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RNA uses amino-acids to build proteins/enzymes Digestive Acids help to break down food into reusable molecular fragments Acids and Bases It is the acids in citrus fruits that give them the sour taste and allows the fruit to stay in a state of preservation till germination Properties of Acids sour taste react with active metals (Al, Zn, Fe), but not Cu, Ag, or Au 2 Al(s) + 6 HCl(aq) 2 AlCl3(aq) + 3 H2(g) Corrosive react with carbonates, producing CO2 marble, baking soda, chalk, limestone CaCO3(s) + 2 HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) change color of vegetable dyes blue litmus turns red react with bases to form ionic salts HCl(aq) + NaOH(aq)NaCl(aq) + H2O(l) 2 Common Acids Chemical Name Formula Uses Strength Nitric Acid HNO3 explosive, fertilizer, dye, glue Strong Sulfuric Acid H2SO4 Hydrochloric Acid HCl Phosphoric Acid H3PO4 Acetic Acid HC2H3O2 explosive, fertilizer, dye, glue, batteries metal cleaning, food prep, ore refining, stomach acid fertilizer, plastics & rubber, food preservation plastics & rubber, food preservation, Vinegar Hydrofluoric Acid HF metal cleaning, glass etching Weak Carbonic Acid H2CO3 soda water Weak Boric Acid H3BO3 eye wash Weak Strong Strong Moderate Weak 3 Structure of Acids binary acids have acid hydrogens attached to a nonmetal atom HCl, HF 4 Structure of Acids oxy acids have acid hydrogens attached to an oxygen atom H2SO4, HNO3 5 Structure of Acids carboxylic acids have COOH group HC2H3O2, H3C6H5O7 only the first H in the formula is acidic the H is on the COOH 6 Properties of Bases also known as alkalis taste bitter alkaloids = plant product that is alkaline often poisonous solutions feel slippery change color of vegetable dyes different color than acid red litmus turns blue react with acids to form ionic salts Neutralization HCl(aq) + NaOH(aq)NaCl(aq) + H2O(l) 7 Common Bases Chemical Name sodium hydroxide potassium hydroxide calcium hydroxide sodium bicarbonate magnesium hydroxide ammonium hydroxide Formula NaOH Common Name lye, caustic soda Uses soap, plastic, petrol refining soap, cotton, electroplating Strength Strong KOH caustic potash Strong Ca(OH)2 slaked lime cement Strong NaHCO3 baking soda cooking, antacid Weak Mg(OH)2 milk of magnesia antacid Weak NH4OH, {NH3(aq)} ammonia water detergent, fertilizer, explosives, fibers Weak 8 Structure of Bases most ionic bases contain OH- ions NaOH, Ca(OH)2 some contain CO32- ions CaCO3 NaHCO3 molecular bases contain structures that react with H+ mostly amine groups Amino acids have a base at one end and an acid at the other, neighboring amino acids can neutralize to form a polypeptide 9 Indicators chemicals which change color depending on the acidity/basicity many vegetable dyes are indicators anthocyanins litmus from Spanish moss red in acid, blue in base phenolphthalein found in laxatives red in base, colorless in acid Anthocyanins give these pansies their dark purple pigmentation and are the pigment in red cabbage that is so sensitive to acidity 10 acids and bases: Arrhenius Theory bases dissociate in water to produce OH- ions and cations ionic substances dissociate in water NaOH(aq) → Na+(aq) + OH–(aq) acids ionize in water to produce H+ ions and anions HCl(aq) → H+(aq) + Cl–(aq) HC2H3O2(aq) H+(aq) + C2H3O2–(aq) 11 Arrhenius Theory HCl ionizes in water producing H+ and Cl– ions NaOH dissociates in water producing Na+ and OH– ions 12 Hydronium Ion the H+ ions produced by the acid are so reactive they cannot exist in water H+ ions are protons instead, they react with a water molecule(s) to produce complex ions, mainly hydronium ion, H3O+ H+ + H2O H3O+ ≅ H+(aq) there are also minor amounts of H+ with multiple water molecules, H(H2O)n+ 13 Arrhenius Acid-Base Reactions the H+ from the acid combines with the OH- from the base to make a molecule of H2O it is often helpful to think of H2O as H-OH the cation from the base combines with the anion from the acid to make a salt acid + base → salt + water HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) H+(aq)+Cl-(aq)+Na+(aq)+OH-(aq)Na+(aq)+Cl-(aq)+H2O(l) H+(aq) + OH-(aq) H2O(l) All acid base reactions have this same net ionic equation in the Arrhenius idea of the acid and base 14 Limitations of the Arrhenius Theory does not explain why molecular substances, like NH3, dissolve in water to form basic solutions – even though they do not contain OH– ions does not explain how some ionic compounds, like Na2CO3 or Na2O, dissolve in water to form basic solutions – even though they do not contain OH– ions does not explain why molecular substances, like CO2, dissolve in water to form acidic solutions – even though they do not contain H+ ions does not explain acid-base reactions that take place outside aqueous solution 15 Acids and bases: Brønsted-Lowry in a Brønsted-Lowry Acid-Base reaction, an H+ is transferred does not have to take place in aqueous solution broader definition than Arrhenius An acid is H+ donor, base is H+ acceptor base structure must contain an atom with an unshared pair of electrons in an acid-base reaction, the acid molecule gives an H+ to the base molecule H–A + :B :A– + H–B+ 16 Brønsted-Lowry Acids Brønsted-Lowry acids are H+ donors any material that has H can potentially be a Brønsted-Lowry acid because of the molecular structure, often one H in the molecule is easier to transfer than others HCl(aq) is acidic because HCl transfers an H+ to H2O, forming H3O+ ions water acts as base, accepting H+ HCl(aq) + H2O(l) → Cl–(aq) + H3O+(aq) Acid base 17 Brønsted-Lowry Bases Brønsted-Lowry bases are H+ acceptors any material that has atoms with lone pairs can potentially be a BrønstedLowry base because of the molecular structure, often one atom in the molecule is more willing to accept H+ transfer than others NH3(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 Tro, Chemistry: A Molecular Approach 18 Amphoteric Substances amphoteric substances can act as either an acid or a base have both transferable H and atom with lone pair Example water acts as base, accepting H+ from HCl HCl(aq) + H2O(l) → Cl–(aq) + H3O+(aq) water acts as acid, donating H+ to NH3 NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq) 19 Brønsted-Lowry: Acid-Base Reactions one of the advantages of Brønsted-Lowry theory is that it allows reactions to be reversible H–A + :B :A– + H–B+ the original base has an extra H+ after the reaction – so it will act as an acid in the reverse process and the original acid has a lone pair of electrons after the reaction – so it will act as a base in the reverse process :A– + H–B+ H–A + :B 20 Conjugate Pairs In a Brønsted-Lowry Acid-Base reaction, the original base becomes an acid in the reverse reaction, and the original acid becomes a base in the reverse process each reactant and the product it becomes is called a conjugate pair the original base becomes the conjugate acid; and the original acid becomes the conjugate base NH3(aq) + H2O(l) Base Acid NH4+(aq) Conjugate Acid + OH–(aq) Conjugate Base 21 Brønsted-Lowry: Acid-Base Reactions H–A acid + HCHO2 acid H 2O + acid + :B base :A– + H–B+ conjugate conjugate base acid H2O base CHO2– conjugate base NH3 base HO– + conjugate base + H 3 O+ conjugate acid NH4+ conjugate acid 22 Conjugate Pairs In the reaction H2O + NH3 HO– + NH4+ H2O and HO– constitute an Acid/Conjugate Base pair NH3 and NH4+ constitute a Base/Conjugate Acid pair 23 Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction H2SO4 + H2O HSO4– + H3O+ When the H2SO4 becomes HSO4-, it lost an H+ so H2SO4 must be the acid and HSO4- its conjugate base When the H2O becomes H3O+, it accepted an H+ so H2O must be the base and H3O+ its conjugate acid H2SO4 acid + H2O base HSO4– + H3O+ conjugate conjugate base acid 24 Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction HCO3– + H2O H2CO3 + HO– When the HCO3 becomes H2CO3, it accepted an H+ so HCO3- must be the base and H2CO3 its conjugate acid When the H2O becomes OH-, it donated an H+ so H2O must be the acid and OH- its conjugate base HCO3– + base H2O H2CO3 acid conjugate acid + HO– conjugate base 25 Practice – Write the formula for the conjugate acid of the following H2O NH3 CO32− H2PO4− 26 Practice – Write the formula for the conjugate acid of the following H2O NH3 H3O+ NH4+ CO32− HCO3− H2PO41− H3PO4 27 Practice – Write the formula for the conjugate base of the following H2O NH3 CO32− H2PO4− 28 Practice – Write the formula for the conjugate base of the following H2O NH3 HO− NH2− CO32− since CO32− does not have an H, it cannot be an acid H2PO41− HPO42− 29 Arrow Conventions chemists commonly use two kinds of arrows in reactions to indicate the degree of completion of the reactions a single arrow indicates all the reactant molecules are converted to product molecules at the end a double arrow indicates the reaction stops when only some of the reactant molecules have been converted into products 30 Strong or Weak a strong acid is a strong electrolyte practically all the acid molecules ionize, → a strong base is a strong electrolyte practically all the base molecules form OH– ions, either through dissociation or reaction with water, → a weak acid is a weak electrolyte only a small percentage of the molecules ionize, a weak base is a weak electrolyte only a small percentage of the base molecules form OH– ions, either through dissociation or reaction with water, 31 Strong Acids The stronger the acid, the more willing it is to donate H HCl(aq) H+(aq) + Cl-(aq) HCl(aq) + H2O(l) H3O+(aq)+ Cl-(aq) use water as the standard base strong acids donate practically all their H’s 100% ionized in water strong electrolyte [H3O+] = [strong acid] 32 Weak Acids weak acids donate a small fraction of their H’s HF(aq) H+(aq) + F-(aq) HF(aq) + H2O(l) H3O+(aq) + F-(aq) most of the weak acid molecules do not donate H to water much less than 1% ionized in water [H3O+] << [weak acid] 33 Polyprotic Acids often acid molecules have more than one ionizable H – these are called polyprotic acids the ionizable H’s may have different acid strengths or be equal 1 H = monoprotic, 2 H = diprotic, 3 H = triprotic HCl = monoprotic, H2SO4 = diprotic, H3PO4 = triprotic 34 Polyprotic Acids polyprotic acids ionize in steps each ionizable H removed sequentially removing of the first H automatically makes removal of the second H harder H2SO4 is a stronger acid than HSO4- 35 HClO4 Conjugate Bases ClO4-1 H2SO4 HI HBr HCl HNO3 H3O+1 HSO4-1 H2SO3 H3PO4 HNO2 HF HC2H3O2 H2CO3 H 2S NH4+1 HCN HCO3-1 HS-1 H 2O CH3-C(O)-CH3 NH3 CH4 OH-1 HSO4-1 I-1 Br-1 Cl-1 NO3-1 H 2O SO4-2 HSO3-1 H2PO4-1 NO2-1 F-1 C2H3O2-1 HCO3-1 HS-1 NH3 CN-1 CO3-2 S-2 OH-1 CH3-C(O)-CH2-1 NH2-1 CH3-1 O-2 Increasing Basicity Increasing Acidity Acids 36 Strengths : Acids and Bases commonly, Acid or Base strength is measured by determining the equilibrium constant of a substance’s reaction with water HA + H2O B: + H2O A-1 + H3O+1 HB+1 + OH-1 the farther the equilibrium position lies to the products, the stronger the acid or base the position of equilibrium depends on the strength of attraction between the base form and the H+ stronger attraction means stronger base or weaker acid 37