Chemistry Articles☠☡


If you slowly pour a handful of salt into a totally full glass of water it will not overflow. In fact, the water level will go down.

It can be seen practically

And predominantly i will be explaining the science behind it here.

When NaCl is dissolved in H2O, it forms 2 ionsThe Na+1ions are attracted to the negative end of the H2O molecules. 

The Cl-1ions are attracted to the positive end of the H2O molecules. 

This force of attraction between water and salt decreases the total volume of the solution, more than the additional volume of Na+1 and Cl-1 ions increases the volume. 

  1. The result is a decrease of the total volume as NaCl is dissolved.


Actually, sodium chloride added to water will decrease the volume of the solution, up to around 2% for a saturated solution. 

Even when fully saturated, that’s not a big change, so you may not have been able to observe it without something with a narrow neck like a volumetric flaskIf you start with a large volume and carefully mark the level, you should be able to see it.

In short, the solvent molecules become more ordered in the vicinity of dissolved (charged) ions and less ordered as we go further away from the dissolved (charged) ions. The increase of solvent density near the ions is offset by the decrease of bulk density in the solvent as distance from the ions increases. This results in an overall net reduction in the observed volume of the solution.

The interaction of the electrostatic field of an ion with water tends to align the dipolar water molecules in the direction of the field. In this way the field tends to disrupt hydrogen bonded structures in liquid water, and to compress the water molecules surrounding an ion. These electrostatic effect give rise to a shrinkage of the water

The same thing happens when pure ethanol is mixed with pure water

Sometimes the deviations can happen in both directions (increasing or decreasing the volume) and changes in volume also occur when mixing two miscible liquids together, sometimes in a rather complex way

  1. A good example is a binary mixture of acetone and chloroform.

 Starting from a pure acetone mixture, as we add chloroform, the volume is more than the sum of the two component volumes, but once we get above 20% chloroform or so, the volume drops below the sum of the two pure component volumes. Why this happens is a bit complicated, but it has to do with different competing factors affecting how compact the local structure around the molecules is


=Increase in volume 






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