Chapter 14 Acids and Bases

Lemons contain citric acid, Citric acid produces H + ions in your mouth H + ions react with protein molecules on your tongue The protein molecule changes shape – sending an electrical signal to your brain “Sour!”

Acids How do I identify an acid? –HCl, H 2 SO 4, HNO 3 –First atom is hydrogen –Produces H + ions in water HCl(aq)  H + (aq) + Cl - (aq) –HCl + H 2 O  H 3 O + (aq) + Cl - (aq) H 2 SO 4 (aq)  HNO 3 (aq) 

Acids and Bases ACIDS Taste sour Dissolve many metals Turn litmus paper red BASES Taste bitter Feel slippery Turn litmus paper blue Sodium hydroxide or “lye” Carbonic acid, phosphoric acid Citric acid Tartaric acid Sodium borate Sodium carbonate “washing soda”

Arrhenius Theory Acids ionize in water to H + ions and anions –HCl(aq)  Bases ionize in water to OH - ions and cations –NaOH(aq)  Neutralization reaction net ionic equation: –

Brønsted-Lowery Theory Acid is H + donor –HCl(aq)  H + (aq) + Cl - (aq) Base is H + acceptor –NH 3 (aq) + H + (aq) ↔ NH 4 + (aq) –H 2 O(l) + H + (aq) ↔ H 3 O + (aq) What else do NH 3 and H 2 O has in common? – In the reaction, a H + from the acid molecule is transferred to the base molecule

Conjugate Acids and Bases NH 3 (aq) + H 2 O(l) ↔ NH 4 + (aq) + OH - (aq) H 2 SO 4 (aq) + H 2 O(l)  HSO 4 - (aq) + H 3 O + (aq) C 5 H 5 N(aq) + H 2 O(l) ↔ C 5 H 5 NH + (aq) + OH - (aq) Base Conjugate Base Conjugate Acid Acid

Strong versus Weak Acids Strong acids completely dissociate into ions –Major species: ions –Minor species: un-ionized acid Weak acids slightly dissociate into ions. –Major species: un-ionized acid –Minor species: ions

Strong versus Weak Acids

Which solution contains the strong acid?

Strong versus Weak Acids Strong AcidsWeak Acids HX (aq)  H + (aq) + X - (aq) HX (aq) H + (aq) + X - (aq) Nitric acid (HNO 3 ) Most organic acids (acetic, oxalic, citric, fatty acids) Sulfuric acid (H 2 SO 4 )Hydrofluoric acid (HF) Hydrochloric acid (HCl)Carbonic acid - soda pop (H 2 CO 3 ) Hydrobromic acid (HBr) Hydroiodic acid (HI) Phosphoric acid - in Coke (H 3 PO 4 )

Which Hydrogen atoms are acidic?

Strong versus Weak Bases Strong bases completely dissociate into ions –Major species: ions –Minor species: un-ionized acid –NaOH(aq)  Na + (aq) + OH - (aq) Weak bases slightly dissociate, producing hydroxide ions. –Major species: un-ionized acid –Minor species: ions –NH 3 (aq) + H 2 O(aq) ↔ NH 4 + (aq) +OH - (aq)

Strong versus Weak Bases Strong BasesWeak Bases MOH (aq)  M + (aq) + OH - (aq) B (aq) + H 2 O (l) BH + (aq) + OH - (aq) Sodium hydroxide (NaOH)Ammonia, NH 3 Potassium hydroxide (KOH) Lithium hydroxide (LiOH) Bicarbonate, HCO 3 - Calcium hydroxide (Ca(OH) 2 ) Strontium hydroxide (Sr(OH) 2 ) Amines (Carbon group-NH 2 ) Barium hydroxide (Ba(OH) 2 ) Water (H 2 O)

Relative Strength of Conjugate Acids and Bases H 2 SO 4 (aq) + H 2 O(l)  HSO 4 - (aq) + H 3 O + (aq) A strong acid has a weak conjugate base A strong base has a weak conjugate acid A weak base has a strong conjugate acid A weak acid has a strong conjugate base Base Conjugate Base Conjugate Acid Acid

Recognizing Acids and Bases Bases need a lone pair of electrons to accept a proton Acids leave behind stable anions

Reactions of Acids and Bases Neutralization Reactions H 2 SO 4 (aq) + Ca(OH) 2 (aq) → Single Replacement Redox 3 H 2 SO 4 (aq) + 2 Al(s) → Acids react with metal oxides… 3 H 2 SO 4 + Al 2 O 3 →

Water NH 3 (aq) + H 2 O(l)  NH 4 + (aq) + OH - (aq) H 2 SO 4 (aq) + H 2 O(l)  HSO 4 - (aq) + H 3 O + (aq) Can act as an acid or base - amphoteric

Water Auto-ionization H 2 O(l) + H 2 O(l) ↔ H 3 O + (aq) + OH - (aq) At equilibrium, the [H 3 O + ] and [OH - ] are constant and equal. –K W = [H 3 O + ][OH - ]=1x at 25 ° C What is the concentration of [H 3 O + ] at equilibrium?

Acidic versus Basic Solutions Every aqueous solution contains water molecules, hydronium ions (H or H + ) and hydroxide ions (OH - ) A neutral solution: –[H+] ~ [OH-] An acidic solution: –[H+] > [OH-] A basic solution: –[OH-] > [H+] H+H+ OH - H2OH2O H2OH2O H2OH2O H2OH2O H+H+ H2OH2O H2OH2O H2OH2O H2OH2O H+H+ H2OH2O H2OH2O H2OH2O H2OH2O H+H+ H+H+

pH scale Neutral: pH ~ 7 Acidic: pH < 7 Basic: pH > 7 pH = - log [H 3 O + ] Significant figures: [H 3 O + ] = 1.0 x pH = 3.00

Measuring pH pH meter Universal Indicators

pH and pOH pOH = - log [OH - ] K W = [H 3 O + ][OH - ] = 1 x pH + pOH = 14 Calculate the pH of a solution with: –[H 3 O + ] = 1.0 x M –pOH = 8.00 –[OH - ] = 1.0 x M Calculate the [H 3 O + ] of a solution with: –pH = 4.00 –pOH = 6.00 –[OH - ] = 1.0 x M Calculate the pH of 0.10 M HNO 3 solution.

pH and pOH pOH = - log [OH - ] K W = [H 3 O + ][OH - ] = 1 x pH + pOH = 14 Calculate the pH of a solution with: –[H 3 O + ] = 9.5 x M –pOH = 4.80 –[OH - ] = 1.3 x M Calculate the [H 3 O + ] of a solution with: –pH = 4.80 –pOH = 5.67 –[OH - ] = 7.2 x M Calculate the pH of 0.10 M H 2 SO 4 solution. Calculate the pH of 0.10 M Ba(OH) 2 solution.

Titrations To a colorless acidic solution, we will add base. When the solution is basic, it will be red. We are looking for the equivalence point where the moles of H + = moles of OH - We will determination of molarity of NaOH solution Oxalic acid solution Add NaOH (with indicator) Basic solution

Calculations H 2 C 2 O 4 + NaOH H 2 O + Na 2 C 2 O 4 Mass of H 2 C 2 O 4 (g) Moles H 2 C 2 O 4 Moles NaOH Concentration of NaOH solution (M) Volume of Added NaOH g 24.7 mL ? M

Buffers resist changes in pH Buffers contain large amount of an weak acid and its conjugate base HCl(aq) + NaC 2 H 3 O 2 (aq)  NaOH(aq) + HC 2 H 3 O 2 (aq)  Which of the following would constitute a buffer solution? (a) H 2 SO 4 & H 2 SO 3 (aq) (b) HF(aq) & NaF(aq) (c) HCl & NaCl (d) NaCl & NaOH