What are water-soluble substances

Water as a solvent

In the solid salt, the positive and negative ions are arranged alternately, resulting in a three-dimensional lattice - the ion lattice. Table salt (= sodium chloride) consists of positively charged sodium ions and a negatively charged chloride ion. These attract each other. If you now put table salt in water, the following happens:

  • The ions are released from their lattice structure and can move freely in the water.
  • The water molecules rearrange the positive sodium ion in such a way that the weakly negatively charged oxygen atom points to the positive sodium ion.
  • The negative chloride ion, on the other hand, is surrounded by the water molecules in such a way that the weakly positively charged hydrogen atoms point towards it.
  • The accumulation of water molecules on dissolved ions is called "hydration".
  • The ions now enclosed by the water molecules dissolve in the water.

How well solid, liquid and gaseous substances can be dissolved in water often depends very much on the temperature.

Fats and oils that have a large molecular structure or are not charged are repelled by the water. You can see this when you add oil to pasta water, for example. The oil does not dissolve, but "floats" on the water.

Incidentally, water-soluble substances are referred to as "Hydrophilic", water-insoluble substances as "Hydrophobic".