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lec21_whc_b - 160 140 120 40 20 0 10 20 Average Standard...

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0 20 40 60 80 100 120 140 160 10 20 30 40 50 60 70 80 90 100 13.48 Standard Deviation 69.56 Average
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Thomas Midgeley made two stunning technical advances: 1) He replaced ammonia in refrigerators, making them safer and allowing vaccinations. 2) He increased the efficiency of internal-combustion engines cheaply.
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Chlorinated-fluorocarbon molecules (CFC) replaced NH 3 as the refrigerant gas in households, saving lives.
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Clare Patterson gave us: 1) The age of the Earth. 2) Warning about globally pervasive lead contamination.
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Last Time Common-ion effect; buffers, solubilities, indicators. p K a + log [acid] pH = [conjugate base] Henderson-Hasselbalch Equation
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Natural pH indicators pH 2 4 6 8 10 12 Color Red Purple Violet Blue Blue-Green Greenish Yellow Flavin in acid is red In base, blue Hydrangea changes color with soil pH and dissolved metal concentrations.
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Indicator Colors and Ranges Litmus paper Universal Indicator: Methyl red + Bromthymol blue + Thymol blue Red Æ Yellow Æ Green Æ blue
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Titrations Used to determine the amount of acid or base in a solution – pH vs. volume Two components – analyte – what is being investigated – titrant – what is being varied Four variations – strong acid/strong base and vice–versa – strong acid/weak base and vice–versa
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Neutralization Reactions and Titration Curves Titration Curve : The plot of pH vs. volume of titrant added. Equivalence point : (or Stoichiometric point) The point in the reaction at which both acid and base have been consumed. i.e. Neither acid nor base is present in excess. (#moles of titrant = #moles of analyte) End point of the indicator: The point at which the indicator changes color. Need to choose indicator that will change color over pH range that includes the equivalence point!
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How much strong base titrant 0.34 M NaOH must be added to neutralize a strong acid analyte (25 mL of 0.5 M HCl) - i.e. to reach
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