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Acids & Bases Svante Arrhenius (1887)

Acids & Bases Svante Arrhenius (1887). ACIDS Turn indicator dye litmus from blue to red React with active metals such as zinc, iron, and tin, dissolving the metal and producing hydrogen gas Taste sour, if diluted enough to be tasted safely

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Acids & Bases Svante Arrhenius (1887)

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  1. Acids & BasesSvante Arrhenius (1887) • ACIDS • Turn indicator dye litmus from blue to red • React with active metals such as zinc, iron, and tin, dissolving the metal and producing hydrogen gas • Taste sour, if diluted enough to be tasted safely • React with certain compounds called alkalis or bases to form water and compounds called salts • BASES • Turn the indicator dye litmus from red to blue • Feel slippery or soapy on the skin • Taste bitter • React with acids to form water and salts

  2. Acids • Arrhenius proposed that these characteristic properties of acids are actually properties of the hydrogen ion (H+), and that acids are compounds that yield H+ in aqueous solutions. • Slightly modified today • Hydronium ion (H3O+) • For simplification, we’ll stick with the H+ terminology.

  3. Acids • Monoprotic • One H+ • Diprotic • Two H+ • Triprotic • Three H+ • Polyprotic • General term for acids that give up more than one H+ • Strong Acids • Ionize completely (or nearly completely) in water • HCl (hydrochloric acid) • Weak Acids • Ionize only slightly in water • CH3COOH (acetic acid)

  4. Bases • Yield hydroxide ions (OH-) in aqueous solutions • Monobasic • One hydroxyl anion • Dibasic • Two hydroxyl anions • Tribasic • Three hydroxyl anions • Polybasic • General term for bases that give up more than one OH- • Strong Bases • Completely ionize • NaOH (sodium hydroxide; lye) • All the bases of Group I and Group II are strong bases • Weak Bases • NH3 (ammonia)

  5. pH Scale • pH = -log [H+]

  6. Brønsted-Lowry Acid-Base Theory • By the 1920’s chemists were working with solvents other than water. • Acid • Proton (H+) donor • Base • Proton (H+) acceptor

  7. Acid-Base Titrations • Method used to determine just how much acid (or base) there is in a solution of unknown concentration • Burette • A piece of laboratory glassware designed to deliver known amounts of liquid into another container

  8. Acid-Base Titrations • One mole of NaOH will react completely with one mole of H+ • Using volumetric analyses with a pH indicator, you can determine the moles of H+

  9. A Word About Moles…. • A mole used in chemistry is something like the dozen we use every day. • A mole simply means that you have 6.02 x 1023 of whatever you’re talking about. • Avogardo’s number • Molarity is defined as the number of moles of solute divided by the number of liters of solution • Molarity (M) = moles of solute • liters of solution

  10. Water Hardness • Calcium (Ca2+) • Magnesium (Mg2+) • Why the concern?

  11. Types of Water Hardness • Temporary • Permanent

  12. EDTA • Ethylenediaminetetracetic acid • Chelating agent

  13. Eriochrome Black T (EBT)

  14. Example Calculations • 50.0 mL sample of tap water analyzed • Beginning volume of EDTA = 22.57 mL • End volume of EDTA = 6.23 mL • Amount of EDTA titrated = 16.34 mL • Questions: • How many moles of EDTA were used? • What is the molarity of metal ion present in the water? • What is the concentration of CaCO3 in ppm in the water?

  15. How many moles of EDTA were titrated? Molarity of EDTA = 0.01000 M Moles of EDTA = (Molarity)(Liters of solution) = (0.01000 mol/L)(0.01634 L) = 0.0001634 moles EDTA = 1.634 x 10-4 moles EDTA

  16. What is the molarity of the metal ion present in the water? Molarity of metal ion = moles of EDTA liters of water sample = 0.00001634 mol EDTA 0.050 L water = 0.003268 mol/L of EDTA = 0.003268 mol/L metal ions

  17. What is the concentration of CaCO3 in ppm in the water? CaCO3 ppm = Molarity of metal ion X molecular weight of Ca2+ X 1000 mg/g CaCO3 ppm = 0.003268 mol/L X 40.08 g/mol X 1000 mg/g CaCO3 ppm = 131 mg/L = 131 ppm

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