Chemical changes Study Guide

The pH scale is a logarithmic scale used to specify the acidity or alkalinity of an aqueous solution. It is inversely related to the hydrogen ion concentration ([H⁺]). This means that as the concentration of hydrogen ions increases, the pH value decreases, indicating a more acidic solution. Conversely, a decrease in hydrogen ion concentration leads to an increase in pH, indicating a more alkaline solution. A key aspect of the pH scale is its logarithmic nature: a change of one pH unit corresponds to a tenfold change in hydrogen ion concentration. Specifically, if the hydrogen ion concentration increases by a factor of 10, the pH of the solution will decrease by 1 unit. For example, a solution with pH 6 has ten times the hydrogen ion concentration of a solution with pH 7, and a solution with pH 5 has one hundred times (10 x 10) the hydrogen ion concentration compared to a solution with pH 7.

When two aqueous solutions of ionic compounds are mixed, their ions can recombine to form new compounds. To decide if a precipitate (an insoluble solid) will form, use solubility rules to test each possible combination of cations and anions. If any of the possible new compounds are insoluble (as indicated by the rules), a precipitate forms and can be named by its ions (e.g., silver chloride). If all new compounds are soluble, no precipitate appears and all ions stay in solution.