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Acid –Base Theories 19.1

Acid –Base Theories 19.1. A. Acids. Describing an Acid. Tastes “sour” Common compound in fruits and vegetables corrosive Forms electrolytes when in aqueous solution (ions!) Is a molecular compound. Explaining Acid Behavior. Acids are hydrogen containing substances , HCl, H 2 SO 4

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Acid –Base Theories 19.1

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  1. Acid –Base Theories 19.1 A. Acids

  2. Describing an Acid • Tastes “sour” • Common compound in fruits and vegetables • corrosive • Forms electrolytes when in aqueous solution (ions!) • Is a molecular compound

  3. Explaining Acid Behavior • Acids are hydrogen containing substances, HCl, H2SO4 • But not all hydrogen containing compounds are acids!!! CH4, C6H12O6 • Dissociate (ionize) by releasing H+ ions (hydrogen ion or proton) into solution. • written as a dissociation Rx • HCl →H+ + OH-

  4. Acid Formulas • Acids are ionic compounds where the cation is H+ (not a metal) • Anion: Periodic table (how many +/-) and Memory (polyatomic ions: nitrate, hydroxide, carbonate, chlorate, sulfate, phosphate • Undissociated it is a neutral compound

  5. Acid Formulas • Example: phosphoric acid • Made of phosphate and enough H+ to neutralize it • Formula of phosphate: • PO43- • Plus 3 H+ • H3PO4

  6. Types of Acids Contains/releases one ionizable H+ , monoprotic acid • HCl → H+ + Cl- Contains/releases two ionizable H+ , diprotic acid • H2SO4→ 2H+ + SO42- Contains/releases three ionizable H+ , triprotic acid • H3PO4→ 3H+ + PO43-

  7. Review Electronegativity • Increases in this direction

  8. Why do acids release H+? • H involved in very polar covalent bonds –attached to a very electronegative element are released as H+ ions • Example HCl: Cl is very electronegative H-Cl --- H+ + Cl- δ+ δ- • On the other hand: CH4 weakly polar molecule: C is not very electronegative, does not release an H+!!!

  9. What does the H+ do? • Reacts with H2O to form an hydronium ion H3O+ a. H+ + H2O → H3O+

  10. Hydrochloric acid (hydrogen chloride) • HCl • Monoprotic acid H - Cl • HCl → H+ + Cl-

  11. Nitric Acid • HNO3 • Monoprotic acid • HNO3 →H+ + NO3-

  12. Carbonic Acid • H2CO3 • Diprotic acid • H2CO3 →2H+ + CO32-

  13. Phosphoric Acid • H3PO4 • Triprotic acid • H3PO4→3 H+ + PO43-

  14. Sulfuric Acid • H2SO4 • Diprotic acid • H2SO4→ 2H+ + SO42-

  15. Formulas of Organic Acids-Acids of Hydrocarbons • Example: CH3COOH • Not all hydrogens are released! • Which bonds are high/low polar very polar Weak polar • Monoprotic

  16. Organic Acids have Carboxyl Groups • COOH group is called a carboxyl group • Makes a molecule acidic • Dissociation: CH3COOH→CH3COO- + H+

  17. Ethanoic Acid (acetic or vinegar acid) • CH3COOH • monoprotic acid • CH3COOH→H+ +CH3COO-

  18. B. Describing a Base • Adjective: basic or alkaline • rare in nature/foods • taste bitter • are part of soaps –make surfaces slippery • Corrosive, often more dangerous than acids • Are part of cleaners, drain openers • Act as electrolyte if aqueous

  19. Base Formulas • Normal ionic neutral compound: metal cation and hydroxide anion (OH-) • Formula ends with OH • Name ends with ‘hydroxide’ • NaOH –sodium hydroxide • Give the formula of Calcium Hydroxide • Ca(OH)2

  20. Base Behavior • Dissociation into metal cation and hydroxide ion, OH- • A base is a hydroxide donor • NaOH → Na+ + OH-

  21. Sodium Hydroxide NaOH • Ionic compound • Releases OH- • NaOH → Na+ + OH- • Other similar base: KOH (potassium hydroxide), CsOH, RbOH

  22. Magnesium hydroxide • Mg(OH)2 • Mg(OH)2 →Mg2+ + 2(OH)- • Similar are Calcium- or Bariumhydroxide

  23. Ammonia NH3 • Exceptional base: • Does not directly release OH- • Instead breaks water apart • NH3 + H2O → NH4+ + OH-

  24. Testing for Acids and Bases • indicator substances that change color • Litmus paper • Commercially available test strips

  25. Acids and Bases together • React with each other • neutralize • form a salt of the base cation and the acid anion and water HCl + NaOH→ NaCl + H2O Practice: Carbonic acid reacts with Calcium hydroxide

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