Common Acids and Their Structures

Common Acids

• Nitric acid (HNO3) is a strong acid used as an explosive, fertilizer, dye, and in glue.
• Sulfuric acid (H2SO4) is a strong acid, used as an explosive, fertilizer, dye, in glue, and in batteries.
• Hydrochloric acid (HCl) is a strong acid used for metal cleaning, food preparation, ore refining, and as stomach acid.
• Phosphoric acid (H3PO4) is a moderate strength acid, and is used as fertilizer, in plastics and rubber, and for food preservation.
• Acetic acid (HC2H3O2) is a weak acid used in plastics, rubber, food preservation, and vinegar.
• Hydrofluoric acid (HF) is a weak acid used for metal cleaning and glass etching.
• Carbonic acid (H2CO3) is a weak acid found in soda water.
• Boric acid (H3BO3) is a weak acid used as an eyewash.

Structures of Acids

• Binary acids have acid hydrogens attached to a nonmetal atom; examples include HCl and HF.
• Oxyacids have acid hydrogens attached to an oxygen atom; examples include H2SO4 and HNO3.
• Carboxylic acids are derived from living organisms; examples include citric acid in lemons and limes, and malic acid in apples, grapes, and wine.

Properties of Acids

• Acids have a sour taste.
• Acids can dissolve many metals.
• Acids turn blue litmus paper red due to a dye that turns red in acidic conditions.

Strong Acids

• Common strong acids include hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI), nitric acid (HNO3), perchloric acid (HClO4), and sulfuric acid (H2SO4).

Common Bases

• Sodium hydroxide (NaOH), also known as lye or caustic soda, is a strong base used in soap, plastics, and petrol refining.
• Potassium hydroxide (KOH), also known as caustic potash, is a strong base used in soap, cotton processing, and electroplating.
• Calcium hydroxide (Ca(OH)2), or slaked lime, is a strong base used in cement.
• Sodium bicarbonate (NaHCO3), or baking soda, is a weak base used in cooking and as an antacid.
• Magnesium hydroxide (Mg(OH)2), or milk of magnesia, is a weak base used as an antacid.
• Ammonium hydroxide (NH4OH or {NH3(aq)}), or ammonia water, is a weak base used in detergents, fertilizers, explosives, and for processing fibers.

Properties of Bases

• Bases have a bitter taste.
• Bases have a slippery feel.
• Many household cleaning solutions, like ammonia, are basic and have that slippery feel.
• Bases turn red litmus paper blue.
• Caffeine is a base and is enjoyed for its bitterness, although it is usually acquired over time.

Strong Bases

• Strong bases include lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2 ), strontium hydroxide (Sr(OH)2 ), and barium hydroxide (Ba(OH)2 ).

Acid-Base Theories

• Svante Arrhenius, a Swedish chemist, proposed in the 1880s that an acid produces H+ ions in aqueous solution, and a base produces OH- ions in aqueous solution.
• The Brønsted-Lowry theory focuses on the transfer of H+ ions in an acid-base reaction, where acids are proton donors and bases are proton acceptors.

Arrhenius Definition for Acid and Base

• Acids produce H+ ions in aqueous solution.
• HCl ionizes in water, producing H+ and Cl- ions.
• Bases produces OH- ions in aqueous solution.
• NaOH dissociates in water, producing Na+ and OH- ions.

Arrhenius Acid and the Hydronium Ion

• The H+ ions are highly reactive and do not exist freely in water; they bond to water molecules as H3O+, which is known as the hydronium ion.

Arrhenius Acid: Molecular and Structural Formulas

• Formic acid's molecular formula is HCHO2.
• Formic acid's structural formula indicates how the atoms are bonded.
• Molecular formulas indicates the number of each type of atom.

Acid Strength

• Strong acids have very weak conjugate bases.
• Weak acids have very strong conjuate bases.

Autoionization of Water

• Water is amphoteric; it can act as either an acid or a base.
• The autoionization: H2O (l)+ H2O (l) -> H3O+ + OH-

Arrhenius Definition and Neutralization

• Acids and bases combine to form water, neutralizing each other.
• Net ionic equation for neutralization reactions: H+ (aq) + OH¯(aq) → H2O (1)

Brønsted-Lowry Definition

• Substances act as bases even though they do not contain OH¯.
• Nonaqueous solvents can not be applied in the Arrhenius definition.
• Acids are proton donors.
• Bases are proton acceptors.

Brønsted-Lowry Acid-Base Reactions

• HCl (aq) + H2O (l) → H3O+ (aq) + Cl− (aq): HCl is the proton donor (acid), and H2O is the proton acceptor (base).
• NH3 (aq) + H2O (l) ⇆ NH4+ (aq) + OH− (aq): H2O is the acid, and NH3 is the base.
• Substances that can act as acids or bases are amphoteric.

Conjugate Acid-Base Pairs

• NH3 and NH4+ are a conjugate acid–base pair related by the transfer of a proton.
• Any two substances related by the transfer of a proton can be considered a conjugate acid–base pair.
• A base accepts a proton and becomes a conjugate acid.
• An acid donates a proton and becomes a conjugate base.

Reactions of Acids and Bases

• When an acid and a base are mixed, the H⁺ from the acid combines with the OH⁻ from the base to form H2O.
• HCl (aq) + KOH (aq) → H2O (l) + KCl (aq): An acid and a base will form water and salt.
• Acid-base reactions generally form water and a salt.
• Carbonates or bicarbonates with acids produces water, gaseous carbon dioxide, and a salt.
• Reactions involving carbonates or bicarbonates are known as gas evolution reactions.
• HI(aq) + NaOH(aq) → H2O(l) + NaI(aq): The first step to balancing this is to identify the acid and base and write the skeletal equation for the production of water and a salt. If the equation is balanced that is the end.

Reactions with Acids

• Metals with acids produces hydrogen gas and a dissolved salt with the metal ion.
• Metal(s) + Acid(aq) → H2(g) + salt(aq) is the general equation.
• Some metals do not readily react with acids.
• Acids with metal oxides produces water and a dissolved salt.
• 2 HCl (aq) + K2O (s) → H2O (l) + 2 KCl (aq): Hydrochloric acid reacts with potassium oxide and produces water and potassium chloride.

Reactions of Bases

• Sodium hydroxide with aluminum and water are one type of base reactions: 2 NaOH (aq) + 2 Al (s) + 6 H2O (l) → 2 NaAl (OH)4 (aq) + 3 H2 (g)
• Aluminum is one of the few metals that dissolves in a base.

Acid-Base Titration

• Acid–base titration is a laboratory procedure used to determine the concentration of an acid or a base.
• Solution stoichiometry is applied to a common laboratory procedure called a titration.
• In a titration, the known concentration of a substance in a solution is reacted with the unknown concentration.
• HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq): Is an acid-base reaction between hydrochloric acid and sodium hydroxide.

Strong Acids

• Hydrochloric acid (HCl) and hydrofluoric acid (HF) appear to be similar, but there is an important difference between these two acids.
• HCl is an example of a strong acid, one that completely ionizes in solution.
• HF is a weak acid, one that does not completely ionize in solution.
• Strong acids are strong electrolytes, so they can conduct electricity.

Weak Acids

• When HF dissolves in water, only a fraction of the dissolved molecules ionize into H3O+ and F¯ ions. The solution contains many intact HF molecules.
• Weak acids are weak electrolytes, so they conduct only dimly.

Weak Bases

• Weak bases contain OH− and dissociate in water, the most common weak bases produce OH− by accepting a proton from water, causing the water to form OH− ions.
• B(aq) + H2O(l) ⇆ BH+ (aq) + OH− (aq) Is the generic equation.
• B is generic for a weak base.

A Weak Base

• When NH3 dissolves in water, it partially ionizes to form NH4+ and OH−. This causes only a fraction of the molecules ionize, while most molecules remain as NH3.

Weak Bases Table

• Ammonia (NH3): NH3 (aq) + H2O (l) ⇆ NH4+ (aq) + OH− (aq)
• Pyridine (C5H5N): C5H5N (aq) + H2O (l) ⇆ C5H5NH+ (aq) + OH− (aq)
• Methylamine (CH3NH2): CH3NH2 (aq) + H2O (l) ⇆ CH3NH3+ (aq) + OH− (aq)
• Ethylamine (C2H5NH2): C2H5NH2 (aq) + H2O (l) ⇆ C2H5NH3+ (aq) + OH− (aq)
• Bicarbonate ion (HCO3−): HCO3− (aq) + H2O (l) ⇆ H2CO3 (aq) + OH− (aq)
• The bicarbonate ion must occur with a positively charged ion such as Na+ that serves to balance the charge but does not have any part in the ionization reaction.

Self-Ionization of Water

• This happens as a product of water being amphoteric.
• Even in pure water, water acts as an acid and a base with itself, a process called self-ionization.

Summarizing PH Levels at 25 degrees Celsius

• In a neutral solution, [H3O+ ] = [OH− ] = 1.0  10 −7 M
• In an acidic solution, [H3O+ ] > 1.0  10 −7 M [OH− ] < 1.0  10 −7 M
• In a basic solution, [H3O+ ] < 1.0  10 −7 M [OH− ] > 1.0  10 −7 M
• In all aqueous solutions, [H3O+ ][OH− ] = 1.0  10 −14

The pH Scale

• Chemists have devised a scale, called the pH scale, based on hydrogen ion concentration to express the acidity or basicity of solutions.
• At 25 °C according to the pH scale, a solution:
  • pH < 7 is an acidic solution
  • pH > 7 is a basic solution
  • pH = 7 is a neutral solution
• A decrease of 1 unit on the pH scale corresponds to an increase in H3O+ concentration by a factor of 10.

Buffers

• Buffers contain significant amounts of both a weak acid and its conjugate base.
• The weak acid neutralizes added base.
• The conjugate base neutralizes added acid.

Human Blood pH

• In healthy individuals, blood pH is between 7.36 and 7.40.
• If blood pH were to drop below 7.0 or rise above 7.8, death would result.

pH Buffer Reaction System

• In the acetic acid sodium acetate buffer system, with added base, acetic acid reacts: NaOH (aq) + HC2H3O2 (aq) → H2O (l) + NaC2H3O2 (aq)
• In the acetic acid sodium acetate buffer system, with added acid, acetate ion reacts: HCl (aq) + NaC2H3O2 (aq) → HC2H3O2 (aq) + NaCl (aq)
• A buffer contains significant amounts of a weak acid and its conjugate base. Because of this the acid consumes any added base, and the base consumes any added acid.

Alkaloids

• Alkaloids are organic bases that occur naturally in many plants and often have medicinal qualities.
• Morphine, for example, is a powerful alkaloid drug that occurs in the opium poppy and is used to relieve severe pain. It is a narcotic, meaning it, dulls the senses and induces sleep and is also highly addictive.
• Amphetamine is another powerful drug related to the alkaloid ephedrine.
• Amphetamine enhances nerve signal transmissions. It is often used to treat attention-deficit disorder and is prescribed under the trade name Adderall. However, it is misused as a stimulant.
• Caffeine and nicotine are other common alkaloids.

The Danger of Antifreeze

• Most kinds of antifreeze used in cars are solutions of ethylene glycol. Every year, thousands of dogs and cats die from ethylene glycol poisoning because they consume improperly stored antifreeze or leaked antifreeze.
• Ethylene glycol has a somewhat sweet taste, which attracts a curious dog or cat and puts yound children at risk.
• Ethylene glycol is metabolized in the liver into glycolic acid, which enters the bloodstream
• The glycolic acid overwhelms the blood’s natural buffering system, causing blood pH to drop to dangerously low levels.
• At this point, the poisoned animal may begin hyperventilating in an effort to overcome the acidic blood’s reduced ability to carry oxygen.
• If no treatment is administered, the animal will eventually go into a coma and die.

Review of Acids and Bases

• Acids have a sour taste, dissolve metals, and turn blue litmus red.
• Bases have a bitter taste, a slippery feel, and turn red litmus blue.
• Arrhenius Definitions: Acids produce H+ in solution and Bases produce OH− in solution.
• Br∅nsted–Lowry Definitions: Acids donate a proton and Bases accept a proton.