This document discusses different methods of expressing concentrations in solutions. It defines key terms like solution, standard solution, concentration, percent concentration, parts per million, parts per billion, molarity, normality, molality and formality. It provides formulas and examples to calculate the concentration values using these different methods for solutions like sodium hydroxide and hydrochloric acid. The key methods covered are percent concentration, parts per million, parts per billion, molarity, normality, molality and formality.