Acid-Base Equilibria: A Review CHM Sinex 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. Answers Don’t look at the answers until you think about the question!!!! PowerPoint 2002 required

How do the following quantities change if the (H + ) increases? variable(H + )pH(OH - )pOH change Answers (H + )(OH - ) = K w or pH + pOH = 14 at 25 o C

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

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

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

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

Will the following solutions buffer? solutionbuffer?solutionbuffer? 0.1 M HCOOH 0.1 M NaHCOO yes 0.1 M HCOOH 0.1 M NaOH no 0.1 M HCl 0.1 M NaCl no 0.1 M HNO NaNO 2 yes 0.1 M HCOOH 0.05 M NaOH yes* 0.1 M NaCOOH 0.05 M NaOH no Answers *can form salt by partial neutralization with base

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

The amino acid glycine is amphoteric. Why is it an acid and a base in one? Loss of H + Gain of H + H 2 N-CH 2 -COOH H 3 N + -CH 2 -COOHH 2 N-CH 2 -COO - Chime structure Use the mouse click to see animation.

The amino acid glycine forms a Zwitterion. How does this happen? Transfer of H + from carboxylic acid group to amine group. H 2 N-CH 2 -COOH H 3 N + -CH 2 -COO A dipolar ion forms. intramolecular acid-base reaction Chime structure Use the mouse click to see animation.

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

saltpHSaltpH NaNO 3 7NaF>7 NaNO 2 >7NaBr7 NH 4 Cl<7KCH 3 COO>7 What is the pH of the following salts in aqueous solution? Answers weak acid anions, A -, produce OH - weak base cations, BH +, produce H +

Rank the following 0.10 M solutions in order of increasing acidity. HClNaCl NaCNNH 4 ClCH 3 COOH KOH HCl > CH 3 COOH > NH 4 Cl > NaCl > NaCN > KOH ______ > ______ > ______ > ______ > ______ > ______ most acid least acid Answer

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

Shifting the aqueous equilibrium heat + HCN  CN - + H + stressresponsestressresponse add HCladd NaCN add NaOH add NaCl remove heat dilute with water Answers

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

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

Picking an indicator Which indicator would work? pK In pK In - 1 pK In + 1 colorchangerangex x Answer

HCl CH 3 COOH/ NaCH 3 COO CH 3 COOHNaCH 3 COONaCl Highly conductive Slightly conductive Highly conductive pH increased with water added pH constant with water added pH increased with water added pH decreased with water added pH constant with water added Blue litmus turned red Red litmus turned blue Neither litmus changed CH 3 COOHHClCH 3 COOH/ NaCH 3 COO NaCl Which solution matches the observations in the table? Answers

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