, Kh, degree of hydrolysis, salt hydrolysis constant

What is Hydrolysis Constant?

The equilibrium constant for the hydrolysis reaction of a salt in water. Related to Ka and Kb of the conjugate acid-base pair through Kw. Hydrolysis constants determine whether salt solutions are acidic, basic, or neutral.

Formula & Notation

Kh = [H⁺][A⁻]/[HA]; related to Ka and Kw: Kh = Kw/Ka (for anion hydrolysis)

Other Names / Synonyms: Hydrolysis constant, Kh, degree of hydrolysis, salt hydrolysis constant

Properties & Characteristics

The hydrolysis constant (Kh) quantifies the extent to which a salt undergoes hydrolysis in water. For the hydrolysis of the anion of a weak acid: A⁻ + H₂O ⇌ HA + OH⁻, Kh = [HA][OH⁻]/[A⁻] = Kw/Ka. For the cation of a weak base: BH⁺ + H₂O ⇌ B + H₃O⁺, Kh = Kw/Kb. A large Kh means significant hydrolysis and a significantly acidic or basic solution from the dissolved salt.

Uses & Applications

Hydrolysis constants are used to calculate the pH of salt solutions, to understand why Na₂CO₃ is alkaline (CO₃²⁻ hydrolyses) and why NH₄Cl is acidic (NH₄⁺ hydrolyses), and to predict the behaviour of metal ions in water (metal cation hydrolysis produces acidic solutions).

Safety Information

Strong hydrolysis of salts (carbonates, sulfides, cyanides) can release toxic gases (H₂S from sulfide acidification, HCN from cyanide acidification). Always test whether acidifying a salt solution releases hazardous gases before conducting reactions in acidic media.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Hydrolysis Constant

Formula Kh = [H⁺][A⁻]/[HA]; related to Ka and Kw: Kh = Kw/Ka (for anion hydrolysis)

Index All "H" terms

Synonyms Hydrolysis constant, Kh, degree of hydrolysis, salt hydrolysis constant

Frequently Asked Questions

What is Hydrolysis Constant?

The equilibrium constant for the hydrolysis reaction of a salt in water. Related to Ka and Kb of the conjugate acid-base pair through Kw. Hydrolysis constants determine whether salt solutions are acidic, basic, or neutral.

What is Hydrolysis Constant used for?

Is Hydrolysis Constant hazardous?

What is the formula for Hydrolysis Constant?

More "H" Terms

Haber Process N₂ + 3H₂ ⇌ 2NH₃ | ΔH = −92 kJ/mol Hafnium Hf Half Cell Half Life Half-Cell E = E° − (RT/nF)lnQ Half-Life A(t) = A₀e^(−λt); t½ = ln2/λ Half-Reaction Halide X⁻ (e.g., F⁻, Cl⁻, Br⁻, I⁻) Halogen F₂, Cl₂, Br₂, I₂, At; Group 17; ns²np⁵ valence configuration Halogenation C-X + Cl₂/Br₂ (hv or AlCl₃) → C-X(halogen); EAS or radical pathway Halogens Hard Acid Hard acid: small, highly charged, low polarisability (e.g., H⁺, Mg²⁺, Al³⁺)

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