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Malonic acid,
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- 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.)arrow_forwardConsider these acids (a) Arrange the acids in order of increasing acid strength from weakest to strongest. (b) Which acid has the smallest pKa value?arrow_forwardThe pH of a 0.10-M solution of propanoic acid, CH3CH2COOH, a weak organic acid, is measured at equilibrium and found to be 2.93 at 25 °C. Calculate the Ka of propanoic acid.arrow_forward
- Calculate the pKa value for each of the following acids. a. Nitrous acid (HNO2), Ka = 4.5 104 b. Carbonic acid (H2CO3), Ka = 4.3 107 c. Dihydrogen phosphate ion (H2PO4), Ka = 6.2 108 d. Sulfurous acid (H2SO3), Ka = 1.5 102arrow_forwardWhich acid has the strongest conjugate base? (a) HNO2 (b) C6H5CO2H (c) HCN (d) HClarrow_forwardHydrazine, N2H4 (having the structure H2NNH2), and its derivatives have been used as rocket fuels. Draw the Lewis electron-dot formula for the hydrazine molecule. Describe the geometries expected about the nitrogen atoms in this molecule. Why would you expect hydrazine to be basic? Which substance, NH3 or N2H4, would you expect to be more basic? Why? Write the chemical equation in which hydrazine reacts with hydrochloric acids to form the salt N2H5Cl. Consider the positive ion of this salt. How does its basic character compare with that of NH3 and N2H4? Explain.arrow_forward
- A solution of acetic acid, HC2H3O2, on a laboratory shelf was of undetermined concentration. If the pH of the solution was found to be 2.57, what was the concentration of the acetic acid? The Ka of acetic acid is 1.7 105.arrow_forwardIn each of the following acid-base reactions, identify the Brnsted acid and base on the left and their conjugate partners on the right. (a) C2H5N(aq) + CH3CO2H(aq) C5H5NH+(aq) + CH3CO2(aq) (b) N2H4(aq) + HSO4(aq) N2H5+(aq) + SO42(aq) (c) [Al(H2O)6]3+ (aq) + OH(aq) [Al(H2O)5OH]2+ (aq) + H2O+()arrow_forwardCalculate Ka for the weak acids that have the following PKa values. (a) 3.9(b) 10.12 (c) 13.07arrow_forward
- 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/Aarrow_forwardRank the compounds in each of the following groups in order of increasing acidity or basicity, as indicated, and explain the order you assign. (a) acidity: NaHSO3, NaHSeO3, NaHSO4. (b) basicity: BrO2-, ClO2-,IO2-. (c) acidity: HOCI, HOBr, HOI. (d) acidity: HOCl, HOClO, HOClO2, HOClO3. (e) basicity: NH2-, HS-, HTe-, PH2-. (f) basicity: BrO-, BrO2-, Bro3-, BrO4-arrow_forwardConsider two acids: HCO2H (formic acid, pKa = 3.8) and pivalic acid [(CH3)3CCO,H, pK = 5.0]. (a) Which acid has the larger K? (b) Which acid is the stronger acid? (c) Which acid forms the stronger conjugate base? (d) When each acid is dissolved in water, for which acid does the equilibrium lie further to the right? %3D The pKa values in Table 2.1 span a large range (-7 to 50). The pK, scale is logarithmic. small difference in pK, translates into a large numerical difference, For example, the diffe between the pK, of NH3 (38) and CH2=CH, (44) is six pKa units. This means that NH, is one million times more acidic than CH,=CH,.arrow_forward
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