How is the purity of substances important?​

Pure substances have the ability to form predictable outcomes from their chemical reactions. Chemists tend to use pure substances when conduction chemial research as impure substances can mess up their experiments.

in chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. the standard formula is c = m/v, where c is the concentration, m is the mass of the solute dissolved, and v is the total volume

c is the answer because when something is left after something evaporates that shows the chemical change.