8.28) The general form of a chemical equation for an acid reacting with water to produce its base form and hydronium can be written as: HA (aq) H₂O (1) A (aq) + H3O+ (aq) Conjugate Pair HA represents the acid form, and A- represents the base form of any conjugate pair. When the pH of a solution is less than the pK, of an acid, then the concentration of the acid form, [HA], is greater than the concentration of the base form, [A-]. ▪ In this case, we say that the acid form is predominant. 1 ● . When the pH of a solution is greater than the pK, of an acid, then the concentration of the base form, [A], is greater than the concentration of the acid form, [HA]. In this case, we say that the base form is predominant. ■ When the pH of a solution is equal to the pK, of an acid, then the concentration of the acid form, [HA], is equal to the concentration of the base form, [A-]. QUESTION: When hydrocyanic acid (HCN) is placed in water, a chemical reaction occurs and an equilibrium is established as shown below. The pK, of HCN is 9.31. Predict whether the acid form (HCN) or the base form (CN) is predominant at pH = 7.4. CN- (aq) + H₂O+ (aq) HCN (aq) + H₂O (1) acid form of Hew is predominant, PH (7.4) is less than the pka (9.31), therefore concentration of the acid form, AHCM] is greater than the concentration of the base form, EN-] of 11

Br CH3OH (f) CH3 CH3 CH3 KO'Bu (h) Br 'BuOH Br CI Bu KCN Ph KO'Bu 'BuOH CH3OH

7. Which of the following would behave as a hydrogen bond acceptor, but not a hydrogen bond donor? H H:0: H I || | Н-с-с-с-н H :0: H ннн ннн Н-с-с-с—Н Н-с-с-с-о- Н-с-с-с-N-H ннн H ннн нннн

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Add curved arrows to show the forming and breaking of bonds in the reaction below. H H H Add/Remove step C H H H

Figure 11-5 A. 1) Hg(0Ac)₂, H₂O B. 1) BH 3 C. D. 2) Na B H4 2) H₂O₂, OH, H₂O 2) OH, DMF ) 1) H Br 1) Hg (0Ac) ₂, H₂O H Br → 3) HBr 3) Ts Cl 2) Brz 3) TSCI ) Br H₂ SO4 4) Br¯ 4) HBr

6. Classify each acid base reaction as a Brønsted or Lewis pair. Label the acid (or electrophile) and the base (or nucleophile). Draw a curved arrow to show how electrons moved to form the new bond(s). i CH3Li -H + Na + CH3Li NaNH, OH Br H3C- O Lit O Lit 핸 Na CH4 NH3 + NaBr

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