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Acids and Bases

Acids and Bases. Acids ( from the Latin acidus / acēre meaning sour ). Why learn about acids?. Guess the names of the following acids!. Used to ferment milk Named after the latin name of ants; often found in ant stings Found in fizzy drinks Also called vitamin C

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Acids and Bases

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  1. Acids and Bases

  2. Acids (from the Latin acidus/acēre meaning sour) • Why learn about acids?

  3. Guess the names of the following acids! • Used to ferment milk • Named after the latin name of ants; often found in ant stings • Found in fizzy drinks • Also called vitamin C • Found in the nucleus of eukaryotic cells • Found in car batteries • Found in your stomach • Found in oranges and lemons

  4. What are acids? • 3 definitions: • Arrhenius definition • Bronsted-Lowry definition • Lewis definition

  5. Arrhenius definition • Acids are substances which increase the concentration of hydronium ions (H3O+) in solution (water). • In this definition, all acids must contain hydrogen. • Does it mean that all compounds which contain hydrogen are acids? • Name some examples of compounds containing hydrogen but are not acids. • The hydronium ions are responsible for the properties of acids!

  6. Textbook definition • Acids are substances which produce hydrogen ions, H+, when dissolved in water.

  7. Properties of acids • Acids have a sour taste. • It is the hydronium ions interacting with the taste receptors that give the taste of sourness.

  8. Acid molecules (Recall) • Are HCl, HNO3 and H2SO4 covalent molecules? • Are they able to conduct electricity?

  9. Properties of Acids • Acids dissolve in water to form solutions which conduct electricity. • Take a look at HCl dissolved in water. What are the ions present in the water? + - O Cl H H H

  10. Properties of Acids • For simplicity’s sake, we often just say that HCldissociates in water to form H+ ions and Cl- ions. Cl H Cl Cl- H+ H

  11. Properties of acids • Dilute acids are irritants, and cause skin to blister or redden. • Concentrated acids are very corrosive.

  12. Properties of acids • What about HCl, HNO3 and H2SO4 dissolved in organic solvents like acetone? Cl Cl- H Cl- Cl H H+ H+ Cl- Cl H H+ Acetone Water

  13. Properties of Acids • Acids turn blue litmus paper red. • What happens here? • Litmus is a mixture of dyes that turns red under acidic conditions and blue under basic conditions. What colour do you think neutral litmus paper is?

  14. Properties of Acids • Acids react with reactive metals to form hydrogen and a salt. • metal + acid → salt + hydrogen • What is meant by a reactive metal?

  15. Reactivity series Potassium Sodium Calcium Magnesium Aluminium Zinc Iron Lead Hydrogen Copper Silver Gold Please Stop Calling Me A Zebra I Love Happy Cats Selling Goldfish More and more reactive

  16. Reaction of metals with acids • 3 widely used acids: • Hydrochloric acid – salts formed are chlorides • Nitric acid – salts formed are nitrates • Sulfuric acid – salts formed are sulfates • metal + acid → salt + hydrogen • Examples • magnesium + hydrochloric acid → ? • Mg(s) + HCl(aq) → MgCl2(aq) +H2(g) • How to test that the gas produced is hydrogen? • Lighted splint test.

  17. Reaction of metals with acids • Copper, silver and gold do not react with dilute acids. • Copper reacts with concentrated nitric acid, but no hydrogen is formed, hence it is not the typical kind of metal-acid reaction. Instead NO2 gas is formed. • Think: Lead is above hydrogen in the Reactivity series. Can you reason out why it shows no visible reaction with sulfuric acid and hydrochloric acid, but reacts with nitric acid? Cu(s)  +  4HNO3(aq)  ——>  Cu(NO3)2(aq)  +  2NO2(g)  +  2H2O(l)

  18. Chemical equations • calcium + hydrochloric acid → ? • zinc + nitric acid → ? • sodium + sulfuric acid → ?

  19. Properties of acids • Acids react with carbonates and hydrogencarbonates to give a salt,carbon dioxide and water. • acid + carbonate → carbon dioxide + salt + water • E.g. hydrochloric acid + sodium carbonate → ? • 2HCl(aq) + Na2CO3(s)→ 2NaCl(aq) + CO2(g) + H2O(l) • What happens if there is not enough HCl? • HCl(aq) + Na2CO3(s)→ NaCl(aq) + NaHCO3(aq) • NaHCO3(aq) + HCl(aq) → NaCl(aq) + CO2(g) + H2O(l)

  20. Properties of acids • How to test for carbon dioxide? • Limewater test – White precipitate formed. What is this white precipitate?

  21. Chemical equations • nitric acid + calcium carbonate → ? • hydrochloric acid + potassium carbonate → ? • sulfuric acid + magnesium carbonate → ?

  22. Properties of acids • Acids react with metal oxides or metal hydroxides to form a salt and water only. • acid + metal oxide/hydroxide → salt + water • E.g. hydrochloric acid + sodium oxide → ? • 2HCl(aq) + Na2O (s)→ 2NaCl(aq) + H2O(l) • E.g. nitric acid + copper(II) hydroxide → ? • 2HNO3(aq) + Cu(OH)2(aq)→ Cu(NO3)2(aq) + 2H2O(l)

  23. Summary of properties of acids

  24. Basicity of acids • The maximum number of hydrogen ions produced by/ number of replaceable hydrogen atoms in a molecule of acid is called the basicity of the acid. • E.g. HCl is monobasic, so it has only 1 replaceable hydrogen. • E.g. H2SO4 is dibasic, so it has 2 replaceable hydrogens. • E.g. H3PO4 is tribasic, so it has 3 replaceable hydrogens. • Write chemical equations for the reaction of sodium hydroxide with these 3 acids.

  25. Basicity of acids • Take a look at ethanoic acid. • CH3COOH(aq)  H+(aq) + CH3COO-(aq) • How many hydrogen atoms does it contain? • What is its basicity?

  26. Importance of acid reactions in water • A piece of magnesium placed in a solution of HCl in a dry organic solvent shows no visible reaction. • When the same piece of magnesium is placed in a solution of HCl dissolved in water (what do you call this solution?), H2 gas is produced. Why?

  27. Importance of acid reactions in water • When the hydrogen chloride molecule dissociates, it is the H+ ions that react with reactive metals and not the chloride ions, Cl-. • For instance, when HCl(aq) reacts with magnesium, 2H+(aq) + Mg(s) → H2(g)+ Mg2+(aq)

  28. Importance of acid reactions in water • Similarly, it is the H+ ions that react with carbonate ions to give water and carbon dioxide gas. • For instance, when HCl(aq) reacts with sodium carbonate, 2H+(aq) + CO32-(aq) → CO2(g)+ H2O(l)

  29. Alka Seltzer tablets • These tablets contain sodium carbonate, potassium carbonate and citric acid. Why is it that they can exist as a tablet without reacting?

  30. Weird acids • Aqua Regia – royal water • Formed by mixing concentrated nitric acid and concentrated hydrochloric acid in 1:3 ratio • Aqua Regiadissolves gold!

  31. Uses of acids • Industrial products • E.g. fertilizers • Food preservation • E.g. ethanoic acid (vinegar) for pickling of vegetables

  32. Sulfuric Acid • Manufacturing of sulfuric acid via Contact process. • Sulfuric acid is used in: • Manufacturing detergents, paints, dyes, plastics • Manufacturing fertiliserse.g ammonium sulfate • Batteries for vehicles • Making synthetic fibres, paints and pigments

  33. Contact Process • 1. Sulfur is burnt in oxygen to form sulfur dioxide. • S(s) + O2(g) → SO2(g) • 2. Sulfur dioxide is further reacted with oxygen to form sulfur trioxide using vanadium (V) oxide, V2O5as a catalyst at high temperature (400-500oC) and medium pressure (1-2 atm). • 2SO2(g) + O2(g) → 2SO3(g)

  34. Contact Process • 3. The sulfur trioxide is then dissolved in concentrated sulfuric acid to give a fuming liquid called oleum, H2S2O7. • SO3(g) + H2SO4(l) → H2S2O7(l) • 4. Water is added to oleum to form concentrated sulfuric acid. • H2O(l) + H2S2O7(l) → 2H2SO4(l)

  35. Uses of sulfuric acid • Manufacture of fertilisers • E.g. Ammonium sulfate. • ammonia + sulfuric acid → ammonium sulfate + water • 2NH3(aq) + H2SO4(aq) → (NH4)2SO4(aq) • E.g. Superphosphate is manufactured by reacting calcium phosphate with conc. sulfuric acid. • Calcium phosphate + sulfuric acid → calcium dihydrogen phosphate + calcium sulfate • Ca3(PO4)2(s) + 2H2SO4(aq) → Ca(H2PO4)2(s) + 2CaSO4(s) • The product of the combination of 2 calcium salts is called superphosphate!

  36. Uses of sulfuric acid • Manufacture of detergents • Treating hydrocarbons with concentrated sulfuric acids give organic acids. • These organic acids are then neutralized with sodium hydroxide to give the detergent.

  37. Uses of sulfuric acid • As battery acids in cars • Dilute sulfuric acid, lead plates, and lead(IV) oxide plates are fitted in batteries. • When sulfuric acid, lead and lead(IV) oxide react, electrical energy is produced.

  38. What are bases? • 3 definitions: • Arrhenius definition • Bronsted-Lowry definition • Lewis definition

  39. Textbook definition • Bases are metal oxides or metal hydroxides. • Bases are substances which react with acids to give a salt and water only. • Bases which are soluble in water are called alkali and they produce hydroxide ions (OH-) in water (Arrhenius definition).

  40. Guess these alkalis/bases • Drink this when you have indigestion • Smells like urine • Also called caustic soda • Also called lime or quicklime • Also called slaked lime • Rust

  41. Examples of bases For instance, when HCl(aq) reacts with zinc oxide, 2HCl(aq) + ZnO(s) → H2O(l)+ ZnCl2(aq)

  42. Properties of alkalisArabic al qalīy = the calcined ashes, referring to the original source of alkaline substance • Alkalis have a bitter taste and soapy feel. • It is the reaction of hydroxide with the fats on our skin that gives the soapy feel.

  43. Properties of alkalis • Alkalis turn red litmus paper blue.

  44. Properties of alkalis • Alkalis produce hydroxide ions when dissolved in water. • Note: The only hydroxides that are soluble are: Group I hydroxides, barium hydroxide and calcium hydroxide (sparingly soluble).

  45. Topics today • Alkalis and properties (continued) • Strength and concentration of acids • pH scale • pH indicators • pH and soil • (oxides)

  46. Properties of alkalis • Why is aqueous ammonia an alkali? • ammonia + water → ammonium ion + hydroxide ion • NH3(g) + H2O(l) → NH4+(aq) + OH-(aq)

  47. Properties of alkalis • Alkalis react with acidsto form a salt and water only. • This reaction is called neutralization. • This is represented as follows: • H+(aq) + OH-(aq) → H2O(l) or • H3O+(aq) + OH-(aq) → 2H2O(l) • Neutralization can take place between bases and acids too.

  48. Properties of alkalis • Consider these reactions: • manganese(IV) oxide + hydrochloric acid → manganese(II) chloride + water + chlorine • MnO2(s) + 4HCl(aq) → MnCl2(aq) + 2H2O(l) + Cl2(g) • manganese(II) oxide + hydrochloric acid → manganese(II) chloride + water • MnO(s) + 2HCl(aq) → MnCl2(aq) + H2O(l) • Which one is a neutralization reaction?

  49. Properties of alkalis • Alkalis heated with ammonium salts give off ammonia gas. • alkali + ammonium salt → ammonia + water + salt • E.g. calcium hydroxide + ammonium chloride → calcium chloride + water + ammonia • Ca(OH)2(aq) + 2NH4Cl(aq) → CaCl2(aq) + 2H2O(l) + 2NH3(g) • OH-(aq) + NH4+(aq) → NH3(g) + H2O(l)

  50. Properties of alkalis • How to test for ammonia? • Litmus test – turns moist red litmus paper blue

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