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ACIDS and BASES

ACIDS and BASES. Acid – Base theories Naming acids and bases Oxides Reactions and properties of acids and bases Strengths of acids and bases. Acid and Base Theories 1) Arrhenius Theory. An acid is a substance that gives H + ion, when dissolved in water.

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ACIDS and BASES

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  1. ACIDS and BASES • Acid – Base theories • Naming acids and bases • Oxides • Reactions and properties of acids and bases • Strengths of acids and bases

  2. Acid and Base Theories1) Arrhenius Theory • An acid is a substance that gives H+ ion, when dissolved in water. For example, hydrochloric acid reacts with water to form hydrogen ions which are transferred to a water molecule to form a hydronium ion (H3O+). But simply the reaction is: HCl H+ + Cl-

  3. Acids which have one ionizable hydrogen atom per molecule are called monoprotic acids. Example: HNO3 H+ + NO3- Acids which have two ionizable hydrogen atom per molecule are called diprotic acids. Example: H2SO4 H+ + HSO4− HSO4− ⇌ H+ + SO42− Acids which have three ionizable hydrogen atom per molecule are called triprotic acids. Example: H3PO4   ⇌ H+ + H2PO4– H2PO4– ⇌ H+ + HPO42– HPO42– ⇌ H+ +  PO43–

  4. A base is a substance that gives OH- ion, when dissolved in water. NaOH → Na+ + OH− Ca(OH)2 → Ca2+ + 2OH- Reaction ofNH3 produce OH-: NH3 + H2O → NH4+ + OH- so it is a base.

  5. Limitations of the Arrhenius theory ONLY FOR AQUEOUS SOLUTIONS!!!!!

  6. Acid and Base Theories2) Bronsted-LowryTheory • An acid is a proton (hydrogen ion, H+) donor. • A base is a proton (hydrogen ion, H+) acceptor. HCO3- and H2CO3 HOH and OH- are conjugate acid-base pairs.

  7. Conjugate acid-base pairs • have only got 1 H+ difference in their structures.

  8. To determine whether a substance is an acid or a base, • count the hydrogens on each substance before and after the reaction. • If the number of hydrogens has decreased that substance is the acid (donates hydrogen ions). • If the number of hydrogens has increased that substance is the base (accepts hydrogen ions)

  9. A- becomes conjugate base of HA and in the reverse reaction it accepts a H from HZ to recreate HA. • HZ+ becomes a conjugate acid of Z and in the reverse reaction it donates a H to A- recreating Z • Which pairs are conjugate acid-base pairs?

  10. Example • What are the formulae for the conjugate acid of the following species? • HS- • CO32- • NH3

  11. Example 2) What are the formulae for the conjugate base of the following species? • HS- • CO32- • NH3 • H2SO4

  12. Acid and Base Theories2) Bronsted-LowryTheory The Bronsted-Lowry theory doesn't go against the Arrhenius theory in any way - it just adds to it.

  13. Naming Acids and BasesA. Naming Acids: The name of the acid is determined based on the name of the anion, specifically, based on the ending of the anion name.  The three possibilities are listed here:

  14. Common Anions

  15. B. Naming Bases Simply use the normal rules for naming compounds; ionic or covalent depending on the elements in the compound. Example: NaOH: Sodium hydroxide Ca(OH)2: Calcium hydroxide NH3: Ammonia

  16. Example: a) Name the following acids and bases: NaOH: H2SO3: H2S : H3PO4: NH3: HCN: Ca(OH)2: H3P: Sodium hydroxide Sulfurous acid Hydrosulfuric acid Phosphoric acid Ammonia Hydrocyanic acid Calcium hydroxide Hydrophosphoric acid

  17. b) Write the formulas of the following acids and bases: Hydrofluoric acid: Carbonic acid: Lithium hydroxide: Nitrous acid: Sulfuric acid: Beryllium hydroxide: Hydrobromic acid: HF H2CO3 LiOH HNO2 H2SO4 Be(OH)2 HBr

  18. Some common acids Sulfuric acid: Nitric acid (kezzap): Hydrochloric acid(tuzruhu) Acetic acid/ethanoic acid/ vinegaric acid Formic acid/methanoic acid • (in ants’ saliva) H2SO4 HNO3 HCl CH3COOH HCOOH

  19. NaOH Some common bases/alkalis Sodium hydroxide(caustic soda): Potassium hydroxide: Magnesium hydroxide (milk of magnesia) Calcium hydroxide Ammonia KOH Mg(OH)2 Ca(OH)2 NH3

  20. Oxides Nonmetal Oxides Metal Oxides CO2, SO2, SO3 etc. show acidic properties (acid anhydride) Na2O, BaO etc. show basicproperties (basic anhydrides) CO, NO, N2O are neutral (have 1 oxygen atom in the formula) Amphoteric metals show both basic and acidic properties such as Al and Zn

  21. Acidic Property of Nonmetal Oxides • The oxides of nonmetals are usually acidic except NO, N2O and CO (They are neutral) • When acidic oxides of nonmetals dissolve in water, they form acidic solutions. CO2 + H2O H2CO3 SO3 + H2O H2SO4 N2O5 + H2O 2HNO3 P4O10 + H2O 4H3PO4 • Acidic nonmetal oxides react with bases to form salts. SO3 + 2KOH K2SO4 + H2O

  22. Carbon dioxide dissolved in water is in equilibrium with carbonic acid: CO2 + H2O ⇌ H2CO3(the equilibrium rxn happens in our blood) ACIDIC OXIDES

  23. They don’t react with water, acids, and bases. NEUTRAL OXIDES

  24. Basic Properties of Metal Oxides • Oxides of metals are usually basic. Na2O + H2O 2NaOH BaO + H2O Ba(OH)2 • Basic oxides react with acids to form salts. CaO + H2SO4 CaSO4 + H2O

  25. Amphoteric Oxides Oxides amphoteric metals are also amphoteric. Al2O3 + HCl AlCl3 + H2O Al2O3 + 2NaOH + 3H2O 2NaAl(OH)4 (sodium tetrahydroxoaluminate)

  26. Properties and Reactions of Acids and Bases • Properties of Acids: • Are corrosive • They taste sour • They form solutions w/ pH less than 7 at 25°C. • They turn litmus dye from blue to red • They conduct electricity (electrolyte) • They react with active metals to form salt and H2 gas. Mg + 2HCl MgCl2 + H2

  27. The acids which do not contain oxygen in their structures can not react with semi noble metals Cu, Hg, Ag.The oxy acids (ACIDS HAVING OXYGEN IN THEIR STRUCTURES)react with these metals producing gases other than H2. Cu + 2H2SO4 CuSO4 + SO2 + 2H2O 3Ag + 4HNO3 3AgNO3 + NO + 2H2O • They react with metal carbonates and hydrogen carbonates(bicarbonate ion) to give a salt, water and carbon dioxide, which appears as effervescence (bubbles). Na2CO3 + 2HCl NaCl + H2O + CO2 CH3COOH (aq)+NaHCO3 (aq)NaCH3COO(aq) +H2O (l) +CO2 ethanoic acid metal hydrogen salt water carbon carbonate dioxide

  28. They react with bases to form salts and water. HCl + NaOH  NaCl + H2O (neutralization) H+ (aq) + OH- (aq)  H2O(l) (net ionic equation)

  29. B. Properties of Bases • They have bitter taste • Aqueous solutions of bases, known as alkali, have a slippery feel. • They turn the litmus dye from red to blue • They react with fats in the skin to form soaps • They conduct electricity (electrolyte) • The most common bases are the oxides, hydroxides and carbonatesof metals, but a number of other compounds, such as ammonia also acts as a base.

  30. They only react with amphoteric metals: Zn, Al Zn + 2NaOH  Na2ZnO2 + H2 2Al + 6 NaOH  2Na3AlO3 + 3H2 • If they are soluble in water they give a solution with pH>7 (at 25 oC). • They react with acids to form a salt. • CaO (s) + 2 HCl (aq)  CaCl2 (aq) + H2O (l) base acid salt water

  31. Amphoteric metals can react with both acids and bases, such as Al, Zn, Sn, Pb, Cr Al + 6HCl AlCl3 + 3H2 2Al + 6NaOH 2Na3AlO3 + 3H2 • Oxides and hydroxides of amphoteric metals are also amphoteric. Al2O3 + HCl AlCl3 + H2O Al2O3 + 2NaOH + 3H2O 2NaAl(OH)4 ZnO + 2 HCl ZnCl2 + H2O ZnO + 2NaOH + H2O Na2Zn(OH)4

  32. Neutralization

  33. Examples of Acids&Bases Acids HCl H2SO4 HNO3 Juices, Soda Bases NaOH Ca(OH)2 KOH Soap, Ammonia, Baking Soda

  34. Relative Strengths of acids and Bases The strength of an acid depends on how easily the proton, H+ is lost or removed from an acid Two factors determine the acidic strength: • The polarity of the bond with H atom:The more polarized the bond is, the more easily the proton is removed and greater the acidic strength. • The size of the atom X (in HX): The greater the atom X, the weaker is the bond and greater the acidic strength.

  35. Periodic Trends for Binary Acids: Down a group:Sizes of the atoms increase. HF HCl Acidic strength increases HBr HI Across a period: Polarity of the bond increases. CH4 NH3 H2O HF Acidic strength inreases.

  36. Oxyacids: HOF HOCl Acidic strength decreases. H-O HOBr bondionizes HOI more easily when the oxygen atom is bonded to a more electronegativeatom.

  37. For a series of oxyacids: HClO HClO2 HClO3 HClO4 Acidity increases As the number of oxygen atoms increases, The oxidation number of central atom (Cl) increases. This increases the ionization of O-H bond. Therefore, acidic strength increases.

  38. Polyprotic Acids and Their Anions: H3PO4 H2PO4- HPO42- H2CO3 HCO3- Acidity decreases H2SO4 HSO4-

  39. Organic Acids Organic acids have carboxyl group (COOH). They are weak acids. Example: HCOOH: Formic acid CH3COOH: Acetic acid

  40. Basic strength • As the volume of the metal increases, it becomes easier to ionize the OH- ion and the basic strength increases. • LiOH • NaOH • KOH Basic strength increases

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