1 / 35

Acid-Base

© Mr. D. Scott; CHS. Acid-Base. Introduction. © Mr. D. Scott; CHS. Acid-Base. Dangers. © Mr. D. Scott; CHS. Acid-Base. In our stomach. © Mr. D. Scott; CHS. Acid-Base. In Agriculture. Decaying plant material makes the soil acidic. Lime ; Ca(OH) 2 raises the soil pH.

garren
Télécharger la présentation

Acid-Base

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. © Mr. D. Scott; CHS Acid-Base Introduction

  2. © Mr. D. Scott; CHS Acid-Base Dangers

  3. © Mr. D. Scott; CHS Acid-Base In our stomach

  4. © Mr. D. Scott; CHS Acid-Base In Agriculture Decaying plant material makes the soil acidic. Lime; Ca(OH)2 raises the soil pH. Most nutrients become unavailable to plants when the soil pH gets too low.

  5. © Mr. D. Scott; CHS Acids ►Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. ►React with certain metals to produce hydrogen gas. ►React with carbonates and bicarbonates to produce carbon dioxide gas Bases ► Have a bitter taste. ► Feel slippery. Many soaps contain bases.

  6. © Mr. D. Scott; CHS Theories about Acids + Bases • Arrhenius 1887 • Bronsted-Lowry 1923 • Lewis 1923 Svante Arrhenius Theory: Acids are substances which release hydrogen ions (H+) in aqueous solution. Bases are substances which release hydroxide ions (OH-) in aqueous solution.

  7. © Mr. D. Scott; CHS - chloride ion + hydrogen ion + OH- Na+ Arrhenius acid is a substance that releases H+ in water  Arrhenius base is a substance that releases OH- in water

  8. © Mr. D. Scott; CHS Problems with the Arrhenius theory NH3 (ammonia) was a well known BASE when placed in water. But how….? There is no hydroxide (OH-) to be released.

  9. © Mr. D. Scott; CHS Brønsted–Lowry Acid-Base Theory Martin Lowry Johannes Brønsted Essentially the same theory from two chemists working independently at approximately the same time. An acid is a molecule or ion that is able to lose, or "donate" a hydrogen cation (proton, H+). A base is a species with the ability to gain or "accept" a hydrogen cation (proton).

  10. © Mr. D. Scott; CHS A Brønsted acid is a proton donor A Brønsted base is a proton acceptor base acid acid base conjugatebase conjugateacid base acid

  11. © Mr. D. Scott; CHS + H H O O [ ] + + - H H H O H O H H H2O (l) H+(aq) + OH-(aq) H2O + H2O H3O+ + OH- Acid-Base Properties of Water autoionization of water conjugate acid base Hydronium ion conjugate base acid Since water can act as either an acid or a base it is called an amphoteric substance.

  12. The Ion Product of Water © Mr. D. Scott; CHS [H+][OH-] Kc = [H2O] H2O (l) H+(aq) + OH-(aq) 2 H2O H3O+ + OH- [H2O] = constant Or, more accurately seen as: Kc of water = Kw = [H+][OH-] The ion-product constant (Kw) is the product of the molar concentrations of H+ and OH- ions at a particular temperature. Solution Is [H+] = [OH-] neutral At 25°C Kw = [H+][OH-] = 1.0 x 10-14 [H+] > [OH-] acidic [H+] < [OH-] basic

  13. © Mr. D. Scott; CHS The Balance of [H+]/[OH-] in Solution At 25°C Kw = [H+][OH-] = 1.0 x 10-14 [H+] [OH-] As one increases, the other decreases. The entire solution can be described therefore by using only one of the two ions. Knowing the [H+] allows you to figure out the [OH-].

  14. © Mr. D. Scott; CHS pH Introduced in 1909, it describes the molar concentration of the H+ found in a solution. Søren Sørensen Danish chemist, famous for the introduction of the concept of pH, a scale for measuring acidity and basicity. Due to the wide range of [H+] that is possible, the molarity values must be mathematically changed in a way that makes them more manageable. H+ 1 x 10-14 1.0 OH- 1.0 1 x 10-14

  15. © Mr. D. Scott; CHS pH – A Measure of Acidity 1 x 10-14 M H+ 1 x 10-13 M H+ 1 x 10-12 M H+ 1 x 10-11 M H+ 1 x 10-10 M H+ 1 x 10-9 M H+ 1 x 10-8 M H+ 1 x 10-7 M H+ 1 x 10-6 M H+ 1 x 10-5 M H+ 1 x 10-4 M H+ 1 x 10-3 M H+ 1 x 10-2 M H+ 1 x 10-1 M H+ 1 x 100 M H+ [H+]

  16. pH – A Measure of Acidity © Mr. D. Scott; CHS pH [H+] pH = -log [H+] Solution Is At 250C neutral [H+] = [OH-] [H+] = 1 x 10-7 pH = 7 [H+] > 1 x 10-7 pH < 7 acidic [H+] > [OH-] basic [H+] < [OH-] [H+] < 1 x 10-7 pH > 7

  17. © Mr. D. Scott; CHS -pH [H+] = 10 Kw Kw [H+] = [OH-] = [OH-] [H+] -pOH [OH-] = 10 pH = - log [H+] [H+] pH pH = pKw - pOH pOH = pKw - pH [OH-] pOH pOH = - log [OH-] pKw = 14 Kw = 1 x 10-14

  18. © Mr. D. Scott; CHS pH of some “every day” substances

  19. © Mr. D. Scott; CHS = [OH-] = 1 x 10-14 Kw 1.3 [H+] Example Problem 1 What is the concentration of OH- ions in a HCl solution whose hydrogen ion concentration is 1.3 M? Kw = [H+][OH-] = 1.0 x 10-14 [H+] = 1.3 M = 7.7 x 10-15M

  20. Example Problem 2 © Mr. D. Scott; CHS The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater? pH = -log [H+] = 10-4.82 = 1.5 x 10-5M [H+] = 10-pH Sig Fig’s and pH: in pH values, the significant figures are ONLY those behind the decimal point. Example Problem 3 The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood? pH + pOH = 14.00 pOH = -log [OH-] = -log (2.5 x 10-7) = 6.60 pH = pKw – pOH = 14.00 – 6.60 = 7.40

  21. Example Problem 4 © Mr. D. Scott; CHS 0.960 mol NaOH 1 mol NaOH 0.332 L solution 40.00g NaOH 38.4 g of caustic soda (NaOH) is dissolved in water making 332 mL of solution. Calculate the pH of the resulting solution. X = 0.960 mol NaOH 38.4 g NaOH = [OH-] = [NaOH] = 2.89 M pOH = -log[OH-] = -log(2.89) pOH = -0.461 pH = pKw - pOH = 14 - (-0.461) pH = 14.461

  22. Example Problem 5 © Mr. D. Scott; CHS 0.0337 mol Ca(OH)2 1 mol Ca(OH)2 0.085 L solution 74.09 g Ca(OH)2 Slaked lime, Ca(OH)2, has thousands of uses and is readily available. If 2.50 g are dissolved in water making 85 mL of solution, what is the pH? X = 0.0337 mol Ca(OH)2 2.50 g Ca(OH)2 [OH-] = 2 X [Ca(OH)2] = (2) = 0.794 M pOH = -log[OH-] = -log(0.794) pOH = 0.100 pH = pKw - pOH = 14 - (0.100) pH = 13.90

  23. Strength of Acids & Bases © Mr. D. Scott; CHS HBr (aq) + H2O (l) H3O+(aq) + Br-(aq) HCl (aq) + H2O (l) H3O+(aq) + Cl-(aq) HI (aq) + H2O (l) H3O+(aq) + I-(aq) HNO3(aq) + H2O (l) H3O+(aq) + NO3-(aq) HClO4(aq) + H2O (l) H3O+(aq) + ClO4-(aq) HClO3(aq) + H2O (l) H3O+(aq) + ClO3-(aq) H2SO4(aq) + H2O (l) H3O+(aq) + HSO4-(aq) Strong Acids are strong electrolytes – 100% ionization 7 Strong Acids (memorize)

  24. © Mr. D. Scott; CHS HF (aq) + H2O (l) H3O+(aq) + F-(aq) HNO2(aq) + H2O (l) H3O+(aq) + NO2-(aq) HSO4-(aq) + H2O (l) H3O+(aq) + SO42-(aq) H2O (l) + H2O (l) H3O+(aq) + OH-(aq) Weak Acids are weak electrolytes – less than 100% ionization The generic acid formula is represented as “HA” WEAK STRONG Partial ionization Complete ionization HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A-HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A- HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A- HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-

  25. © Mr. D. Scott; CHS HA(aq) + H2O(l)H3O+(aq) + A-(aq) HA(aq) H+(aq) + A-(aq) [H+][A-] Ka = [HA] weak acid strength Ka Weak Acids and Acid Ionization Constants The generic acid formula is represented as “HA” Ka is the acid ionization constant

  26. © Mr. D. Scott; CHS Ka of Monoprotic Weak Acids Table

  27. © Mr. D. Scott; CHS Strength vs Concentration Concentrated Dilute H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ A-H+ H+ A-A- A-H+ H+ A-H+ Strong HA H+ A- HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A-HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A- HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A- HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA H+ A- HA HA HA H+ A- HA HA HA H+ A- HA Weak

  28. © Mr. D. Scott; CHS H2O NaOH (s) Na+(aq) + OH-(aq) H2O KOH (s) K+(aq) + OH-(aq) H2O Ba(OH)2(s) Ba2+(aq) + 2OH-(aq) Bases…Strong & Weak Hydroxides of Group I metals and Ca, Sr, and Ba are STRONG BASES. Strong Bases are strong electrolytes – complete dissociation

  29. Weak Bases are weak electrolytes © Mr. D. Scott; CHS F-(aq) + H2O (l) OH-(aq) + HF (aq) NO2-(aq) + H2O (l) OH-(aq) + HNO2(aq) This process is called “hydrolysis.” Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations (H+) (conventionally referred to as protons) and hydroxide anions (OH−). Hydrolysis is tremendously important in biological reactions.

  30. © Mr. D. Scott; CHS Weak Bases Table of Kb Values

  31. Example Problem 6 © Mr. D. Scott; CHS HNO3(aq) + H2O (l) H3O+(aq) + NO3-(aq) Ba(OH)2(s) Ba2+(aq) + 2OH-(aq) What is the pH of a 2 x 10-3 M HNO3 solution? HNO3 is a strong acid – 100% ionization. 0.0 M 0.0 M Start 0.002 M 0.0 M 0.002 M 0.002 M End = -log(0.002M) = 2.7 pH = -log [H+] Example Problem 7 What is the pH of a 1.8 x 10-2 M Ba(OH)2 solution? Ba(OH)2 is a strong base – 100% dissociation. 0.0 M 0.0 M Start 0.018 M 0.0 M 0.018 M 0.036 M End pH = pKw – pOH = 14.00 - -log(0.036M) = 12.56

  32. © Mr. D. Scott; CHS Multiprotic Acids H2SO4 Acids with more than one ionizable hydrogen. Step 1 Complete ionization (Strong) Step 2 Incomplete ionization (Weak) =1.2 x 10-2

  33. © Mr. D. Scott; CHS Multiprotic Acids Step 1 Phosphoric acid Ka = 7.5 x 10-3 Step 2 Ka = 6.2 x 10-8 Step 3 Ka = 4.8 x 10-13 With each successive step, it becomes harder to remove the H+ ion. H2PO4- is therefore a weaker acid than H3PO4, and HPO4-2 is a weaker acid than H2PO4-.

  34. © Mr. D. Scott; CHS Ka of Multiprotic Weak Acids Table

  35. © Mr. D. Scott; CHS Lewis Acids & Bases Lewis offered an acid base theory that was different from but yet consistent with the Brønsted–Lowry approach. Both theories were given in the same year (1923). Gilbert N Lewis Acid = electron (e-) pair “acceptor” Base = electron (e-) pair “donor”

More Related