The volume of water in your glass decreases by 2 when you mix salt into the water it is because the water molecules pull the sodium chloride salt apart into sodium and chloride ions

The Volume of Water Decreases When Salt is Added: Understanding the Science Behind It

Have you ever wondered why the volume of water seems to decrease when you mix salt into it? It’s a fascinating scientific phenomenon that can be explained by the interaction between water molecules and salt molecules. In this article, we will delve into the nitty-gritty details of why the volume of water in your glass appears to be reduced by 2% when salt is added.

At the molecular level, water (H2O) consists of two hydrogen atoms bonded to a single oxygen atom. These molecules are highly polar, meaning they have a positive charge on the hydrogen side and a negative charge on the oxygen side. On the other hand, sodium chloride (NaCl), commonly known as table salt, is made up of sodium (Na+) and chloride (Cl-) ions.

When salt is added to water, an intriguing phenomenon occurs. The water molecules surround the sodium and chloride ions, causing them to dissociate or separate from each other. This process is known as dissolution. The polar nature of water allows it to attract and surround the charged ions, breaking the ionic bond that held the sodium and chloride ions together in the solid salt crystals.

As the salt dissolves in water, the water molecules pull the sodium and chloride ions apart due to their opposing charges. The positive hydrogen ends of the water molecules attract the negative chloride ions, while the negative oxygen ends draw in the positive sodium ions. This attraction between the water molecules and the ions is known as hydration.

During the dissolution process, water molecules form a layer around each sodium and chloride ion, effectively isolating them from each other. This hydration layer causes the water molecules to arrange themselves in a way that takes up more space compared to when they were in their original state. Consequently, this rearrangement of water molecules leads to a noticeable decrease in the volume of water.

It’s important to note that although the volume of water appears to diminish, the actual number of water molecules and sodium chloride ions remains constant. Only their arrangement and spatial distribution change, resulting in the observed reduction in volume.

In summary, when you add salt to water, the water molecules interact with the sodium and chloride ions, breaking them apart and forming separate hydration layers around each ion. This rearrangement of water molecules takes up more space, causing a 2% decrease in the volume of water in your glass. Understanding this scientific phenomenon adds a layer of wonder to the simple act of seasoning your food or experimenting in the lab.

Source: USGS