Acids bases

Acids and bases
For thousands of years people have known that vinegar, lemon juice and many other foods taste sour. However, it was only a few hundred years ago when it was discovered that these things taste sour - because they are all acids.
In the seventeenth century, the English writer and amateur chemist Robert Boyle first labeled substances as either acids or bases (he called bases alkalis) according to the following characteristics:
• Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases.
• Bases feel slippery, change litmus blue, and become less basic when mixed with acids.
According to Brønsted-Lowry definition of acid is any substance that can donate a hydrogen ion, and the base is defined as any substance that can accept a hydrogen ion. In essence, a base is the opposite of an acid.
(Under the Brønsted definition, acids are often referred to as proton donors because an H+ ion - hydrogen minus its electron - is simply a proton)
For example, hydrochloric acid (HCl) dissolves in water and releases hydrogen ions as follows:
HCl H+(aq) + Cl-(aq)
Similarly H2SO4 (sulfuric acid), HNO3 (nitric acid), HBr are acids as they dissociate in water to give H+ ion.
Conversely the compounds like sodium hydroxide (NaOH) , baking soda or sodium bicarbonate (NaHCO3) are bases because they take off the H+ ions from solution. For example:
H Cl + Na OH Na Cl + H2O
H Cl + Na HCO3 Na Cl + H2 CO3
Properties of acids
Taste : All dilute acid taste sour. The sour taste of lemon juice or unripe fruits and sour milk comes from acid. Lemon juice contains citric acids whereas vinegar contains dilute acetic acid.
Action on litmus: Acids turn litmus blue. However weak acids like carbonic acid can only turn litmus to dark purplish red.
Corrosive action: Strong acids like sulfuric acid and nitric acid, are highly corrosive and causes burning effect on skin.
Action with metals: Metals react with dilute sulfuric acid or hydrochloric acid to liberate hydrogen gas.
Na + H Cl Na Cl + H2
Action with carbonates: Almost all acids liberate carbon dioxide from a carbonate
Ca CO3 + H2 SO4 Ca SO4 + CO2 + H2 O



pH scale of acidity
The Acids increases the concentration of H+ ion where as a base decreases concentration of H+ ion in a solution. The acidity or basicity of something therefore can be measured by its hydrogen ion concentration.
The pH scale of acidity is described by the formula:
pH = -log [H+]
Here [H+] = hydrogen ion concentration measured in moles of H+ per liter of solution.
For example, a solution with [H+] = 1 x 10-7 moles/liter has a pH equal to 7 (a simpler way to think about pH is that it equals the exponent on the H+ concentration, ignoring the minus sign)
The pH scale ranges from 0 to 14. Substances with a pH between 0 and less than 7 are acids (pH and [H+] are inversely related - lower pH means higher [H+] and a stronger acid). Substances with a pH greater than 7 and up to 14 are bases (the higher the pH, the stronger the base). Right in the middle, at pH = 7, are neutral substances, for example, pure water.
The relationship between [H+] and pH is shown in the table below alongside some common examples of acids and bases in everyday life.



Strong and Weak Acids and Bases
Many hardware stores sell "muriatic acid" a 6 M solution of hydrochloric acid HCl(aq)to clean bricks and concrete. Grocery stores sell vinegar, which is a 1 M solution of acetic acid: CH3CO2H. Although both substances are acids, you wouldn't use muriatic acid in salad dressing, and vinegar is ineffective in cleaning bricks or concrete.
The difference between the two is that muriatic acid is a strong acid and vinegar is a weak acid. Muriatic acid is strong because it is very good at transferring an H+ ion to a water molecule. In a 6 M solution of hydrochloric acid, 99.996% of the HCl molecules react with water to form H3O+ and Cl- ions.
HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
Vinegar is a weak acid because it is not very good at transferring H+ ions to water. In a 1 M solution, less than 0.4% of the CH3CO2H molecules react with water to form H3O+ and CH3CO2- ions.
CH3CO2H(aq) + H2O(l) H3O+(aq) + CH3CO2-(aq)
More than 99.6% of the acetic acid molecules remain intact.
Alkalis
A basic hydroxide that is soluble in water is called alkali. Sodium hydroxide (Na OH), potassium oxide (K OH), calcium hydroxide (Ca (OH)2)
These are bitter in taste and turn red litmus blue. NaOH and KOH have strong corrosive action on skin.
Neutralization
Neutralization is reaction between acid and base in which the end products are water molecule and salt.
H Cl + Na OH Na Cl + H2O
H2 SO4 + Ca (OH)2 Ca SO4 + H2O
Salt
A salt consists of an aggregate of metallic ions and acidic ions. A salt is derived from an acid to which it corresponds by replacing the H+ ion of the acid by an equivalent number of metal ions.
Acid Salt
H+ Cl- Na+ Cl-
(H-)2 SO42- Cu2+ SO42-
Acid salt
If the negative ion of the salt is further capable of further ionization to yield H+ ion then the salt is called acid salt. But if not than it is a normal salt

Acid salt Normal salt
Sodium hydrogen sulfate
Sodium sulfate

Sodium hydrogen carbonate
Sodium carbonate