Question

CAN YOU PLEASE EXPLAIN HOW TO DETERMINE METHOD I SHOULD USE TO FIND THE PH IN SUCH PROBLEMS. WHAT RULES SHOULD I FOLLOW OR THINK OF TO DETERMINE SUCH QUESTIONS. (STRONG ACID, STRONG BASE, BUFFER 1, BUFFER 2, WEAK ACID, WEAK BASE ETC)

PLEASE: dont solve if you dont explain briefly, and explain to me how I can determine it by myself.

The acid H2A has Ka1 = 2.00 ∙ 10-5 and Ka2 = 5.00 ∙ 10-9. We have a buffer consisting of 0.0300 moles of HA– and 0.0100 moles of A2– and adds 0.0500 moles of H3O +. What kind of system do we have and how to calculate the pH? Buffer 1 = H2A / HA– Buffer 2 = HA– / A2–

Answer 1

Strong acid dissociate completely so concentration of H⁺ion is same as concentration of acid e.g. HCl , HNO3 etc .

Strong base also dissociate completely and we can calculate H⁺ as [H⁺] = K_w/[OH^-] .

For weak acid dissociation is not completely. [H⁺] = √(c.K_a)

For weak base dissociation is not completely, [OH^-] = √(c.K_b)

pH = - log[H⁺]

In the given problem , the moles of added H₃O⁺ is larger than the moles of conjugate base present . Hence complete neutralization will takes place and buffer system would be destroyed .

Since volume of solution is not given, I have assumed it as 1 liter .