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solubility equilibrium and thermodynamics


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d. (2 points) Indicate whether the pH at the equivalence point for each of the following titrations is below 7, at 7, or above 7. Titration of:


HClO with NaOH ____________________


HClO4 with KOH ____________________


C2H5NH2 with HNO3 ____________________


NaOH with HBr ____________________


e. (1 points) For each of the following processes, predict whether the entropy change is positive (S > 0), negative (S < 0), or approximately equal to zero (S  0).


Liquid NH3 evaporates ____________________


NH3(g) + HCl(g)  NH4Cl(s) ____________________


2NF3(g)  N2(g) + 3F2(g) ____________________


Gaseous CO2 is forced under pressure into ____________________

sugar water



2. (8 points) Calculate the pH of the solution formed by mixing 200.0 mL of 0.100 M HBr with 200.0 mL of 0.100 M Ba(OH)2.






Answer is 7 because it is a perfect water making reaction.


Barium hydroxide is a base and hydrochloric acid is an acid and the molar ratios are the same so there fore it is neutral. I e 7.00.


Acid + base= h20 + neutral product
















3. (24 points) (a) Calculate the solubility of Ni(OH)2 in water in units of grams per liter (g/L). The Ksp for Ni(OH)2 is 1.6 x 10-16. (b) What is the molar solubility of Ni(OH)2 in a solution that contains 0.035 M Ni2+? © At what pH will a precipitate of Ni(OH)2 form if NaOH is added to a solution that contains 0.000100 M Ni2+? (d) Will a precipitate of Ni(OH)2 form if 25.0 mL of 0.0057 M Ni(NO3)2 solution is mixed with 300.0 mL of 0.0150 M NaOH?






















4. (8 points) (a) Calculate the G for the solubility equilibrium reaction of FeS. (b) If standard state concentrations of reactants and products were mixed, in which direction would this reaction proceed spontaneously?



Calculate the solubility product of mackinawite at 25°C:

FeS(s) « Fe2+ + S2-


DrG° = Df G°Fe2+ + Df G°S2- - Df G°FeS(s)

DrG° = -90.0 + (85.8) - (-93.0) = 88.8 kJ mol-1





5. (12 points) (a) Calculate Srxn at 25C for the reaction of hydrogen sulfide with oxygen. The chemical equation is


H2S(g) + 2O2(g)  H2SO4(l)


Does this represent an increase or decrease in the order of the system? (b) Can we tell whether this reaction is spontaneous from this number? Why or why not? © If this reaction is spontaneous, what can you conclude about the enthalpy change for the reaction? Explain briefly.



















6. (16 points) For a particular reaction, H = -55.7 kJ and S = -103.0 J/K. (a) Is the reaction endothermic or exothermic? (b) Does the reaction lead to an increase or decrease in the disorder of the system? © Calculate G at 100C. Is this reaction spontaneous at this temperature under standard conditions? (d) At what temperature will G = 0? If the temperature is increased above this value, will the reaction be spontaneous?



























7. (7 points) Ka for acetic acid at 25C is 1.754 x 10-5. Ka for acetic acid at 50C is 1.633 x 10-5. What are H and S for the ionization of acetic acid?


8. Short Answer (18 points)


a. A chemical reaction cannot be spontaneous in both the forward and back reactions. In terms of the 2nd law of thermodynamics and Gibbs free energy, explain why this is true.






















b. Fluoride is added to drinking water to fight tooth decay. Explain the chemical basis for adding fluoride ion to drinking water and how this fights tooth decay. Be specific in your answer. Note that hydroxyapetite (tooth enamel) has the general formula Ca10(PO4)6(OH)2.




c. How does the entropy of the surroundings change as energy flows out of the system? Explain briefly!






















d. What does it really mean when we say that an inorganic salt is “insoluble”?




e. Explain what it means when an inorganic compound, such as AgCl, is said to be “insoluble”.























f. How would you expect the spontaneity of the following reaction to behave with a change in temperature? Explain your answer.


COCl¬2(g)  CO(g) + Cl2(g)

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