Unit 11: Equilibrium / Acids & Bases Text Questions from Corwin

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1 Unit 11: Equilibrium / Acids & Bases Name: KEY Text Questions from Corwin How can a reversible reaction proceed? spontaneously in both the forward and reverse directions 2. When is a reversible reaction in a state of equilibrium? when the rates of the forward and reverse reactions are equal 3. What are two things that equilibrium does NOT mean? it doesn t mean that the reaction has stopped; it doesn t mean the amounts of R and P are equal 4. A chemical reaction at equilibrium implies a _dynamic_, _reversible_ process. 5. How can we define the rate of reaction? as the rate at which concentrations of reactants decrease per unit time 6. At equilibrium the _ratio_ of product concentrations to reactant concentrations remains _constant_ at a given _temperature_ How is Le Chatelier s principle stated? when a reversible rxn at eq is stressed by a in [ ], T, or P, the eq shifts to relieve the stress 8. Answer shift left, shift right, or no shift to describe what happens when the equilibrium of the reaction shown is disrupted by each of the following stressors. N 2 O 4 (g) + heat 2 NO 2 (g) A. increase the N 2 O 4 concentration E. cool the reaction B. decrease the NO 2 concentration F. increase the pressure C. increase the NO 2 concentration G. decrease the pressure D. heat the reaction H. add an inert gas no shift What is an acid? any substance that releases hydrogen ions, H +, in water 10. What color does litmus turn in the presence of hydrogen ions? red 11. How do acids taste? sour 12. What is a base? any substance that releases hydroxide ions, OH, in water 13. List three properties of bases. they are slippery, taste bitter, and turn litmus blue 14. What two things are produced when an acid and a base react? a salt and water

2 15. In terms of ph, describe acids bases neutral substances. 16. What is a buffer? ph < 7 ph > 7 ph = 7 a solution that resists changes in ph when an acid or base is added 17. What does a buffer do to maintain its ph? it consumes excess hydrogen or hydroxide ions 18. Of what two things is a buffer composed? an aqueous solution of a weak acid or base and one of its salts What is the difference between an Arrhenius acid and an Arrhenius base? A. acid/base = a substances that ionizes in water to produce hydrogen/hydroxide ions 20. What is the difference between ionization and dissociation? ionization is when m c in a polar compound form anions and cations; dissociation is when the existing ions in an ionic compound separate 21. Why do we call hydrochloric acid a strong acid? hydrofluoric acid a weak acid? it ionizes nearly 100% it ionizes about 1% 22. What is the formula for the hydronium ion, and when is it formed? H 3 O + ; when an H + ion attaches to a water m cule 23. A base is considered either strong or weak depending on how much of it dissociates 24. In a neutralization reaction, each salt is composed of what? the cation from the reacting base and the anion from the acid What is the difference between a Bronsted-Lowry acid and a Bronsted-Lowry base? a B-L acid is a proton donor; a B-L base is a proton acceptor 26. Unlike Arrhenius acids, Bronsted-Lowry acids and bases depend on what? the particular reaction 27. What is an amphiprotic substance? one that is capable of both accepting and donating a proton A. What is an acid-base indicator? a soln that is sensitive to ph and changes color B. Give three examples of indicators. methyl red, bromthymol blue, and phenolphthalein 29. Describe what the color indicates in a phenolphthalein solution. ph >= 9, pink; ph < 9, colorless

3 To find the molar _concentration_ of an unknown solution, we use another solution of known _concentration_. This procedure is called a _titration_. 31. In a titration, what happens when the endpoint is reached? the indicator changes color What is a standard solution? a solution in which the concentration is known precisely 33. Chemists routinely use standard solutions to analyze substances 34. A. To standardize a solution of acid, chemists use a weighed quantity of a solid base B. To standardize a solution of base, chemists use a weighed quantity of a solid acid 35. What is one application of a standard solution? to determine the molar mass of a solid acid or base What did Arrhenius correctly conclude? that the ions in a solution are responsible for the electrical conductivity 37. Because water is a poor conductor, we conclude that only a few ions are present in pure water 38. Write the two equivalent equations that illustrate the autoionization of water and identify each term. H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) AND H 2 O(l) H + (aq) + OH (aq) water water hydronium ion hydroxide ion water hydrogen ion hydroxide ion 39. At 25 o C, what is the concentration of hydrogen ions in pure water? 1.0 x 10 7 mol/l 40. Why are the concentrations of H + and OH equal? because each molecule of water that ionizes yields one H + and one OH 41. What are the symbol and value of the ionization constant for water at 25 o C? K w = 1.0 x Write the equation that relates the hydrogen and hydroxide ion concentrations at 25 o C. [H + ] [OH ] = 1.0 x Summarize the three conclusions possible when comparing the hydrogen ion concentration to the hydroxide ion concentration. [H + ] > [OH ] acid [H + ] < [OH ] base [H + ] = [OH ] neutral A. Circle the ph that is more acidic: ph = 2 or ph = 5 B. Circle the ph that is more basic: ph = 8 or ph = 13

4 45. The ph scale uses WHAT to express acidity or basicity? powers of A solution of ph 3 is how many times more acidic than one with ph 4? ten times 47. Write the equation for calculating ph. ph = log [H + ] Human blood must be maintained in what range of ph? What is the rule for significant digits on logarithms? the # of sig figs in the given value (i.e., the [ ]) must equal the number of decimal places in the log 50. Write the equation for calculating the hydrogen ion concentration from the ph. [H + ] = 10 ph Why is water a weak conductor of electricity? because it is very slightly ionized 52. What is the difference between a strong and a weak electrolyte? strong: the aqueous soln is a good conductor; weak: the aqueous soln is a poor conductor 53. A. List three examples of strong electrolytes. strong acids, strong bases, and soluble ionic compounds B. List three examples of weak electrolytes. weak acids, weak bases, and slightly soluble ionic compounds 54. A solution s conductivity is proportional to what? the number of ions in solution 55. Why do we write the formulas of weak electrolytes in nonionized form? because weak electrolytes are only slightly ionized How is each substance in the total ionic equation written? as it predominantly exists in solution 57. What are spectator ions? ions that appear on both sides of the equation 58. How can we simplify the total ionic equation? by eliminating the spectator ions 59. What does the net ionic equation show? only the substances undergoing reaction

5 Unit 11: Equilibrium / Acids & Bases Name: Text Questions from Corwin How can a reversible reaction proceed? 2. When is a reversible reaction in a state of equilibrium? 3. What are two things that equilibrium does NOT mean? 4. A chemical reaction at equilibrium implies a, process. 5. How can we define the rate of reaction? 6. At equilibrium the of product concentrations to reactant concentrations remains at a given How is Le Chatelier s principle stated? 8. Answer shift left, shift right, or no shift to describe what happens when the equilibrium of the reaction shown is disrupted by each of the following stressors. N 2 O 4 (g) + heat 2 NO 2 (g) A. increase the N 2 O 4 concentration E. cool the reaction B. decrease the NO 2 concentration F. increase the pressure C. increase the NO 2 concentration G. decrease the pressure D. heat the reaction H. add an inert gas What is an acid? 10. What color does litmus turn in the presence of hydrogen ions? 11. How do acids taste? 12. What is a base? 13. List three properties of bases. 14. What two things are produced when an acid and a base react?

6 15. In terms of ph, describe acids bases neutral substances. 16. What is a buffer? 17. What does a buffer do to maintain its ph? 18. Of what two things is a buffer composed? What is the difference between an Arrhenius acid and an Arrhenius base? 20. What is the difference between ionization and dissociation? 21. Why do we call hydrochloric acid a strong acid? hydrofluoric acid a weak acid? 22. What is the formula for the hydronium ion, and when is it formed? 23. A base is considered either strong or weak depending on 24. In a neutralization reaction, each salt is composed of what? What is the difference between a Bronsted-Lowry acid and a Bronsted-Lowry base? 26. Unlike Arrhenius acids, Bronsted-Lowry acids and bases depend on what? 27. What is an amphiprotic substance? A. What is an acid-base indicator? B. Give three examples of indicators. 29. Describe what the color indicates in a phenolphthalein solution.

7 To find the molar of an unknown solution, we use another solution of known. This procedure is called a. 31. In a titration, what happens when the endpoint is reached? What is a standard solution? 33. Chemists routinely use standard solutions to 34. A. To standardize a solution of acid, chemists use a weighed quantity of B. To standardize a solution of base, chemists use a weighed quantity of 35. What is one application of a standard solution? What did Arrhenius correctly conclude? 37. Because water is a poor conductor, we conclude 38. Write the two equivalent equations that illustrate the autoionization of water and identify each term. 39. At 25 o C, what is the concentration of hydrogen ions in pure water? 40. Why are the concentrations of H + and OH equal? 41. What are the symbol and value of the ionization constant for water at 25 o C? 42. Write the equation that relates the hydrogen and hydroxide ion concentrations at 25 o C. 43. Summarize the three conclusions possible when comparing the hydrogen ion concentration to the hydroxide ion concentration A. Circle the ph that is more acidic: ph = 2 or ph = 5 B. Circle the ph that is more basic: ph = 8 or ph = 13

8 45. The ph scale uses WHAT to express acidity or basicity? 46. A solution of ph 3 is how many times more acidic than one with ph 4? 47. Write the equation for calculating ph Human blood must be maintained in what range of ph? 49. What is the rule for significant digits on logarithms? 50. Write the equation for calculating the hydrogen ion concentration from the ph Why is water a weak conductor of electricity? 52. What is the difference between a strong and a weak electrolyte? 53. A. List three examples of strong electrolytes. B. List three examples of weak electrolytes. 54. A solution s conductivity is proportional to what? 55. Why do we write the formulas of weak electrolytes in nonionized form? How is each substance in the total ionic equation written? 57. What are spectator ions? 58. How can we simplify the total ionic equation? 59. What does the net ionic equation show?