Water is called the universal solvent because it dissolves more substances than any other common liquid.
What Makes Water a Good Solvent?
Water's remarkable ability to dissolve various substances stems from its unique properties:
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Polarity: Water molecules are polar, meaning they have a slightly positive charge on one side (hydrogen atoms) and a slightly negative charge on the other (oxygen atom). This polarity allows water molecules to attract and interact with other polar molecules and ionic compounds.
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Hydrogen Bonding: Water molecules form hydrogen bonds with each other and with other polar molecules. These bonds help to break apart the forces holding solutes together.
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Small Size: The small size of the water molecule allows it to effectively surround solute particles, preventing them from re-associating.
How Water Dissolves Different Types of Substances
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Ionic Compounds (e.g., Salt): Water molecules surround the positive and negative ions that make up the ionic compound. The positive ends of water molecules are attracted to the negative ions, and the negative ends are attracted to the positive ions. This process, called hydration, pulls the ions apart and disperses them throughout the water, dissolving the salt.
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Polar Covalent Compounds (e.g., Sugar): Water molecules form hydrogen bonds with the polar covalent compound. These hydrogen bonds weaken the intermolecular forces holding the solute molecules together, allowing them to disperse throughout the water.
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Non-Polar Compounds (e.g., Oil): Water does not easily dissolve non-polar substances. Because water is polar, it is more attracted to itself than to non-polar molecules. This causes the non-polar substance to separate from the water, like oil and water. This is why water is often referred to as a "polar" solvent.
Why "Universal" Solvent is a Misnomer
While water dissolves more substances than other common liquids, it doesn't dissolve everything. Substances like oil, fats, and some plastics don't dissolve well in water because they are non-polar. Therefore, the term "universal solvent" is a bit of an overstatement, but it highlights water's exceptional dissolving capabilities.
In summary, water's polarity, hydrogen bonding capabilities, and small molecular size make it an excellent solvent for a wide range of substances, earning it the nickname "universal solvent."
