Adding 100 ml of an 0.01 molar solution of HCl (0.01 M) to 1 liter of pure water lowers the pH from 7 to 3. The acidity of solutions is usually expressed by the so-called hydrogen ion exponent or pH (pH = 7 for neutral solutions, below 7 for acid solutions, and above 7 for alkaline solutions). As a result, both when H + and OH − ions are added, these ions are bound, and consequently, the acidity of the solution scarcely changes. On the other hand, when a buffer system is alkalized-that is, when a strong base (for example, NaOH) is added, the OH − ions are bound to the H + ions present in the buffer system owing to the dissociation of acetic acid and form a weak electrolyte-water:Īs the H + ions are expended in binding the OH − ions, newer and newer CH 3COOH molecules dissociate so that the equilibrium (1) shifts to the left. When a strong acid that yields many H + ions is added to a buffer system, the ions are bound to CH 3COO − ions and form weak (that is, only slightly dissociating) acetic acid: ![]() This salt, a strong electrolyte, dissociates almost entirely-that is, it yields many CH 3COO − ions. ![]() The acidity of buffer solutions changes little when they are diluted or when certain amounts of acids or bases are added.Ī mixture of solutions of acetic acid CH 3COOH and its sodium salt CH 3COONa is an example of a buffer system. ![]() (also buffer solutions or buffer mixtures), systems that maintain a certain concentration of H + ions-that is, a certain acidity of the medium.
0 Comments
Leave a Reply. |