H O N O R S C H E M I S T RY – S E M E S T E R 2

Acids & Bases

Name Some Acids

Name some familiar acids. Where are they found?

Acetic acid (vinegar)

Hydrochloric acid (in your stomach, pools)

Citric acid (citrus fruits)

Ascorbic acid (Vitamin C)

Sulfuric acid (car batteries, acid rain)

Carbonic acid (carbonated sodas)

Acids give tart, sour, tangy taste (e.g., vinegar, lemon)

Acids

Are electrolytes

Example: HCl dissolving in water

HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)

Forms hydronium (H3O+) when dissolved in H2O

H3O+ able to transfer charge quicker than other ions

React with metals above hydrogen in the activity series

Produce hydrogen gas (H2)

Example: HCl(aq) + Zn(s) → H2(g) + ZnCl2(aq)

Resistant to acids!

Acidity in Aqueous Solutions

Aqueous solutions with large number of H3O+ =

acidic

Acid Classification

Strong acids = dissociate completely in solvent

Example: HNO3 (nitric acid)

HNO3(l) + H2O(l) → H3O+(aq) + NO3

-(aq)

Weak acids = release only few H+ in aqueous

solution

Example: HOCl (hypochlorous acid)

HOCl(l) + H2O(l) ↔ H3O+(aq) + ClO-(aq)

Strong vs. Weak Acids

Bases

Are electrolytes

Form hydroxide (OH-) when

dissolved in H2O

Range from very soluble to

nearly insoluble

Form basic (alkaline) solutions

Examples: Baking soda, ammonia, lye, carbonates and

phosphates

Ammonia fertilizer

Alkaline Solutions

Are slippery to the touch

React with oils in our skin

convert oils to soap

used in cleaning agents

Base Classification

Strong base = dissociates completely in a solvent

Example: NaOH(s) → Na+(aq) + OH-(aq)

Weak base = releases few OH- in aqueous solutions

Example: NH3(aq) + H2O(l) ↔ NH4+(aq) + OH-(aq)

majority of NH3 remains un-ionized!

Arrhenius Classification

Swedish scientist, Svante Arrhenius

Acids, dissolved in water, increase concentration

of hydrogen ions (H+)

Bases, dissolved in water, increase concentration

of hydroxide ions (OH-)

© 2012 Pearson Education, Inc.

Brønsted-Lowry Classification

Johannes Brønsted (Danish), Thomas Lowry

(British) independently defined ‘acid’ in 1923

Brønsted Lowry

Brønsted-Lowry acid

= substance that donates a proton (hydrogen nucleus) to

another substance

Example: HCl + H2O → H3O+ + Cl-

Brønsted-Lowry Classification

Brønsted-Lowry base

= substance that accepts a proton (= hydrogen atom)

Example: NH3 + H2O → NH4+ + OH-

Brønsted-Lowry Classification

Conjugate Acids & Bases

Per Brønsted-Lowry:

Lose a proton = acid

Accept a proton = base

“conjugate” from Latin “conjugare” (to join together)

Acid / base reactions yield conjugate bases and acids

Conjugate acid = forms when base gains a proton

Conjugate base = forms when acid loses a proton

Conjugate Acids & Bases

Strong acid conjugate base is extremely weak

Weak acid conjugate base is weak base

Strong base conjugate acid is extremely weak

Conjugate Acid-Base Pairs

Amphoteric Species

Amphoteric = substance with properties of both

acid AND base

Self-ionization of water