much weaker coffee!
Solubility in water:
Molecules are often classified by how they interact with water. Molecules that like to interact with water
are called “hydrophilic”, or water-loving. These molecules like to interact with water because, like
water, they are charged, so are attracted to the water molecules and can form links with them. This is
what occurs when a substance “dissolves”. For example, when salt is added to water, it will dissolve.
Salt is made of Na+ ions and Cl- ions held together, and in the presence of water, these ions will
separate and be attracted to and form bonds with the water molecules. Because the salt has been
split into individual Na+ and Cl- ions, it is no longer visible to the naked eye because the separated
ions are too small. However, if the mixture is heated to evaporate all the water, only the Na+ and Clions
will be left, which will then be free to rejoin with each other to form the original salt.
The boiling point of water can be changed if substances added to it, depending on the relative boiling
point of the added substances. For example, water will boil at a slightly higher temperature if salt is
present because salt has a much higher boiling point than water. The more salt contained in the water,
the higher the boiling point of the solution. However, if alcohol, which has a boiling point lower than
that of pure water, is added to water, it will decrease the boiling point of the final mixture.
The freezing point of water is also changed by adding substances to it, however all substances added
to water will act to decrease its freezing point. This is because any other substance present will act to
get in the way of the water molecules as they try to make bonds with each other to form ice, so
temperatures lower than freezing are required to freeze the water.
This explains why salt is often added to ice on the roads to encourage it to melt – it causes the ice will
melt at a lower temperature.
IV/I - 2 (of 2)
Non-solubility in water:
Many molecules however do not interact with water. They are called “hydrophobic”, or water-hating.