How to tell if it is an acid or base?

[Madeera_Mian_3B]

The 7th edition textbook problem Fundamental J 1, identify which is a Bronsted Acid or Base: NH3, HBR, KOH, H2SO3, Ca(OH)2. How do we know which one is a Bronsted acid or base?

[Lumbini Chandrasekera 1B]

You can tell from the chemical formula whether it is likely to produce H+ protons (acid) or OH- hydroxides (base), but for something like NH3 you would have to see what is would do when adding water. When adding water, it would form NH4+ and OH-, which is a hydroxide, making NH3 a base.

[Esther Ahn 4I]

Acids also tend to have the form HA where A is an element and bases tend to have the form BOH where B is an element.

[LuisG14A1J]

Acids and bases are generally visible whether something has H or OH ions within the compound. NH₃ just has to be known that Ammonia is a weak base. There are some several compounds that just have to be known what they are so we can use them quickly and commonly.
To also find out if a compound is acidic or basic is if has electron lone pair, in this case NH₃ has 1 open lone pair that means it is able to accept a hydrogen, though weakly (not too much), which makes it a weak base.

Typically, everything with the H in the front is denoted that way to give that indicator that the Hydrogen atoms can be stolen or traded in acid or base reactions.
In the examples given, It should be simple enough to see that those with the Hydrogen indicators in the front are acidic and those with the Hydroxide ions (OH) are basic. H₂SO3 is a weak acid.

"any acid that is not one of the seven strong is a weak acid (e.g. H₃PO₄, HNO₂, H₂SO₃, HClO, HClO₂, HF, H₂S, HC₂H₃O₂ etc.)

Those are weak acid examples.

These are the main 7 strong acids for low level chemistry.
HCl, HBr, HI,
,HNO₃, H₂SO₄, HClO₄, & HClO₃

[John Kim Lec3Dis3L]

A general rule of thumb is to see whether the molecule predominantly contains (H^+) or (OH^-). Hope this helps!