There are 3 different acid/base theories
-Arrenius
→ acid frees ion H+ in water (HCl ⇒ H+ + Cl-) ⇢ HCl acid
→ base frees ion OH- in water. (NaOH ⇒ Na+ + OH-) ⇢ NaOH base
→ this theory doesn't explain "why meh NH3 is a base?". NH3 cannot frees OH- ion but the pH meter shows basic pH.
So, this theory was abandoned
-Brönsted-Lowry
→ acid gives protons (H+ ion) to an another substance that receives it.
→ HCl + H2O ⇒ H3O+ + Cl- In this reaction, HCl gives a proton to the water
which becomes oxonium ion, so HCl is the acid because it gives H+ and water is the base because it takes H+.
→Now, you can watch the reaction from the products to the reagents and you can see that H3O+ is an acid because it
can give H+ ion and Cl- is a base because the only thing it can do is to receive H+ ions.
In the acid-base reaction, every acid has its conjugate base and every base has its conjugated acid. In this example,
HCl is the acid and Cl- is its conjugated base; H2O is the base and oxonium ion is its conjugated acid.
-Lewis
→It's the same as Brönsted-Lowry theory but the difference is about the exchanges.
→In this theory, the base has a free electron pair that can give to an another substance who takes this electron pair,
the acid
If you need more help or better explanations, please just contact me and I'd be very happy to help you
(sorry for the bad English, but I'm still learning
)