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Chemical Reactions 2: Equilibrium & Oxidation-Reduction

Chemical Reactions 2: Equilibrium & Oxidation-Reduction. Acid-Base Equilibrium. Acids Fruit juices, soft drinks, gastric juices Sour taste Red and blue litmus paper turn Red Arrhenius: acids release H + when dissolved in Water (aqueous solution)

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Chemical Reactions 2: Equilibrium & Oxidation-Reduction

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  1. Chemical Reactions 2: Equilibrium & Oxidation-Reduction

  2. Acid-Base Equilibrium Acids • Fruit juices, soft drinks, gastric juices • Sour taste • Red and blue litmus paper turn Red • Arrhenius: acids release H+ when dissolved in Water (aqueous solution) HF (l) + H2O H+(aq) + F-(aq) H2SO4(l) + H2O 2H+(aq) + SO42-(aq) HI (l) + H2O H+(aq) + I-(aq)

  3. Acid-Base Equilibrium Acids • Strong Acids dissociate completely • Weak Acids DO NOT dissociate completely • Weak Acids establish a dissociation equilibrium HA(aq) H+(aq) + A-(aq) *In the case of strong acids, such equilibrium is almost entirely displaced toward formation of ions

  4. Acid-Base Equilibrium Dissolution Constant of Acids aHA(aq) bH+(aq) + cA-(aq) _Ka value is a measure of acid’s strength _Weak acids have low values of Ka

  5. Acid-Base Equilibrium

  6. Acid-Base Equilibrium Bases • Cleaning products, some heartburn medication • Bitter taste • Feel slippery (react with oil in skin forming a kind of soap) • Red and blue litmus paper turn Blue • Arrhenius: bases release OH- when dissolved in Water (aqueous solution) NaOH(s) + H2O Na+(aq) + OH-(aq) Mg(OH)2(s) + H2O Mg2+(aq) + 2OH-(aq) NH4OH (l) + H2O NH4+(aq) + OH-(aq)

  7. Acid-Base Equilibrium Bases • Strong Bases dissociate completely • Weak Bases DO NOT dissociate completely • Weak Bases establish a dissociation equilibrium BOH(aq) B+(aq) + OH-(aq) *In the case of strong bases, such equilibrium is almost entirely displaced toward formation of ions

  8. Acid-Base Equilibrium Dissolution Constant of Acids aBOH(aq) bB+(aq) + cOH-(aq) _Kbvalue is a measure of base’s strength _Weak bases have low values of Kb

  9. Acid-Base Equilibrium

  10. Acid-Base Equilibrium pH • Property that distinguishes acidic, basic and neutral solutions • Measures the concentration of H+ ions in solution • Can be determined by indicator, pH paper, pH meter, etc.

  11. Acid-Base Equilibrium pH • pH scale: 0 – 14 • pH < 7 (Acidicsolution) _0 < pH < 3 (STRONGLY Acidic) _4 < pH < 6 (Slightly Acidic ) • pH = 7 (NEUTRAL solution) • pH > 7 (Basic solution) _8 < pH <11 (Slightly Basic) _12 < pH < 14 (STRONGLY Basic)

  12. Acid-Base Equilibrium pH pH = - log c(H+) • Log makes differences of one unit, to be ten times different • Example: If A (pH = 3), B (pH = 1), C (pH = 9) Then B is 100 times more acidic than A

  13. Acid-Base Equilibrium [H+] = 10-pH

  14. Acid-Base Equilibrium Indicate True or False: __B (c(H+)=10-2 M) has pH = 3 __A (c(H+)=10-4 M) is 100 times more basic than B __C (neutral pH) is 1000 times more basic than D (c(H+)=10-5 M) __D (c(H+)=10-5 M) is a million times more acidic than E (pH = 10) Order these substances from more acidic to most basic: Order these substances from highest pH to lowest: F T F F B – A – D – C – E E – C – D – A – B

  15. Acid-Base Equilibrium pH & Environment (Water bodies) BEFORE • High Pollution • High Toxic levels • At mercy of private companies disposal policies • No environmental regulation

  16. Acid-Base Equilibrium pH & Environment (Water bodies) AFTER • Lower levels of Pollution • Lower levels of Toxicity • Constant monitoring of pH levels • Government environmental regulation

  17. Acid-Base Equilibrium Neutralization Reaction • Involves an acid (pH < 7) and a base (pH > 7) • Produces salt and water (pH = 7)

  18. Acid-Base Equilibrium Titration (CaVa = CbVb) • Experimental technique to determine the concentration of an acid or a base • Uses known volumes of acid and base • Uses a known value of concentration • With all three variables (Va, Vb, Ca or Cb) finds Cbor Ca using the Dilution formula (CaVa = CbVb) • Titration needs an indicator to determine the final point

  19. Acid-Base Equilibrium What is an indicator?!

  20. Acid-Base Equilibrium Indicator • Usually weak acids or weak bases • Indicator’s colour changes according to the level of pH of the solution that it is added to • Colour change usually in a range (e.g. pH = 4.5 – 5.5)

  21. Acid-Base Equilibrium Titration technique

  22. Acid-Base Equilibrium Example: Determine the concentration of a solution of HCl, if 15ml of this acid are titrated with 25ml of NaOH. The concentration of the latter is 0.45M. Determine the pH of the HCl solution. CaVa = CbVb Ca= CbVb / Va Ca = (0.45M) (25ml) / (15ml) Ca= 0.75 M pH = - log c(H+) pH = - log (0.75) pH = - (-0.12) pH = 0.12

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