CHE-1102 Lecture Notes - Lecture 8: Ionic Compound, Solubility Equilibrium, Equilibrium Constant

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16 Aug 2016

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Saturated solution: no more solute will dissolve. Solubility product constant: equilibrium constant for ionic compounds that are only slightly soluble. Ksp is not the same as solubility. Ksp: only one value for a given solid at a given temperature. Solubility, and thus ksp, changes with t. When ionic salt dissolves in water it dissociates into separate hydrated ions. Caf2 (s) ca2+ (aq) + 2f- (aq) As dissolution occurs, ions build up and collide. Solids do not appear in the ksp expressions. Number of moles of ionic solid that dissolves per 1 l di water to form a saturated solution at 25 c. Determine the final equilibrium concentration of ca2+ (aq) and co3. 6. 7 x 10-5 mol of caco3 (s) will dissolve per 1l di water producing 6. 7 x 10-5 m. Ca2+ (aq) and 6. 7 x 10-5 m co3. At 25 c, the solubility of agcl is 1. 34 x 10-5m. Ksp = 1. 3 x 10-12 = (x)(x)

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THIS IS A FOUR PART QUESTION. HELP NEEDED. THANK YOU VERY MUCH.

a) Using the solubility of Ca(IO3) 2 that you determined in pure water, calculate the value of K sp using only concentrations, that is assuming that all activity coefficients are 1.0. Use 3 sig figs. Solubility of Ca(IO3)2 in Water: 0.00828 mols/L

b) Using the solubility of Ca(IO3)2 that you determined in 0.01M KIO3 as a solvent (the answer from part a), calculate the value of Ksp using only concentrations, that is assuming that all activity coefficients are 1.0. Solubility of Ca(IO3)2 = 0.00327

c) The next few questions will incorporate activity effects into the calculation of Ksp for Ca(IO3)2 using your data from the saturated solution of Ca(IO3)2 in pure water.To do so, we must first know the ionic strength of the solutions. Use your value of the solubility of Ca(IO3)2 in pure water to calculate the ionic strength of that solution.

d) Using the value of the ionic strength of a saturated solution of Ca(IO3)2 in pure water, use TABLE I under the solubility product experiment from the laboratory manual, and enter the activity coefficient for Ca2+ ions listed there at the ionic strength closest to that of the saturated solution of Ca(IO3)2 in pure water. If your ionic strength happens to lie exactly between two values in TABLE I, then use the activity coefficient for the higher ionic strength.

If you need any other information, please let me know.

Silver bromide, AgBr (s), is an essential reagent in black and white film developing. It is,

however, only sparingly soluble in water. AgBr (s) has K = 5.0 Ã 10-13, making it difficult to

rinse AgBr from the film negative with water.

Instead, excess AgBr is removed by an aqueous solution of sodium thiosulfate (Na2S2O3), which forms the complex ion Ag(S2O3)23-:

Ag+ (aq) + 2 S2O32- (aq) Ag(S2O3)23- (aq) Kf = 4.7 Ã 10+13 a) To see how this helps, first determine the molar solubility of AgBr (s) in water.

b) The large formation constant of Ag(S2O3)23- (aq) means that almost all of the silver is complexed with the thiosulfate. To determine how much, calculate the [Ag+] at equilibrium in a 1.0 L solution that initially contains 0.001 M silver ions and 0.200 M sodium thiosulfate. Do so by setting up an ICE table and assuming that x is small compared to 0.200 (but not 0.001). Show that this results in a value of x = [Ag(S2O3)23-] = 0.001. In other words, all of the Ag+ complexes.

c) Your result from part b suggests that no Ag+ remains in solution. This obviously canât be correct, since it would result in an infinitely large reaction quotient that wouldnât be equal to an admittedly large equilibrium constant. To determine the correct [Ag+], use the equilibrium concentrations determined in part b as your initial concentrations in a new ICE table. Then use Kf to determine [Ag+]. [This approach is called a stoichiometric shift and is useful when a reaction starts with only reactants but goes almost to completion. Is essence, we are approaching the equilibrium from the direction of all Ag(S2O3)23- and no Ag+ as opposed to the direction of all Ag+ and no Ag(S2O3)23-.]

d) Before we determine the solubility of AgBr (s) in a thiosulfate solution, we need to know the appropriate equilibrium constant. To find it, determine the value of the equilibrium constant for the reaction:

AgBr (s) + 2 S2O32- (aq) <-->Ag(S2O3)23- (aq) + Br - (aq) Kc = ??

e) Finally, calculate the molar solubility of AgBr (s) in 1.0 M sodium thiosulfate. In other words, what is [Ag(S2O3)23-] for the reaction given in part d when the initial concentration of thiosulfate is 1.0 M?

1) Consider the following equation: Rate = k [CH₃I]² [C₁₅H₁₁N]

i) If the concentration of C₁₅H₁₁N is doubled, does the rate constant:

A) Increase

B) Decrease

C) Remain unchanged

ii) If the concentration of of CH₃I is decreased by a factor of 3, the time it takes for the reaction to finish will:

A) Increase by a factor of 3

B) Increase by a factor of 9

C) Decrease by a factor of 9

D) Remain Unchanged

iii) If the temperature increases how will the activation energy change:

A) It will increase

B) It will decrease

C) It will remain unchanged

2) During a titration of a weak acid with a strong base you add an additional small amount of base after reaching the equivalence point.

i) How does the pH of the solution change?

A) Increase

B) Decrease

C) Remain unchanged

ii) How does the K_a of the acid change?

A) Increase

B) Decrease

C) Remain unchanged

3) You combine a solution of silver nitrate (AgNO₃) and a solution of sodium carbonate (Na₂CO₃) to form solid silver carbonate (Ag₂CO₃) and aqueous sodium nitrate (NaNO₃), the net ionic equation is listed below. You observe the white solid, Ag₂CO₃ in the test tube. You add a strong acid (HNO₃) to the mixture and it reacts with the carbonate ions as listed in the equations below. What would you expect to observe when adding the strong acid to the test tube?

2 Ag⁺_(aq) + CO₃^2-_(aq) <--> Ag₂CO_3(s)

2 H⁺_(aq) + CO₃^2-(aq) <--> H₂CO₃

H₂CO₃ -> H₂O_(l) + CO_2(g)

A) An increase in the amount of white solid

B) A color change of the solid

C) A decrease in the amount of white solid

D) No change in the amount of white solid

4) K_sp of BaF₂ at room temperature is 1.84 x 10^-7. It is also known that the reaction of dissolution of BaF₂ is endothermic. Imagine that you have a saturated solution of BaF₂ at equilibrium, that has some undissolved BaF₂ precipitated on the bottom of the test tube.

4.1) If the temperature is increased how would that affect:

i) The solubility of BaF₂

A) Increase

B) Decrease

C) Remain Unchanged

ii) The solubility constant of BaF₂

A) Increase

B) Decrease

C) Remain unchanged

4.2 An additional amount of BaF₂ was added to the solution how would that affect:

i) The solubility of BaF₂

A) Increase

B) Decrease

C) Remain unchanged

ii) The solubility constant of BaF₂

A) Increase

B) Decrease

C) Remain unchanged

4.3 If NaF is added to the solution how will it affect:

i) The solubility of BaF₂

A) Increase

B) Decrease

C) Remain Unchanged

ii) The solubility constant of BaF₂

A) Increase

B) Decrease

C) Remain unchanged

CHE-1102 Lecture Notes - Lecture 8: Ionic Compound, Solubility Equilibrium, Equilibrium Constant

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