Question

Which of these neutralization reactions has a ph < 7 when equal molar amounts of acid and base are mixed. select one:
a. ch3co2h(aq) + naoh(aq) ⇌ h2o(l) + nach3co2(aq)
b. hcl(aq) + c5h5n(aq) ⇌ c5h5nhcl(aq)
c. h2so4(aq) + 2 koh(aq) ⇌2 h2o(l) + k2so4(aq)
d. hcl(aq) + naoh(aq) ⇌ h2o(l) + nacl(aq)?

Answer 1

The correct answer is B.
Strong acids completely dissociates to give hydrogen ions . Weak bases can only partially dissociate to give hydroxide ions .
Therefore when equal amounts of acid and base are mixed, while Acid is completely dissociated and gives out hydrogen ions but base only gives out a fraction of hydroxide ions.
Therefore number of hydrogen ions in the solution will be higher than hydroxide ions, resulting in an acidic pH. Therefore pH <7

Answer 2

Answer:

$HCl(aq) + C_5H_5N(aq) <--> C_5H_5NHCl(aq)$

Explanation:

Hello,

In this case, as the pH must remain less than 7 we must look for a strong acid and a weak base with a 1 to 1 mole relationship in the chemical reaction since equal molar amounts are to be mixed. This is due to the fact the the whole acid will dissociate and as the weak base does not completely dissociate, there will be remaining hydride ions causing the required pH. In such a way, the best combination is hydrochloric acid (strong acid) with pyridine (weak base) because they have the aforesaid mole relationship and there will be unreacted hydride ions causing a less than 7 pH considering the reaction:

$HCl(aq) + C_5H_5N(aq) <--> C_5H_5NHCl(aq)$

Best regards.