In chemistry we attempt to use the behavior

we see of materials to postulate microscopic phenomena at the atomic and molecular scale. 

For example, we studied the properties of liquids. We saw that water boils at a very high temperature for a substance with a molecular weight of 18, thus we postulate that some forces we call hydrogen bonds hold individual water molecules together.

Conversly, we use the information we get at the molecular level to explain what we actually experience.  For example, we looked at the crystal structure of ice as determined by x-ray analysis.   We could calculate that individual water molecules in ice were held far enough apart in the crystal to make the overall density of crystalline ice less than water.  The crystal structure explains why ice floats on water.

In studying chemistry, we are forced to represent both this microscopic realm and our tangible surroundings through imperfect symbols. 

Our representations always lack some precision in expressing reality. 

For example, the symbol H₂O as the structure of water gives us the ratio of hydrogen to oxygen, but fails to tell us the oxygen is bonded to each of the hydrogens and the angle of the bonds between the three atoms is 109^o.

Warning!  Acid-base chemistry depends upon an understanding of chemical equilibrium.  But our representations of equilibrium are generally flawed by the fact that when we DO anything to a system at equilibrium, we disturb the system and it is no longer in equilibrium.  For example, we will do many calculations in chemistry expressing equilibrium conditions after one or more conditions has changed.  But in most real world systems, true equilibrium conditions are never reached since systems are influenced by ever-changing conditions.

We rely on drugs to make us healthy when we are sick and to keep us healthy when we are well.  We can:

swallow them or

inject them or

inhale them.

but the trick is to make these drugs chemically available to our body's systems as they are needed.