Question

What is the conjugate acid of `HCO_3^-`?

Answer 1

A conjugate acid is a substance that is formed when a base receives a proton, or `H^(+)`.

So, in order to determine the conjugate acid for a given base, all you have to know is that

`"base" + H^(+) -> "conjugate acid of that base"`

In your case, the base is hydrogen carbonate, or `HCO_3^(-)`. If you write the equation you'll get

`HCO_3^(-) + H^(+) -> H_2CO_3`

Carbonic acid, or `H_2CO_3`, will be the conjugate acid of hydrogen carbonate.