Acids and Bases

HCl + H2O  H3O+ + Cl– Arrhenius – + Acids form hydronium ions (H3O+) Arrhenius - In aqueous solution… Acids form hydronium ions (H3O+) HCl + H2O  H3O+ + Cl– H Cl O – + acid

NH3 + H2O  NH4+ + OH- Arrhenius – + Bases form hydroxide ions (OH-) Arrhenius - In aqueous solution… Bases form hydroxide ions (OH-) NH3 + H2O  NH4+ + OH- H N O – + base

HCl + H2O  Cl– + H3O+ Bronsted-Lowry acid conjugate base base Acids are proton (H+) donors. Bases are proton (H+) acceptors. HCl + H2O  Cl– + H3O+ acid conjugate base base conjugate acid

Definitions H2O + HNO3  H3O+ + NO3– B A CA CB

Amphoteric - can be an acid or a base. Definitions NH3 + H2O  NH4+ + OH- B A CA CB Amphoteric - can be an acid or a base.

Polyprotic - an acid with more than one H+ Give the conjugate base for each of the following: HF H3PO4 H3O+ F - H2PO4- H2O Polyprotic - an acid with more than one H+

Br - HSO4- CO32- HBr H2SO4 HCO3- Give the conjugate acid for each of the following: Br - HSO4- CO32- HBr H2SO4 HCO3-

Lewis Acids are electron pair acceptors. Bases are electron pair donors. Lewis base Lewis acid

Properties ACIDS BASES electrolytes  electrolytes sour taste bitter taste turn litmus red turn litmus blue react with metals to form H2 gas slippery feel vinegar, milk, soda, apples, citrus fruits ammonia, lye, antacid, baking soda ChemASAP

Properties of Acids Acids taste sour Acids effect indicators Blue litmus turns red Phenolphthalein turns clear/colorless Acids have a pH lower than 7 Acids are proton (hydrogen ion, H+) donors Acids react with active metals, produce H2 Acids react with carbonates Acids neutralize bases

Acids to know: Strong Acids Weak Acids Sulfuric acid, H2SO4 Phosphoric acid, H3PO4 Hydrochloric acid, HCl Acetic acid, HC2H3O2 Nitric acid, HNO3

Nitric Acid Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid – its reactive components evaporate easily Stains proteins (including skin!)

Acetic Acid Used in the manufacture of plastics Used in making pharmaceuticals Acetic acid is the acid present in vinegar

Acids are Proton Donors Monoprotic acids Diprotic acids Triprotic acids H3PO4 HCl H2SO4 HC2H3O2 H2CO3 HNO3

Ionization of HCl and formation of hydronium ion, H3O+ H2O + HCl  H3O+ + Cl- Proton acceptor Proton donor

Strong vs Weak & Concentrated vs Dilute From last unit Concentrated: A lot of solute has been dissolved Dilute: A small amount of solute has been dissolved THESE HAVE TO DO WITH AMOUNT DISSOLVED From this unit Strong: substance breaks up completely into ions Dilute: substance does not break up completey into ions THIS HAS NOTHING TO DO WITH HOW MUCH! If you had only 1 molecule, but it was broken into ions, it would be strong!

STRONG ACID WEAK ACID STRONG BASE WEAK BASE

Strong Acids vs. Weak Acids Strong acids are assumed to be 100% ionized in solution (good proton donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor proton donors). H3PO4 HC2H3O2 Organic acids

Strong Acid Dissociation

Weak Acid Dissociation

ConcepTest Which of the following "molecular" pictures best represents a concentrated solution of the weak acid HA? A B

Acids Effect Indicators Blue litmus paper turns red in contact with an acid. Phenolphthalein turns clear/colorless in an acid.

Acids have a pH less than 7

Products of Neutralization HCl + NaOH  NaCl + H2O H2SO4 + Ca(OH)2  CaSO4 + 2 H2O HNO3 + KOH  KNO3 + H2O The products of neutralization are always a ______ and _______. salt water

Properties of Bases Bases effect indicators Red litmus turns blue Bases taste bitter Bases effect indicators Red litmus turns blue Phenolphthalein turns pinkish Bases have a pH greater than 7 Bases are proton (hydrogen ion, H+) acceptors Solutions of bases feel slippery Bases neutralize acids

Examples of Bases Sodium hydroxide (lye), NaOH Potassium hydroxide, KOH Magnesium hydroxide, Mg(OH)2 Calcium hydroxide (lime), Ca(OH)2

Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple/pink in a base.

Bases have a pH greater than 7

Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

Self-Ionization of Water H2O + H2O  H3O+ + OH-

Ion Concentration in Water

Kw – Ionization Constant for Water In pure water at 25 C: [H3O+] = 1 x 10-7 mol/L (M) [OH-] = 1 x 10-7 mol/L (M) Kw is a constant at 25 C: Kw = [H3O+][OH-] Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-14 M2

Concentrations of H3O+ and OH- Since [H3O+] = [OH-] in pure water, it is neutral. When [H3O+]  [OH-] , the solution is acidic. When [H3O+]  [OH-], the solution is basic.

Concentrations of H3O+ and OH- Kw = [H3O+] [OH- ] = 1.0 x 10-14 M2 [H3O+] = Kw = 1.0 X 10-14 M2 [OH-] [OH-] [OH -] = Kw . = 1.0 X 10-14 M2 [H3O+] [H3O+ ] Assume that strong acids and bases are completely ionized in solution

Examples of Calculating [H3O+] and [OH-] Kw = 1.0 x 10-14 M2 = [H3O+] [OH-] EX. If you have 2.0 x 10-4 M H3O+, then Kw = 1.0 x 10-14 M2 = (2.0 x 10-4 ) x [OH-] [OH-] = Kw = 1.0 x 10-14 M2 = 0.5 x 10-10 M OH- [H3O+] 2.0 x 10-4 M

Calculating [H3O+] and [OH-] Kw = 1.0 x 10-14 M2 = [H3O+] [OH-] From the previous slide: [OH-] = 0.5 x 10-10 M [H3O+] = 2.0 x 10-4 M [H3O+]  [OH-] , the solution is acidic.

pH Scale Expressing the acidity or alkalinity in terms of concentration (how much—concentrated or dilute) of ions can be cumbersome since the values tend to be small. A more convenient way to express concentration is to use pH: pH “hydrogen power” (French “pouvoir hydrogene”)

pH Scale pH INCREASING ACIDITY INCREASING BASICITY NEUTRAL a measure of the concentration of H3O+ ions in solution measured with a pH paper, pH meter or an indicator with a wide color range Ranges from 0-14 Each number is 10x more concentrated than the next. (2 has 10x more H3O+ ions than 3) INCREASING ACIDITY INCREASING BASICITY NEUTRAL

pH Scale The pH of a solution is defined as the negative of the common logarithm of the hydronium ion concentration. [H3O+] pH is expressed by the following: pH = - log [H3O+] The common logarithm of a number is the power to which 10 must be raised to equal the number.

pH Scale EX. [H3O+] = 1.0 x 10-5 M pH = 5 When the concentration of [H3O+] in solution is an integral power of 10, such as 1M or 0.01 M = 1.0 x 10-2, the pH of the solution is the exponent of the hydronium ion’s concentration with the sign changed. EX. [H3O+] = 1.0 x 10-5 M pH = 5

pH Scale pH = - log [H3O+] = -log (1.0 x 10 -7) = -(-7) = 7 Example: A neutral solution has a [H3O+] of 1.0 x 10-7 The pH is determined as follows: pH = - log [H3O+] = -log (1.0 x 10 -7) = -(-7) = 7

pH Scale A neutral solution would have [OH-] = 1.0 x 10-7 M. pOH can also be determined, however it can only be determined from [OH-] concentration pOH = - log [OH-] A neutral solution would have [OH-] = 1.0 x 10-7 M. Therefore, the pOH = 7 pH + pOH = 14.0

pH and pOH Calculations

pH SCALE OF COMMON HOUSEHOLD PRODUCTS

Sample Problem: What is the pH of a 1.0 x 10-3 M NaOH solution? Since [NaOH] is 1x10-3 M, and it’s a 1:1 ratio of Na:OH, then [OH-]=1.0x10-3 Using this we can solve for pOH Once we have pOH, then pH=14-pOH

Sample Problem What is the pH of a solution if the [H3O+] is 3.4 x 10-5 M? Use the calculator to find: pH = -log [H3O+] = -log (3.4 x 10-5 )

Finding [H3O+] and [OH-] from pH and pOH [H3O+] = 10 (-pH) [OH-] = 10 (-pOH)

Sample Problem What is the [OH-] of a solution whose pH = 3.00?

Formulas! Finding [H3O+] and [OH-] Finding pH and pOH [H3O+] = Kw [OH-] [OH -] = Kw [H3O+] Finding pH and pOH pH = -log (H3O+) pOH = -log (OH-) pH + pOH = 14 Finding [H3O+] and [OH-] from pH, pOH [H3O+] = 10 (-pH) [OH-] = 10 (-pOH)

H+, OH-, and pH

pH Scale

pH + pOH = 14

Measuring pH with wide-range paper

Narrow-Range pH Paper

pH Indicators and their ranges

Neutralization & Titrations ACID + BASE  SALT + WATER HCl + NaOH  NaCl + H2O strong strong neutral HC2H3O2 + NaOH  NaC2H3O2 + H2O weak strong basic Salts can be neutral, acidic, or basic. Neutralization does not mean pH = 7.

If you have equal amounts… Strong Acid + Strong Base = Neutral (pH=7) Strong Acid + Weak Base = Acidic (pH < 7) Weak Acid + Strong Base = Basic (pH>7)

Titration standard solution unknown solution Titration Process in which a standard solution is used to determine the concentration of an unknown solution.

Titration dramatic change in pH Equivalence Point Point at which equal amounts of H3O+ and OH- have been added. Determined by… indicator color change dramatic change in pH

Equivalence point The equivalence point is not always neutral When strong base reacts with strong acid, EP is neutral When strong base reacts with a weak acid or strong acid reacts with weak base, EP will not be at pH 7

Equivalence points Weak Acid titrated with strong base Weak base titrated with strong acid

moles H3O+ = moles OH- MV n = MV n Titration moles H3O+ = moles OH- MV n = MV n M: Molarity V: volume n: # of H+ ions in the acid or OH- ions in the base

Titration H3O+ M = ? V = 50.0 mL n = 2 OH- M = 1.3M V = 42.5 mL n = 1 42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H2SO4. Find the molarity of H2SO4. H3O+ M = ? V = 50.0 mL n = 2 OH- M = 1.3M V = 42.5 mL n = 1 MV# = MV# M(50.0mL)(2) =(1.3M)(42.5mL)(1) M = 0.55M H2SO4

Or you can solve by setting up factor label mL KOH  L KOH  moles KOH (using molarity 1.3 moles / 1 liter)  moles of H2SO4 (from rxn stoich ratios) Then divide moles H2SO4 by volume H2SO4 in L (change from mL)