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Acids and Bases

Acids and Bases

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Acids and Bases

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  1. Acids and Bases

  2. Acids • Taste sour • Begin with H • Found in many foods and drinks • Turn blue litmus paper red • pH 0-6.9 • Corrosive • Forms H+ (or H30+)ions in solutions Hydrogen Hydronium

  3. Bases • Bitter • End in OH • Turn red litmus paper blue • pH 7.1-14 • Found in many cleaning products • Slippery • Corrosive • Forms OH- ions in solution Hydroxide

  4. Acids and Bases • Neutral: H+ = OH- • Acidic: H+ > OH- • Basic: H+ < OH- • ↑H+ = ↓OH- = more acidic = ↓ pH ac idic • ↓H+ = ↑OH-= more basic = ↑ pH

  5. Water = Neutral H2O = HOH HOH → H+ + OH- Free Hydrogen ion bonds with water molecule to form Hydronium ion H+ and H3O+ used interchangeably

  6. Hydronium Ion = Hydrogen Ion • Self ionization - two water molecules react to form a hydronium ion (H3O+) and hydroxide ion. H20 → H+ + OH-

  7. pH scale • Shows the strength of acid or base on a scale of 0-14. • Numbers below 7 = acids…the lower the number, the more acidic • Numbers above 7 – bases…the higher the number the more basic.

  8. pH and pOH • pH + pOH = 14 • If the pH = 2, what is pOH • If the pH = 4, what is the pH • If the pOH = 7, what is the pH

  9. Calculating pH • Formula: pH = -log [ H+ ] • You can calculate pH by finding the negative logarithm of the concentration of hydrogen ions.

  10. Calculating pH • A solution contains 1.0 x 10-8 mol/L of H+ ions, what is the pH of this solution? • Formula: pH= -log [H+] • pH = -log (1.0 x 10-8) • pH = 8 = Base

  11. Calculating pH • A solution contains 3.5 x 10-5 M of H+ ions, what is the pH of the solution? • Formula: pH= -log [H+] • pH= -log ( 3.5 x 10-5) • pH = 4.5 = acid

  12. pH and Water • Water is amphoteric; it can act as both an acid and a base in an aqueous solution. • Water contains an equal number of H+ and OH- ions. H2O H+ + OH-

  13. Ion Product Constant of Water • Kw is the ion product constant for water. • Represents the equilibrium for the self ionization of water. • Formula: Kw = [H+][ OH-]

  14. [H+] = 1.0 x 10-7 • [ OH-]= 1.0 x 10-7 • What is the Kw? • Kw= (1.0 x 10-7) x (1.0 x 10-7) Kw= 1.0 x 10-14 This is a constant on your STAAR Chart

  15. Kw= [H+][OH-] Kw= 1.00x10-14 List the Knowns H+ = 1.0 x 10-5 1.00 x 10-14 = 1.0 x 10-5 [OH-] plug into formula • The H- concentration of an aqueous solution is 1.0 x 10-5M. What is the OH- ion concentration? [OH-] = 1.00 x 10-14/ 1.0 x 10-5 = 1.0 x 10 -9mol/L M

  16. The OH- concentration of an unknown solution is 2.4 x 10-4. What is the H+ concentration of the solution? Is the unknown solution acidic, basic, or neutral? • Kw= [H+][OH-] • 1.0 x 10-14 = [H+][ 2.4 x 10-4] • [H+] = 1.0 x 10-14/ 2.4 x 10-4 • [H+] = 4.16x 10-11 • -log(4.16 x 10-11)= pH= 10.4 • = Basic solution

  17. Acid Base Reactions HA + BOH → HOH + B+A- • Acid + Base = neutralization reaction • Acid + Base → water + salt (always) • Salt = (+) ion from base & (-) ion from acid • Positive ions are always listed first

  18. Arrhenius • Swedish Chemist Svante Arrhenius created a model for acids and bases in 1883.

  19. Arrhenius Model- Acid H+ (aq) + Cl- (aq) • HCl (g) • Acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution.

  20. Arrhenius Model- Base • Base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in aqueous solution. NaOH (s) Na+(aq) + OH- (aq)

  21. Bronsted- Lowry Model • Danish chemist Bronsted and English chemist Lowry proposed a model that focuses on the Hydrogen Ion • An Acid is a hydrogen-ion donor • A Base is a hydrogen-ion acceptor

  22. Ionization • The Bronsted-Lowry Model also shows if and acid or base is strong based on ionization. • Strong acid- completely ionized • Weak acid- partial ionization

  23. Strength and Concentration • Strength – how completely it ionizes Strong – ionizes completely or almost completely Weak – ionizes partly • Concentration Concentrated - a lot of acid/base in water. Dilute – a little acid/base in water.

  24. 12 M HCl is a strong acid with a high concentration • Adding 6L of water to this solution would do what to the solution: strong acid, dilute solution • Vinegar has acetic acid, which is weak, in low concentration = dilute • 12 M acetic acid would still be weak, because it only partially ionizes, but it would be a concentrated solution, because there is a lot of acid dissolved in a little water.

  25. Strong Acids • Since strong acids are completely ionized they produce the maximum number of ions. • Strong acids are good conductors • Reaction only moves in one direction, represented with an arrow in one direction.

  26. HCl H+ + Cl- • HBr H+ + Br– • H2SO4 H+ + HSO4 _

  27. Weak Acids • An acid that ionizes partially in dilute aqueous solutions • Produce fewer ions, so they are poor conductors • Reactions move both directions until equilibrium is reached, represented by an arrow in both directions

  28. HF H+ + F- • H2S H+ + HS- • H2CO3 H+ + HCO3-

  29. Conjugate Acid • The species produced when a base accepts a hydrogen ion to form an acid Conjugate Base The species that results when an acid donates a hydrogen ion to form a base.

  30. Conjugate acid – base pairs • 2 compounds with the same chemical formula, but the acid of the pair will have 1 more H NH3 & NH4- H2SO4 & HSO4- H2O & H3O+

  31. Bronsted-Lowry Model Conjugate aCID aCID • NH3 + H2O → NH4++ OH- bASE Conjugate BASE

  32. Precipitate Reactions • When two compounds come together to form an aqueous compound and a solid compound. • 2NaOH(aq)+CuCl2(aq) 2NaCl(aq)+Cu(OH)2(s) • KI(aq) + AgNO3(aq)KNO3(aq) + AgI(s) • Use your STAAR chart to check solubility • If insoluble – compound will precipitate or settle out of solution as a solid

  33. Oxidation-Reduction Reaction • A reaction in which electrons are transferred from one atom to another • 2KBr(aq) + Cl2(aq)  2KCl(aq) + Br2(aq) • The chlorine on the left steals electrons from the bromine in KBr to become KCl and Br2 on the right.

  34. Oxidation- Reductions Reaction

  35. Remember Acid-Base Reaction • Form SALT + WATER • Mg(OH)2 + 2HCl  MgCl2 + H20 base + acid  salt + water • Salt = any ionic compound made up of a cation (+) from a base and an anion (-) from an acid

  36. Identify the following reaction: as 1) precipitation, 2) oxidation-reduction, or 3)acid-base • 2K+ Br2  2KBr • H3N + CsOH  Cs3N + H2O • MgCl2 + Li2CO3  MgCO3 + LiCl Look on STAAR chart to see if either compound Is insoluble

  37. Titration • Use known solution (standardsolution) to find the concentration of an unknown solution • Drop by drop process • Endpoint – point of color change of indicator • When neutralized

  38. Buffers • Resist changes or swings in pH • Blood pH approx 7.4 • Fatal if fall or rise more than 0.3 pH units • Buffers in your blood prevent big changes when, for example, you eat an orange (citric acid)