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What are ACIDS ?

What are ACIDS ?. Chemicals that... taste sour (lemon, vinegar) react with active metals to produce H 2 gas turn litmus paper red react with bases to form water and a “salt” are corrosive produce H + ions in solution (donate H + ). What are BASES ?. Chemicals that… Taste bitter

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What are ACIDS ?

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  1. What are ACIDS? • Chemicals that... • taste sour (lemon, vinegar) • react with active metals to produce H2 gas • turn litmuspaper red • react with bases to form water and a “salt” • are corrosive • produce H+ ions in solution (donate H+)

  2. What are BASES? • Chemicals that… • Taste bitter • Have a slippery or soapy feel • turn litmuspaper blue • react with acids to form water and a “salt” • are caustic • Produce OH- ions in solution (accept H+)

  3. Hydrangea in acidic soil Hydrangea in basic soil

  4. Problems with Acids • Corrosive to metals • Can degrade materials such as • Paper • Fibers • Glass • Marble, Frescos • Archaeological artifacts • Artists, historians, archaeologists, museum curators seek “acid free” materials

  5. SAPONIFICATION: ester hydrolysis under basic conditions polar non-polar

  6. micelle

  7. Fresco Chemicals silicon dioxide (sand) • SiO2 • CaO calcium oxide (quicklime) • H2O dihydrogen oxide (water) calcium hydroxide (slaked lime) • Ca(OH)2 • CO2 carbon dioxide • CaCO3 calcium carbonate (limestone)

  8. Limestone • A sedimentary rock consisting of remains of marine shellfish and fossils • Composed of the chemical calcium carbonate (CaCO3)

  9. CaCO3(s) Reactant or Starting materials Calcination of Limestone CaO(s) + CO2(g) Products • Calcium carbonate (limestone) is decomposed by heat to produce calcium oxide (quicklime) and carbon dioxide gas.

  10. Slaking Quicklime CaO(s) + H2O(l)Ca(OH)2(aq) + HEAT • Calcium oxide (quicklime) reacts with water to form Calcium hydroxide (slaked lime). • This reaction is EXOTHERMIC.

  11. Apply, Pounce and Paint • Apply to wall. • Paint while wet

  12. (Carbonation of Lime Plaster) Drying or Curing of the Fresco Ca(OH)2(aq) + CO2(g)CaCO3(s) + H2O(l) Where does the CO2 come from? What happens to the water?

  13. carbonation calcined (FRESCO) Lime Plaster Quicklime Slaked (water) Mixed with sand Slaked Lime From Rocks to Frescoes Limestone

  14. Anatomy of a Fresco Intonaco + Pigment (calcified surface) Arriccio Mortar Rough Plaster Wall

  15. SO2(g) + O2(g) SO3(g) SO3(g) + H2O(l)H2SO4(l) NO(g) + H2O(l)HNO3(l) Deterioration of Frescoes • Industrially polluted atmospheres contain SO2 and NO2 gases from burning fossil fuel. • SO2 and NO2 react with oxygen and water to produce sulfuric acid and nitric acid.

  16. Effect of Acids on Frescos Calcium carbonate is converted to calcium sulfate (gypsum) Gypsum is partially soluble in the water and it forms larger crystals within the intonaco layer and can cause the fresco to blister and flake off. CaCO3(s) + H2SO4(l)CaSO4(s) + H2O(l) + CO2(g)

  17. CaSO4.2H2O + (NH4)2CO3 (NH4)2SO4 + CaCO3 + 2H2O (NH4)2SO4 + Ba(OH)2 BaSO4 + 2NH3 + 2H2O White and very insoluble! Restoration of Frescoes Reversing the chemical reactions. 1. Clean the fresco with ammonium carbonate. 2. Consolidate with barium hydroxide.

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