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Titration Curves. 7. Strong Acid / Strong Base:. eg:. HCl titrated with NaOH. Equivalence point at pH = 7 for all strong acid / strong base titrations. HCl + NaOH H 2 O + NaCl. 8. Then… CN - + H 2 O HCN + OH -. Weak Acid / Strong Base:. eg:.
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Titration Curves 7 Strong Acid / Strong Base: eg: HCl titrated with NaOH • Equivalence point at pH = 7 for all strong acid / strong base titrations HCl + NaOH H2O + NaCl
8 Then… CN- + H2O HCN + OH- Weak Acid / Strong Base: eg: HCN titrated with NaOH • Equivalence point at pH > 7 for all weak acid / strong base titrations Buffering effect of weak acid HCN + NaOH H2O + NaCN
5 Then… NH4+ + H2O H3O+ + NH3 Strong Acid / Weak Base: eg: NH3 titrated with HCl Buffering effect of weak base • Equivalence point at pH < 7 for all strong acid / weak base titrations NH4Cl NH3 + HCl NH4+ + Cl-
Note: Choice of indicator depends on pH of equivalence point. eg: If pH of equivalence point is 3.8, what indicator(s) would be appropriate? Bromocresol green Methyl orange
Acid / Base Anhydrides Acid Anhydrides: • Oxygen containing compounds that react with water to produce acids. eg: SO2(g) + H2O(l) H2SO3(aq) SO3(g) + H2O(l) H2SO4(aq) CO2(g) + H2O(l) H2CO3(aq) • Acid anhydrides are non-metal oxides (tend to be gases) eg: SO2 , NO2 , CO …
Base Anhydrides: • Oxygen containing compounds that react with water to produce bases. eg: Na2O (s) + H2O(l) 2 NaOH(aq) CaO(s) + H2O(l) Ca(OH)2(aq) K2O (s) + H2O(l) 2 KOH(aq) • Base anhydrides are metal oxides (tend to be solid) eg: Na2O, MgO, Rb2O , Fe2O3 …
Acid Rain: • Normal rain is slightly acidic due to the acid anhydride CO2 in the atmosphere. eg: CO2(g) + H2O(l) H2CO3(aq) • When other acid anhydride gases are present (due to pollution) rain becomes more acidic – pH < 5.6 eg: SO2(g) + H2O(l) H2SO3(aq) 2 NO2(g) + H2O(l) HNO2(aq) + HNO3
Limestone deposits (CaCO3) in the ground have a natural buffering effect against acid rain. eg: H2SO3(aq) + CaCO3(s) CaSO3(aq) + CO2(g) + H2O(l) • Continuous acid rain leads to: Depletion of limestone deposits. Leaching of mineral deposits. Damage to man-made structures. Damage to plants and animals.