# How can I determine the formula of an acid?

First you need to determine if the acid is binary (only H and one other element) or ternary (H and more than one other element).

#### Explanation:

Binary acids will have names which begin with the prefix "hydro". The ending of the name for the acid will come from the second element found in the acid.

HCl = hydrochloric
HBr = hydrobromic

Notice how chlorine changes to chloric and bromine changes to bromic.

Ternary acids do not have the prefix hydro in their names unless the polyatomic ion has a name which has the "ide" suffix. The name comes from the element listed first in the polyatomic ion (oxyanion).

${H}_{3} P {O}_{4}$ = phosphoric acid
${H}_{3} P {O}_{3}$ = phosphorous acid

Because ${H}_{3} P {O}_{4}$ contains the polyatomic ion phosphate, the ending for the name of the acid will be "ic".

Because ${H}_{3} P {O}_{3}$ contains the polyatomic ion phosphite, the ending for the name of the acid will be "ous".

You should memorize
"ate" goes to "ic"
"ite" goes to "ous"

Here is a video to help further with this concept.

Video from: Noel Pauller

Hope this helps!