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How do you know whether a molecule is an acid or a base? I was doing the problems in 6D and I didn't know how to set up some of the equilibrium equations because I didn't know if they were acids or bases. Is there a way to tell?
Acids donate their protons and are usually written as HA, where A is the rest of the molecule. Bases accept protons and usually have an OH somewhere within the molecule (an exception to this is the weak base NH3). Really long molecules with an amine group (NH2) are usually bases as the nitrogen atom in this group tends to accept protons from water to produce OH-. Molecules with a carboxyl group (COOH) donate their proton to water and act as an acid.
For the salts in topic 6D, their acidity and basicity depend on whether cations and anions affect the pH of the solution. If the cations are in group I and group II, then they generally do not affect the pH of the solution. If parts of the salt are the conjugate acid of a weak base, then it would make the solution acidic, and if parts of the salt are the conjugate base of a weak acid, then it would make the solution basic. The conjugate acid of strong bases and the conjugate bases of strong acids do not affect pH.
We learned in 14A how to determine if a molecule is an acid or base. You can determine by its characteristics. Lewis acids accept electron pairs, so they tend to have a negative charge (Lewis acid), produce H3O+ (Arrhenius acid), and donate H+ (Bronsted acid). On the other hand, bases donate electron pairs (tend to have a positive charge), produce OH-, and accept H+.
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