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Acids and Bases

Acids and Bases. History of Acids and Bases. In the early days of chemistry chemists were organizing physical and chemical properties of substances. They discovered that many substances could be placed in two different property categories:. Substance B Bitter taste

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Acids and Bases

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  1. Acids and Bases

  2. History of Acids and Bases In the early days of chemistry chemists were organizing physical and chemical properties of substances. They discovered that many substances could be placed in two different property categories: • Substance B • Bitter taste • Reacts with fats to make soaps • Do not react with metals • Turns red litmus blue • Reacts with A substances to make salt and water • Substance A • Sour taste • Reacts with carbonates to make CO2 • Reacts with metals to produce H2 • Turns blue litmus pink • Reacts with B substances to make salt water Arrhenius was the first person to suggest a reason why substances are in A or B due to their ionization in water.

  3. Definitions • Acids – produce H+ • Bases - produce OH- • Acids – donate H+ • Bases – accept H+ • Acids – accept e- pair • Bases – donate e- pair Arrehenius only in water Bronsted-Lowry any solvent Lewis used in organic chemistry, wider range of substances

  4. Arrhenius Theory • The Swedish chemist Svante Arrhenius proposed the first definition of acids and bases. • (Substances A and B became • known as acids and bases) • According to the Arrhenius model: • “acids are substances that dissociate in water to produce H+ ions and bases are substances that dissociate in water to produce OH- ions” • NaOH (aq) Na+ (aq) + OH- (aq)Base • HCl (aq)  H+ (aq) + Cl- (aq) Acid

  5. ACIDS Taste sour Turn litmus React with active metals – Fe, Zn React with bases BASES Taste bitter Turn litmus Feel soapy or slippery (react with fats to make soap) React with acids General properties blue to red red to blue

  6. What is an acid? • An acid is a solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour". • The more H + ions, the more acidic the solution.

  7. Properties of an Acid • Tastes Sour • Conduct Electricity • Corrosive, which means they break down certain substances. Many acids can corrode fabric, skin,and paper • Some acids react strongly with metals • Turns blue litmus paper red Picture from BBC Revision Bites http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/acids_bases_1.shtml

  8. Uses of Acids • Acetic Acid = Vinegar • Citric Acid = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch. • Ascorbic acid = Vitamin C which your body needs to function. • Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics. • Car batteries

  9. What is a base? • A base is a solution that has an excess of OH- ions. • Another word for base is alkali. • Bases are substances that can accept hydrogen ions

  10. Properties of a Base • Feel Slippery • Taste Bitter • Corrosive • Can conduct electricity. (Think alkaline batteries.) • Do not react with metals. • Turns red litmus paper blue.

  11. Uses of Bases • Bases give soaps, ammonia, and many other cleaning products some of their useful properties. • The OH- ions interact strongly with certain substances, such as dirt and grease. • Chalk and oven cleaner are examples of familiar products that contain bases. • Your blood is a basic solution.

  12. Conjugate acid- compound formed when a base gains a hydrogen ion. • Conjugate base – compound formed when an acid loses a hydrogen ion.

  13. The Bronsted-Lowry Concept Conjugate pairs CH3COOHCH3COO- HCl Cl- NH4+NH3 HNO3NO3-

  14. Neutralization In general: Acid + Base  Salt + Water All neutralization reactions are double displacement reactions. HCl + NaOH  NaCl + HOH

  15. Back to objectives Salts • NEUTRALIZATION REACTIONS: • reaction between an acid and a base to form a salt and water • acid + base -----> salt + water • HCl + Na(OH) -----> NaCl+ H(OH) • H(NO3) + Na(OH) -----> Na(NO3) + H(OH)

  16. Does pure water conduct electrical current? Water is a very, very, very weak electrolyte. H2O  H+ + OH- For pure water: (H+) = (OH-) = 10-7M This is neutrality and at 25oC is a pH = 7. water

  17. Let’s examine the behavior of an acid, HA, in aqueous solution. HA

  18. 100% dissociation of HA HA H+ Strong Acid A- Would the solution be conductive?

  19. Partial dissociation of HA HA H+ Weak Acid A- Would the solution be conductive?

  20. HA  H+ + A- HA H+ Weak Acid A- At any one time, only a fraction of the molecules are dissociated.

  21. Strong and Weak Acids/Bases Strong acids/bases – 100% dissociation into ions HClNaOH HNO3KOH H2SO4 Weak acids/bases – partial dissociation, both ions and molecules CH3COOHNH3

  22. acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area pH 1-14 scale for the chemists 2 3 4 5 6 7 8 9 10 11 12 acidic (H+) > (OH-) neutral @ 25oC (H+) = (OH-) distilled water basic or alkaline (H+) < (OH-) normal rain (CO2) pH = 5.3 – 5.7 fish populations drop off pH < 6 natural waters pH = 6.5 - 8.5

  23. Indicators • Show a color change to identify an acid or base • Types: • Litmus paper • Red – acid • Blue – base • Phenolphthalein (liquid) • Clear – acid, neutral • Pink – base

  24. pH • pH SCALE: • Range of numbers from 0 to 14 • Indicates acid, base, and neutral along with strength

  25. pH Scale

  26. pH of Common Substances Timberlake, Chemistry 7th Edition, page 335

  27. Reactions with indicators

  28. pH paper • pH paper changes color to indicate a specific pH value.

  29. What is an oxide? • An oxide is a compound of oxygen and another element. • Most oxides can be grouped into four types: • acidic oxides • basic oxides • amphoteric oxides • neutral oxides

  30. Acidic oxides • Oxides of non-metal • Acidic oxides are often gases at room temperature.

  31. Acidic oxides • React with water to produce acids. • Example: sulphur trioxide + water sulphuric acid SO3 + H2O H2SO4

  32. Acidic oxides • React with bases and alkalis to produce salts • Example: carbon dioxide + sodium hydroxide sodium carbonate + water CO2 + 2NaOH Na2CO3 + H2O

  33. Examples of acidic oxides

  34. Basic oxides • Oxides of metal • Basic oxides are often solids at room temperature. • Most basic oxides are insoluble in water. Calcium oxide (quicklime)

  35. Basic oxides • React with acids to produce salts and water only. • Example: Magnesium oxide + hydrochloric acid magnesium chloride + water MgO + 2HCl MgCl2 + H2O This is a neutralisation reaction

  36. Examples of basic oxides

  37. Amphoteric oxides • Oxides of metal • Can behave as acidic oxides or as basic oxides Zinc oxide

  38. Neutral oxides • Non-metals that form oxides that show neither basic nor acidic properties. • Insoluble in water.

  39. Examples of neutral oxides

  40. - H+ + H+ When life goes either way amphoteric (amphiprotic) substances Acting like a base Acting like an acid HCO3- H2CO3 CO3-2 accepts H+ donates H+

  41. pH The biological view in the human body acidic basic/alkaline 1 2 3 4 5 6 7 8 9 10 11 blood saliva urine gastric juice pancreatic juice vaginal fluid bile cerebrospinal fluid Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th ed., Wiley (2003)

  42. - H+ + H+ Show how water can be amphoteric. H2O

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