[PDF] Acid-Base Practice Problems

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Organic Chemistry Jasperse Acid-Base Practice Problems A. Identify each chemical as either an "acid" or a "base" in the following reactions, and identify "conjugate" relationships. -You should have one acid and one base on each side -You should have two conjugate pairs 1. 2. 3. 4. 5. B. Choose the More Basic for Each of the Following Pairs (Single Variable). You can use stability to decide. 6. NH3 NaNH2 7. NaOH H2O 8. 9. 10. 11. CH3CH2OH + NaOHCH3CH2ONa + H2OCH3CH2NHLi + CH3OHCH3CH2NH2 + CH3OLiCH3CH2CO2H + CH3MgBrCH3CH2CO2MgBr + CH4CH3OH + H3O+H2O + CH3OH2+CH3CH2NH3+ + CH3OHCH3CH2NH2 + CH3OH2+NHONHNaONaPhO

PhO O

NHNaNHNaOTTKeys:

1. Charge

2. Elecronegativity

3. Resonance

C. Rank the basicity of the following sets: Multiple Variable Problems 12. CH3MgBr CH3NHNa CH3NH2 13. 14. 15. D. Choose the More Acidic for Each of the Following Pairs: Single Variable Problems 16. 17. 18. 19. 20. 21. O

O O OH

NHNaONaOOHONaNHOOOHONH

3 NH 4 OH 2 OH OH NH 2 CH 3

NH2OHOH

OH O NH 2 NH 2 OTT

E. Rank the acidity of the following sets: Multiple Variable Problems 22. 23. 24. 25. 26. F. Draw arrow to show whether equilibrium favors products or reactants. (Why?) 27. 28. G. For the following acid-base reaction, a. put a box around the weakest base in the reaction b. put a circle around the weakest acid c. draw an arrow to show whether the equilibrium goes to the right or left. (4pt) 29. OH2OOHOOHHFNH2NH3OOHOH2OOHNH2OHOOHNH2NH3ONH2OOHNH2HeOOHOH

2 O + OH + HOH O HO O

ONH2OHNH++ONaNH2NHNaOH++TTKeys:

1. Charge

2. Elecronegativity

3. Resonance

Chem 341 Jasperse Ch. 1 Structure + Intro 12 Acid-Base Chemistry (Section 1.13-18) Acidity/Basicity Table Entry Class Structure Ka Acid Strength Base Base Strength 1 Strong Acids H-Cl, H2SO4 102 2 Hydronium H3O+, ROH+ cationic 100 H2O, HOR neutral 3 Carboxylic Acid 10-5 4 Ammonium Ion (Charged) 10-12 5 Water 10-16 6 Alcohol 10-17 7 Ketones and Aldehydes 10-20 8 Amine (N-H) (iPr)2N-H 10-33 9 Alkane (C-H) 10-50 Quick Checklist of Acid/Base Factors 1. Charge 2. Electronegativity 3. Resonance/Conjugation y When neutral acids are involved, it's best to draw the conjugate anionic bases, and then think from the anion stability side. • The above three factors will be needed this semester. The following three will also become important in Organic II. 4. Hybridization 5. Impact of Electron Donors/Withdrawers 6. Amines/Ammoniums Cl

O S O OHO , ROH O RO O R N R HR

Charged, but only

weakly acidic! R N R R

Neutral, but basic!

HOH HO ROH RO O ! H O ! (iPr) 2

N Li

RCH 3 RCH

2TTTBase

StabilityT

e x t1. Cations more acidic than neutrals; anions more basic than neutrals

2. Carbanions < nitrogen anions < oxyanione < halides in stability

3. resonance anions more stable than anions without resonance

Chem 341 Jasperse Ch. 1 Structure + Intro 13 More Detailed Discussion of Acid/Base Patterns/Factors to remember 1. Charge Factor: central atom being equal, cations are more acidic than neutrals (H3O+ > H2O, NH4+ > NH3), and anions more basic than neutrals (hydroxide > water). 2. Electronegativity Factor: • Acidity H-C < H-N < H-O < H-X (halogen) • Anion Stability • Basicity • Electronegativity • Why: All neutral acids produce an anion after losing an H • The more stable the anion Z- that forms, the more acidic the parent H-Z will be. (The Product Stability/Reactivity principle). • The anion stability correlates the love for electrons (electronegativity). • Summary of Key Relationships: • ANION STABILITY and the ACIDITY of a neutral acid precursor. • ANION STABILITY and the BASICITY of the anion (inverse relationship) • ANION BASICITY and the ACIDITY OF THE CONJUGATE ACID are inversely related (the stronger the acidity of the parent acid, the weaker the basicity of the conjugate anion) • KEY: WHEN THINKING ABOUT ACIDITY AND BASICITY, FOCUS ON THE STABILITY OF THE ANION. 3. Resonance/Conjugation: Anion resonance is stabilizing, so an acid that gives a resonance-stabilized anion is more acidic. And an anion that forms with resonance will be more stable and less basic. • Oxygen Series Examples: Acidity: sulfuric acid > carboxylic acid > water or alcohol • Note: Resonance is normally useful as a tiebreaker between oxygen anions, nitrogen anions, or carbon anions O

S O OHO

Anion Basicity:

O O O < < O S O OHO O O O > >

Anion Stability:TTT

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