© Macmillan Learning Write the Henderson-Hasselbalch equation for a propanoic acid solution (CH, CH,CO,H, pK, = 4.874). ΠΑΙ pH PK, +log [HA] Answer Bank Using the equation to calculate the quotient [A]/[HA] at three different pH values. [A-] pH = 4.105 0.1702 [HA] [AT] pH=4.874 [HA] pH = 5.317 [AT] 1.44 = [HA]

Estimate the pH that results when the following two solutions are mixed. a) 50 mL of 0.3 M CH3COOH and 50 mL of 0.4 M KOH b) 100 mL of 0.3 M CH3COOH and 50 mL of 0.4 M NaOH c) 150 mL of 0.3 M CH3COOH and 100 mL of 0.3 M Ba(OH)2 d) 200 mL of 0.3 M CH3COOH and 100 mL of 0.3 M Ba(OH)2

Estimate the pH of a solution in which bromcresol green is blue and thymol blue is yellow. (See Fig. 14-8.)

For oxyacids, how does acid strength depend on a. the strength of the bond to the acidic hydrogen atom? b. the electronegativity of the element bonded to the oxygen atom that bears the acidic hydrogen? c. the number of oxygen atoms? How does the strength of a conjugate base depend on these factors? What type of solution forms when a nonmetal oxide dissolves in water? Give an example of such an oxide. What type of solution forms when a metal oxide dissolves in water? Give an example of such an oxide.

Calculate the pH of a solution prepared by mixing 49.0 mL of butyric acid, HC4H7O2, with 6.15 g of KOH in water. The following data about butyric acid may be helpful: density=0.9595g/mL;K a =1.54105

Composition diagrams, commonly known as alpha plots, are often used to visualize the species in a solution of an acid or base as the pH is varied. The diagram for 0.100 M acetic acid is shown here. The plot shows how the fraction [alpha ()] of acetic acid in solution, =[CH3CO2H][CH3CO2H]+[CH3CO2] changes as the pH increases (blue curve). (The red curve shows how the fraction of acetate ion, CH3CO2, changes as the pH increases.) Alpha plots are another way of viewing the relative concentrations of acetic acid and acetate ion as a strong base is added to a solution of acetic acid in the course of a titration. (a) Explain why the fraction of acetic acid declines and that of acetate ion increases as the pH increases. (b) Which species predominates at a pH of 4, acetic acid or acetate ion? What is the situation at a pH of 6? (c) Consider the point where the two lines cross. The fraction of acetic acid in the solution is 0.5, and so is that of acetate ion. That is, the solution is half acid and half conjugate base; their concentrations are equal. At this point, the graph shows the pH is 4.74. Explain why the pH at this point is 4 74.

Develop a set of rules by which you could predict the pH for solutions of strong or weak acids and strong or weak bases without using a calculator. Your predictions need to be accurate to 1 pH unit. Assume that you know the concentration of the acid or base and that for the weak acids and bases you can look up the pKa (log Ka) or Ka values. What rules would work to predict pH?

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The pH of a 0.0200 M solution of an unknown acid is 2.56. What is the Ka of this acid? To solve this problem: Write the acid dissociation equilibrium for the generic acid “HA” Set up an ICE chart ( with x = the concentration of H3O+ at equilibrium) Write the expression for Ka. Fill this in with the concentrations of H3O+, A- and HA at equilibrium, in terms of x. What is x? Can you find it from the given information?  You should be able to use the pH to get the concentration of H3O+, which is x.  Do this. Now that you know x, plug in into the Ka expression and find Ka.

The values of the dissociation constants for H3PO4 are given in the table above.  If a solution has a pH of 1, which of the following chemical species would have the lowest concentration? a) H+ b) H2PO4- c) HPO42- d) PO43-