Unit 5: Equilibrium

Question 1

If Q > K

Answer 1

A precipitate forms

Question 2

If Q = K

Answer 2

The solution is saturated, but no precipitate forms

Question 3

If Q

Answer 3

More solute can be added

Question 4

Solubility to Ksp

Answer 4

• multiply the solubility by the coefficient of each ion in the dissociation reaction
• the equilibrium concentrations of the ions are those values plus the initial concentration (usually 0)
• plug those concentrations into the Ksp equation

Question 5

Ksp to solubility

Answer 5

Use X variables multiplied by the coefficients of the dissociated ions to represent the equilibrium concentrations of those ions. Set equal to Ksp and solve for x. Then solve for each concentration.

Question 6

Calculations involving the common ion effect

Answer 6

Calculate the equilibrium concentrations using stoichiometric proportions and Ksp, then solve and compare equilibrium concentrations to the initial concentration to see how much dissociated

Question 7

Common ion effect

Answer 7

The solubility of a solid is LOWERED if the solution already contains ions common to the solid

Question 8

Will a precipitate form? How to know

Answer 8

1. Calculate the concentrations of the ions in question.
2. Plug these concentrations into the Ksp equation to find Q.
3. Compare Q to K

Question 9

Buffered solutions contain…

Answer 9

• a weak acid and conjugate base

- OR a weak base and conjugate acid

Question 10

When H+ is added to a buffered solution,

Answer 10

It reacts to completion with the weak base – either combines with A- or B to form HA or BH+

Question 11

When OH- is added to a buffered solution,

Answer 11

It reacts essentially to completion with the weak acid present – combines with either HA to make A- and H2O or BH+ to make B and H2O

Question 12

Optimal buffering occurs when…

Answer 12

[HA] = [A-] ; when pH = pKa

Question 13

Strong acid - strong base titration curve

Answer 13

1. pH changes gradually with constant slope until close to the equivalence point
2. Equivalence point occurs at 7

Question 14

Weak - strong acid/base titration curve

Answer 14

1. The initial pH is closer to 7 because the [H+] or [OH-] concentration is smaller
2. Near the beginning, pH changes more rapidly than with a strong solution, but then levels off near the halfway point due to buffering
3. The pH at the equivalence point depends on the strong species that determines the pH of the salt formed

Question 15

Arrhenius model

Answer 15

Acids produce H+ in solution; bases produce OH-

Question 16

Bronsted-Lowry model

Answer 16

An acid is a proton donor; a base is a proton acceptor