Acids and Bases
Acids
Those substances which turn blue litmus solution red are called acids. The term ‘acid’ has been derived from the Latin word ‘acidus’ which means sour.
Example: HCl, H2SO4 , HNO 3 etc
Properties of acids
- Acids have a sour taste
- Acids turn blue litmus to red.
- It conducts electricity.
- They produce H+ ions when mixed with water.
- Acids lose their acidity when mixed with a base.
- The reaction of acid and metal to form salt and hydrogen gas (H).
Zn + H2SO4 ———> ZnSO4 + H2
(V) The reaction of acids with metal carbonates or metals hydrogen-carbonates to form a salt, carbon dioxide and water.
Na2CO 3 + 2HCl ———> 2NaCl + CO2 + H2O
NaHCO3 + HCl ———> NaCl + CO2 + H2O
(VI) Acids react with bases to form salt and water.
Na OH + HCl ———> Na Cl + H 2 O
(VII) Acids react with metal oxides to form salt and water.
Cu O + 2 HCl ———> Cu Cl 2 + H 2 O
Organic acids
The acids present in plant materials are called organic acids. Organic acids are naturally occurring acids. It is not harmful to eat and drink substances containing naturally occurring acids in them.
Example: Acetic acid, Citric acid, Lactic acid etc.
- Acetic acid is found in vinegar.
- Lactic acid is found in sour milk or curd.
- Butyric acid present in butter.
- Citric acid is present in lemons and oranges.
- Oxalic acid present in tomatoes.
Mineral acids
The acids prepared from the minerals of the earth are called minerals acids. The mineral acids are man-made acids.
Example: Hydrochloric acid, Sulphuric acid and Nitric acid.
Hydrochloric acids
It is also called muriatic acid.
- It is found in the stomach.
- The chemical formula of hydrochloric acid is HCl.
- pH value of HCl is 0.
- It activates the enzyme.
- Before galvanization, iron is washed in HCl.
- It is used as a bathroom cleaner.
- It is used as an Aqua-Regia solution. Aqua Regia is also called Royal acids. Colour of aqua regia is yellowish-orange.
- It is used in leather cleaning.
Sulphuric acids
It is also called the king of acids/ king of chemical/ oil of vitriol.
- It is called battery acid because it is used in the battery.
- pH value of Sulphuric acid is 1.
- It is present in Acid rain.
- It is used in the fire extinguisher.
Nitric acid
It is used to make Aqua-Regia Solution. It is used to make explosives.
Example of explosives: RDX, TNT and Gun powder.
RDX: Abbreviation of RDX is Research development explosives or Royal Demolition explosive.
- The chemical name of RDX is cyclotrinitro methyl trinitro Amine.
- RDX is discovered by Fredrick Henning.
- The chemical formula of RDX is C 3 H 6 O 6 N 6.
TNT: Abbreviation of TNT is Trinitrotoluene.
- TNT is discovered by Joseph Wilbrand in 1863.
- The chemical formula of TNT is C 7 H 5 O 6 N 3.
Gun Powder: Gun powder is discovered by Rojjer Baken. It is the mixture of nitric acid, potassium nitrate, sulphur and charcoal.
Types of Acids
Strong acids
An acid which is completely ionized in water and thus produces a large amount of hydrogen ions is called a strong acid. All the mineral acids are strong acids.
Ex: HCl, H 2 SO 4, and H NO 3.
Weak acids
An acid which is partially ionized in water and thus produces a small amount of hydrogen ions is known as a weak acid. The organic acids are weak acids.
Ex: Acetic acid, formic acid, citric acid, tartaric acid, citric
Concentrated acids: It is one which contains the minimum possible amount of water in it.
Dilute acids: It is one which contains much more water in it.
Diluting acids: The dilution of a concentrated acid should always be done by adding concentrated acid to water gradually with stirring and not by adding water to concentrated acid.
Acids have corrosive nature
Some acids are highly corrosive in nature which means that they corrode or rust metals. Acids are never stored in metal containers because they gradually corrode & eat up the metal containers.
Ex: If concentrated sulphuric acid falls accidentally on skin, clothes or wood, it causes severe burns on the skin; it cuts holes in the clothes and burns the wood producing black spots on its surface.
What do all acids have in common?
An acid is a substance which dissociates on dissolving in water to produce hydrogen ions.
HCl ───── H+ + Cl–
H NO 3 ───── H+ + N O 3–
Bases
It is a chemical substance which can neutralize an acid. Bases are substances that, in aqueous solution, release hydroxide ions.
Example: Na OH, K OH, Mg(OH)2, NH 4 OH etc.
Properties of bases
- Bases have a bitter taste & soapy to touch.
- Bases conduct electricity in solution.
- All metal oxides and metal hydroxides are bases.
- A base soluble in water is known as an alkali.
- All the bases change the colour of red litmus to blue.
- Bases react with some metals to form hydrogen gas (H).
2NaOH + Zn ───── Na2ZnO 2 + H 2
- Bases react with acids to form salt and water (H2O).
2NaOH + H2SO 4 ───── Na2SO4 + 2H2O
- Bases react with non-metal oxides to form salt and water (H2O).
Ca(OH)2 + CO2 ───── CaCO 3 + H2O
Types of Bases
Strong Bases
A weak base is one that only partially dissociates to give ions in solution.
Ex: Na OH, K OH etc.
Weak Bases
A strong base is one that fully dissociates to give ions in solutions.
Ex: NH 4 OH, Ca(OH)2 etc.
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