BASIC CONCEPTS of CHEMISTRY
Please revise: names of element, Periodic Table (understanding the notation), acid, base and salt nomenclature
1. Definitions of acid and base
There are several methods of defining acids and bases. While these definitions don't contradict each other, they do vary in how inclusive they are. Antoine Lavoisier, Humphry Davy, and Justus Liebig also made observations regarding acids and bases, but didn't formalize definitions.
Svante Arrhenius
acids produce H + ions in aqueous solutions , e.g.
HBr → H + + Br – HNO 2 → H + + NO 2 -
H 2 SO 4 → H + + HSO 4 - HSO 4 - ↔ H + + SO 4 2-
bases produce OH - ions in aqueous solutions, e.g.
KOH → K + + OH -
Mg(OH) 2 → Mg(OH) + + OH - Mg(OH) + ↔ Mg 2+ + OH - Zn(OH) 2 ↓ ↔ Zn(OH) + + OH - Zn(OH) + ↔ Zn 2+ + OH -
o water required, so only allows for aqueous solutions
o only protic acids are allowed; required to produce hydrogen ions
o only hydroxide bases are allowed
Johannes Nicolaus Brønsted - Thomas Martin Lowry
acids are proton donors
bases are proton acceptors Examples:
acid 1 base 2 base 1 acid 2 HBr + H 2 O ↔ Br - + H 3 O + HCl + NH 3 ↔ Cl - + NH 4 +
H 2 O + NH 3 ↔ OH - + NH 4 +
NH 4 + + H 2 O ↔ NH 3 + H 3 O + H 2 O + CN - ↔ OH - + HCN
o queous solutions are permissible
o bases besides hydroxides are permissible
o only protic acids are allowed
Gilbert Newton Lewis (last restrictive of acid-base definition)
acids are electron pair acceptors
bases are electron pair donors Examples:
acid base
H 3 O + + NH 3 ↔ H 2 O + NH 4 +
AlCl 3 + Cl - ↔ AlCl 4 -
Al 3+ + H 2 O ↔ Al(H 2 O) 6 3+
BCl 3 + NH 3 ↔ BCl 3 NH 3
Properties of Acids
taste sour (don't taste them!)... the word 'acid' comes from the Latin acere, which means 'sour'
acids change litmus (a blue vegetable dye) from blue to red
their aqueous (water) solutions conduct electric current (are electrolytes)
react with bases to form salts and water
evolve hydrogen gas (H 2 ) upon reaction with an active metal (such as alkali metals, alkaline earth metals, zinc, aluminum)
Properties of Bases
taste bitter (don't taste them!)
feel slippery or soapy (don't arbitrarily touch them!)
bases don't change the color of litmus; they can turn red (acidified) litmus back to blue
their aqueous (water) solutions conduct and electric current (are electrolytes)
react with acids to form salts and water Question:
Which of them are acids or bases: NH 4 +
, OH - , CN - , ClO 4 -
, HCl, HCN, NH 3 ·H 2 O , BF 3 , Cl - , Fe 3+ , SO 3 , H 2 O, H 3 O + , NH 4 + , NH 2 - , FeCl 3 , Ag + , H 2 PO 4 - , S 2- , Cu 2+ , F - , NH 3 , CoCl 2 ?
2. Formulas of common acids and bases
Here are the names and formulas of some of the common acids and bases.
Binary Acids:
A binary compound consists of two elements. Binary acids have the prefix hydro in front of the full name of the nonmetallic element. They have the ending -ic. Examples include hydrochloric and hydrofluoric acid.
Hydrofluoric Acid - HF Hydrochloric Acid - HCl Hydrobromic Acid - HBr Hydroiodic Acid - HI Hydrosulfuric Acid - H 2 S
Ternary Acids:
Ternary acids commonly contain hydrogen, a nonmetal, and oxygen. The name of the most common form of the acid consists of the nonmetal root name with the -ic ending, The acid containing one less oxygen atom than the most common form is designated by the -ous ending. An acid containing one less oxygen atom than the -ous acid has the prefix hypo- and the -ous ending. The acid containing one more oxygen than the most common acid has the per- prefix and the -ic ending.
Nitric Acid - HNO 3
Nitrous Acid - HNO 2
Hypochlorous Acid - HClO Chlorous Acid - HClO 2 Chloric Acid - HClO 3
Perchloric Acid - HClO 4
Sulfuric Acid - H 2 SO 4 Sulfurous Acid - H 2 SO 3
Phosphoric Acid - H 3 PO 4
Phosphorous Acid - H 3 PO 3 Carbonic Acid - H 2 CO 3
Acetic Acid - HC 2 H 3 O 2
Oxalic Acid - H 2 C 2 O 4 Boric Acid - H 3 BO 3
Silicic Acid - H 2 SiO 3
Bases:
Sodium Hydroxide - NaOH Potassium Hydroxide - KOH
Ammonium Hydroxide - NH 3 ·H 2 O (NH 4 OH) Calcium Hydroxide - Ca(OH) 2
Magnesium Hydroxide - Mg(OH) 2
Barium Hydroxide - Ba(OH) 2 Aluminum Hydroxide - Al(OH) 3
Ferrous Hydroxide or Iron (II) Hydroxide - Fe(OH) 2
Ferric Hydroxide or Iron (III) Hydroxide - Fe(OH) 3 Zinc Hydroxide - Zn(OH) 2
Lithium Hydroxide – LiOH
3. Strength of acids and bases
Strong electrolytes are completely dissociated into ions in water. The acid or base molecule does not exist in aqueous solution, only ions. Weak electrolytes are incompletely dissociated.
Strong acids
Strong acids completely dissociate in water, forming H+ and an anion, e.g. HCl + H 2 O → H 3 O + + Cl -
Since it is a strong acid it dissociates completely, you will not have any HCl. In solution we have H 3 O + and Cl - ions which concentration is equal HCl concentration.
There are six strong acids. The others are considered to be weak acids. You should commit the strong acids to memory:
HCl - hydrochloric acid
HNO 3 - nitric acid
H 2 SO 4 - sulfuric acid
HBr - hydrobromic acid
HI - hydroiodic acid
HClO 4 - perchloric acid
100% dissociation isn't true as solutions become more concentrated. If the acid is 100%
dissociated in solutions of 1.0 M or less, it is called strong. Sulfuric acid is considered strong only in its first dissociation step.
H 2 SO 4 → H + + HSO 4 -
What Is the Strongest Acid?
None of the strong acids traditionally listed in a chemistry text holds the title of World's Strongest Acid. The record-holder used to be fluorosulfuric acid (HFSO 3 ), but the carborane superacids H(CHB11Cl11) are hundreds of times stronger than fluorosulfuric acid and over a million times stronger than concentrated sulfuric acid. The superacids readily release protons, which is a slightly different criterion for acid strength than the ability to dissociate to release a H + ion (a proton). The carborane acids are incredible proton donors, yet they are not highly corrosive. Corrosiveness is related to the negatively-charged part of the acid. Hydrofluoric acid (HF), for example, is so corrosve it dissolves glass. The fluoride ion attacks the silicon atom in silica glass while the proton is interacting with oxygen. Even though it is highly corrosive, hydrofluoric acid is not considered to be a strong acid because it does not completely dissociate in water.
Weak acids
A weak acid only partially dissociates in water to give H + and the anion. Examples of weak acids include hydrofluoric acid, HF, and acetic acid, CH 3 COOH.
e.g. HF + H 2 O ↔ H 3 O + + F -
In solution molecules HF and H 3 O + and F - ions are in equilibrium with each other. We have to use the equilibrium expression to determine what concentration each species is at when the system is at equilibrium. The equilibrium expression is following:
Weak acids include:
Molecules that contain an ionizable proton. A molecule with a formula starting with H usually is an acid.
Organic acids containing one or more carboxyl group, -COOH. The H is ionizable.
Anions with an ionizable proton. (e.g., HSO 4 -
→ H + + SO 4 2-
)
Cations
o transition metal cations
o heavy metal cations with high charge
o