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The Chemistry of Acids and Bases. Acids. Acids. Bases. Some Properties of Acids. Produce H + Taste sour Corrode metals Electrolytes React with bases to form a salt and water pH is less than 7 Turns blue litmus paper to red “Blue to Red A-CID”

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some properties of acids
Some Properties of Acids
  • Produce H+
  • Taste sour
  • Corrode metals
  • Electrolytes
  • React with bases to form a salt and water
  • pH is less than 7
  • Turns blue litmus paper to red “Blue to Red A-CID”
  • React with certain metals to produce hydrogen gas.
  • React with carbonates and bicarbonates to produce carbon dioxide gas
some common acids
Some Common Acids

Monoprotic acids: one acidic (ionizable)hydrogen

HNO3 - nitric acid

HCl - hydrochloric acid

Diprotic acids: two acidic (ionizable)hydrogens

H2SO4 - sulfuric acid

Triprotic acids: three acidic (ionizable)hydrogens

H3(PO4)phosphoric acid

H3(C6H5O7) citric acid

some properties of bases
Some Properties of Bases
  • Produce OH- ions in water
  • Taste bitter, chalky
  • Are electrolytes
  • Feel soapy, slippery
  • React with acids to form salts and water
  • pH greater than 7
  • Turns red litmus paper to blue “Basic Blue”
some common bases
Some Common Bases

NaOH sodium hydroxide lye

KOH potassium hydroxide liquid soap

Ba(OH)2 barium hydroxide stabilizer for plastics

Mg(OH)2 magnesium hydroxide Milk of magnesia

Al(OH)3 aluminum hydroxide Maalox (antacid)

acid base definitions
Acid/Base definitions

Definition #1: Arrhenius (traditional)

Acids – produce H+ ions (H3O+)HX  H+(aq) + X-(aq)

Bases– produce OH- ions

XOH -----> X+(aq) + OH-(aq)

(problem: some bases don’t have hydroxide ions!)


Arrhenius acid is a substance that produces H+ (H3O+) in water

Arrhenius base is a substance that produces OH- in water

But: some bases don’t have hydroxide ions!

Now what?????

acid base definitions1
Acid/Base Definitions

Definition #2: Brønsted – Lowry

Acids – proton donor

Bases – proton acceptor


A Brønsted-Lowry acid is a proton donor

A Brønsted-Lowry base is a proton acceptor





H+ + Base = Conjugate acid of Base+Acid = H+ + Conjugate base of Acid-

learning check
Learning Check!

Label the acid, base, conjugate acid, and conjugate base in each reaction:

HCl + OH-Cl- + H2O

H2O + H2SO4   HSO4- + H3O+

acids base definitions
Acids & Base Definitions

Definition #3 – Lewis Acids and Bases

Lewis acid – a substance that accepts an electron pair

Lewis base – a substance that donates an electron pair

lewis acids bases
Lewis Acids & Bases

Formation of hydronium ion is also an excellent example.

Electron pair of the new O-H bond originates on the Lewis base


Water molecules collide with one another:

self-ionization reaction 2H2O H3O+ + OH-

The reaction does not form very much H3O+ or OH-. 1 Liter water = ~55 moles of water molecules,

but only forms 1.0 x 10-7 moles of H3O+ and OH-

[H3O+] and [OH-] in pure water = 1.0 x 10-7 M.

It is the 7 in the exponent or power of this number that gives neutral water a pH of 7.

ionization constant of water
Ionization constant of water

Why isn’t water in the equilibrium constant Kw ?

Neutral solution: [H3O+] = [OH-] = [10-7]

pH = - log [H+]

pOH = - log [OH-]

Neutral solution: pH = pOH= 7

Acidic Solutions: [H+] > [OH-]

Basic Solutions (Alkaline): [OH-] > [H+] pH + pOH must always add up to 14

ph scale indicates strength of acid or base
pH Scale: indicates strength of acid or base

Example: If [H+] = 1 X 10-10pH = - log 1 X 10-10

pH = - (- 10)

pH = 10 basic

pOH = 4

Example: If [H+] = 1.8 X 10-5pH = - log 1.8 X 10-5

pH = - (- 4.74)

pH = 4.74 acidic

pOH = 9.26

try these
Try These!

Find the pH of these:

1) A 0.15 M solution of Hydrochloric acid

2) A 3.00 X 10-7 M solution of Nitric acid

3) A 0.15 M solution of sodium hydroxide

ph testing
pH testing
  • There are several ways to test pH
    • Blue litmus paper (red = acid)
    • Red litmus paper (blue = basic)
    • pH paper (multi-colored)
    • pH meter (7 is neutral, <7 acid, >7 base)
    • Universal indicator (multi-colored)
    • Indicators like phenolphthalein
    • Natural indicators like red cabbage, radishes
ph indicators
pH indicators
  • Indicators are dyes that can be added that will change color in the presence of an acid or base.
  • Some indicators only work in a specific range of pH

Buret with standardized solution

End point – Visual

Equivalence Point: Stoichiometric

The point at which neutralization is achieved (acid = base)

Unknown solution

Past End point

End point

strong acids vs weak acids
Strong Acids vs Weak Acids
  • An acid that nearly completely dissociates
  • All molecules of the acid break up to form the ions soluble in water
  • An acid that only slightly dissociates in a water solution
  • Only a small percent of acid molecules donate their hydrogen, and most remain the same.

A strong acid essentially ionizes 100%.

HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)

0.10 mol 0.10 mol 0.10 mol

After ionization: a few molecules;but many ions

Weak acids have much lower percent ionization.

CH3COOH(l) + H2O(l) H3O+(aq) + CH3COO-(aq)0.10 mol << 0.10 mol << 0.10 molmany molecules few ions

Only about 5% ionization at 25C

strong acids and bases
Strong Acids and Bases

Strong Acids Strong Bases

HClO4perchloric acid LiOHlithium hydroxide

HCl hydrochloric acid NaOHsodium hydroxide

HNO3 nitric acid KOH potassium hydroxide

H2SO4 sulfuric acid RbOHrubidium hydroxide

HBrhydrobromic acid CsOHcesium hydroxide

HI hydriodic acid Ca(OH)2calcium hydroxide

HClO3Chloric acid*Sr(OH)2strontium hydroxideBa(OH)2barium hydroxide

Not included in every list


Acids: Concentration vs. Strength



H+ A- H+ A- H+ A- H+ A-HA

A- H+ A- H+ A- H+ A- H+ A -

H+ A- HA H+ A- H+ A- H+ A-

A- H+ A- H+ A- H+ A- H+ A- H+

H+ A - H + A - H + A -HA H + A -

A- H+ A- H+ A- H+ A- H+ A–

H+ A- H+ A- H+ A- H+ A- H+

A- H+ A- H+ A- H+ A- H+ A-

HA A- H+ A- H+ A- H+ A- H+

H+ A - H+ A - HA

A - H+ A - H+ A –

H+ A - H+ A - H+

A - HA H+ A -

H+ A - H+ A - H+













H+ A - HA HA

HA HAH + A –

HA H + A – HA HA


  • All information and equations reference bases also.
strengths of conjugate acid base pairs
Strengths Of Conjugate Acid-Base Pairs
  • The stronger an acid, the weaker is its conjugate base.
  • The stronger a base, the weaker is its conjugate acid.
  • An acid-base reaction is favored in the direction from the stronger member to the weaker member of each conjugate acid-base pair.
for biological systems
For biological systems:
  • Ionization of a strong acid is TOO BIG!
  • Ionization of water itself is way TOO LITTLE!
  • Ionization of a weak acid is JUST RIGHT!
weak acids their conjugate bases and buffers
Weak acids, their conjugate bases, and buffers…
  • Weak acids have only a modest tendency to shed their protons (definition of an acid).
  • When they do, the corresponding negatively charged anion becomes a willing proton acceptor, and is called the conjugate base.
  • The properties of a buffer rely on a balance between a weak acid and its conjugate base.
  • And a titration curve looks like this…
  • A bufferis a solution of a weak acid and its conjugate base that resists changes in pH in both directions—either up or down.
  • A buffer works best in the middle of its range, where the amount of undissociated acid is about equal to the amount of the conjugate base.
  • One can soak up excess protons (acid), the other can soak up excess hydroxide (base).
pk a 4 76

pH 7








0 equiv. of NaOH 1.0


pKa = 4.76

Titration of acetic acid with sodium hydroxide

Buffering range: only small pH changes result from addition of base or acid

50% dissociation