Experiment 4 (solubility)

Question 1

Solubility Equilibrium

Answer 1

-equilibrium between an ionic solid and its dissociated cations and anions (in a saturated solution)
-Precipitate builds upon seeds

Question 2

Ksp

Answer 2

-solubility constant
-Ksp = [A+]^a [B-]^b
(Where A+(aq) + B-(aq) → AB (s))
-describes the extent to which a solid ionic compound dissolves in a solvent

Question 3

Super saturated solution

Answer 3

-Q > Ksp
-a solution that holds more solute than it can normally dissolve at a given temperature.
-This means the solution is in a non-equilibrium state, and the extra solute is dissolved despite exceeding the typical solubility limit
-This unstable state can be disrupted, causing the excess solute to precipitate out and form crystal

Question 4

Saturated solution

Answer 4

-Q = Ksp
-A solution with solute that dissolves until it is unable to dissolve anymore, leaving the undissolved substances at the bottom

Question 5

Unsaturated solution

Answer 5

-Q < Ksp
-a solution where the amount of dissolved solute is less than the maximum amount the solvent can hold at that temperature

Question 6

Common ion effect

Answer 6

-the presence of ions in common with the solid decreases the solubility of the solid
–e.g. the solubility of AgCl in a HCl solution is lower than in pure water
-However, adding a large amount of Cl- to a saturated AgCl solution increases the solubility of AgCl
-The solubility of AgCl is affected by two equilibria:
–AgCl ←> Ag+ + Cl- and Ag+ + 2Cl- ←> AgCl2-

Question 7

Solubility

Answer 7

-the maximum amount of solute that can be dissolved in 1 L of solution (to make a saturated solution)
-in moles/L or grams/L

Question 8

Molar solubility

Answer 8

-the number of moles of a solute that dissolve to form a liter of a saturated solution
-measured in M (moles/L)
-To find molar solubility, solve for s in Ksp expression

Question 9

Example: finding molar solubility of Ca(OH)2 in different solvents

Answer 9

-Prepare the saturated Ca(OH)2 solutions in two different solvents (pure H2O and standard NaOH)
-Use dry container to receiver the filtrate (film of particles may form on surface)
-During pipetting process, the pipet tip should touch the bottom of the container
-Results:
–Volume of HCl needed for titration and [OH-] total is greater for Ca(OH)2 in NaOH than pure H2O, while [Ca2+] molar solubility decreases in NaOH
–Ca(OH)2 has higher molar solubility in pure water solvent than NaOH
Common ion effect
–Ksp is same for both H2O and standard NaOH
–To calculate [OH-] in NaOH solution, take OH-(total) - OH-(NaOH)
–OH-(total)= M(OH-) from titration
–M(OH)V(OH) = M(HCl)V(HCl)

Question 10

Dilution equation

Answer 10

-M1V1 = M2V2

Question 11

pH and solubility

Answer 11

-the solubility of a basic salt increases with [H3O+] in the solution
–Example: the solubility of CaCO3 increases in acidic solutions
—CaCO3(s) → Ca2+(aq) + CO3(2-)(aq)
—CO3(2-) + H3O+ → HCO3- + H2O
—HCO3- + H3O+ → CO2 + 2H2O
-Therefore, many metal oxides, hydroxides, sulfides, sulfites, and carbonates are soluble in strong acids