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Arrhenius Definition

Arrhenius Definition. An acid is a substance which forms H + ions as the only positive ion in aqueous solution. An alkali is a substance which forms OH - ions as the only negative ion in aqueous solution. A base is an insoluble hydroxide. The Brønsted-Lowry Concept of Acids and Bases.

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Arrhenius Definition

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  1. Arrhenius Definition An acid is a substance which forms H+ ions as the only positive ion in aqueous solution. An alkali is a substance which forms OH- ions as the only negative ion in aqueous solution.A base is an insoluble hydroxide.

  2. The Brønsted-Lowry Concept of Acids and Bases An acid is a proton donor. A base is a proton acceptor. Johannes Nicolaus Brønsted Thomas Martin Lowry

  3. The Lewis Concept of Acids and Bases An acid is an electron acceptor. A base is an electron donor. Gilbert Newton Lewis (October 23, 1875 – March 23, 1946)

  4. pH = - log [H+] The pH of distilled water is 7, this is neutral. Any solution with a pH below 7 (i.e. pH 1.0 to pH 6.9) is an acid and any solution with a pH above 7 (i.e. pH 7.1 to pH 14) is an alkali. Acidic solutions have a pH between 1 and 6.9 Alkaline solutions have a pH between 7.1 and 14. Neutral solutions are neither acidic nor alkaline so their pH is 7.

  5. Acids all produce Hydrogen ions (H+). Acids like Hydrochloric acid produce lots of Hydrogen ions; this is because when Hydrogen Chloride gas dissolves in water the molecules of Hydrogen Chloride dissociate into Hydrogen ions and Chloride ions. HCl(aq) = H+ + Cl- Vant Hoff factor =2 The important fact here is that every HCl that splits up produces 1 H+ so 2 moles of HCL will produce 2 moles of H+

  6. Water also dissociates to produce ions, this time it is Hydrogen ions and Hydroxyl ions .H2O(l) = H+ + OH- Sodium Hydroxide also dissociates to produce ions when it is dissolved in water, this time it is Sodium ions and Hydroxyl ions. NaOH(aq) = Na+ + OH-

  7. In each case we can measure or calculate the concentration of Hydrogen ions present. We use the symbol [H+], we use square brackets to mean that it is the concentration of Hydrogen ions. In a 1 molar HCl(aq) Hydrogen Chloride solution known as Hydrochloric acid [H+] = 0.01 = pH 2 In H2O(l) water [H+] = 0.0000001 = pH 7 In NaOH(aq) Sodium Hydroxide solution [H+] = 0.00000000000001 = pH 14

  8. The Dissociation of Water 2H2O(l) H3O+(aq) + OH-(aq)

  9. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Strong acid weak acid weak alkali Strong alkali Crossword

  10. pH + pOH must always = 14

  11. Arrhenius Definition An acid is a substance which forms H+ ions as the only positive ion in aqueous solution Brønsted-Lowry A base is a proton acceptor. An acid is a proton donor. Neutralization needs equal amounts of H+ & OH- Always makes water and a salt. pH = -log[H3O+] pH + pOH = 14 [H3O+] x [OH-]=1 x 10-14 Acids Using Titration allows you to work out the Concentration of a an acid or alkali Providing you know 3 of the items below M1V1 = M2V2

  12. Neutralization To make Neutral Acid Salt Alkali Water Neutral Aqueous

  13. Adding Acid to Alkali You come here it’s just as far! You acid breathed heathen! Oiy! come over here and I’ll rip your hydroxide off! 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

  14. Acid  -  A substance that has the potential to donate a proton (H+) or accept an electron pair. Base  -  A substance that can accept a proton, release OH-, or donate an electron pair. Arrhenius Model  -  Arrhenius proposed that acids are substances that produce protons, H+, in aqueous solution, whereas bases produce hydroxide ions, OH-, in aqueous solution. Bronsted-Lowry Definition  -  Bronsted and Lowry define an acid as a proton (H+) donor and a base as a proton acceptor. Compare this model with the Arrhenius Model and the Lewis definition. Lewis Definition  -  Lewis defined an acid as an electron pair acceptor and a base as an electron pair donor. Compare his model with the Arrhenius model and the Bronsted-Lowry definition.

  15. pH + pOH always equals 1 14

  16. I’m afraid you’re wrong this time Try Again

  17. pH + pOH always equals 1 14

  18. pH + pOH always equals 14 “A base is a proton acceptor” is a definition by Bronsted - Lowry Lewis

  19. I’m afraid you’re wrong this time Try Again

  20. pH + pOH always equals 14 “A base is a proton acceptor” is a definition by 0.001 M NaOH has a pH of 11 3

  21. I’m afraid you’re wrong this time Try Again

  22. pH + pOH always equals 14 “A base is a proton acceptor” is a definition by Bronsted Lowry 0.001 M NaOH has a pH of 11 Congratulations you made it

  23. The Proton in Water: Arrhenius Theory An acid as a substance that ionizes in water to give hydrogen ions, and a base as a substance that ionizes in water to give hydroxide ions. Hydrochloric acid, HCl, is a strong acid, and is very soluble in water. It dissociates into its component ions in the following manner: HCl (g) H+ (aq) + Cl- (aq) The hydrogen ion interacts strongly with a lone pair of electrons on the oxygen of a water molecule. The resulting ion, H3O+ is called the hydronium ion.

  24. Strong acids are so named because they react completely with water, leaving no undissociated molecules in solution. Consequently, [H+] normally equals the original concentration of the acid x VHF For example, in a 0.10 M aqueous solution of the strong acid, nitric acid, [H+] = 0.10 = 0.1M pH = 1

  25. Dissociating HNO3 H+ NO3-

  26. Dissociating X X HNO3 H+ NO3-

  27. The Brønsted-Lowry Concept of Acids and Bases An acid is a proton donor. A base is a proton acceptor. Johannes Nicolaus Brønsted Thomas Martin Lowry

  28. Conjugate Acid-Base Pairs Conjugate means having a common derivation, linked. Let's look at the reaction of NH3 and H2O again: NH3 + H2O NH4+ + OH- The reverse of this reaction is: NH4+ + OH- NH3 + H2O In this case, NH4+ acts as an acid which donates a proton to OH-. OH- acts as a base.

  29. H3O+ + A- HA + H2O H3O+ + A- If HA is a strong acid because it gives up its proton readily, then A- is a weak base because it has little affinity for the proton. If HA is a weak acid because it donates very few protons to the water, then A- has a high affinity for a proton, and A- is a stronger base than water. HA + H2O

  30. Writing acid equilibrium equations The Ka for any acid solution in equilibrium: HX (aq) H+ (aq) + X- (aq) is defined as:

  31. acid-base reactions are written as HX (aq) X- (aq) + H+ (aq). and that others have been written as HX (aq) + H2O (l) X- (aq) + H3O+ (aq)

  32. The exclusion of pure solids and liquids from equilibrium constant expressions such as Ka is especially important here because it makes the equilibrium expressions for these two reactions the same, provided that H+ and H3O+ are considered to be the same. Thus, either form of the acid-base equilibrium equation can be used.

  33. . Common Strong Acids and Bases Acids Bases HCl - hydrochloric acid VHF 2 NaOH - sodium hydroxide HNO3 - nitric acid KOH - potassium hydroxide H2SO4 - sulfuric acid Ca(OH)2 - calcium hydroxide

  34. Most substances that are acidic in water are actually weak acids. Because weak acids dissociate only partially in aqueous solution, an equilibrium is formed between the acid and its ions. The ionization equilibrium is given by: HA(aq) H+(aq) + A-(aq) where X- is the conjugate base. For calculation purposes, the following is assumed:

  35. Strong and weak acids Ka

  36. The equilibrium constant is then: Ka= { [H+][A-] / [HA] } Products/reactants

  37. Calculating the pH for Solutions of Weak Acids Calculate the pH of a 0.10 M solution of acetic acid. If the Ka = 1.8 x 10-5. STEP 1: Write the ionization equilibrium for acetic acid: HC2H3O2 (aq) H+ (aq) + C2H3O2- (aq) STEP 2: Create an I.C.E. grid, and determine the concentration from information provided in the problem: HC2H3O2 (aq) H+ (aq) + C2H3O2- (aq)

  38. + HC2H3O2 H+ C2H3O2-

  39. STEP 3: Substitute the equilibrium concentrations into the equilibrium constant expression: The equilibrium constant expression is: Ka = { [H+][C2H3O2-] / [HC2H3O2] } Ka = { (x)(x) / (0.10 - x) } = 1.8 x 10-5 This equation has only one unknown and can be solved using the quadratic formula. However, we can make things easier:

  40. STEP 4: Remove the denominator x as it is very small compared to the initial conc of the acid The equation becomes: 1.8 x 10-5 = {(x)(x) / 0.10} 1.8 x 10-5 = {X2/ 0.10} 0.1 x 1.8 x 10-5 = {X2/ 0.10} x 0.1 1.8 x 10-6 = X2 x = 1.3 x 10-3 M = [H+].

  41. STEP 5: Now we find pH: pH = -log(1.3 x 10-3M) pH = 2.89 If you need to find the pH of a weak base its exactly the same process only you would calculate pOH and then subtract that value from 14 to find the pH

  42. 2. Identify a conjugate acid-base pair in the reaction NH3 + H2O ‹–› NH4+ + OH- a.NH3 and OH- b.H2O and OH- c.H2O and NH4+ d.NH3 and H2O

  43. 3. Compared to strong acids, weak acids produce __________ ions and conduct electricity __________ efficiently. a.fewer, more b.more, more c.fewer, less d.more, less

  44. 4.A 0.001M solution of HCl is ____________. a.a dilute acid solution b.neutral c.a weak acid solution d.a concentrated acid solution

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