hydro-

Quick Definition

Meaning: Water

Origin: Greek (hydor = water)

Pronunciation: HY-droh

Why It Matters

Hydro- appears in hundreds of chemistry terms and is one of the most versatile prefixes. It can indicate water as a reactant (hydrolysis), a solvent (hydrophilic), or a component (hydrocarbon). The common mistake is assuming hydro- always means 'water is present' — in hydrophobic, it actually means 'water-fearing,' describing what the molecule repels, not contains. In organic chemistry, the prefix often signals a hydrogen atom rather than water itself: hydrogenation adds H2 across a double bond, while hydrolysis splits a molecule using water. Context is everything. Another trap: students see 'hydro' in 'hydrochloric acid' and assume it means water, when it actually refers to hydrogen. HCl is hydrogen chloride dissolved in water, but the 'hydro' comes from the hydrogen, not the water. When decoding, ask yourself: is this about water as a molecule (H2O), or about hydrogen as an element (H)? The surrounding root usually tells you.

Examples

• Hydrolysis
• Hydrophilic
• Hydrocarbon
• Hydrogenation

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