Coca Cola And The Acid-base Terminology: Good Bye To The Laboratory Jargon

Coca Cola and the Acid-Base Terminology: Good bye to the laboratory jargon

Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke University of Muenster Germany

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Hans-Dieter Barke University of Muenster Germany

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Hans-Dieter Barke University of Muenster Germany

Barke‘s 3-level concept (1988) .

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Hans-Dieter Barke University of Muenster Germany

Hans-Dieter Barke - University of Muenster Germany

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Johnstone‘s chemical triangle (2000)

Beakermodel or Mental model on Johnstone‘s „submicro level“: ions as acids or bases by neutralization reaction

Hans-Dieter Barke - University of Muenster Germany

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BROENSTED and his ideas about acid particles and base particles in his essay „On the theory of the acid-base function“ (1923) His central mental model: A acid



B + H+ base proton

Citation of BROENSTED: „The A and B molecules are called corresponding acids and bases: by losing a proton, any molecule A is transformed in a minus-charged base molecule (today: ion)“ Because a free proton does not exist in solution, BROENSTED added: A + acid1 or:

H3O+ acid1

H2 O base2 +

OHbase2

 

B- + base1

H3O+ acid2

H2O + H2O base1 acid2

H2O molecules (not „water“) can be acid particles or base particles !!! Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke - University of Muenster Germany

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Recepi for producing Coca-Cola (William Foundstone, 1883)

For one gallone Coca Cola syrup (3.8 L) you need: Sugar Sucrose caramel Caffeine Phosphoric acid

dissolve 2400 g in a minimum of water 37 g …. 90 g (for the deep brown color) 3.1 g 11 g … 14 g

Coca leaves 1.1 g (dissolve in alcohol, filter and add to syrup) Cola nuts 0.4 g (dissolve in alcohol, filter and add to syrup) To this mixture comes: 30 g lemon juice, 19 g Glycerol, 1.5 g Vanilline, some other different oils – and water until 1 gallone of syrup. For the Coca-Cola drink: dilute 1 part of the syrup with 6 parts of water saturated with carbon dioxide. Prosit!!! Hans-Dieter Barke - University of Muenster Germany

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Protolysis of H3PO4 molecules: by the pH 2.7 of Coca Cola nearly 80 % of H2PO4-(aq) ions exist beside 20 % of H3PO4 molecules acid particles are H3O+(aq) ions, H2PO4-(aq) ions and H3PO4 molecules

Hans-Dieter Barke - University of Muenster Germany

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Protolysis of H3PO4 and H2CO3 molecules: equilibria and pKs values H3PO4 + H2O pH(Coke) = 2,7

 H3O+(aq) + H2PO4–(aq) 

c(H3O+)  2 mmol/L

H2PO4–(aq) + H2O  H3O+(aq) + HPO42-(aq)

HPO42-(aq) + H2O  H3O+(aq) + PO43-(aq) Also carbonic acid is involved in Coca Cola: CO2(g)  CO2(aq)

CO2(aq) + H2O  H2CO3(aq) H2CO3(aq) + H2O  H3O+(aq) + HCO3–(aq)

HCO3-(aq) + H2O  H3O+(aq) + CO32-(aq) Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke - University of Muenster Germany

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Acid-base reactions by gastric antacids – containing mostly calcium carbonate, sodium bicarbonate or aluminum hydroxide Our stomach contains hydrochloric acid with the pH of 1 – 1.5. If too much acid comes up into the gullet we get heartburn. To reduce that bad feeling we can take an antacid tablet – containing sodium bicarbonate (NaHCO3), calcium carbonate (CaCO3) or aluminum hydroxide (Al(OH)3) . „Antacid Tablets“ containing calcium carbonate: Hydrochloric acid 2 HCl(aq)

+ calcium carbonate +

CaCO3(s)  CaCl2(aq) + H2O + CO2(aq, g)

H3O+(aq) + Cl-(aq) + Ca2+CO32-(s) Protontransfer: 2 H3O+(aq) + CO32-  H2CO3(aq) + 2 H2O H2CO3(aq)  H2O + CO2(aq, g) Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke - University of Muenster Germany

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Acid-base reactions by baking powder – containing a solid acid (can be citric acid or tartaric acid) and a solid base (mostly NaHCO3) Ingredients in „Pengembang Kue“ from Indonesia: Sodium bicarbonate + sodium dihydrogen phosphate NaHCO3(s) + NaH2PO4(s)  water  Na2HPO4(aq) + H2O + CO2(aq, g) Na+(aq) + HCO3-(aq) + Na+(aq) + H2PO4-(aq) Protontransfer: HCO3-(aq) + H2PO4-(aq)  H2CO3(aq) + HPO42-(aq) H2CO3(aq)  H2O + CO2(aq) CO2(aq)

 CO2(g) - makes the cake gaseous

Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke - University of Muenster Germany

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Preconcepts and school-made misconceptions  Preconcepts: brought by children through observation in

their every-day life: combustion („something is going into the air“), transmutation of substances („copper changes from red to green“), gases as substances („they have no mass“), „sun rotates around the earth“, etc.

 School-made misconceptions: developed by

inappropriate teaching or difficult topics: chemical equilibrium („reactants and products show same concentration“), weak acids („they have a pH of 3 or above“), redox reactions („oxygen is always involved“), etc. Hans-Dieter Barke - University of Muenster Germany

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Example of redox reactions („oxygen is always involved“) Which of following reactions represents a redox reactions?

1. HCl(aq) + Mg



2. HCl(aq) + MgO



3. HCl(aq) + Mg(OH)2 

Hans-Dieter Barke - University of Muenster Germany

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Students misconceptions or their „laboratory jargon“ – answering questions to Broensted‘s acid-base theory -

Sulfuric acid gives two protons

- hydrochloric acid gives one proton - water can be an acid or a base - autoprotolysis of water - concentration of water c = 55.5 mol/L - sodium hydroxide dissociates into ions - by neutralization a salt is produced -

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by neutralization molecules react strong acids have a low pH weak acids have a pH of 3 and above weak acids are weak concentrated

H2SO4 molecules in pure sulfuric acid H3O+(aq) ions are giving protons! H2O molecules !!! of H2O molecules !!! 55.5 mol H2O molecules per Liter solid NaOH contains Na+ and OH- ions, they are separated by H2O molecules H2O molecules are produced, two kinds of ions are remaining !!! mostly H3O+(aq) and OH-(aq) ions contain only ions, dilution up to pH 6 equilibrium of molecules and ions equilibrium of molecules and ions

Hans-Dieter Barke - University of Muenster Germany

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School-made misconceptions (Sopandi 2003): molecules and ions in „Bonaqua“ mineral water

Hans-Dieter Barke - University of Muenster Germany

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School-made misconceptions (Sopandi 2003): molecules and ions in mineral water

Hans-Dieter Barke - University of Muenster Germany

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Hausgemachte Fehlvorstellungen

Antworten aus St. Petersburg (Dr. V. Davydow)

Hans-Dieter Barke - University of Muenster Germany

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School-made misconceptions: molecules and ions in pure and diluted sulfuric acid

Hans-Dieter Barke - University of Muenster Germany

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School-made misconceptions: molecules and ions in strong and weak acids

Hans-Dieter Barke - University of Muenster Germany

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Prevention of misconceptions  Arrhenius-Acids are SUBSTANCES, mostly aqueous solutions which contain H+(aq) ions: hydrochloric acid, sulfuric acid solution, nitric acid solution, acetic acid solution  Broensted-Acids

are PARTICLES, donating H+ ions (protons) to other particles: H2SO4 molecules in pure sulfuric acid (H2SO4), H3O+(aq) ions (also HSO4- ions) in diluted sulfuric acid, HSO4- ions are acid particles in solid sodium hydrogensulfate (NaHSO4) H3O+(aq) ions are acid particles in diluted hydrochloric acid solution, H3O+(aq) ions are acid particles in diluted nitric acid solution, HAc molecules are acid particles in pure solid acetic acid (CH3COOH), HAc molecules and H3O+(aq) ions in acetic acid solution, HCit molecules are acid particles in solid citric acid, HCit molecules and H3O+(aq) ions in citric acid solution, etc Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke - University of Muenster Germany

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Proton Transfer from electron cloud to electron cloud Christen, Baars: Chemie. Frankfurt 1997 (Diesterweg)

Hans-Dieter Barke - University of Muenster Germany

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Prevention of misconceptions: molecules and ions as acid or base PARTICLES Example: hydrogen chloride – water reaction

Hans-Dieter Barke - University of Muenster Germany

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Prevention of misconceptions: molecules and ions as acid or base PARTICLES Example: ammonia – hydrogen chloride reaction

Hans-Dieter Barke - University of Muenster Germany

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Prevention of misconceptions: ions as acids or bases by neutralization of strong acids

hydrochloric acid

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H3O+(aq) + Cl-(aq) + H3O+(aq)

+

sodium hydroxide solution  sodium chloride solution Na+(aq) + OH-(aq)  Na+(aq) + Cl-(aq) + 2 H2O OH-(aq)



Hans-Dieter Barke - University of Muenster Germany

2 H2O

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Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke - University of Muenster Germany

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Hans-Dieter Barke - University of Muenster Germany

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