A lake in Upstate New York has been significantly affected by acid rain. The current pH of the lake is 4.72 and organisms in the lake have been severely impacted by elevated aluminum concentrations. Assume that the aluminum concentrations in the water are controlled by the following reactions: Al(OH)3(s) = Al³+ + 30H- A13+ + OH AIOH2+ H2O H++ OH- Ksp = 3.0 x10-34 K₁ = 2.8 ×108 Kw = 1.01 x10-14 a) Find the equilibrium concentration of [A13+] in the lake. μmol/L b) Find the total dissolved aluminum concentration, Al, in units of μg Al/L. μg Al/L

Table 13-4 lists the stepwise Ka values for some polyprotic acids. What is the difference between a monoprotic acid, a diprotic acid, and a triprotic acid? Most polyprotic acids are weak acids; the major exception is H2SO4. To solve for the pH of a solution of H2SO4, you must generally solve a strong acid problem as well as a weak acid problem. Explain. Write out the reactions that refer to Ka1 and Ka2 for H2SO4. For H3PO4, Ka1 = 7.5 103, Ka2 = 6.2 108, and Ka3= 4.8 1013. Write out the reactions that refer to the Ka1, Ka2and Ka3equilibrium constants. What are the three acids in a solution of H3PO4? Which acid is strongest? What are the three conjugate bases in a solution of H3PO4? Which conjugate base is strongest? Summarize the strategy for calculating the pH of a polyprotic acid in water.

Amino acids are an important group of compounds. At low pH, both the carboxylic acid group (CO2H) and the amine group (NHR) are protonated. However, as the pH of the solution increases (say, by adding base), the carboxylic acid proton is removed, usually at a pH between 2 and 3. In a middle range of pHs, therefore, the amine group is protonated, but the carboxylic acid group has lost the proton. (This is called a zwitterion.) At more basic pH values, the amine proton is dissociated. What is the pH of a 0.20 M solution of alanine hydrochloride, [NH3CHCH3CO2H]Cl?

Does the pH of the solution increase, decrease, or stay the same when you (a) Add solid sodium oxalate, Na2C2O4, to 50.0 mL of 0.015-M oxalic acid? (b) Add solid ammonium chloride to 100. mL of 0.016-M HCl? (c) Add 20.0 g NaCl to 1.0 L of 0.012-M sodium acetate, NaCH3COO?

Malic acid is a weak diprotic organic acid with Ka1 = 4.0 104 and Ka2 = 9.0 105. a Letting the symbol H2A represent malic acid, write the chemical equations that represent Ka1 and Ka2. Write the chemical equation that represents Ka1 Ka2. b Qualitatively describe the relative concentrations of H2A, HA, A2, and H3O+ in a solution that is about one molar in malic acid. c Calculate the pH of a 0.0175 M malic acid solution and the equilibrium concentration of [H2A]. d What is the A2 concentrationin in solutions b and c?

Weak base B has a pKb of 6.78 and weak acid HA has a pKa of 5.12. a Which is the stronger base, B or A? b Which is the stronger acid, HA or BH+? c Consider the following reaction: B(aq)+HA(aq)BH+(aq)+A(aq) Based on the information about the acid/base strengths for the species in this reaction, is this reaction favored to proceed more to the right or more to the left? Why? d An aqueous solution is made in which the concentration of weak base B is one half the concentration of its acidic salt, BHCl, where BH+ is the conjugate weak add of B. Calculate the pH of the solution. e An aqueous solution is made in which the concentration of weak acid HA twice the concentration of the sodium salt of the weak acid, NaA. Calculate the pH of the solution. f Assume the conjugate pairs B/BH+ and HA/A are capable of being used as color-based end point indicators in acidbase titrations, where B is the base form indicator and BH is the acid form indicator, and HA is the acid form indicator and A is the base form indicator. Select the indicator pair that would be best to use in each of the following titrations: (1) Titration of a strong acid with a strong base. (i) B/BH+ (ii) HA/A (2) Titration of a weak base with a strong acid. (i) B/BH+ (ii) HA/A

An aqueous solution contains a mixture of 0.0500 M HCOOH (Ka = 1.77 104) and 0.150 M CH3CH2COOH (Ka = 1.34 105). Calculate the pH of this solution. Because both acids are of comparable strength, the H+ contribution from both acids must be considered.

For conjugate acidbase pairs, how are Ka and Kb related? Consider the reaction of acetic acid in water CH3CO2H(aq)+H2O(l)CH3CO2(aq)+H3O+(aq) where Ka = 1.8 105 a. Which two bases are competing for the proton? b. Which is the stronger base? c. In light of your answer to part b. why do we classify the acetate ion (CH3CO2) as a weak base? Use an appropriate reaction to justify your answer. In general, as base strength increases, conjugate acid strength decreases. Explain why the conjugate acid of the weak base NH3 is a weak acid. To summarize, the conjugate base of a weak acid is a weak base and the conjugate acid of a weak base is a weak acid (weak gives you weak). Assuming Ka for a monoprotic strong acid is 1 106, calculate Kb for the conjugate base of this strong acid. Why do conjugate bases of strong acids have no basic properties in water? List the conjugate bases of the six common strong acids. To tie it all together, some instructors have students think of Li+, K+, Rb+, Cs+, Ca2+, Sr2+, and Ba2+ as the conjugate acids of the strong bases LiOH, KOH. RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. Although not technically correct, the conjugate acid strength of these cations is similar to the conjugate base strength of the strong acids. That is, these cations have no acidic properties in water; similarly, the conjugate bases of strong acids have no basic properties (strong gives you worthless). Fill in the blanks with the correct response. The conjugate base of a weak acid is a_____base. The conjugate acid of a weak base is a_____acid. The conjugate base of a strong acid is a_____base. The conjugate acid of a strong base is a_____ acid. (Hint: Weak gives you weak and strong gives you worthless.)

Calculate the pH of a 0.072 M aqueous solution of aluminum chloride, AlCl3. The acid ionization of hydrated aluminum ion is Al(H2O)63+(aq)+H2O(l)Al(H2O)5OH2+(aq)+H3O+(aq) and K4 is 1.4 103.

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