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Defining Acids and Bases

Defining Acids and Bases. Ch. 15. Acid Characteristics. NEVER TATE OR TOUCH CHEMICALS Latin (acidus) meaning sour/tart Citric acid (citrus fruits), lactic acid (yogurt) Stinging sensation if contacts broken skin Reacts vigorously with metals Good conductor of electricity.

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Defining Acids and Bases

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  1. Defining Acids and Bases Ch. 15

  2. Acid Characteristics • NEVER TATE OR TOUCH CHEMICALS • Latin (acidus) meaning sour/tart • Citric acid (citrus fruits), lactic acid (yogurt) • Stinging sensation if contacts broken skin • Reacts vigorously with metals • Good conductor of electricity.

  3. Base Characteristics • Bitter taste • Mild basic doesn’t sting except in eyes. • Feels smooth, slippery • Does not react with most metals • Good conductor of electricity.

  4. Arrhenius Definition • Acid-substance that dissociates in water to produce hydrogen ions (H+) • Arrhenius acid • Base-substance that dissociates in water top produce hydroxide ions (OH-) • Arrhenius base • Limited to aqueous solutions • Doesn’t cover all bases ex. NH3 ammonia (no OH group)

  5. Example • Determine which is an Arrhenius acid and Arrhenius base • HCl • H2SO4 • NaOH • KOH • HBr • NaHCO3

  6. Bronsted-Lowry Definitions • An acid is a proton (H+) donor • A base is a proton acceptor • H+ simply a proton that is strongly attracted to electrons in water molecules. • Attraction produces hydronium ion, H3O+ • When HCl is dissolved in water it produces a proton, water is a base. • HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq)

  7. Example • Identify the acid and base in each reaction: CN- (aq) + H2O (l) HCN (aq) + OH- (aq) CH3COOH (aq) + H2O (l) H3O+ (aq) + CH3COO- H2O (l) + NH3 (l) NH4+ (aq) + OH- (aq)

  8. Water • Water is a base when HCl is dissolved in water. • Water is an acid when ammonia is dissolved in water NH3 (g) +H2O NH4+ (aq) + OH- (aq) • Amphoteric- a substance that can act as either an acid or a base.

  9. Types of Acids • Monoprotic acid-donates only one proton • HCl, HBr • Polyprotic acids- more than one acidic hydrogen donated (diprotic, triprotic) • H2SO4, H3PO4

  10. Identifying Acids • Acidic hydrogen- the hydrogen in an acid that can be donated. • HCl: one acidic • H2SO4: two • HC2H3O2: one • Why are some H acidic and some not? • Acidic hydrogen have slight positive charge while part of a molecule • Bonded to very elctroneg. elements (O, N, halogen) • If bonded to C, not acidic

  11. 3 Categories of Acids • Binary acid-hydrogen and one other element HCl, HBr, HI • Oxy acid-binary acid with oxygen H2SO4, HNO3, H3PO4 • Carboxylic acid-organic acid (acid with carbon) HC2H3O2 • Most are weak • Carboxyl group (-COOH) • Donates hydrogen in carboxyl group to form carboxylate ion.

  12. Acid Properties • The stronger the X-H bond the less acidic (compare bond dissociation energies) • The more polar the X-H bond the stronger the acid (use electronegativities) • The more polar H-O-X bond-stronger acid

  13. Strength of Oxyacids • The more oxygen hooked to the central atom, the more acidic the hydrogen. • HClO4>HClO3>HClO2>HClO • Remember that the H is attached to an oxygen atom • The oxygens are electronegative. • Pull electrons away from hydrogen.

  14. Identifying Bases • Bronsted-Lowry base always contains an unshared pair of electrons. • Two Categories • Anions • (Cl-, Br-, I-, NO3-, O2-, OH-) • Amines (related to ammonia) • Contains N with unshared pair of electrons • Methylamine CH3NH2

  15. Naming Acids • If the formula has oxygen in it write the name of the anion, but change: • ate to ic acid • ite to –ous acid • Watch out for sulfuric and sulfurous and phosphorous and phosphoric • Name the following acids: • H2CrO4, HMnO4, HNO2

  16. Naming Acid • If the acid doesn’t have oxygen add the prefix hydro • Change the suffix –ide to –ic acid • All binary acids follow this rule. • Name the following acids • HCl, H2S, HCN

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