Question

How many of the following responses are true?

1. The % dissociation of H₃PO₄ is lower than that of a strong acid because K_a1, K_a2, and K_a3 are all less than 1  
2. Acetic acid is a weak acid and will dissociate completely in water
3. HCl is a strong acid and will dissociate completely in water
4. When dissolved in water, only the first two dissociations of H₃PO₄ will both produce a significant amount of the H⁺ ion
5. Successive K_a values for polyprotic acids become smaller, and are therefore more important in determining the pH of a solution

Answer 1

1. True, as degree of dissociation depend on Ka of acid.
2. False, weak acid does not completely dissociates in water. Some part of it will dissociates depending on degree of dissociation.
3. True, as degree of dissociation is almost equal to one, therefore it will completely dissociates in water
4. True, as Ka3 will much-much lesser than Ka1 and Ka2, therefore it won't be able to produce significant amount of H+.
5. False, as successive Ka values becomes smaller as compared to previous, therefore they won't be able to produce significant amount of H+.