Intermediate Topic 328 of 1102 States of Matter & Solutions
Solvation and Hydration
Surrounding of solute particles by solvent molecules or specifically water.
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In-depth explanation of Solvation and Hydration
Solvation is the process in which solvent molecules surround and bind to solute particles, stabilizing them in solution. When the solvent is water the process is called hydration. In water, cations are attracted to the partially negative oxygen atoms and anions to the partially positive hydrogen atoms, so the particles become wrapped in a hydration shell. The strength of solvation depends on the charge density of the ion, so small, highly charged ions are more strongly hydrated than large, singly charged ones. Solvation releases energy and is an essential part of the enthalpy of dissolution.
Going deeper: Solvation and Hydration
Key ideas: Hydration enthalpy increases with charge density, charge divided by radius: Li+ is about -520 kJ/mol, Na+ -405, K+ -321, Cs+ -263, Mg2+ about -1920, Al3+ about -4660. Ions have first shell coordination numbers of 4 to 9, such as 6 for most transition-metal ions, forming complexes such as the hexaaquacopper ion. Hydrated ion size follows the opposite trend to crystal size.
Common mistakes and connections: Students think Li+ moves faster in water because it is smaller; the larger hydration shell makes Li+ less mobile than Cs+. Another error is that the solvent just surrounds ions without bonds; in many cases bonds to metal ions are coordinate. Water in hydrates, such as CuSO4 with 5 H2O, is crystal water. Links to dissolution enthalpy, ionic mobility and coordination chemistry.
Visualization of Solvation and Hydration
Solvation surrounds ions with solvent molecules; in water this hydration stabilizes dissolved ions such as the hydronium ion. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The lithium ion, being smaller and more highly charged per unit volume, has a larger hydration shell than the caesium ion.
Frequently asked questions about Solvation and Hydration
What is Solvation and Hydration?
Surrounding of solute particles by solvent molecules or specifically water.
Is Solvation and Hydration a beginner, intermediate or advanced topic?
Solvation and Hydration is a intermediate topic in States of Matter & Solutions. It builds on the vocabulary of beginner topics in this area.
What should I learn before Solvation and Hydration?
Study these earlier topics in States of Matter & Solutions first: Solid Solutions, Alloys, Dissolution Enthalpy.
What comes after Solvation and Hydration?
It is the last topic in States of Matter & Solutions. Explore the other areas for more chemistry.
Can I practise Solvation and Hydration with quizzes?
Yes. The interactive lesson includes a self-check question on Solvation and Hydration, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Solvation and Hydration fits in States of Matter & Solutions
Solvation and Hydration is topic 109 of 109 in States of Matter & Solutions.