Hóa học - Chapter 6: Acids and bases

Chapter 6Acids andBases*Stomach Acid & Heartburnthe cells that line your stomach produce hydrochloric acidto kill unwanted bacteriato help break down foodto activate enzymes that break down foodif the stomach acid backs up into your esophagus, it irritates those tissues, resulting in heartburnacid refluxGERD = gastroesophageal reflux disease = chronic leaking of stomach acid into the esophagus*Curing Heartburnmild cases of heartburn can be cured by neutralizing the acid in the esophagusswallowing saliva which contains bicarbonate iontaking antacids that contain hydroxide ions and/or carbonate ions*Properties of Acidssour tastereact with “active” metalsi.e., Al, Zn, Fe, but not Cu, Ag, or Au2 Al + 6 HCl ® 2 AlCl3 + 3 H2corrosivereact with carbonates, producing CO2marble, baking soda, chalk, limestoneCaCO3 + 2 HCl ® CaCl2 + CO2 + H2Ochange color of vegetable dyesblue litmus turns redreact with bases to form ionic salts *Common Acids*Structures of Acidsbinary acids have acid hydrogens attached to a nonmetal atomHCl, HF*Structure of Acidsoxy acids have acid hydrogens attached to an oxygen atomH2SO4, HNO3*Structure of Acidscarboxylic acids have COOH groupHC2H3O2, H3C6H5O7only the first H in the formula is acidicthe H is on the COOH*Properties of Basesalso known as alkalistaste bitteralkaloids = plant product that is alkalineoften poisonoussolutions feel slipperychange color of vegetable dyesdifferent color than acidred litmus turns bluereact with acids to form ionic saltsneutralization*Common Bases*Structure of Basesmost ionic bases contain OH ionsNaOH, Ca(OH)2some contain CO32- ionsCaCO3 NaHCO3molecular bases contain structures that react with H+mostly amine groups*Indicatorschemicals which change color depending on the acidity/basicitymany vegetable dyes are indicatorsanthocyaninslitmus from Spanish mossred in acid, blue in basephenolphthaleinfound in laxativesred in base, colorless in acid*Arrhenius Theorybases dissociate in water to produce OH- ions and cationsionic substances dissociate in water NaOH(aq) → Na+(aq) + OH–(aq)acids ionize in water to produce H+ ions and anionsbecause molecular acids are not made of ions, they cannot dissociate they must be pulled apart, or ionized, by the water HCl(aq) → H+(aq) + Cl–(aq)in formula, ionizable H written in frontHC2H3O2(aq) → H+(aq) + C2H3O2–(aq) *Arrhenius TheoryHCl ionizes in water,producing H+ and Cl– ionsNaOH dissociates in water,producing Na+ and OH– ions*Hydronium Ionthe H+ ions produced by the acid are so reactive they cannot exist in waterH+ ions are protons!!instead, they react with a water molecule(s) to produce complex ions, mainly hydronium ion, H3O+H+ + H2O  H3O+there are also minor amounts of H+ with multiple water molecules, H(H2O)n+*Arrhenius Acid-Base Reactionsthe H+ from the acid combines with the OH- from the base to make a molecule of H2Oit is often helpful to think of H2O as H-OHthe cation from the base combines with the anion from the acid to make a saltacid + base → salt + waterHCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)*Problems with Arrhenius Theorydoes not explain why molecular substances, like NH3, dissolve in water to form basic solutions – even though they do not contain OH– ionsdoes not explain how some ionic compounds, like Na2CO3 or Na2O, dissolve in water to form basic solutions – even though they do not contain OH– ionsdoes not explain why molecular substances, like CO2, dissolve in water to form acidic solutions – even though they do not contain H+ ionsdoes not explain acid-base reactions that take place outside aqueous solution*Brønsted-Lowry Theoryin a Brønsted-Lowry Acid-Base reaction, an H+ is transferreddoes not have to take place in aqueous solutionbroader definition than Arrheniusacid is H donor, base is H acceptorbase structure must contain an atom with an unshared pair of electronsin an acid-base reaction, the acid molecule gives an H+ to the base molecule H–A + :B  :A– + H–B+*Brønsted-Lowry AcidsBrønsted-Lowry acids are H+ donorsany material that has H can potentially be a Brønsted-Lowry acidbecause of the molecular structure, often one H in the molecule is easier to transfer than othersHCl(aq) is acidic because HCl transfers an H+ to H2O, forming H3O+ ionswater acts as base, accepting H+HCl(aq) + H2O(l) → Cl–(aq) + H3O+(aq)acid base*Brønsted-Lowry BasesBrønsted-Lowry bases are H+ acceptorsany material that has atoms with lone pairs can potentially be a Brønsted-Lowry basebecause of the molecular structure, often one atom in the molecule is more willing to accept H+ transfer than othersNH3(aq) is basic because NH3 accepts an H+ from H2O, forming OH–(aq)water acts as acid, donating H+NH3(aq) + H2O(l)  NH4+(aq) + OH–(aq)base acid