1 acids and bases chapter 15. 2 acids and bases the concepts acids and bases were loosely defined as...
TRANSCRIPT
1
Acids and BasesChapter 15
2
Acids and Bases• The 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 classified – salty-tasting, sour-tasting, sweet-tasting, bitter-
tasting • Sour-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
Acids• React with certain metals to
produce hydrogen gas.• React with carbonates and
bicarbonates to produce carbon dioxide gas
• Have a bitter taste• Feel slippery. • Many soaps contain bases.
Bases
4
Properties of Acids Produce H+ (or H3O+) ions in water (the hydronium ion is
a hydrogen ion attached to a water molecule)
Taste sour
Corrode metals
Good Electrolytes
React with bases to form a salt and water
pH is less than 7
Turns blue litmus paper to red
5
Properties of Bases Generally produce OHGenerally produce OH-- ions in water ions in water
Taste bitter, chalkyTaste bitter, chalky
Are electrolytesAre electrolytes
Feel soapy, slipperyFeel soapy, slippery
React with acids to form salts and waterReact with acids to form salts and water
pH greater than 7pH greater than 7
Turns red litmus paper to blueTurns red litmus paper to blue
6
Arrhenius DefinitionArrhenius
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 DefinitionAcid - 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 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 pair
HB+ - conjugate acid of base :B
Conjugate Acid Base Pairs
9
Note: Water can act as acid or base
Acid Base Conjugate Acid Conjugate Base
HCl + H2O H3O+ + Cl-
H2PO4- + H2O H3O+ + HPO4
2-
NH4+ + H2O H3O+ + NH3
Base Acid Conjugate Acid Conjugate Base :NH3 + H2O NH4
+ + OH-
PO43- + H2O HPO4
2- + OH-
Examples of Bronsted-Lowry Acid Base Systems
10
Lewis
Acid - an electron pair acceptor
Base - an electron pair donor
G.N. Lewis Definition
11
pH and acidityHNO3 + NaOH H2O + NaNO3
HC2H3O2 + H2O H3O+ + C2H3O2-
NH3 + HCl NH4+ + Cl-
HSO4- + HPO4
-2 H2SO4 + PO4-3
HSO4- + HPO4
-2 SO4-2 + H2PO4
-1
12
Acid Strength Strong Acid - Transfers all of its protons to water; - Completely ionized or dissociated; - Strong electrolyte; - The conjugate base is very weak
Weak Acid - Transfers only a fraction of its protons to water;
- Only partly ionizes or dissociates; - Weak electrolyte; - The conjugate base is stronger As acid strength decreases, base strength
increases. The stronger the acid, the weaker its conjugate base The weaker the acid, the stronger its conjugate base
13
Base Strength
Strong Base - all molecules accept a proton; - completely ionizes or dissociates; - strong electrolyte; - conjugate acid is very weak
Weak 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.
14
Common Strong AcidsStrong AcidsStrong Acids
Hydrochloric Acid, HCl
Hydrobromic Acid, HBr
Hydroioidic Acid, HI
Nitric Acid, HNO3
Sulfuric Acid, H2SO4
Chloric Acid, HClO3
Perchloric Acid, HClO4
15
Common Strong BasesStrong BasesStrong Bases
Any Group 1 Hydroxide and any Group 2 Hydroxide below Mg.
Sodium Hydroxide, NaOH
Potassium Hydroxide, KOH
*Barium Hydroxide, Ba(OH)2
*Calcium Hydroxide, Ca(OH)2
*While strong bases they are not very soluble
16
pH and acidity
The pH values of several common substances are shown at the right.
Many common foods are weak acids
Some medicines and many household cleaners are bases.
17
The pH Scale
pH [H3O+ ] [OH- ] pOH
18
pH and acidity1. Acidity or Acid Strength depends on Hydronium Ion
Concentration [H3O+]
2. 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) = 7
4. pH range of solutions: 0 - 14
pH < 7 (Acidic) [H3O+] > 1 x 10-7 M
pH > 7 (Basic) [H3O+] < 1 x 10-7 M
19
pH and acidity Important Equations pH = - log [H3O+]
[H3O+] = 10-pH
pOH = - log [OH-] [OH-] = 10-pOH
pH + pOH = 14
Kw = [H3O+] [OH-] = 1.0 x10-14
In pure water: [H3O+] = [OH-] = 1.0 x10-7
20
Calculating the pHpH = - log [H3O+]
Example 1: If [H3O+] = 1 X 10-10
pH = - log 1 X 10-10
pH = - (- 10)pH = 10
Example 2: If [H3O+] = 1.8 X 10-5
pH = - log 1.8 X 10-5
pH = - (- 4.74)pH = 4.74
21
pH and acidity
If 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.
22
Indicators