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Acids and Bases

Acids and Bases. November 28, 2011. Characteristics of Acids & Bases . Acids Sour taste Electrolytic Many produce hydrogen ions pH less than 7 Vinegar, lemon juice, stomach acid, carbonated drinks (coke). Characteristics of Acids & Bases . Bases alkaline Bitter taste Electrolytic

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Acids and Bases

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  1. Acids and Bases November 28, 2011

  2. Characteristics of Acids & Bases • Acids • Sour taste • Electrolytic • Many produce hydrogen ions • pH less than 7 • Vinegar, lemon juice, stomach acid, carbonated drinks (coke)

  3. Characteristics of Acids & Bases • Bases • alkaline • Bitter taste • Electrolytic • Many produce hydroxide ions (OH-) • pH greater than 7 • Windex, antacid tablets, blood, baking soda

  4. Dissociation of Acids and Bases • Dissociation means breaking up… not being associated anymore • Acids and bases dissociate (break up) in water • The more dissociation, the stronger the acid or base • The more dissociation, the stronger the electrolyte • Strong acids & bases = strong electrolytes

  5. Dissociation of Acids • Many acids break up to form H+ and an anion • Example: HCl dissociates in to H+ and Cl- • The H+ ion combines with H2O to form H3O+ • This is called HYDRONIUM • The concentration of hydronium = [H3O+] = pH

  6. Dissociation of Bases • Many bases break up to form OH- and a cation • Example: NaOH dissociates in to OH- and Na+ • The OH- ion is called hydroxide

  7. Dissociation of Water • Water is constantly dissociating and reassociating • Because there’s a balance of hydronium and hydroxide, water is neither an acid nor a base… or maybe it’s both an acid and a base?

  8. Amphiprotic = Amphoteric • Water is amphiprotic/amphoteric • Water can act as an acid or a base… • It can produce both H+ and OH-

  9. Acid-Base indicators • Indicator: substance that shows if a chemical is an acid or a base • Phenolphthalein: colorless in acid, pink in base • Bromthymol blue: yellow in acid, blue in base • Purple cabbage juice: pink in acid, green in base • pH paper: range of colors for all pH values

  10. pH scale • pH stands for power or potential of Hydronium • It is calculated by finding the exponent of the concentration of H3O+ and then switching its sign • For example…the H3O+ concentration of an acid is 1 x 10-3 M • The exponent is -3; switch the sign and the pH is 3

  11. pH and logarithms • Logarithms are the math of exponents • Practice: log10 1000 = log3 9 = log5 5 =

  12. pH and logarithms • pH is calculated by finding the exponent of the concentration of H3O+ and then switching its sign • pH is the negative common logarithm of [H3O+] • Common logarithm means always base 10 [H3O+] = 1 x 10-8 M -log (1 x 10-8) = -(-8) = 8

  13. Logarithms and your calculator • How to find logs on your calculator… • LOG button • ( button • numbers • Use ^ for powers • Use (-) for negative numbers • ) button • ENTER/=

  14. Practice… log (1 x 10^-6) = log (3.5 x 108) = log 1,000,000 = -log (4 x 10-10) =

  15. Calculate pH • Find the pH (negative log) of the following concentrations… • [H3O+] = 1 x 10-2 • [H3O+] = 1 x 10-4 • [H3O+] = 3.4 x 10-6 • [H3O+] = 1.9 x 10-12

  16. [H3O+] and [OH-] • We can also calculate pOH • [OH-] = 1 x 10-8 • pOH = 8 • pH and pOH will always add up to 14… • If the pH is 7, then pOH is 7 • If the pH is 3, then pOH is ____ • If pH is 13, then pOH is ____

  17. [H3O+] and [OH-] • The pH of a solution is 10. What is its [OH-]? • The pOH of a solution is 2. What is its [H3O+]?

  18. Scavenger pHunt! • Teams of TWO will be given a list of questions. • Clues are scattered around the room. • You may also use open computers and/or smart phones. • Time starts… NOW

  19. Time remaining… http://www.online-stopwatch.com/full-screen-stopwatch/

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