Questions & Answers about Señor, añada la sal a la sopa.
Why does añada end in 'a' if the dictionary form of the verb is añadir?
How would this sentence change if I were speaking to a friend instead of a "Señor"?
You would use the informal (tú) command. For regular verbs, the affirmative tú command looks exactly like the normal "he/she/it" present tense form of the verb. So, añadir becomes añade. The sentence would be: Añade la sal a la sopa.
Is there a rule for why it's feminine la sal instead of masculine el sal?
There is no strict rule here. While most words ending in 'a' are feminine and 'o' are masculine, words ending in consonants like 'l' can be either. For example, el sol (the sun) is masculine, but la sal (the salt) is feminine. You just have to memorize it as la sal.
Could I say "en la sopa" instead of "a la sopa"?