ACIDS, BASES AND SALTS

Chemical compounds can be broadly classified into three categories Acids,Bases and Salts.

ACIDS

The word acid is derived from a Latin word 'acere' or 'acidus' meaning'sour'.

All acids have one property in common that is they all are sour in taste.

Most people think that acids are fuming corrosive dangerous liquids. However all acids are not like this.e.g.vinegar contains acetic acid and it is used to preserve the food.(pickles).

Classification of acids 

 

ORGANIC ACIDS: The acids produced by the plants and animals are known as organic acids. Eg.acetic acid, oxalic acid, tannic acid etc.

MINERAL ACIDS: These are prepared in laboratories and are corrosive in nature. Eg. Hydrochloric acid, Sulphuric acid and Nitric acid.

PROPERTIES OF ACIDS

1. They have a sour taste.

2. They are corrosive in nature. Most acids especially the strong ones can burn our skin and react with many materials are corrosive liquids and also destroy paper and clothes.

3. They turn blue litmus paper  to red and methyl orange indicator to pink.

4. They are good conductors of electricity,as they allow the passage of electric current through them .

BASICITY OF ACIDS:The number of hydrogen ions (H+) furnished by one molecule of an acid on dissolving in water, is called BASICITY of acid. Eg. One molecule of hydrochloric acid,HCl furnishes one hydrogen ion,therefore ,it's basicity is 1. So hydrochloric acid is a monobasic acid.

One molecule of sulphuric acid ,H2SO4 furnishes two hydrogen ions,therefore it's basicity is 2.  Hence it is a dibasic acid.

USES OF ACIDS

1. Hydrochloric acid , Sulphuric acid and Nitric acid are important reagents used in laboratory.

2. They are used in the manufacture of fertilizers.

3. They are used in the manufacture of paper, dyes, artificial silks ,rayon, drugs,etc..

4. Nitric acid is used in the manufacture of explosives such as TNT(trinitrotoluene).

5. Nitric acid is used in the purification of metals such as gold and silver.

6. Sulphuric acid is used in car batteries.

7. Acetic acid is used as a table acid (vinegar).

8. Carbonic acid is commonly called plain soda . When it is mixed with citric acid and sugar it is used  for making soft drinks.

BASES

Bases are the substances that are bitter to taste and feel soapy or slippery to the skin. They react with acids to form salt and water. They are usually metallic oxides or hydroxides. The name of all bases starts with the name of a metal and ends with the oxide or hydroxide.

All bases are not soluble in water. Those that are soluble are called Alkalis eg. Sodium hydroxide, potassium hydroxide are Alkalis and used in laboratories. Most other metal oxides and hydroxides are insoluble in water . They are bases but not Alkalis. Thus all Alkalis are bases,but all bases are not Alkalis.

ACIDITY OF BASES: The number of hydroxyl ions (OH-) furnished by one molecule of a base on dissolving in water is called acidity of base.

PROPERTIES OF BASES/ALKALIS

1. They are bitter in taste and feel slippery.

2. All bases turn red litmus paper to blue.

3. They turn phenolphthalein to pink and methyl orange to yellow.

4. They react with acids to give salt and water. Hence they are known as antacids.

Note: ANTACIDS, a type of medicine that controls the acid levels in the stomach for controlling acidity.

USES OF BASES.

1.Alkalis  are used in the manufacture of soap from vegetable oils.

2. Calcium oxide and calcium hydroxide are used for neutralisation of acids in soil.

3. They are used in making of mortar fir building and construction purposes.

4. Calcium hydroxide is used for preparing bleaching powder.

5. Magnesium hydroxide and Aluminium hydroxide are used as antacids for relieving acidity in the stomach.

6. They are used in paper industry, manufacture of medicines,,in manufacture of artificial fibres like rayon,nylon,etc.

INDICATORS

An indicator is a chemical substance that changes its colour to indicate the presence of chemical substances. They change colour when put into an acid or basic medium to confirm their nature. Some common indicators are methyl orange, phenolphthalein,Litmus paper, turmeric ,china rose petals ,etc.

NATURAL  INDICATORS.

LITMUS: A NATURAL DYE

Litmus is the most commonly used indicator extracted from the plants called lichens. In neutral water litmus has pale  purple colour. This turns red when acid is added to it and turns blue with Alkalis. Litmus is available in the firm of a solution or as strips of paper as red and blue litmus paper. 

In an acidic solution, blue litmus paper turns red while red litmus paper remains unchanged. In an alkaline solution,red litmus paper changed to blue while the blue litmus paper remains unchanged. In a neutral solution, the colour of both ,red abd blue litmus paper remains unchanged.

 

CHINA ROSE INDICATOR

This shows red( magenta) colour in acidic solution and turns green in alkaline solution.

TURMERIC..

It is used as a spice in Indian recipesas it imparts colour to curries. Turmeric shows yellow colour in neutral and acidic medium but turns red in alkaline medium.

OLFACTORY INDICATORS

An Olfactory indicator is a substance whose smell varies depending on whether it is mixed with an acidic or basic solution. Olfactory indicators can be used in the laboratory to test whether a solution is a base or an acid, a process called olfactory titration. Eg. Onion, clove oil, vanilla extract etc.

NEUTRALISATION:

When an acidic solution and basic solutions are mixed together in suitable amounts,the acidic and basic nature of acid and base gets destroyed. This process is called neutralisation.

The resulting solution is neither acidic nor basic. In neutralisation reaction, heat is always produced or evolved.

In neutralisation reaction, new substance formed is called a salt. A salt may be acidic, basic or neutral in nature. Thus we can define neutralisation as "  It is a reaction between an acid and a base resulting in the formation of salt and water with the evolution of heat."

Acid and Base- gives -salt and water and heat.

Eg.

HCl + NaOH ------------- NaCl+ H2O+ heat

SALTS.

 

A salt is formed by the neutralisation of acid with a base. 

Properties of Salts:

1. Salts are usually soluble in water. Most of the salts are solids with high melting and boiling points.

2. Salt solutions in water are good conductors of electricity.

3. Some salts have few water molecules attached to them are called hydrated salts.

The water molecules attached to salts are called water of crystallization. These are usually fixed and are loosely bound to the salt molecule.  Eg. Copper sulphate CuSO4.5H2O , blue in colour , Iron Sulphate,FeSO4.7H2O, green in colour.

When the hydrated salts looses the water of crystallization, the residue left behind is  called an anhydrous salt. Eg. CuSO4,white in colour. 

Anhydrous salts regain their colour on addition of water.

USES OF SALTS

They are used for domestic and industrial purposes.

Domestic purposes:

1. Common salt is used as table salt. It is used for preservation of food , raw fish and meat.

2. Washing soda is used in the manufacture of detergents to wah clothes. It is also used in fire extinguisher.

3. Baking soda is used for making baking powder. It is also used in the preparation of antacid tablets.

 

Industrial purposes:

1.Copper sulphate is used as fungicide in agriculture. It is also used in printing industry and in electroplating.

2. Plaster of paris is used for making statues,and for setting broken bones.

3. Alum is used for purifying drinking water,in dyeing industry and in leather industry.

4. Potassium nitrate is used in the manufacture of explosives like gun powder, fertilizers and crackers.

5. Ammonium carbonate (smelling salt) is a  chemical compound used for increasing consciousness and provides relief from common cold.

 

Some common names of salts are 

Common salt or table salt --- sodium chloride

Washing soda --- sodium bicarbonate

Baking soda --- sodium carbonate

Smelling salt--- Ammonium carbonate

Green vitrol---- Hydrated ferrous sulphate

Blue vitrol----Hydrated copper sulphate

Epsom salt--- Hydrated magnesium sulphate

Chalk /limestone/marble ---- Calcium carbonate

White vitrol---- Hydrated zinc sulphate

Plaster of paris--- Hydrated calcium Sulphate

Potash alum( phitakri)----- Potassium aluminium Sulphate

Nitrate--- Potassium nitrate

FAMILY OF SALTS

Salts having the same positive or negative radicals belong to a family . Eg. Chloride family salts --- sodium chloride, potassium chloride, ammonium chloride,calcium chloride, ferrous chloride etc.

Eg. Sodium family salts--- sodium chloride,sodium sulphate,sodium phosphate,sodium carbonate etc 

NEUTRALISATION IN EVERYDAY LIFE

Some of the useful effects of neutralisation in our daily life are: 

1. Indigestion Treatment

Our stomach contain hydrochloric acid. It helps us to digest food. But sometimes oily food makes the stomach produce too much of hydrochloric acid, a condition called hyperacidity. This leads to indigestion which Is painful and causes heartburns. To relieve indigestion, antacid tablets containing calcium carbonate, magnesium hydroxide are prescribed.

2. Ant bite

When an ant bites, it inject formic acid into the skin. The effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate).

3. Bee sting

A bee sting is acidic and can be neutralised by washing with soap solution which is an alkali. A wasp sting is alkaline and can be neutraised by vinegar which is a weak acid.

4. Soil treatment 

Excessive use of chemical fertilizers makes the soil acidic. Plants do not grow well when the soil is either too acidic or too basic. When the soil is acidic, it is treated with bases like quick lime ( calcium oxide) or slaked lime ( calcium hydroxide) . If the soil is basic , organic matter is added which releases acids that neutralises the basic nature of the soil.

5. Factory waste

The wastes of many factories contain acids. If they are allowed to flow into the water bodies,the acids kills fishes and other aquatic organisms. The factory waste is therefore neutraised by adding suitable basic substances.

6. Tooth decay

The enamle of our teeth is the hardest substance in our body which is insoluble in water. When we eat sugary foods or sweets ,large amount of acid is produced in the mouth. The saliva produced by salivary glands is alkaline which neutralises these acids. The excess acid is removed by cleaning the teeth with tooth paste which is basic in nature .

7. Fire extinguishers( soda- acid extinguishers) 

It contains a bottle of Sulphuric acid and a solution of sodium hydrogen carbonate. In case of a fire break out the plunger is struck.  When the acid mixes with the sodium hydrogen carbonate solution, neutralisation reaction takes place and produces carbon dioxide which gushes out on the fire and the fire is brought under control since carbon dioxide does not support burning.