Question

For the reaction C5H5N(aq) + H2O(l) C5H5NH+(aq) + OH-(aq), which of the following is a conjugate acid-base pair?

a. C5H5N, C5H5NH+
b. C5H5NH+, OH-
c. H2O, OH-
d. C5H5N, H2O

Answer 1

Answer: b.
`C_5H_5NH^+`,
`OH^-`

Step-by-step explanation:

According to the Bronsted-Lowry conjugate acid-base theory, an acid is defined as a substance which looses donates protons and thus forming conjugate base and a base is defined as a substance which accepts protons and thus forming conjugate acid.

For the given chemical equation:

`C_5H_5N(aq.)+H_2O(l)\rightarrow C_5H_5NH^+(aq.)+OH^-(aq.)`

Here,
`C_5H_5N` is accepting a proton, thus it is considered as a base and after accepting a proton, it forms
`C_5H_5NH^+` which is a conjugate acid.

And,
`H_2O` is losing a proton, thus it is considered as an acid and after loosing a proton, it forms
`OH^-` which is a conjugate base.

Hence, the correct answer is b.
`C_5H_5NH^+`,
`OH^-`

Answer 2

A conjugate acid results when a chemical species receives a hydrogen ion. Moreover, the conjugate base is what is formed after the conjugate acid has been formed. In this case, C5H5N accepts a hydrogen ion, becoming a conjugate acid and the species left over is OH-, making it the conjugate base. Therefore, the answer is B.