Acids and bases


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Acids and bases

  1. 1. Bases Acids and
  2. 2. Look at some examples, and see if you can figure out what an acid is… <ul><li>HCl (Hydrochloric acid) </li></ul><ul><li>HNO 3 (Nitric acid) </li></ul><ul><li>H 2 SO 4 (Sulfuric acid) </li></ul><ul><li>H 3 PO 4 (Phosphoric acid) </li></ul>
  3. 3. Acid/Base definitions <ul><li>Definition #1: Arrhenius (traditional) </li></ul><ul><ul><li>Acid – has hydrogen in the formula, and produces H + ions in water </li></ul></ul><ul><ul><li>Base – has OH in the formula, and produces OH - ions in water </li></ul></ul>
  4. 4. Acids and bases in water: <ul><li>Arrhenius Acid: </li></ul><ul><li>HCl (aq)  H + + Cl - </li></ul><ul><li>HCl is an acid because it has H in the formula, and increases the amount of H + in water. </li></ul><ul><li>Arrhenius Base: </li></ul><ul><li>NaOH (aq)  Na + + OH - </li></ul><ul><li>NaOH is a base because it has OH in the formula and increases the amount of OH - in water. </li></ul>
  5. 5. The Arrhenius definition had a problem… <ul><li>Some bases (like ammonia, NH 3 ) don’t have OH in the formula. </li></ul>
  6. 6. Bronsted-Lowry definitions: (new and improved definitions) <ul><li>Acids are substances that give away hydrogen ions. (This definition is practically the same.) </li></ul><ul><li>Bases are substances that accept hydrogen ions. </li></ul>
  7. 7. Bronsted-Lowry definition: <ul><li>Acids are substances that give away hydrogen ions. </li></ul><ul><li>Example: HCl gives away hydrogen to water: </li></ul><ul><li>HCl (aq) + H 2 O  H 3 O+ (aq) + Cl- (aq) </li></ul><ul><li>Draw the hydrogen ion. What does it consist of? </li></ul>
  8. 8. A hydrogen ion is simply a proton. <ul><li>Acids are also called “proton donors.” </li></ul>
  9. 9. Bronsted-Lowry definition: <ul><li>A base is a hydrogen ion acceptor. </li></ul><ul><li>Another way of saying the same thing: </li></ul><ul><li>A base is a proton acceptor. </li></ul>
  10. 10. An acid is a proton donor A base is a proton acceptor acid base
  11. 11. Practice question: <ul><li>In the reaction </li></ul><ul><li>HBr( aq ) + NH 3 ( aq )  NH 4 + ( aq ) + Br – ( aq ) </li></ul><ul><li>Identify the acid and the base. </li></ul>
  12. 12. Practice question <ul><li>In the reaction </li></ul><ul><li>HSO 4 – + H 2 O  H 3 O + + SO 4 2- </li></ul><ul><li>Identify the acid and the base. </li></ul>
  13. 13. Practice question: <ul><li>In the equation </li></ul><ul><li> HCl( g ) + H 2 O( l )  H 3 O + ( aq ) + Cl – ( aq ) </li></ul><ul><li>which formula is a Brønsted-Lowry acid? </li></ul>
  14. 14. Tell-tale signs of an acid: <ul><li>sour taste </li></ul><ul><li>(orange juice and lemonade contain citric acid) </li></ul><ul><li>turns litmus paper red </li></ul><ul><li>(by reacting with a chemical in </li></ul><ul><li>the litmus paper) </li></ul><ul><li>reacts with metals to produce </li></ul><ul><li>hydrogen gas </li></ul>
  15. 15. Chemists write the formulas for acids with the H at the front, so they’re easy to identify as acids: <ul><li>HCl (Hydrochloric acid) </li></ul><ul><li>HNO 3 (Nitric acid) </li></ul><ul><li>H 2 SO 4 (Sulfuric acid) </li></ul><ul><li>H 3 PO 4 (Phosphoric acid) </li></ul>
  16. 16. Tell-tale signs of a base: <ul><li>bitter taste </li></ul><ul><li>slippery feel </li></ul><ul><li>turns litmus paper blue </li></ul><ul><li>(Conveniently, base, bitter, and blue all start with B!) </li></ul>
  17. 17. Some substances, like water act like an acid sometimes and act like a base other times. Substances that can act as an acid or a base are called amphoteric.
  18. 18. Neutralization reactions: If you combine an acid with a base… <ul><li>Predict the products: </li></ul><ul><li>HCl + NaOH  ? </li></ul><ul><li>Hint: It’s a special kind of double replacement reaction! </li></ul>
  19. 19. If you combine an acid with a base… <ul><li>HCl + NaOH  H 2 O + NaCl </li></ul><ul><li>This is called a neutralization reaction because the acid and base neutralize each other. </li></ul>
  20. 20. If you combine an acid with a base… <ul><li>HCl + NaOH  H 2 O + NaCl </li></ul><ul><li>The products of any neutralization reaction are water and a salt. </li></ul>
  21. 21. Acid / Base reactions: Produce water and a salt (and sometimes carbon dioxide). Hint: concentrate on the water first. Remember, water has the formula H OH. Complete and balance the following: H Cl + K OH  H Cl + Ca( OH ) 2  H OH + KCl 2 Require equal numbers 2 H OH + CaCl 2
  22. 22. 1. Ba( OH ) 2 + H 3 PO 4  2. H C 2 H 3 O 2 + Na OH  3. H 2 SO 4 + K OH  4. H 2 CO 3 + Na OH 
  23. 23. Everyday application: <ul><li>The stomach secretes acids to help digest foods. These acids, which include hydrochloric acid, have a molarity of about 0.1M. </li></ul><ul><li>Antacids, like Tums, Maalox, Mylanta and Alka-seltzer are simple bases that neutralize stomach acids. </li></ul>
  24. 24. Acids and Bases: Strength <ul><li>What makes an acid a strong acid? </li></ul><ul><li>It ionizes completely in water! </li></ul><ul><li>These are strong acids (in order of increasing strength): </li></ul><ul><li>HNO 3 (nitric acid) </li></ul><ul><li>HCl (hydrochloric acid) </li></ul><ul><li>HBr (hydrobromic acid) </li></ul><ul><li>HI (hydroiodic acid) </li></ul><ul><li>H 2 SO 4 (sulfuric acid) </li></ul><ul><li>HClO 4 (perchloric acid) (the strongest) </li></ul>
  25. 25. Strong acids: <ul><li>HCl + H 2 O  H 3 O + + Cl- </li></ul>Remember, strong acids ionize completely in water. The reaction goes all the way to the right. A single arrow is used. There are virtually no HCl molecules left intact.
  26. 26. One more reminder: “Weak” does not mean the same thing as “diluted.” HCl, for example is always a strong acid. If you add 1000 liters of water to it, it will be diluted, but still strong because what little there is will be completely dissociated.
  27. 27. Electrolytes: <ul><li>Acids and bases are both examples of electrolytes. </li></ul><ul><li>Electrolytes are compounds that form ions when dissolved in water. </li></ul><ul><li>They’re called electrolytes because they can conduct electricity through water. </li></ul>
  28. 28. More on electrolytes: <ul><li>If two wires connected to a light bulb and to a power source are placed in a beaker of water, the light bulb will not glow . If an electrolyte, such as sodium chloride , is dissolved in the water, the light bulb will glow because the solution can now conduct electricity. The amount of electric current that can be carried by an electrolyte solution is proportional to the number of ions dissolved. Thus, the bulb will glow more brightly if the amount of sodium chloride in the solution is increased. </li></ul>
  29. 29. Practice Questions
  30. 30. Which of these could be used to determine whether a substance is a base? A Thermometer B Litmus paper C Balance D Bunsen burner
  31. 31. An element common to all acids is – a. chlorine b. hydrogen c. oxygen d. sodium
  32. 32. The pH Scale…
  33. 33. The pH scale is a way of expressing the concentration of acids. Under 7 = acid 7 = neutral Over 7 = base
  34. 34. pH is the negative log of the H + concentration.
  35. 35. pH is the negative log of the H + concentration. What????
  36. 36. It’s easier than it sounds! If H + is…. 1 x 10 -3 pH = 3 1 x 10 -7 pH = 7 1 x 10 -12 pH = 12