1. Acids and Bases RNA uses amino-acids to build proteins/enzymes 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 Digestive Acids help to break down food into reusable molecular fragments

2. 2 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 AlCl 3(aq) + 3 H 2(g)  Corrosive  react with carbonates, producing CO 2  marble, baking soda, chalk, limestone CaCO 3(s) + 2 HCl (aq)  CaCl 2(aq) + CO 2(g) + H 2 O (l)  change color of vegetable dyes  blue litmus turns red  react with bases to form ionic salts HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)  sour taste  react with active metals (Al, Zn, Fe), but not Cu, Ag, or Au 2 Al (s) + 6 HCl (aq)  2 AlCl 3(aq) + 3 H 2(g)  Corrosive  react with carbonates, producing CO 2  marble, baking soda, chalk, limestone CaCO 3(s) + 2 HCl (aq)  CaCl 2(aq) + CO 2(g) + H 2 O (l)  change color of vegetable dyes  blue litmus turns red  react with bases to form ionic salts HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)

3. 3 Common Acids

4. 4  binary acids have acid hydrogens attached to a nonmetal atom  HCl, HF  binary acids have acid hydrogens attached to a nonmetal atom  HCl, HF Structure of Acids

5. 5  oxy acids have acid hydrogens attached to an oxygen atom  H 2 SO 4, HNO 3  oxy acids have acid hydrogens attached to an oxygen atom  H 2 SO 4, HNO 3

6. 6 Structure of Acids  carboxylic acids have COOH group  HC 2 H 3 O 2, H 3 C 6 H 5 O 7  only the first H in the formula is acidic  the H is on the COOH  carboxylic acids have COOH group  HC 2 H 3 O 2, H 3 C 6 H 5 O 7  only the first H in the formula is acidic  the H is on the COOH

7. 7 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 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) + H 2 O (l)  also known as alkalis  taste bitter  alkaloids = plant product that is alkaline  often poisonous  solutions feel slippery  change color of vegetable dyes 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) + H 2 O (l)

8. 8 Common Bases

9. 9 Structure of Bases  most ionic bases contain OH - ions  NaOH, Ca(OH) 2  some contain CO 3 2- ions  CaCO 3 NaHCO 3  molecular bases contain structures that react with H +  mostly amine groups  most ionic bases contain OH - ions  NaOH, Ca(OH) 2  some contain CO 3 2- ions  CaCO 3 NaHCO 3  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

10. 10 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  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

11. 11 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) HC 2 H 3 O 2 (aq) H + (aq) + C 2 H 3 O 2 – (aq)  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) HC 2 H 3 O 2 (aq) H + (aq) + C 2 H 3 O 2 – (aq)

12. 12 Arrhenius Theory HCl ionizes in water producing H + and Cl – ions NaOH dissociates in water producing Na + and OH – ions

13. 13 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, H 3 O + H + + H 2 O  H 3 O + ≅ H + (aq)  there are also minor amounts of H + with multiple water molecules, H(H 2 O) n +  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, H 3 O + H + + H 2 O  H 3 O + ≅ H + (aq)  there are also minor amounts of H + with multiple water molecules, H(H 2 O) n +

14. 14 Arrhenius Acid-Base Reactions  the H + from the acid combines with the OH - from the base to make a molecule of H 2 O  it is often helpful to think of H 2 O 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) + H 2 O (l) H + (aq) +Cl - (aq) +Na + (aq) +OH - (aq)  Na + (aq) +Cl - (aq) +H 2 O (l) H + (aq) + OH - (aq)  H 2 O (l)  All acid base reactions have this same net ionic equation in the Arrhenius idea of the acid and base  the H + from the acid combines with the OH - from the base to make a molecule of H 2 O  it is often helpful to think of H 2 O 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) + H 2 O (l) H + (aq) +Cl - (aq) +Na + (aq) +OH - (aq)  Na + (aq) +Cl - (aq) +H 2 O (l) H + (aq) + OH - (aq)  H 2 O (l)  All acid base reactions have this same net ionic equation in the Arrhenius idea of the acid and base

15. 15 Limitations of the Arrhenius Theory  does not explain why molecular substances, like NH 3, dissolve in water to form basic solutions – even though they do not contain OH – ions  does not explain how some ionic compounds, like Na 2 CO 3 or Na 2 O, dissolve in water to form basic solutions – even though they do not contain OH – ions  does not explain why molecular substances, like CO 2, 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  does not explain why molecular substances, like NH 3, dissolve in water to form basic solutions – even though they do not contain OH – ions  does not explain how some ionic compounds, like Na 2 CO 3 or Na 2 O, dissolve in water to form basic solutions – even though they do not contain OH – ions  does not explain why molecular substances, like CO 2, 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

16. 16 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 +  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 +

17. 17 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 H 2 O, forming H 3 O + ions  water acts as base, accepting H +  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 H 2 O, forming H 3 O + ions  water acts as base, accepting H + HCl (aq) + H 2 O (l) → Cl – (aq) + H 3 O + (aq) Acid base

18. Tro, Chemistry: A Molecular Approach 18 Brønsted-Lowry Bases  Brønsted-Lowry bases are H + acceptors  any material that has atoms with lone pairs can potentially be a Brønsted- Lowry base  because of the molecular structure, often one atom in the molecule is more willing to accept H + transfer than others  NH 3 (aq) is basic because NH 3 accepts an H + from H 2 O, forming OH – (aq)  water acts as acid, donating H +  Brønsted-Lowry bases are H + acceptors  any material that has atoms with lone pairs can potentially be a Brønsted- Lowry base  because of the molecular structure, often one atom in the molecule is more willing to accept H + transfer than others  NH 3 (aq) is basic because NH 3 accepts an H + from H 2 O, forming OH – (aq)  water acts as acid, donating H + NH 3 (aq) + H 2 O(l)  NH 4 + (aq) + OH – (aq) base acid

19. 19 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) + H 2 O (l) → Cl – (aq) + H 3 O + (aq)  water acts as acid, donating H + to NH 3 NH 3(aq) + H 2 O (l) → NH 4 + (aq) + OH – (aq)  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) + H 2 O (l) → Cl – (aq) + H 3 O + (aq)  water acts as acid, donating H + to NH 3 NH 3(aq) + H 2 O (l) → NH 4 + (aq) + OH – (aq)

20. 20 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  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

21. 21 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 NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH – (aq) Base Acid Conjugate Acid Conjugate Base  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 NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH – (aq) Base Acid Conjugate Acid Conjugate Base

22. 22 H–A + :B :A – + H–B + acidbaseconjugate conjugate base acid HCHO 2 + H 2 O CHO 2 – + H 3 O + acid baseconjugate conjugate base acid H 2 O + NH 3 HO – + NH 4 + acid baseconjugate conjugate base acid Brønsted-Lowry: Acid-Base Reactions

23. 23 Conjugate Pairs In the reaction H 2 O + NH 3 HO – + NH 4 + H 2 O and HO – constitute an Acid/Conjugate Base pair NH 3 and NH 4 + constitute a Base/Conjugate Acid pair

24. 24 Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction H 2 SO 4 + H 2 O HSO 4 – +H 3 O + acid base conjugate conjugate base acid H 2 SO 4 + H 2 O HSO 4 – +H 3 O + When the H 2 SO 4 becomes HSO 4 -, it lost an H + so H 2 SO 4 must be the acid and HSO 4 - its conjugate base When the H 2 O becomes H 3 O +, it accepted an H + so H 2 O must be the base and H 3 O + its conjugate acid

25. 25 Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction HCO 3 – + H 2 O H 2 CO 3 +HO – base acid conjugate conjugate acid base HCO 3 – + H 2 O H 2 CO 3 +HO – When the HCO 3  becomes H 2 CO 3, it accepted an H + so HCO 3 - must be the base and H 2 CO 3 its conjugate acid When the H 2 O becomes OH -, it donated an H + so H 2 O must be the acid and OH - its conjugate base

26. 26 Practice – Write the formula for the conjugate acid of the following H 2 O NH 3 CO 3 2− H 2 PO 4 −

27. 27 Practice – Write the formula for the conjugate acid of the following H 2 OH 3 O + NH 3 NH 4 + CO 3 2− HCO 3 − H 2 PO 4 1− H 3 PO 4

28. 28 Practice – Write the formula for the conjugate base of the following H 2 O NH 3 CO 3 2− H 2 PO 4 −

29. 29 Practice – Write the formula for the conjugate base of the following H 2 OHO − NH 3 NH 2 − CO 3 2− since CO 3 2− does not have an H, it cannot be an acid H 2 PO 4 1− HPO 4 2−

30. 30 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  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

31. 31 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,  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,

32. 32 Strong Acids  The stronger the acid, the more willing it is to donate H  use water as the standard base  strong acids donate practically all their H’s  100% ionized in water  strong electrolyte  [H 3 O + ] = [strong acid]  The stronger the acid, the more willing it is to donate H  use water as the standard base  strong acids donate practically all their H’s  100% ionized in water  strong electrolyte  [H 3 O + ] = [strong acid] HCl (aq)  H + (aq) + Cl - (aq) HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq)

33. 33 Weak Acids  weak acids donate a small fraction of their H’s  most of the weak acid molecules do not donate H to water  much less than 1% ionized in water  [H 3 O + ] << [weak acid]  weak acids donate a small fraction of their H’s  most of the weak acid molecules do not donate H to water  much less than 1% ionized in water  [H 3 O + ] << [weak acid] HF (aq) H + (aq) + F - (aq) HF (aq) + H 2 O (l) H 3 O + (aq) + F - (aq)

34. 34 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, H 2 SO 4 = diprotic, H 3 PO 4 = triprotic  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, H 2 SO 4 = diprotic, H 3 PO 4 = triprotic

35. 35 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  H 2 SO 4 is a stronger acid than HSO 4 -  polyprotic acids ionize in steps  each ionizable H removed sequentially  removing of the first H automatically makes removal of the second H harder  H 2 SO 4 is a stronger acid than HSO 4 -

36. 36 Increasing Acidity Increasing Basicity

37. 37 Strengths : Acids and Bases  commonly, Acid or Base strength is measured by determining the equilibrium constant of a substance’s reaction with water HA + H 2 O  A -1 + H 3 O +1 B: + H 2 O  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  commonly, Acid or Base strength is measured by determining the equilibrium constant of a substance’s reaction with water HA + H 2 O  A -1 + H 3 O +1 B: + H 2 O  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