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Chapter 9

Chapter 9. Acids, Bases and Salts. Section 1. Acids, Bases and pH. Key Ideas. What are acids ? What are bases ? What is pH?. Acids.

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Chapter 9

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  1. Chapter 9 Acids, Bases and Salts

  2. Section 1 Acids, Bases and pH

  3. Key Ideas • What are acids? • What are bases? • What is pH?

  4. Acids • Each of the foods shown in the picture tastes sour because it contains an acid. Citrus fruits, such as grapefruits, lemons, limes, and oranges, contain citric acid. Apples contain malic acid, and grapes contain tartaric acid.

  5. Acids • Substances that Ionize (break apart, dissolve) in waterto form hydrogen ions, (H+) • H+ ions attach to water molecules to make hydronium ions, (H3O+) General Structure: HA + H2O A- + H3O+ [acid] + [water]  [deprotonated acid] + [hydronium ion]

  6. Properties of acids • sour taste • conduct electric current • Corrosive (damage skin and other materials) • Turns blue litmus paper red

  7. Strong vs. Weak Acids • Strong acids ionize completely in water • Every molecule dissolved in water breaks apart into separate ions • Strong acids conduct electricity very well, so they are strong electrolytes • Weak acids do not ionize completely in water • Some of the molecules remain intact and some break apart into separate ions • Weak acids do not conduct electricity as well, so they are weak electrolytes

  8. Bases • Substances that form hydroxide ions (OH-) when dissolved in water • The base steals a hydrogen atom from water, and water becomes OH- General Structure: B+ H2O BH++ OH- [base] + [water]  [protonated base] + [hydroxide ion]

  9. In the ionization process shown below, water donates a hydrogen ion to ammonia to form an ammonium ion, NH4+, and leaves a hydroxide ion, OH−, behind.

  10. Properties of Bases • Bitter taste • Smooth/slick/slimy feel • Can conduct electricity when dissolved in water • Turn red litmus paper blue

  11. Strong Bases vs. Weak Bases • Strong bases are called metal hydroxides(ionic compounds that contain a metal ion and an OH-) • Example: NaOH (Sodium hydroxide) • Completely dissociate (break apart) in water NaOH → Na+ + OH− • All strong bases are strong electrolytes (they conduct electricity well when dissolved in water). • Weak bases do not dissociate in water • Example: ammonia, NH3, does not contain hydroxide ions, but it is still a base. It forms hydroxide ions when it dissolves in water. • Weak bases do not ionize completely in water, so they conduct electricity poorly. They are weak electrolytes.

  12. Uses for Bases

  13. Electrolytes • A substance that conducts electricity when dissolved in water. • When acids and bases ionize in water, the charged ions are able to move around in the solution and conduct electricity

  14. pHcan range from 0 to 14 • Neutral: pH = 7 • [H3O+]=[OH-] • Acidic: pH is less than 7 • [H3O+] > [OH-] • Basic: pH is greater than 7 • [OH-]>[H3O+]

  15. Measuring pH of a Solution • Indicators: substances that change colors to show pH level • pH paper: gives a rough estimation of the pH of a substance. • Litmus paper: blue turns red when dipped in acid, red turns blue when dipped in base • pH meter: determines the amount of electric current created by the movement of the ions in the solution. • Usually more accurate than pH paper

  16. Small differences in pH mean large differences inacidity. • pH of apple juice ~ 3 • pH of coffee ~ 5. • Difference of two pH units means apple juice is 102, or 100 times, as acidic as coffee. • When antacid tablets form basic solution with a pH of ~ 8. • So, coffee is about 103, or 1,000 times, as acidic as a solution of antacid tablets.

  17. Importance of Acids and Bases • In your body: • Enzymes in your body will not work if your blood is too acidic or too basic. • In the environment: • Acid Rain • Normal rain has a pH of about 5.6, so it is slightly acidic. • Pollution can cause acid rain, which has a pH that is less than 5.0. • Acid rain results from emissions of sulfur dioxide, SO2, and nitric oxide, NO, which are gases from coal-burning power plants and automobiles. The gases react with compounds in the air to form sulfuric acid, H2SO4, and nitric acid, HNO3

  18. Section 2 Reactions between acids and bases

  19. Key Ideas • What is a neutralization reaction? • To a chemist, what is a salt?

  20. Neutralization reactions • Reaction between an acid and a base • Example: reaction between your stomach acid and heartburn medication

  21. Neutralization: a reaction between ions • hydrochloric acid is a strong acid; it ionizes completely HCl + H2O → H3O+ + Cl− • sodium hydroxide is a strong base; it dissociates completely NaOH → Na+ + OH− • When mixed together, the solutions neutralize H3O++ Cl− + Na+ + OH−→ Na+ + Cl− + 2H2O

  22. Spectator Ions • Do not change during the reaction (like “spectators” watching on the sidelines) • Combine to form salts • In the previous reaction, Na+ and Cl− are spectator ions • If you do not include the spectator ions, the equation for the neutralization reaction looks like this: H3O+ + OH− → 2H2O All of the H3O+ and OH− ions react to form water; the resulting solution is neutral.

  23. Neutral solutions are not always formed • The pH of solution depends on • amounts of acid and base • strength of acid and base strongacid + weakbase = slightly acidic solution. weakacid + strongbase = slightly basicsolution.

  24. Salts • To a chemist, a salt can be almost any combination of cations and anions

  25. Uses of Salts • Cooking (baking soda) • Seasoning (table salt) • Cleaning • highway de-icing • Ceramic glazes • home water softeners • fire extinguishers

  26. chalk (calcium carbonate, CaCO3) • walls in your house may be made of gypsum (calcium sulfate, CaSO4) • Photographic film contains silver bromide, AgBr, and silver iodide, AgI • medical diagnosis (barium sulfate, BaSO4) • can be used to block X rays. After barium sulfate coats the large intestine, the form of the intestine shows up on an X-ray image

  27. Section 3 Acids, Bases and Salts in the Home

  28. Key Ideas • What household products contain acids, bases and salts?

  29. Cleaning Products • Improve water’s ability to clean because they help water mix with oily substances (emulsifier!).

  30. Soaps

  31. Detergents • Salts of sodium, potassium, and ammonium. • Useful for cleaning in hard water to avoid soap scum • The anions in detergents do not form insoluble salts with the ions in hard water. • Soap scum settles on clothing, dishes, your skin, and your hair. The scum also makes a ring around the bathtub or sink. Most shampoos, liquid hand soaps, and body washes contain detergents, not soap.

  32. Bleach • a very strong disinfectant (kills viruses and bacteria) andstain remover • does not remove the substance causing the stain, justchanges the substance to a colorless form. When mixed with water, bleach releases an oxygen atom, which reacts with the colored molecule and bleaches it. • never mix bleach with an acid! • produces deadly chlorine gas, Cl2 • never mix bleach with ammonia! • Produces toxic chloramine gas, NH2Cl

  33. Healthcare products • orange juice contains vitamin C (ascorbic acid), which your body needs to grow and repair bone and cartilage. • Antacids are basic substances that you swallow to neutralize stomach acid when you have an upset stomach.

  34. Shampoos • Most shampoos are made from detergents so they don’t leave soap scum. • The appearance of your hair is affected by the pH of your shampoo. Hair looks best when it is kept at either a slightly acidic pH or very close to neutral. A shampoo that is too basic can cause strands of hair to swell, which gives them a dull, lifeless appearance. Shampoos are usually pH balanced—that is, they are made to be in a specific pH range, usually between 5 and 8. Shampoos that have higher pH values are better at cleaning oil from your hair. Shampoos that have lower pH values protect dry hair.

  35. Acids can be used as antioxidants. • Some fruits turn brown when they are cut. • This is because molecules in the apple react with oxygen in the air to form brown compounds. • You can prevent the browning of fruit by pouring lemon juice on it. • The citric acid in lemon juice acts as an antioxidant and prevents oxygen from reacting with the molecules in the apple that form the brown substances. • Vitamin C, ascorbic acid, is another example of a natural antioxidant.

  36. Acids, bases, and salts in the kitchen. • Vinegar or citrus juices are used to make marinades that can tenderize meats. • The acids cause the protein molecules in the meat to unravel. As a result, the meat becomes more tender. • Milk curdles if you add an acid to it, like when yogurt is being made. Bacteria change lactose, a sugar in milk, into lactic acid. The lactic acid changes the shape of the protein casein, causing the milk to become a thick gel. • Baking soda is added to cookies so that they rise when baked.

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