Acid and Base

16.1 Acids and Bases Arrhenius acid produces H + in aqeuous solution Arrhenius base produces – OH in aqueous solution E.g Strong acid HCl(g)  H + (aq) + Cl - (aq)  Strong base NaOH(s)  Na + (aq) + - OH(aq)

16.1 Acids and Bases Bonsted-Lowry acids: proton (H + ) donor Bronsted_Lowry bases: proton (H + ) acceptor Conjugated acids: new acid that resulted from accepting H + Conjugated bases: new base that resulted from losing H + E.gHA(aq) + H 2 O(l)  H 3 O + (aq) + A - (aq) HCl(aq) + H 2 O (l)  H 3 O(aq) + Cl - (aq)

Examples Which of the following represent conjugate acid-base pairs? a. HF, F - b. NH 4 +, NH 3 c. HCl, H 2 Od. HClO 4, ClO 4 -  Write the following base for each of the following a.HClO 2 b. H 2 SO 3 c.NH 3

16.2 Acid Strength Strong acids: completely ionized or completely dissociated Forward reaction is predominated Most of HA is dissociated Conjugated base is weak and has low attraction for proton HA(aq) + H 2 O(l)  H 3 O + (aq) + A - (aq)

Acids Strength Weak acids: partially ionized or dissolved Reverse reactions is predominated Most of HA is undissociate Conjugated base is strong and has high attraction for proton HC 2 H 3 O 4 (aq) + H 2 O(l) H 3 O + (aq) +C 2 H 3 O 4 - (aq)

Acids Diprotic acids: acids that can furnish two protons H 2 SO 4 (aq)  H + (aq) + HSO 4 - (aq) HSO 4 - (aq) H + (aq) + SO 4 2- (aq0 Oxyacids: acidic hydrogen is attached to an oxygen Organic acids: those with a carbon-atom backbone

16.3 Water as an Acid and a Base Amphoteric substance: substance that can behave as an acid or as a base H 2 O(l) + H 2 O (l) H 3 O + (aq) + - OH(aq) At 25 o C [H 3 O + ]= [ - OH] = 1.0 x M K w = [H 3 O+] x [ - OH] = 1.0 x K w = ion-product constant of water

Water as an acid and as a base [H 3 O + ] = [ - OH] neutral solution [H 3 O + ] > [ - OH] acidic solution [H 3 O + ] < [ - OH] basic solution

Examples Calculate [H 3 O + ] or [ - OH] as required for each of the following solution at 25 o C and state whether the solution is neutral, acidic, or basic. 1.0 x M – OH 3.4 x M H 3 O x M – OH 10.0 M H 3 O +

Using Ion-Product Constant in Calculations Is it possible for an aqueous solution at 25 o C to have [H 3 O + ] = M and [ - OH] = M? Which is greater, [ - OH] or [H 3 O + ], if [H 3 O + ] = 2.8 x M in an aqueous solution at 25 o C?

16.4 The pH scale pH scale provides a compact way to represent solution acidity Express the common logarithm (base 10 log) pH = - log [H 3 O + ] scale : 1.00 to Smaller pH => more acidic

The pOH scales Represents solution basicity pOH = - log [ - OH] Scale from 1.00 to Smaller pOH => more basic

Examples Calculate the pH value for each of the following solution at 25 o C A solution in which [H 3 O + ] = 1.0 x10 -9 M A solution in which [ - OH] = 5.0 x M

Examples Calculate the pH and pOH for each of the following solutions at 25 o C 1.0 x M – OH 3.6 x M H 3 O +

Calculate pH from pOH pH + pOH = The pH of blood is about 7.4 What is the pOH of blood? A sample of rain in an area with severve air pollution has a pH of 3.5. What is the pOH of this rain water

Calculating [H3O+] from pH Recall pH = -log [H 3 O + ] Inverse log (-pH) = inverse log (log[H 3 O + ]) inverse log (-pH) = [H 3 O + ] 10 -pH = [H 3 O + ] E.G Convert pH = 7.0 to [H 3 O + ] *Similar calculation is applied to pOH 10 -pOH = [ - OH]

Examples The pH of a human blood sample was measured to bee What is the [H 3 O + ] in this blood? The pH of rainwater in a polluted area was found to be What is the [H 3 O + ]? The pOH of water in a fish tank is found to be What is the [ - OH]? The pOH of a liquid drain cleaner was found to be What is the [ - OH] for this cleaner?

16.5 Calculating the pH of strong Acid Solution Recall that strong acids are completely ionized when dissolved in water E.g HCl(aq)  H + (aq) + Cl - (aq) 0.10 M0.10M 0.10M

Calculating pH of Strong Acid Solutions Calculate the pH of 0.10 HNO 3 Calculate the pH of a 1.2 x HBr

16.6 Buffer Solution Buffer solution is one that resists a change in its pH even when a strong acid or base is added to it. Buffer solution is made of a weak acid and its conjugated base HA(aq) + H 2 O(l)  H 3 O + (aq) + A - Addition of H + reacts with the base A - Addition of – OH reacts with weak acid

Examples Our blood system is controlled by H 2 CO 3 (aq) + H 2 O(l)  HCO 3 - (aq) + H 3 O + (aq) Write the reaction equation for Addition of HCl Addition of NaOH