{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

119_3_Acids&Bases_07F

# 119_3_Acids&Bases_07F - III ACIDS and BASES Harris Chap...

This preview shows pages 1–11. Sign up to view the full content.

1 III. ACIDS and BASES Harris: Chap 6: 105 – 111; Ex. 6 H; Chap 9: Ex. 9 B-G

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 Weak Mono-protic Acids General Problem: Calculate the pH of a solution of a weak acid, HA, of known formality, F, and ionization constant K A . Necessary definitions: pH = -log[H 3 O + ] [X] = mol X per L of solution pK A = -log K A F = formality or analytical concentration = C T = total moles of compound added per L (dm 3 ) of solution, regardless of any dissociation.
3 Weak Mono-protic Acids: Fundamental Equations 1. Acid ionization reaction: HA + H 2 O H 3 O + + A K A =[H 3 O + ][A ]/[HA] 2. Water ionization reaction: 2H 2 O H 3 O + + OH K W =[H 3 O + ][OH ] 3. Charge balance: [H 3 O + ] = [A ] + [OH ] 4. Species balance: F = [HA] + [A ]

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
4 Weak Mono-protic Acids Standard approximations: Chemical: Since the ionization of the acid is the dominant reaction forming H 3 O + , assume it is the only reaction producing H 3 O + . If K A *F >> K W , then the [H 3 O + ] from the ionization of water (~1*10 -7 M) is much less than the [H 3 O + ] from the ionization of the weak acid and can be neglected (= 0). or Rxn (1) >> Rxn (2) Rxn(1) ONLY Mathematical: The solution must be acidic and [H 3 O + ] >> [HO ] Therefore, [H 3 O + ] 2245 [A ] >> [OH ]
5 Weak Mono-protic Acids, Standard Approximation Rxn: HA + H 2 O H 3 O + + A Equations: K A =[H 3 O + ][A ]/[HA] F = [HA] + [A ] [H 3 O + ] 2245 [A ] F, K A will be known Results: [ ][ ] [ ] - - + - = A F A O H A K 3 [ ] [ ] + + - = O H F O H K 3 2 3 A [ ] [ ] 0 F K O H K O H A 3 A 2 3 = - + + +

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
6 Weak Mono-protic Acids: Aspirin Calculate the pH of a saturated solution of aspirin (HA) Aspirin (acetylsalicylic acid, C 9 H 8 O 4 , or 2-acetoxybenzoic acid) Data from Merck Index 1 g in 300 mL H 2 O K A = 3.27*10 -4 S 2245 { (1 g)/(180.15 g/mol)}/(0.3 L) = 0.019 M = F HA H 3 O + + A - K A = [H 3 O + ] 2 /(F - [H 3 O + ]) [H 3 O + ] 2 +K A [H 3 O + ] -K A *F = 0 a*x 2 + b*x+ c = 0 TI 82,TI 85:(Poly); TI 89 (Solve) HP 48: Solve poly a = 1, b = 3.27*10 –4 , c = -0.019*3.27*10 –4 [H 3 O + ] = 2.33*10 –3 M pH = 2.63 {[H 3 O + ] > 1*10 –7 M pH < 7}
7 Weak Mono-protic Acids: Aspirin K A = [H 3 O + ] 2 /(F-[H 3 O + ]) 3.27*10 -4 = x 2 /(0.019 - x) TI85 Solver HP48 Solve equation TI89 F2 Solve TI82 Math(Solve) x = [H 3 O + ] = 0.00233 pH = 2.63 The procedure gives only one solution with TI 82, TI85 and HP48. You need an initial guess (<0.019). TI89 gives both + and – solutions and no guess is needed. Check answer to ensure that the chosen solution is physically real. It’s easy to mis-punch numbers.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
8 Drug Delivery/Transport/Absorption and pH Ionic compounds generally do not penetrate/diffuse efficiently through biological membranes. The salts of many {large} organic acids or bases are more soluble in water than the free (undissociated) acid or base. What fraction of aspirin is present as the anion and what fraction is present as the undissociated acid in aqueous solution? C C C C C C C OH O H H H H O C O CH 3
9 Weak Mono-protic Acids: Aspirin HA + H 2 O H 3 O + + A - F{HA} = 0.019 M [H 3 O + ] = [A - ] = 2.33*10 -3 M Per cent unionized = 88 % + - 3 A H O A K = [HA] �� � �� � + - 3 [H O ] = [A ] 2 - - A = F - [A ] � � � � 0.00233 Per cent ionized = *100 = 12% 0.019

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
10 Weak Mono-protic Acids: Hydroxylamine Hydrochloride, HONH 3 Cl A white crystalline solid (salt), very soluble in water: A reducing agent in photography, antioxidant. pH{0.125 F solution}= ?
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 40

119_3_Acids&Bases_07F - III ACIDS and BASES Harris Chap...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online