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problem 1: The Ksp 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?

problem 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. find out the [H3O+], [H2C2O4], [HC2O42-], [C2O42-] 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)       

problem 3
: When sodium hydroxide and hydrochloric acid are reacted together, their standard enthalpy change of reaction (ΔH1o)can be find outd:

NaOH(aq) + HCl(aq) ↔ NaCl(aq) + H2O(l)     ΔH1o = -55.86 kJ/mol

This equation can be rewritten as:

OH-(aq) + H3O+(aq) ↔ 2 H2O(l)     ΔH1o = -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) ↔ C3H5O2-(aq) + H2O(l)     ΔH2o = -49.23 kJ/mol

a) Using all the knowledge you have of chemistry, describe (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) describe, as best you can, the sign of ΔSo in part (d).

problem 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).

problem 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)

ΔHo = 25.1 kJ/mol; ΔSo = 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) find out 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? describe your answer.   

problem 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) find out the pH of this buffer.   

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

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

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