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More on Conjugate Acid-Base Pairs MORE ON CONJUGATE ACID-BASE PAIRS: HSO4- (aq) + HOH (aq) ⇄ H3O+ (aq) + SO4 2- (aq) base acid acid base H2CO3 + SO3 2- ⇄ HSO3 - + HCO3 - acid base base acid NH3 + NH3 ⇄ NH4+ + NH2- acid base base acid NOTE THAT AMMONIA IS ALSO AMPHOTERIC!! WHAT IS THE CONJUGATE BASE FOR: Answers a) HI I- b) H3PO4 H2PO4- c) HSO4- SO4-2 d) H2 H- WHAT IS THE CONJUGATE ACID FOR: Answers a) HO2- H2O2 b) SO4-2 HSO4- c) C2H3O2- HC2H3O2 e) NH2- NH3 Note: NEUTRALIZATION: Arrhenius: ACID + BASE ⇄ SALT + WATER Bronsted: ACID + BASE ⇄SALT + SOLVENT! SOME COMMON ACIDS: Chemical name: SULPHURIC ACID Chemical Formula: H2SO4 Commercial/common name: oil of vitriol, battery acid Properties: -cheap to make (raw materials needed are sulphur, oxygen and hydrogen) -good dehydrating agent (removes water from substances) -good neutralizer of bases (strong acid) -strong exothermic reaction when mixed with water -good oxidizing agent -strong electrolyte (this is why it is used in car batteries) Common uses: -fertilizers, explosives, dyes, insecticides, detergents, plastics, car batteries Chemical name: HYDROCHLORIC ACID Chemical Formula: HCl Commercial/common name: muriatic acid Properties: -choking odour in concentrated solutions -good electrolyte -does not produce sulphates with ions, like sulphuric acid does Common uses: -metal oxide cleaners, removing "scale" from kettles, stomach acid, catalysts Chemical name: NITRIC ACID Chemical Formula: HNO3 Commercial/common name: none Properties: -suffocating odour -yellow stain on skin (due to the action of the acid on protein) -very reactive with almost all metals Common uses: -ammonium and phosphate fertilizers, explosives, plastics, dyes, lacquers Chemical name: ACETIC ACID Chemical Formula: CH3COOH Commercial/common name: vinegar (if 5% aqueous solution) Properties: -only affects highly reactive metals -weak electrolyte when diluted Common uses: -food preservation, manufacture of textiles and plastics SOME COMMON BASES: Chemical name: SODIUM HYDROXIDE Chemical Formula: NaOH Commercial/common name: caustic soda, lye Properties: -very corrosive -strong exothermic reaction when mixed with water -good dehydrating agent (RAPIDLY removes water from air) Common uses: -soap, oven cleaner, drain cleaner Chemical name: POTASSIUM HYDROXIDE Chemical Formula: KOH Commercial/common name: caustic potash Properties: -similar to NaOH but lower MP Common uses: -electrolyte in alkaline batteries, liquid soaps (due to lower MP) Chemical name: AMMONIA Chemical Formula: NH3 Commercial/common name: NH3 (aq) NH4OH is called ammonium hydroxide Properties: -colourless, highly toxic, corrosive gas with strong odour -strong exothermic reaction when mixed with water -very soluble in water Common uses: -manufacture of nitric acid, explosives, fertilizers, synthetic fibers, refrigerant gas ACIDIC AND BASIC ANHYDRIDES AN OXYGEN-CONTAINING COMPOUND THAT REACTS WITH WATER PRODUCING AN ACIDIC SOLUTION IS CALLED AN ACIDIC ANHYDRIDE. eg. SO3 + H2O H2SO4 AN OXYGEN-CONTAINING COMPOUND THAT REACTS WITH WATER PRODUCING A BASIC SOLUTION IS CALLED A BASIC ANHYDRIDE. eg. Na2O + H2O 2NaOH WHEN A BASIC ANHYDRIDE AND AN ACIDIC ANHYDRIDE COMBINE, THEY FORM A SALT. eg. N2O5 + Na2O 2NaNO3 THE REACTION (as written above) IS A NEUTRALIZATION WITHOUT THE FORMATION OF WATER. N2O5 IS THE ACIDIC ANHYDRIDE OF HNO3 eg. 2HNO3 N2O5 + H2O acid anhydride water ANHYDRIDE MEANS WITHOUT WATER SO A BASIC ANHYDRIDE IS A BASE WITHOUT WATER eg. Ca(OH)2 CaO + H2O base anhydride water Interesting fact: Grass thrives in alkaline soil. Adding Lime, CaO, increases the alkalinity or basicity of the soil by the following reaction: CaO + H2O Ca(OH)2 anhydride water base SOME COMPOUNDS CAN BE AMPHIPROTIC ANHYDRIDES: eg. BeO Al2O3 GeO2 As4O6 Ga2O3 SnO2 Sb4O6 PbO2 STRONG / WEAK / CONCENTRATED / DILUTE STRONG BASE: -any metallic hydroxide which is very soluble in water is a strong base. -if it is not soluble it is a weak base. GROUP I hydroxides: LiOH, NaOH, KOH, RbOH, CsOH, FrOH and also Ca and Ba hydroxides are strong bases: Ca(OH)2 and Ba(OH)2 Other GROUP 2 hydroxides are only slightly soluble & are therefore weak bases. STRONG ACID: -the strongest acid is always the one in which the ionizable hydrogen can be most easily removed HClO4 PERCHLORIC ACID HI HYDROIODIC ACID HBr HYDROBROMIC ACID HCl HYDROCHLORIC ACID HNO3 NITRIC ACID H2SO4 SULPHURIC ACID dissociate ~100% in water at RTP STRONG IS NOT THE SAME AS CONCENTRATED!!! Concentrated: proportion of solute to solvent molecules is near the maximum value (there are a lot of moles of acid/base solute compared to the solvent in the solution) Strong: dissociates well and has MANY ions; favours formation of products (conducts current well) DILUTE IS NOT THE SAME AS WEAK!!! Dilute: low proportion of solute to solvent (nowhere near the max) (not many moles of acid/base relative to solvent in the solution) Weak: dissociates poorly and has FEW ions; favours reactants (conducts current poorly in water) eg. 0.010 M HCl is a dilute strong acid Consider: H2SO4 + 2KOH K2SO4 + 2H2O strong strong neutral acid base salt pH ~7 (NH3 (aq)) HCl + NH4OH NH4Cl + H2O strong weak acidic acid base salt pH <7 3HC2H3O2 + Fe(OH)3 Fe(C2H3O2)3 + 3H2O weak weak neutral acid base salt pH ~7 H2CO3 + 2KOH K2CO3 + 2H2O weak strong basic acid base salt pH >7 Strongest acid in water: hydronium ion Strongest base in water: hydroxide ion ALL OF CHAPTER NINE HAS BEEN COMPLETED!!! NOW DO WORKSHEET 4.2 FOR HOMEWORK Wkst 4.2: Arrhenius and Brønsted-Lowry Acids Using Brønsted-Lowry definitions, identify… a) the missing conjugate… ACID BASE ACID BASE - -2 F HPO4 -2 SO3 H2O NH3 HNO2 - + HCO3 PH4 - H2O HC2O4 b) the ACID-BASE conjugate pairs in the following reactions… - - HBr + Cl HCl + Br -2 - - CO3 + H2O HCO3 + OH - + HS + H3O H2S + H2O - - -2 HSO3 + HSO4 H2SO3 + SO4 + - HNO2 + NH3 NH4 + NO2 - - -2 HS2O3 + PH2 PH3 + S2O3 c) Neutralization and salt pH Salt pH HCl(aq) + Cu(OH)2(aq) H2O(l) + CuCl2(aq) pH<7 strong acid weak base Acidic salt H3PO4(aq) + NaOH(aq) + H2CO3(aq) + Pb(OH)4(aq) + H2SO4(aq) + Fe(OH)3(aq) + HClO4(aq) + LiOH(aq) + + H2O(l) + ZnI2(aq) + H2O(l) + AlF3(aq) + H2O(l) + KBr(aq) Wkst 4.2: Arrhenius and Brønsted-Lowry Acids Using Brønsted-Lowry definitions, identify… a) the missing conjugate… ACID BASE ACID BASE - -2 -3 HF F HPO4 PO4 - -2 - HSO3 SO3 H2O OH + - NH4 NH3 HNO2 NO2 - + H2CO3 HCO3 PH4 PH3 + - -2 H3O H2O HC2O4 C2O4 b) the ACID-BASE conjugate pairs in the following reactions… - - HBr + Cl HCl + Br Acid Base Acid Base -2 - - CO3 + H2O HCO3 + OH Base Acid Acid Base - + HS + H3O H2S + H2O Base Acid Acid Base - - -2 HSO3 + HSO4 H2SO3 + SO4 Base Acid Acid Base + - HNO2 + NH3 NH4 + NO2 Acid Base Acid Base - - -2 HS2O3 + PH2 PH3 + S2O3 Acid Base Acid Base c) Neutralization and salt pH Salt pH 2 HCl(aq) + Cu(OH)2(aq) 2 H2O(l) + CuCl2(aq) pH<7 strong acid weak base Acidic salt H3PO4(aq) + 3 NaOH(aq) 3 H2O(l) + Na3PO4(aq) pH>7 Weak acid Strong base Basic salt 2 H2CO3(aq) + Pb(OH)4(aq) 4 H2O(l) + Pb(CO3)2(aq) pH~7 Weak acid Weak base Neutral salt 2 3 H2SO4(aq) + Fe(OH)3(aq) 6 H2O(l) + Fe2(SO4)3(aq) pH<7 Strong acid Weak base Acidic salt HClO4(aq) + LiOH(aq) H2O(l) + LiClO4(aq) pH~7 Strong acid Strong base Neutral salt 2 HI(aq) + Zn(OH)2(aq) 2 H2O(l) + ZnI2(aq) pH<7 Strong acid Weak base Acidic salt 3 HF(aq) + Al(OH)3(aq) 3 H2O(l) + AlF3(aq) pH~7 Weak acid Weak base Neutral salt HBr(aq) + KOH(aq) H2O(l) + KBr(aq) pH~7 Strong acid Strong base Neutral salt .
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