Salt does not melt ice through osmosis. The ice melting process caused by salt is due to freezing point depression, a colligative property, not osmosis.
Here's a breakdown:
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Osmosis: Osmosis is the movement of water molecules from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration) across a semi-permeable membrane. This process equalizes the concentration of solutes on both sides of the membrane. Ice isn't a semi-permeable membrane, so osmosis doesn't directly apply.
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Freezing Point Depression (The Correct Explanation): When salt (typically sodium chloride, NaCl) is added to ice, it dissolves in any liquid water present on the surface. The salt dissociates into sodium (Na+) and chloride (Cl-) ions. These ions interfere with the ability of water molecules to form the organized crystalline structure of ice.
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Disruption of Lattice Structure: The sodium and chloride ions insert themselves into the water's lattice structure that is forming as water freezes into ice.
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Lower Freezing Point: Because these ions interfere with ice crystal formation, the water requires a lower temperature to freeze. The freezing point of water is depressed.
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Ice Melts: If the temperature is above the new, lower freezing point, the ice will melt. The amount the freezing point is lowered depends on the concentration of salt.
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Why it's NOT Osmosis: Osmosis requires a semi-permeable membrane and a difference in water concentration on either side of the membrane. Melting ice with salt doesn't fit this scenario. The melting occurs due to the disruption of ice crystal formation, not the movement of water across a membrane.
In summary, salt melts ice by lowering the freezing point of water through the disruption of the ice's crystal lattice structure by sodium and chloride ions. This is freezing point depression, a colligative property, and distinct from osmosis.
