Acids, Bases, and Salts

Properties of acids Sour (the edible ones, don’t try the others!) React with many metals to form hydrogen (corrosive) Can conduct electricity well (electrolytes) dependent upon the degree of dissociation (ionization) STRONG ACIDS : HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4 These 6 acids ionize (dissociate) 100% “Weak” acids ionize less than 100%, strength is relative!

Properties of Bases Bitter, slippery (again many are not edible) Ever had your mouth washed out with soap? I hope not! Many are solids, the term alkali applies to bases Again, strength depends upon degree of dissociation (ionization) as well as conductivity (strong or weak electrolytes) STRONG BASES (100% dissociation) are the hydroxides (OH - ) of groups I and II, except Be

Definitions of acids and bases Arrhenius definitions Acid – contains H and ionizes to form H + (equivalent to H3O +, hydronium ion) Base – contains OH and ionizes to form OH - Bronsted –Lowry definitions Acid – proton donor Base – proton acceptor Conjugate acid – an acid that forms when a base gains a proton Conjugate base – a base that forms when an acid loses a proton Amphoteric (amphiprotic) a substance which has the properties of an acid and a base.

Arrhenius

Bronsted - Lowry

Amphoteric - Amphiprotic

“Types” of acids Monoprotic acids – one H (HBr) Polyprotic acids – more than one H for example - diprotic 2 H (H 2 SO 4 ), triprotic, 3 H (H 3 PO 4 ) etc. Binary acids – 2 kinds of elements (H 2 S) Ternary acids – 3 kinds of elements (H 3 PO 3 ) Carboxylic acids (organic acids) – COOH, carboxylic group (HC 2 H 3 O 2 = CH 3 COOH)

Self ionization of water H 2 O (l) + H 2 O (l) ⇆ H 3 O + (aq) + OH - (aq) K w = [H 3 O + ][OH - ] ALWAYS = 1x K a HNO 2 K b NH 3

Logs base ten A log base ten is simply the power to which 10 is raised (log ) on the calculator Antilog of a number is 10 raised to that power (10 x ) on the calculator -log (anything) = p(anything)

Key pH Relationships pH = -log [H 3 O + ] (or [H + ] ) pOH = -log [OH - ] [H 3 O + ] = antilog –pH [OH - ] = antilog –pOH pH + pOH = 14 [H 3 O + ][OH - ] = 1x10 -14

pH scale pH less than 7 –> acid (pOH > 7) pH greater than 7 –> base (pOH < 7) pH= 7 –> neutral

Examples pH= 4 pOH= [H3O + ]= [OH - ]= pH= pOH=8.9 [H3O + ]= [OH - ]=

Examples pH= pOH= [H 3 O + ]= [OH - ]=2.3x10 -5 pH= pOH= [H 3 O + ]= 6.8x [OH - ]=

Measuring pH Indicators weak organic acids or bases which change color with pH (pHydrion paper, universal indicators are a mixture of indicators) pH meter

Molecular and ion forms of phenolphthalein

Acid and bases – neutralization reactions, titration, equilibria, buffers, antacids

Neutralization Reaction ACID + BASE  SALT + WATER Salt – the cation of an acid combined with the anion of a base Examples (ionic, net ionic) HCl (aq) + NaOH (aq)  NaCl (aq) + HOH (l) H 2 SO 3(aq) + 2KOH (aq)  K 2 SO 3(aq) + 2HOH (l)

Titrations Titration – a method to determine the concentration of an substance in solution by adding a solution of known volume and concentration until the reaction is completed, which is usually indicated by a change in color. Equivalence point – the point at which the two solutions used are present in equivalent amounts (MOLES ACID = MOLES BASE) Titrant – a solution of known concentration (standard solution) used to titrate a solution of unknown concentration Transition range – the pH range through which an indicator changes color End point- the point at which a marked color change takes place

Performing a titration 1

Performing a titration 2

Titrating acids and bases

Titration curve – strong acid and strong base

Titration curve – weak acid and strong base

Titration calculations n = cV n= moles, c = concentration in moles/liter, V = volume in liters (c H3O + )(V H3O + ) = (c OH - )(V OH - ) OR V a M a #H’s = V b M b #OH’s Both represent moles H 3 O + = moles OH - What volume of.250 M nitric acid is needed to neutralize mL of.195 M KOH solution?

If 35 mL of.45 M sulfuric acid is used to titrate 50 mL of of sodium hydroxide, what is the concentration of the sodium hydroxide?

Equilibria of weak acids and bases Calculate the [H 3 O + ] of a.150 M acetic acid solution.

Find the K a if a.50 M solution of a weak acid has a hydronium ion concentration of 1.3x10 -4 M.

Buffers – a weak acid and its salt (conjugate base) which resists change in pH Blood – hyperventilate - H 2 CO 3, NaHCO 3 H 2 CO 3 (aq) + H2O (l) ⇆ H3O + (aq) + HCO3 - (aq) HCO3 - (aq) + H3O + (aq) ⇆ H 2 CO 3 (aq) + H2O (l) H 2 CO 3 (aq) + OH - (aq) ⇆ HCO3 - (aq) + H2O (l)

Antacids Bases (NaHCO 3, CaCO 3, Al(OH) 3, Mg(OH) 2 ) that counteract stomach acid. Beware of excess metals, watch their use. Perhaps a better diet would help!