1. The resistance of buffer solutions to change in pH values is due to the presence of a weak acid and its conjugate base (or a weak base and its conjugate acid) in the solution. This allows the buffer solution to neutralize added acid or base without significant changes in pH. For example, a buffer solution containing acetic acid (CH3COOH) and sodium acetate (CH3COONa) will resist changes in pH when small amounts of acid or base are added.
2. Acid-base indicators change color based on the pH of the solution they are in. They are typically weak acids or bases that change their molecular structure and color in response to changes in hydrogen ion concentration. For example, phenolphthalein is a commonly used acid-base indicator that is colorless in acidic solutions and pink in basic solutions.
Reasons for the following statements:
1. Indirect or back titration may be used with certain acids or bases instead of direct titrations when the analyte reacts slowly with the titrant or when the endpoint is difficult to detect. This method involves adding an excess of a known reagent to react with the analyte, then titrating the remaining excess reagent. This allows for more accurate determination of the analyte concentration.
2. The Arrhenius theory of acid-base definitions has limited application because it only considers substances that ionize in water to produce H+ or OH- ions as acids or bases. This definition does not account for substances that can act as acids or bases in non-aqueous solvents or those that do not ionize but still exhibit acidic or basic properties. Other theories, such as the Brønsted-Lowry and Lewis definitions, provide a broader and more comprehensive understanding of acid-base reactions.