2 Acids and BasesThe concepts acids and bases were loosely defined as substances that change some properties of water.One of the criteria that was often used was taste.Substances were classifiedsalty-tasting, sour-tasting, sweet-tasting, bitter-tastingSour-tasting substances would give rise to the word 'acid', which is derived from the Greek word oxein, which mutated into the Latin verb acere, which means 'to make sour'Vinegar is a solution of acetic acid. Citrus fruits contain citric acid.
3 Bases Acids React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gasBasesHave a bitter tasteFeel slippery.Many soaps contain bases.
4 Properties of AcidsProduce H+ (or H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule)Taste sourCorrode metalsGood ElectrolytesReact with bases to form a salt and waterpH is less than 7Turns blue litmus paper to red
5 Properties of Bases Generally produce OH- ions in water Taste bitter, chalkyAre electrolytesFeel soapy, slipperyReact with acids to form salts and waterpH greater than 7Turns red litmus paper to blue
6 Arrhenius Definition Arrhenius Acid - Substances in water that increase the concentration of hydrogen ions (H+).Base - Substances in water that increase concentration of hydroxide ions (OH-).
7 Bronsted-Lowry Definition Acid - neutral molecule, anion, or cation that donates a proton.Base - neutral molecule, anion, or cation that accepts a proton.HA + :B HB :A-HCl + H2O H3O Cl-Acid Base Conj Acid Conj Base
8 Conjugate Acid Base Pairs Conjugate Base - The species remaining after an acid has transferred its proton.Conjugate Acid - The species produced after base has accepted a proton.HA & :A- - conjugate acid/base pair:A- - conjugate base of acid HA:B & HB+ - conjugate acid/base pairHB+ - conjugate acid of base :B
9 Examples of Bronsted-Lowry Acid Base Systems Note: Water can act as acid or baseAcid Base Conjugate Acid Conjugate BaseHCl + H2O H3O Cl-H2PO4- + H2O H3O HPO42-NH4+ + H2O H3O NH3Base Acid Conjugate Acid Conjugate Base : NH H2O NH OH-PO H2O HPO OH-
10 G.N. Lewis Definition Lewis Acid - an electron pair acceptor Base - an electron pair donor
14 pH and acidityAcidity or Acid Strength depends on Hydronium Ion Concentration [H3O+]The pH system is a logarithmic representation of the Hydrogen Ion concentration (or OH-) as a means of avoiding using large numbers and powers.pH = - log [H3O+]pOH = - log [OH-]In pure water [H3O+] = 1 x 10-7 M pH = - log(1 x 10-7) = 7pH range of solutions:pH < 7 (Acidic) [H3O+] > 1 x 10-7 MpH > 7 (Basic) [H3O+] < 1 x 10-7 M
16 Calculating the pH pH = - log [H3O+] Example 1: If [H3O+] = 1 X pH = - log 1 X 10-10pH = - (- 10)pH = 10Example 2: If [H3O+] = 1.8 X 10-5 pH = - log 1.8 X 10-5pH = - (- 4.74)pH = 4.74
17 pH and acidityIf a substance has a pH of 3.5, determine: [H3O+], [OH-], pOH and whether it is acidic, basic, or neutral.If a substance has an [OH-] of 8.7 x 10-5, determine: pH, pOH, [H3O+] and whether it is acidic, basic, or neutral.
19 Acid StrengthStrong Acid - Transfers all of its protons to water; Completely ionized or dissociated; Strong electrolyte; The conjugate base is very weakWeak Acid - Transfers only a fraction of its protons to water;- Only partly ionizes or dissociates; Weak electrolyte; The conjugate base is strongerAs acid strength decreases, base strength increases.The stronger the acid, the weaker its conjugate baseThe weaker the acid, the stronger its conjugate base
20 Base StrengthStrong Base - all molecules accept a proton; completely ionizes or dissociates; strong electrolyte; conjugate acid is very weakWeak Base - fraction of molecules accept proton; partly ionizes or dissociates weak electrolyte; the conjugate acid is stronger.As base strength decreases, acid strength increases.The stronger the base, the weaker its conjugate acid.The weaker the base the stronger its conjugate acid.
22 Dissociation of Strong Acids Strong acids completely dissociation (broke down) to the ions that make them up.HCl H+1 + Cl-1HNO3 H+1 + NO3-1If you know the concentration or molarity of a strong acid, you also know the amount of H+ ions and can find the pH (-log [H+])0.1 M HCl = 0.1 M H+, pH = -log 0.1 = 1.0
23 Common Strong Bases Strong Bases Any Group 1 Hydroxide and any Group 2 Hydroxide below Mg.Sodium Hydroxide, NaOHPotassium Hydroxide, KOH*Barium Hydroxide, Ba(OH)2*Calcium Hydroxide, Ca(OH)2*While strong bases they are not very soluble
24 Dissociation of Strong Bases Like strong acids, strong bases also completely dissociate to the ions that make them up.KOH K+1 + OH-1Ca(OH)2 Ca OH-1Just like with strong acids, if you know the molarity of a strong base, you can determine the pOH and therefore the pH.0.01 M NaOH = 0.01 M OH-,pOH = -log 0.01 = 2.0 and pH = 12.0
25 pH of Strong Acids and Strong Bases Determine the pH of 0.25 M KOH.Determine the pH of M H2SO4.Determine the pH of M Ca(OH)2.
26 Dissociation of Weak Acids Weak acids only dissociate to a very small degree, most break down to ions less than 5%. So an equilibrium is established where there is a small amount of product (H+ and conjugate base) but most of the acid does not break down.These acids are weak electrolytes versus strong acids are strong electrolytes.
27 Dissociation of Weak Acids To determine the pH of a weak acid, an “ICE” chart must be used.I = Initial concentrationsC = ChangeE = Equilibrium concentrationsUnless otherwise noted, the initial concentrations of the products are zero.
28 Dissociation Constants For a generic weak acid dissociation,the equilibrium expression would beThis equilibrium constant is called the acid-dissociation constant, Ka.HA(aq) + H2O(l) A−(aq) + H3O+(aq)[H3O+] [A−][HA]Ka =
29 Dissociation of Weak Acids Equilibrium expressions are written as products/reactants, and liquids and solids are left out of the expressions.Ka are used to tell the relative strength of the acid.You will be given the Ka value for each weak acid.
30 Dissociation of Weak Acids Determine the pH of M HC2H3O2.Ka = 1.8 X 10-5.
31 Dissociation of Weak Acids Determine the pH of 1.0 M hypoiodous acid, HIO. Ka of HIO = 2.3 x
32 Determination of Ka for a Weak Acid If you are given the initial concentration of the weak acid, and the equilibrium concentration of the conjugate base or H+, you can determine the Ka of the acid.Remember the initial concentrations of both products are zero.If you know the equilibrium concentration of the conjugate base or H+, you also know the value of “x” in the “C” step of the “ICE” chart.
33 Determination of Ka for a Weak Acid Determine the Ka of a weak acid when the initial concentration of HA as M and the equilibrium concentration of H+ = M.Equation: HA + H2O A-1 + H3O+1
34 TitrationTitration – technique for determining the unknown concentration of an acid or base.Titration involves delivery (from a buret) of a measured volume of a solution of known concentration (the titrant, usually a base) into a volume of solution of unknown concentration (the analyte, usually an acid).
35 TitrationEquivalence or stoichiometric point – point in a titration where enough titrant has been added to react exactly with the analyte.Equivalence pt: moles of acid = moles of base
37 TitrationThe equivalence point is often marked by an indicator (commonly phenolphthalein), which is added at the beginning of the titration. It changes color at (or just after) the equivalence point.The point where the indicator actually changes color is called the endpoint of the titration.
39 Titration Calculations 2.00 mL of an unknown concentration of HCl was titrated with 0.25 M NaOH. If mL of NaOH was needed to reach the stoichiometric point, what is the concentration of the HCl?Equation: HCl + NaOH NaCl + H2O
40 Titration Calculations 2 drops of phenolphthalein is added to mL of an 0.75 M of HCl. If mL of NaOH is needed to completely react with all of the HCl, what is the concentration of the NaOH?