Acids and Bases  Elmhurst College
Acids Neutralization & Salts Acid-Base Strength  Chemistry Department
Bases pH  Indicators  Virtual ChemBook

 

Neutralization Reaction - Acids + Bases

Romanian Translation by Alexander Ovsov

Introduction and Definitions:

A salt is any compound which can be derived from the neutralization of an acid and a base. The word "neutralization" is used because the acid and base properties of H+ and OH- are destroyed or neutralized. In the reaction, H+ and OH- combine to form HOH or H2O or water molecules. A neutralization is a type of double replacement reaction. A salt is the product of an acid-base reaction and is a much broader term then common table salt as shown in the first reaction.

The following are some examples of neutralization reactions to form salts.

a. HCl + NaOH --> NaCl + HOH

b. H2SO4 + 2 NH4OH --> (NH4)2SO4 + 2 HOH

c. 2 NaOH + H2CO3 --> N2CO3 + 2 NaOH

See the graphic on the left. Carbon dioxide in the breath reacts first with the water to form carbonic acid:

CO2 + H2O --> H2CO3

The carbonic acid then further reacts with the lime water in the neutralization reaction. The phenolphthalein is pink in the presence of base and turns colorless when all of the base has been neutralized and there is a slight excess of the carbonic acid.

d. Lime water: Ca(OH)2 + H2CO3 --> CaCO3 + 2 HOH

Practice:

HNO3 + KOH --> +
  H3PO4 + 3 NaOH -->   +  

The non-metal oxide gases react with water to produce acids (ammonia produces a base).

Example:
SO2 + HOH === H2SO3
2 NO2 + HOH === HNO2 + HNO3
Cl2 + HOH === HClO + HCl

SO3 + HOH-->
   NH3 + HOH -->  

 

In the home the corrosive gases are produced by smoking, aerosol oven cleaners, disinfectant sprays, window cleaners, etc. The improper mixing of a toilet bowl cleaner (HCl) or any acid with a chlorine-type bleach may produce fatal results from the generation of chlorine gas. The addition of ammonia to bleach also produces a poisonous gas, chloroamine.

 Health Effects of Acids and Bases:

Acids and bases are examples of corrosive poisons which react locally on tissue cells. Chemicals that are very basic or very acidic are reactive. These chemicals can cause severe burns. Automobile battery acid is an acidic chemical that is reactive. Automobile batteries contain a stronger form of some of the same acid that is in acid rain. Household drain cleaners often contain lye, a very alkaline chemical that is reactive.

Acids and bases are capable of causing severe "burns" similar to burns produced by heat. These materials act by first dehydrating cellular structures. Then proteins structures are destroyed by the action of acid or base which catalyzes the splitting of peptide bonds. Smaller and smaller fragments result, leading to the ultimate disintegration of the tissue.

The eyes and lungs are particularly sensitive to corrosive poisons. The cornea of the eyes is damaged by acid or base burns. Pulmonary edema (filling with water) occurs when highly concentrated corrosive pollutants (acute poisoning) reach the lungs. The lining of the nose, sinuses and lungs become irritated and water logged (by dehydration of cells). This occurs in an attempt to dilute the toxic agent. This waterlogged condition prevents the normal exchange of oxygen and carbon dioxide. The victim may die of immediate suffocation, a secondary attack of bacteria leading to pneumonia, or suffer permanent lung damage. Long term subchronic acid-base dosage effects are less well understood.

Air pollutants such as sulfur oxides, nitrogen oxides, chlorine, and ammonia all have corrosive effects on the respiratory tract. The solubility of the gases in water determines their fate. The most soluble gases, such as ammonia and sulfur oxides, are promptly adsorbed to the moist surfaces of the upper airways causing nasal and throat irritation. Less soluble gases, such as nitrogen oxides and chlorine, produce their effects in the depths of the lungs causing pulmonary edema, pneumonia, and emphysema (loss of elasticity and surface area).

 

The above graphic demonstrates the following reactions. The phenolphthalein is pink in the presence of a base and colorless after the citric acid neutralizes the base.

A bottle of drain cleaner contains lye (NaOH). First-Aid treatment is to give citrus juice (citric acid) or vinegar (acetic acid). Write reactions.


H3C6H8O6 + NaOH --> +
 HC2H3O2 + NaOH -->   +  

 

First-Aid Treatments Use Neutralization:

The interpretation of "Danger" and First-Aid labels on household cleaners provides an exercise in the use of acid-base principles.

Example:

A toilet bowl cleaner - Danger: Corrosive - produces chemical burns. Contains Hydrochloric Acid. Do not get in eyes, on skin. May be fatal if swallowed. Do not breath vapor or fumes. First-Aid: Internal - Call physician. Drink a teaspoon of magnesia, chalk, small pieces of soap, raw egg white, or milk. External - Eyes - Wash with water for 15 minutes. Skin - Wipe acid off gently, flood with water, cover with moist magnesia or baking soda.

Solution: The First-Aid consists of either diluting the acid, coating the stomach lining, or neutralizing it.

Mg(OH)2 + HCl --> MgCl2 + HOH
magnesia

The laboratory contains red bottles for acid burns which contain baking soda (NaHCO3). Write the neutralization reaction by applying the Bronsted definition.   
 HCl +  NaHCO3 -->  NaCl + H2CO3

Bronsted acids or bases, above?
 
H2CO3 continues to decompose to make bubbles of CO2.

Stomach Antacids:

Antacids are supposed to decrease the amount of hydrochloric acid in the stomach by reacting with excess acid. They are used in the treatment of gastric hyperacidity and peptic ulcers. Some of the ingredients in antacids are: Magnesia (MgO), milk of magnesia (Mg(OH)2, calcium carbonate (CaCO3), sodium bicarbonate (NaHCO3), dihydroxyaluminum sodium carbonate (NaAl(OH)2CO3), aluminum hydroxide gel (Al(OH)3). Several of these will habe top be recognized as Bronsted bases.