Question

Salt of strong acid and weak base have pH value:
a.) Less than 7
b.) More than 7
c.) Only 7
d.) Only 14

Answer 1

Solution of salt of strong acid and weak base have mostly characteristics of strong acid only. Thus, the pH value of salt will be acidic.

Complete-step- by- step answer:
Before jumping to direct results, let’s see the concept first.
So, acid is a substance capable of donating ${H^ + }$ ions in the solution while base is a substance capable of donating $O{H^ - }$ ions.

The word strong means it will donate ${H^ + }$ ions very easily and dissociation will be almost 100% while the word weak means the dissociation of $O{H^ - }$ will not be 100%. It will be less than that.
So, salt of strong acid and weak base will contain more number of ${H^ + }$ ions because the acid is strong and it will be almost 100% dissociated while the number of $O{H^ - }$ ions will be less in the solution.

We have studied that pH is the negative log of activity of Hydrogen ions i.e.,
pH= $- \log \left[ {{H^ + }} \right]$

Thus, if the concentration of Hydrogen ions is more, pH would be less i.e., the system will be acidic.
So, pH will be less than 7.

The option a.) is the correct answer.

Note: Salts of strong acids and weak bases do not hydrolyse because the anion becomes spectator ion and is not able to attract ${H^ + }$ ions while cation from weak bases donate a proton to water forming hydronium ion. The most common example of strong acid and weak base studied is the reaction between HCl and $N{H_4}OH$.