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What does salt do to water bonds?

Published in Chemistry 2 mins read

Salt disrupts the hydrogen bonds between water molecules. When salt (typically sodium chloride, NaCl) is added to water, it dissolves into its constituent ions: sodium (Na+) and chloride (Cl-). These ions then interact with the water molecules.

How Salt Disrupts Water Bonds:

  1. Dissociation: Salt, an ionic compound, dissociates into positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-) when introduced to water.

  2. Hydration: Water molecules are polar, meaning they have a slightly positive (hydrogen) and slightly negative (oxygen) end. This polarity allows them to form hydrogen bonds with each other. However, the charged sodium and chloride ions are more strongly attracted to the polar water molecules than the water molecules are to each other. The negative chloride ions attract the positive hydrogen ends of water molecules, and the positive sodium ions attract the negative oxygen ends of water molecules. This process is called hydration.

  3. Interference with Hydrogen Bonding: The strong interaction between the ions and water molecules interferes with the hydrogen bonds that hold the water molecules together. This disruption lowers the freezing point of water, as more energy is required to form the rigid structure of ice because the hydrogen bonds have already been partially broken by the presence of the ions.

Effects of Disrupted Water Bonds:

  • Lowered Freezing Point: This is why salt is used to melt ice on roads and sidewalks. The salt interferes with the formation of ice crystals by disrupting the hydrogen bonds.
  • Increased Boiling Point: Similarly, salt slightly increases the boiling point of water. Again, this is because more energy is needed to overcome the attraction between water molecules and the ions to transition into the gaseous phase.
  • Changes in Water Properties: The presence of salt ions alters various other properties of water, such as its electrical conductivity and density.

In summary, salt's presence in water leads to the separation of water molecules due to stronger attraction of water molecules with salt ions, instead of other water molecules. The sodium and chloride ions attract water molecules, interfering with their hydrogen bonds and changing the solution's properties.