Acid and Base

16.1 Acids and BasesArrhenius acid produces H+ in aqeuous

solutionArrhenius base produces –OH in aqueous

solutionE.g

Strong acidHCl(g) H+(aq) + Cl-(aq) Strong base

NaOH(s) Na+(aq) + -OH(aq)

16.1 Acids and BasesBonsted-Lowry acids: proton (H+) donorBronsted_Lowry bases: proton (H+) acceptorConjugated acids: new acid that resulted

from accepting H+

Conjugated bases: new base that resulted from losing H+

E.g HA(aq) + H2O(l) H3O+(aq) + A-(aq)

HCl(aq) + H2O (l) H3O(aq) + Cl-(aq)

Examples Which of the following represent conjugate

acid-base pairs?

a. HF, F- b. NH4+, NH3

c. HCl, H2O d. HClO4, ClO4-

Write the following base for each of the following

a. HClO2 b. H2SO3 c. NH3

16.2 Acid StrengthStrong acids:

completely ionized or completely dissociated

Forward reaction is predominated Most of HA is

dissociatedConjugated base is

weak and has low attraction for proton

HA(aq) + H2O(l) H3O+(aq) + A-(aq)

Acids StrengthWeak acids: partially ionized or dissolved Reverse reactions is predominated

Most of HA is undissociateConjugated base is strong and has high attraction for

protonHC2H3O4(aq) + H2O(l) H3O+(aq) +C2H3O4

-(aq)

AcidsDiprotic acids: acids that can furnish two

protons H2SO4(aq) H+(aq) + HSO4

-(aq)

HSO4-(aq) H+(aq) + SO4

2- (aq0Oxyacids: acidic hydrogen is attached to

an oxygen Organic acids: those with a carbon-atom

backbone

16.3 Water as an Acid and a BaseAmphoteric substance: substance that

can behave as an acid or as a baseH2O(l) + H2O (l) H3O+ (aq) + -OH(aq)

At 25oC[H3O+]= [-OH] = 1.0 x 10-7 M

Kw = [H3O+] x [-OH] = 1.0 x 10-14

Kw = ion-product constant of water

Water as an acid and as a base[H3O+] = [-OH] neutral solution

[H3O+] > [-OH] acidic solution

[H3O+] < [-OH] basic solution

ExamplesCalculate [H3O+] or [-OH] as required for

each of the following solution at 25oC and state whether the solution is neutral, acidic, or basic.1.0 x 10-5 M –OH3.4 x 10-4 M H3O+

2.0 x 10-2 M –OH10.0 M H3O+

Using Ion-Product Constant in CalculationsIs it possible for an aqueous solution at 25oC

to have [H3O+] = 0.010 M and [-OH] = 0.010 M?

Which is greater, [-OH] or [H3O+], if [H3O+] = 2.8 x 10-5M in an aqueous solution at 25oC?

16.4 The pH scalepH scale provides a

compact way to represent solution acidity

Express the common logarithm (base 10 log)

pH = - log [H3O+] scale : 1.00 to 14.00Smaller pH => more

acidic

The pOH scalesRepresents solution basicitypOH = - log [-OH]Scale from 1.00 to 14.00Smaller pOH => more basic

ExamplesCalculate the pH value for each of the

following solution at 25oC

A solution in which [H3O+] = 1.0 x10-9M

A solution in which [-OH] = 5.0 x 10-5 M

ExamplesCalculate the pH and pOH for each of the

following solutions at 25oC1.0 x 10-3 M –OH3.6 x 10-9 M H3O+

Calculate pH from pOHpH + pOH = 14.00

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 pHRecall pH = -log [H3O+]

Inverse log (-pH) = inverse log (log[H3O+])

inverse log (-pH) = [H3O+]

10-pH = [H3O+]

E.G Convert pH = 7.0 to [H3O+]

*Similar calculation is applied to pOH10-pOH = [-OH]

ExamplesThe pH of a human blood sample was

measured to bee 7.41. What is the [H3O+] in this blood?

The pH of rainwater in a polluted area was found to be 3.50. What is the [H3O+]?

The pOH of water in a fish tank is found to be 6.59. What is the [-OH]?

The pOH of a liquid drain cleaner was found to be 10.50 What is the [-OH] for this cleaner?

16.5 Calculating the pH of strong Acid SolutionRecall that strong acids are completely

ionized when dissolved in waterE.g HCl(aq) H+(aq) + Cl-(aq) 0.10 M 0.10M 0.10M

Calculating pH of Strong Acid SolutionsCalculate the pH of 0.10 HNO3

Calculate the pH of a 1.2 x 10-6 HBr

16.6 Buffer SolutionBuffer 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 baseHA(aq) + H2O(l) H3O+(aq) + A-

Addition of H+ reacts with the base A-

Addition of –OH reacts with weak acid

ExamplesOur blood system is controlled by

H2CO3(aq) + H2O(l) HCO3-(aq) +

H3O+(aq)

Write the reaction equation forAddition of HCl

Addition of NaOH