Question

question 12 (1 point)
a titration involving a very weak base with a strong acid was performed. what is the ph at the
equivalence point?

ph > 7
ph < 7
ph = 7
the ph cannot be determined.

question 13 (1 point)
brønsted-lowry bases contain at least one what?

hydroxide group
atom with one electron pair
proton donating group
metal ion

question 14 (1 point)
if an acid has a ( k_a ) of ( 4.1 \times 10^{-9} ) then what can we assume is the source of ( h_3o^+ ) ions?

the source of ions is from the acid.
the source of ions is from the water.
the ions come from both water and acid.
the ions come from both conjugate acid and base pairs.

Explanation:

Question 12

When a very weak base is titrated with a strong acid, the salt formed undergoes hydrolysis. The conjugate acid of the weak base is formed, which donates protons, making the solution acidic. So, the pH at the equivalence point is less than 7.

According to the Brønsted - Lowry theory, a base is a proton ($\ce{H+}$) acceptor. A Brønsted - Lowry base must have at least one atom with a lone pair of electrons to accept a proton. Hydroxide group is related to Arrhenius bases, proton - donating groups are Brønsted - Lowry acids, and metal ions are not a requirement for Brønsted - Lowry bases.

A very small $K_a$ (like $4.1\times10^{-9}$) indicates a very weak acid. Weak acids dissociate very little, so the contribution of $\ce{H3O+}$ from the acid is negligible. In aqueous solution, the main source of $\ce{H3O+}$ comes from the auto - ionization of water ($\ce{H2O + H2O
ightleftharpoons H3O+ + OH-}$).

Answer:

B. $\text{pH} < 7$

Question 13