Standard enthalpy change of reaction

Question

Question 1: The K_sp of the phosphate fertilizer CaHPO₄. 2 H₂O is 2.7 x 10^-7 at 25 ^oC.  What is the molar concentration of a saturated solution? What mass of this compound will dissolve in 3.0 L of water at this temperature?

Question 2: Oxalic acid (H₂C₂O₄) has been implicated in diseases such as gout and kidney stones. A high concentration of oxalic acid is found in the leaves of mature rhubarb plants, and is the reason we discard that part. Calculate the [H₃O⁺], [H₂C₂O₄], [HC₂O₄^2-], [C₂O₄^2-] and the pH of a 1.24 M solution of oxalic acid. (Ka(H₂C₂O₄) = 5.4 x 10^-2; Ka(HC₂O₄) = 5.4 x 10^-5)       

Question 3: When sodium hydroxide and hydrochloric acid are reacted together, their standard enthalpy change of reaction (ΔH₁^o)can be calculated:

NaOH(aq) + HCl(aq) ↔ NaCl(aq) + H₂O(l)     ΔH₁^o = -55.86 kJ/mol

This equation can be rewritten as:

OH^-(aq) + H₃O⁺(aq) ↔ 2 H₂O(l)     ΔH₁^o = -55.86 kJ/mol

When sodium hydroxide is reacted with propionic acid the standard enthalpy change of reaction (ΔH₂o)can also be determined:

NaOH(aq) + C₃H₅O₂H(aq) ↔ C₃H₅O₂Na(aq) + H₂O(l)  ΔH₂o = -49.23 kJ/mol

This equation can be rewritten as:

OH^-(aq) + C₃H₅O₂H(aq) ↔ C₃H₅O^2-(aq) + H₂O(l)     ΔH₂o = -49.23 kJ/mol

a) Using all the knowledge you have of chemistry, explain (or show) why you can simplify the above equations.

b) Use the above information to determine the standard enthalpy change of the ionization of propionic acid (ΔH₃o):                            

C₃H₅O₂H(aq) + H₂O(l) ↔ C₃H₅O₂^-(aq) + H₃O ⁺(l)        ΔH₃o = ?

c) Determine the ΔGo for the ionization of propionic acid (Ka = 1.3 x 10^-5)

d) Determine the ΔSo for the ionization of propionic acid.   

e) Explain, as best you can, the sign of ΔSo in part (d).

Question 4: Draw out the Lewis structures of the following two compounds.

BeCl₂ + 2Cl^- →

a) Identify which compound is the Lewis acid and which is the Lewis base. What are the definitions of a Lewis acid and a Lewis base?

b) Draw the Lewis structure(s) of the product(s).

Question 5: Desiccants (drying agents) can often be regenerated by heating. A desiccant that is commonly regenerated is:

CaSO₄. 2H₂O:                           

CaSO₄. 2H₂O(s) → CaSO₄(s) + 2H₂O(g)

ΔH_o = 25.1 kJ/mol; ΔS_o = 69.3 J/molK
Regeneration is carried out at 250 ^oC.

a) What is the ΔGo for this reaction?

b) What is the equilibrium constant at 25 ^oC?   

c) Calculate ΔG for the reaction at 250 ^oC, if the partial pressure of water is 0.021 atm?

d) Is regeneration of this desiccant an enthalpy- or entropy-driven process? Explain your answer.   

Question 6: You make up 0.100 L of a buffer containing 1.00 M acetic acid and 1.10 M sodium acetate. The Ka of acetic acid is 1.8 x 10^-4.

a) Calculate the pH of this buffer.   

b) You then add 30.00 mL of 0.100 M HCl to the solution. Calculate the pH value after this addition.                                       

c) Calculate the pH if the same amount of HCl were added to 0.100 L of water.