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Acids and Bases November 28, 2011

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

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

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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

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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 H 2 O to form H 3 O + This is called HYDRONIUM ▫The concentration of hydronium = [H 3 O + ] = pH

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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

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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?

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

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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

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

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pH and logarithms Logarithms are the math of exponents Practice: log 10 1000 = log 3 9 = log 5 5 =

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pH and logarithms pH is calculated by finding the exponent of the concentration of H 3 O + and then switching its sign pH is the negative common logarithm of [H 3 O + ] ▫Common logarithm means always base 10 [H 3 O + ] = 1 x 10 -8 M -log (1 x 10 -8 ) = -(-8) = 8

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

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Practice… log (1 x 10^-6) = log (3.5 x 10 8 ) = log 1,000,000 = -log (4 x 10 -10 ) =

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Calculate pH Find the pH (negative log) of the following concentrations… [H 3 O + ] = 1 x 10 -2 [H 3 O + ] = 1 x 10 -4 [H 3 O + ] = 3.4 x 10 -6 [H 3 O + ] = 1.9 x 10 -12

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[H 3 O + ] 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 ____

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[H 3 O + ] and [OH - ] The pH of a solution is 10. What is its [OH - ]? The pOH of a solution is 2. What is its [H 3 O + ]?

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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

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

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