Solubility Homework Set Worked Out Solutions

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Unformatted text preview: q) NiCO3 (s) HCl‐ This strong acid can neutralize CO32‐ because this anion is the conjugate base of a weak acid. This removes CO32‐, shifting the reaction to the right and increasing solubility. NiCl2‐ common ion, therefore decreases solubility. NaCl‐ no effect. Na2CO3‐ common ion, therefore decreases solubility. NH3‐ Ni+ forms the complex ion Ni(NH3)62+, increasing solubility. 14 Dr. Fus CHEM 123 53. The solubility of how many of the following salts will be affected by strong acid? NaNO3 BaF2 AgBr Cu3(PO4)2 Conjugate bases of weak acids will be affected by strong acid. This includes: Cu3(PO4)2 and BaF2. 54. Zinc oxalate is a slightly soluble salt. How many of the following reagents would be expected to decrease the solubility of ZnC2O4? NaOH HCl ZnCl2 Na2C2O4 NH3 Zn2+(aq) + C2O42‐(aq) ZnC2O4 (s) Na2C2O4‐common ion, therefore decreases solubility. NH3‐ Zn2+ forms the complex ion Zn(NH3)42+, increasing solubility. NaOH‐ Zn2+ forms the complex ion Zn(OH)42‐, increasing solubility. HCl‐ C2O42‐ is the conjugate base of a weak acid (HC2O4‐), and is therefore a weak base itself. It can be neutralized by HCl, a strong acid, thereby decreasing the concentration of C2O42‐ and shifting the equilibrium to the right and increasing solubility. ZnCl2‐ common ion, therefore decreases solubility. 55. Which of the following reagents would increase the solubility of Ni(OH)2(s)? NaOH HCl NH3 Ni(NO3)2 Ni2+(aq) + 2OH‐(aq) NiOH2 (s) Ni(NO3)2‐common ion, therefore decreases solubility. NaOH‐ common ion, therefore decreases solubility. HCl‐ H+ neutralizes OH‐, decreasing the concentration of OH‐ and shifting the equilibrium to the right, increasing solubility. NH3‐ Ni2+ forms the complex ion Ni(NH3)62+, increasing solubility. 56. The molar solubility of _____________ is not affected by the pH of the solution. a) MnS b) AlCl3 c) KNO3 d) NaF e) Na3PO4 To be unaffected by pH, BOTH the cation and anion must be conjugate salts of strong acids/bases. Even if one is the conjugate salt of a weak acid/base, the solubility will be affected by a change in pH. Of the ions, only KNO3 has both ions as conjugate salts of strong acids/bases (KOH and HNO3 are a strong base and strong acid, respectively). 15 Dr. Fus CHEM 123 57. For which salt should the aqueous solubility be most sensitive to pH? a) Ca(NO3)2 b) CaF2 c) CaCl2 d) CaBr2 e) CaI2 All of the cations are Ca2+, the conjugate salt of the strong base Ca(OH)2. It cannot be neutralized by changes in pH. Of all the anions, only F‐ is the conjugate base of a weak acid. The rest are conjugate bases of strong acids. Therefore CaF2 is most sensitive to pH. Precipitation and Separation of Ions (Section 17.6) To determine whether or not precipitation occurs, you need to compare Ksp to Q, the reaction quotient. The equation for Q appears the same as that for Ksp: Q= [products] [reactants] However, these concentrations can be at any point and do not necessarily correspond to equilibrium concentrations, as they do f...
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