ap chem homework

AP CHEM HOMEWORK 3-11-2015 Read: 684-693 1. Why are buffers important to humans? 2. What do buffers do? 3. Carbonic Acid (CHOOH) reacts with water to form hydronium and carbonate ions. Ka=4.4x10-7. a. b. c. d.

Write the equilibrium reaction for the above. Find the hydrogen ion concentration and pH for a 1.0M solution of carbonic acid. If we add a 1.0M solution of potassium carbonate (KCOO) to the solution in b, which species in b would increase and which would decrease. Calculate the hydrogen ion concentration and pH of the solution in c.

4. A certain buffer is made by dissolving NaHCO3 and Na2CO3 in some water. Write equations to show how this buffer neutralizes added H+ and OH-. 5. A CPHS student adds a solution of acetic acid (0.75M) to a solution of sodium acetate (0.25M). a. Write dissociation reactions for both solutions indiviuallly. b. Determine the common ion for both solutions. c. Calculate the pH of the acetic acid solution before they are mixed. d. The student determines that the pH of the combined solutions is 4.74. Did the hydrogen ion concentration increase, decrease or stay the same. e. Why are the pH values different in c and d. 6. Calculate the pH of each of the following solutions. a. 0.100 M propanoic acid (HC3H5O2, Ka = 1.3x10-5) b. 0.100 M sodium propanoate (NaC3H5O2, Kb = 7.5x10-5) c. pure H2O d. a mixture containing 0.100 M HC3H5O2 and 0.100 M NaC3H5O2. 7. Calculate the pH after 0.020 mol HCl is added to 1.00 L of each of the four solutions in problem 6. 8. Calculate the pH after 0.020 mol NaOH is added to 1.00 L of each of the four solutions in problem 7. 9. Buffered solutions are simply solutions that react to stress as described by Le Chatelier’s principle. Explain how buffered solutions fit this description.

10. Calculate the pH of a buffer solution prepared by dissolving 21.46 g of benzoic acid (HC7H5O2, Ka = 6.4 x 10–5) and 37.68 g of sodium benzoate in 200.0 mL of solution. 11. Calculate the pH after 0.010 mol gaseous HCl is added to 250.0mL of each of the following buffered solutions. a. 0.050 M NH3 0.15 M NH4Cl b. 0.50 M NH3 1.50 M NH4Cl c. Do the two original buffered solutions differ in their pH or their capacity? d. What advantage is there in having a buffer with a greater capacity? 12. How does buffering work? 13. Wen is the Henderson-Hasselbach equation useful? Give an example. 14. List the 3 most important characteristics of buffer solutions.