A sodium fatty acid salt is a compound that contains a sodium ion (Na+) and a fatty acid anion, which is a negatively charged molecule derived from a fatty acid. The general formula for a sodium fatty acid salt is CH3(CH2)nCOO-Na+, where n is the number of carbon atoms in the fatty acid chain.

A carboxylic salt, on the other hand, is a compound that contains a positively charged ion (usually a metal ion) and a carboxylate anion, which is a negatively charged molecule derived from a carboxylic acid. The general formula for a carboxylic salt is M+(RCOO-)n, where M+ is the positively charged ion, R is the alkyl group of the carboxylic acid, and n is the number of carboxylate anions in the salt.

So, while both sodium fatty acid salts and carboxylic salts contain negatively charged anions, they differ in the type of anion present and the positive ion that they are paired with. Sodium fatty acid salts contain fatty acid anions and sodium ions, while carboxylic salts contain carboxylate anions and various positively charged ions.