Exam 2 Part 2 - Hydrolysis of Salts & Polyprotic Acids

Are anions associated with conjugate bases or acids?

• Conjugate bases (strong acids)

will be basic

Are cations associated with conjugate bases or acids?

• Conjugate acids (bases)

will be acidic

How do you know if an anion is neutral?

• Neutral: anion is a conjugate base of a strong acid (Cl-, Br-, NO3-, I-, ClO4-)

anions of strong acids

How do you know if an anion is basic?

• Basic: anion is a conjugate base of a weak acid (everything else)

How do you know if a cation is neutral?

• Neutral: cation is a conjugate acid of strong base (Grp 1 + OH- and Ba2+, Sr2+, and Ca2+ + OH-)

How do you know if a cation is acidic? What is the exception?

• Acidic: cation is a conjugate acid of a weak base (everything else, NO H)

Is BaBr acidic, basic, or neutral?

• Ba+; neutral

• Br-; neutral

NEUTRAL

Is Al(NO3)3 acidic, basic, or neutral?

• Al3+; acidic

• NO3-; neutral

ACIDIC

What equation can be used to find K_A or K_B value when given K_A and K_B?

• K_W=K_A x K_B

What does Kw represent when using the (K_W=K_A x K_B)  equation?

• Kw = 1.0 × 10^(-14)

What are the steps to calculating pH of a salt?

1. Determine whether salt is acidic, neutral, or basic

2. Use ICE table; hydrolysis

3. Set expression equal to Ka or Kb to find  [H3O+] or [OH-]

4. Solve for pOH or pH

When an anion contains an H, what must you do to figure out if the salt is acidic, neutral, or basic?

• Compare K_A and K_B values; one at each arrow of dissociation

CHOOSE larger K value

If 3 K values are given, how many times will the given ion be dissociated?

• 4 times; 3 arrows

INCLUDE CHARGES

If 2 K values are given, how many times will given ion be dissociated?

• 3 times; 2 arrows

INCLUDE CHARGES

Which direction do the Ka values point? What occurs to the anion at each dissociation?

• Points toward right; anion loses H+ ion

Which direction do the Kb values point? What occurs to the anion at each dissociation?

• Point toward left; anion gains H+ ion

How do you choose which K_A(1, 2, 3) and K_B (1, 2, 3)values to compare?

• Choose arrows of K_A and K_B value only going AWAY from given anion

After comparing, which K_A and K_B value do you choose?

• Choose larger one; to determine if anion is acidic or basic

In the dissociation of polyprotic acids, which Ka value do you use?

• Use first dissociation, Ka1