Consider a buffer solution comprised of HF and F. The K₂ of HF is 6.3 x 10-4. If the pH of the buffer solution is 2.96 and [HF] = 0.115 M, how many moles of F* are present? The volume of the buffer solution is 426 mL. Remember: if you want to express an answer in scientific notation, use the letter "E". For example "4.32 x 104" should be entered as "4.32E4". Answer:

Consider a buffer solution comprised of HF and F. The K₂ of HF is 6.3 x 10-4. If the pH of the buffer solution is 2.96 and [HF] = 0.115 M, how many moles of F* are present? The volume of the buffer solution is 426 mL. Remember: if you want to express an answer in scientific notation, use the letter "E". For example "4.32 x 104" should be entered as "4.32E4". Answer:

General, Organic, and Biological Chemistry

7th Edition

ISBN:9781285853918

Author:H. Stephen Stoker

Publisher:H. Stephen Stoker

Chapter10: Acids, Bases, And Salts

Section: Chapter Questions

Problem 10.115EP

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Each symbol in the box below represents a mole of a component in one liter of a buffer solution; represents the anion (X-), = the weak acid (HX), = H+, and =OH. Water molecules and the few H+ and OH- ions from the dissociation of HX and X- are not shown. The box contains 10 mol of a weak acid, , in a liter of solution. Show what happens upon (a) the addition of 2 mol of OH- (2 ). (b) the addition of 5 mol of OH- (5 ). (c) the addition of 10 mol of OH- (10 ). (d) the addition of 12 mol of OH- (12 ). Which addition (a)-(d) represents neutralization halfway to the equivalence point?
8-71 Explain why you do not need to know the chemical formula of a buffer compound to use it.
Enough water is added to the buffer in Question 30 to make the total volume 5.00 L. (a) Calculate the pH of the buffer. (b) Calculate the pH of the buffer after adding 0.0250 mol of HCl to 0.376 L of the buffer. (c) Calculate the pH of the buffer after adding 0.0250 mol of KOH to 0.376 L of the buffer. (d) Compare your answers to Question 30 (a-c) with your answers to (a-c) of this problem. (e) Comment on the effect of dilution on the pH of a buffer and on its buffer capacity. Â
A friend asks the following: Consider a buffered solution made up of the weak acid HA and its salt NaA. If a strong base like NaOH is added, the HA reacts with the OH to form A. Thus the amount of acid (HA) is decreased, and the amount of base (A) is increased. Analogously, adding HCI to the buffered solution forms more of the acid (HA) by reacting with the base (A). Thus how can we claim that a buffered solution resists changes in the pH of the solution? How would you explain buffering to this friend?
What is an acidbase indicator? Define the equivalence (stoichiometric) point and the end point of a titration. Why should you choose an indicator so that the two points coincide? Do the pH values of the two points have to be within 0.01 pH unit of each other? Explain.
A solution of weak base is titrated to the equivalence point with a strong acid. Which one of the following statements is most likely to be correct? a The pH of the solution at the equivalence point is 7.0. b The pH of the solution is greater than 13.0. c The pH of the solution is less than 2.0. d The pH of the solution is between 2.0 and 7.0. e The pH of the solution is between 7.0 and 13.0. The reason that best supports my choosing the answer above is a Whenever a solution is titrated with a strong acid, the solution will be very acidic. b Because the solution contains a weak base and the acid (titrant) is used up at the equivalence point, the solution will be basic. c Because the solution contains the conjugate acid of the weak base at the equivalence point, the solution will be acidic.
Another way to treat data from a pH titration is to graph the absolute value of the change in pH per change in milliliters added versus milliliters added (pH/mL versus mL added). Make this graph using your results from Exercise 61. What advantage might this method have over the traditional method for treating titration data?
You have a solution of the weak acid HA and add some HCl to it. What are the major species in the solution? What do you need to know to calculate the pH of the solution, and how would you use this information? How does the pH of the solution of just the HA compare with that of the final mixture? Explain.
Enough water is added to the buffer in Question 29 to make the total volume 10.0 L. Calculate (a) the pH of the buffer. (b) the pH of the buffer after the addition of 0.0500 mol of HCl to 0.600 L of diluted buffer. (c) the pH of the buffer after the addition of 0.0500 mol of NaOH to 0.600 L of diluted buffer. (d) Compare your answers to Question 29(a)-(c) with your answers to (a)-(c) in this problem. (e) Comment on the effect of dilution on the pH of a buffer and on its buffer capacity.
What is the pH of a buffer that is 0.150 M in a weak acid and 0.150 M in the acids conjugate base? The acids ionization constant is 6.8 106.
Use the same symbols as in Question 61 ( = anion, =OH) for the box below. (a) Fill in a similar box (representing one liter of the same solution) after 2 mol of H+ (2) have been added. Indicate whether the resulting solution is an acid, base, or buffer. (b) Follow the directions of part (a) for the resulting solution after 2 mol of OH- (2 ) have been added. (c) Follow the directions of part (a) for the resulting solution after 5 mol of OH- (5 ) have been added. (Hint: Write the equation for the reaction before you draw the results.)
A quantity of 0.25 M sodium hydroxide is added to a solution containing 0.15 mol of acetic acid. The final volume of the solution is 375 mL and the pH of this solution is 4.45. a What is the molar concentration of the sodium acetate? b How many milliliters of sodium hydroxide were added to the original solution? c What was the original concentration of the acetic acid?

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