The Acidic/Basic Nature of Anhydrides and Salts

As a way to visualize how substances other than acids and bases can have acidic and basic properties, we placed some litmus solution in various aqueous solutions.  Pictured below is how the litmus looked in distilled water, hydrochloric acid, and sodium hydroxide.  Notice the light purplish color in the water, the light pink/peach color in the hydrochloric acid, and the deep purple color in the sodium hydroxide.  

H₂O                HCl                 NaOH

Pictured below are two solutions representing the anhydrides.  The one on the left was formed by blowing bubbles in the solution.  The pink color is due to carbon dioxide, an acidic anhydride.  The flask on the right, contains CaO (commonly known as lime) and is a deep color due to the basic nature of the basic anhydride CaO.  

CO₂                  CaO

The final image below shows how salts can have varying acid/base natures.  Notice the NaCl is the same light purplish color that the distilled water is, indicating that NaCl is a neutral salt.  The NaHCO₃ (baking soda) and the NaC₂H₃O₂ are the same deep purple color that sodium hydroxide is, indicating their basic nature.  Notice the litmus reveals that the other salt, the NH₄Cl (smelling salt) is an acidic salt.

NaCl    NaHCO₃        NH₄Cl    NaC₂H₃O₂