Acid-Base Equilibria: A Review

1. PowerPoint 2002 required Acid-Base Equilibria:A Review CHM 102 - Sinex Don’t look at the answers until you think about the question!!!! Answers Try to answer the questions posed before pushing the answer buttons using the cursor (move mouse). This is set up as a PowerPoint show so it will not print.

2. How do the following quantities change if the (H+) increases? (H+)(OH-) = Kw or pH + pOH = 14 at 25oC Answers

3. 4 1.8 x 10-5 2 1.8 x 10-4 3 6.5 x 10-5 1 very large – strong acid How does the percent dissociation vary for the following acids? Ranks the acids (1-strongest…). What do you need to look up to address this question? Acetic acid Formic acid Benzoic acid Hydrochloric acid Hint– Ka’s Answer

4. Decreasing electronegativity of central atom How does the structure differ for the series of compounds listed below? Answer What is the cause of the Kb variation for the series? Answer

5. How do the strengths vary as the position of the fluorine changes? Weaker acids carboxylic acids amines Stronger bases Answer These are all substituted benzenes. – Chime structure Press again to repeat

6. HCOOH HCN How do the two weak acids below differ based on the distribution diagram? HCN is weaker than HCOOH. HCOOH HCN Answers Push the acid buttons to return or flip to either diagram.

7. Will the following solutions buffer? *can form salt by partial neutralization with base Answers

8. How do you prepare a buffer with a pH of 4.5? Ideally find a weak acid with a pKa of 4.5 and prepare a solution where (HA) = (A-). Ideal Answer In reality, acetic acid with a pKa of 4.74 is the closest to the required pH. So what next? Real Answer For acetic acid, the salt/acid ratio is found from rearranging the Ka and substituting in the pH:

9. The amino acid glycine is amphoteric. Why is it an acid and a base in one? Gain of H+ Loss of H+ H3N+-CH2-COOH H2N-CH2-COO- H2N-CH2-COOH Chime structure Use the mouse click to see animation.

10. The amino acid glycine forms a Zwitterion. How does this happen? Transfer of H+ from carboxylic acid group to amine group. Use the mouse click to see animation. - + A dipolar ion forms. H2N-CH2-COOH Chime structure H3N+-CH2-COO- intramolecular acid-base reaction

11. Which species of glycine goes where on the distribution diagram? Answers

12. What is the pH of the following salts in aqueous solution? weak acid anions, A-, produce OH- weak base cations, BH+, produce H+ Answers

13. Rank the following 0.10 M solutions in order of increasing acidity. NH4Cl CH3COOH NaCN HCl NaCl KOH ______ > ______ > ______ > ______ > ______ > ______ most acid least acid HCl > CH3COOH > NH4Cl > NaCl > NaCN > KOH Answer

14. Why does the pH of a sodium cyanide decrease on dilution? On dilution, less and less hydroxide ion is produced by hydrolysis of the salt. Answer

15. Shifting the aqueous equilibrium heat + HCN  CN- + H+ Answers

16. Identify the substance being titrated in the titration curves. a b c b a a a- strong acid 0.10 M, pH = 1 b- strong acid 0.001 M, pH =3 c- weak acid 0.10 M, pKa =6 Answer

17. For acetic acid being titrated with NaOH, what is the solution composition at each labeled point? A- + NaOH e A- only d (HA) = (A-) b c A- > HA a HA only Answers

18. color change range pKIn+ 1 Picking an indicator pKIn pKIn- 1 Which indicator would work? x 3 2 x 1 Answer

19. Which solution matches the observations in the table? NaCl CH3COOH/ NaCH3COO NaCH3COO CH3COOH HCl Answers

20. Why does the pH of neutrality change? As temperature increases, Kw increases; hence (H+) increases, which causes pH to decrease. Answers