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Acids and Bases

This guide provides a comprehensive overview of acids and bases, detailing their properties, behaviors, and reactions. Learn about the characteristics of acids, such as their sour taste, ability to turn blue litmus paper red, and the formation of hydrogen ions in solutions. Explore bases, known for their bitter taste and slippery feel, that turn red litmus paper blue. Understand pH calculations, the pH scale, and the significance of water as an amphoteric substance. This resource is essential for grasping fundamental concepts of acid-base chemistry.

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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)

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