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Acids, Bases and Salts

Chapter: Acids, Bases and Salts

We know that the sour and bitter tastes of food are due to acids and bases, respectively, present in them. Acids are sour in taste and change the colour of blue litmus to red, whereas, bases are bitter and change the colour of the red litmus to blue. Litmus is a natural indicator, turmeric is another such indicator.

Acids

Physical Properties Of Acids

  1. Acids are sour in taste
  2. Acids turn blue litmus to red
  3. Acid solution conduct electricity( They are electrolyte)
  4. Acids can destroy fabric
  5. Acids can cause skin burns

Chemical Properties Of Acids

1 . Neutralization

An acid when reacts with a base produces salt and water. This is called neutralization.

HCl + NaOH  → NaCl+ H2O

2 . Reaction of acids with carbonates and bicarbonates

This reaction can be summarized as

Metal carbonate/Metal hydrogen carbonate + Acid→ Salt + Carbon dioxide + Water

Acids combine with carbonates to produce salt, water and carbon dioxide

CaCO3 + 2HCl → CaCl2 + CO2 +H2O

3 . Reaction of metal oxides with acids

Metal oxides will combine with acids and give rise to salt and water. The reaction of a metal with an acid can be summarized as

Acid + Metaloxide → Salt + Water

Bases

Physical Properties Of Bases

  1. Bases are bitter in taste
  2. Bases have a slippery touch
  3. Bases conduct electricity
  4. Bases turn red litmus to blue litmus

Chemical Properties Of Bases

1 . Neutralization

A base when reacts with acid produces salt and water. This is called neutralization.

2 . Reaction of base with water

Bases generate hydroxide ions in water.(OH ions). Bases which are soluble in water are called alkalis.

NaOH → Na+ + OH-

(in the presence of water)

3 . Reaction of bases with metals

When bases react with metals, hydrogen is formed.

2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2O

How Strong are Acid or Base Solutions ?

We can judge the strength of acid or base by using a universal indicator which is a mixture of several indicators. The universal indicator shows different colors at different concentrations of hydrogen ions in a solution.

A scale for measuring hydrogen ion concentration in a solution has been developed and this is called pH scale where p stands for ‘potenz’ in German (power).

The strength of acids and bases depends on the number of H+ ions and OH ions produced, respectively. If we take hydrochloric acid and acetic acid of the same concentration, say one molar, then these produce different amounts of hydrogen ions. Acids that give rise to more H+ ions are said to be strong acids, and acids that give less H+ ions are said to be weak acids.

Importance of pH in Everyday Life

  1. Our body works in the pH range of 7.0 to 7.8.
  2. Our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach.
  3. Plants require a specific pH range for their healthy growth.
  4. Tooth decay starts when the pH of the mouth is lower than 5.5.

Salts

Did u ever see what the salt which we use is in our daily life? It is called common salt. It is chemically called as Sodium chloride. It is formed by the combination of hydrochloric acid and sodium hydroxide solution and hence is called sodium chloride. This is the salt that you use in food.

pH of Salts

Salts of a strong acid and a strong base are neutral with pH value of 7. On the other hand, salts of a strong acid and weak base are acidic with pH value less than 7 and those of a strong base and weak acid are basic in nature, with pH value more than 7.

Chemicals from Common Salt

Sea water contains many salts in it. Sodium chloride is purified from salts of sea water. Then we can find deposits of solid salt which are brown in color due to presence of impurities. This is called Rock Salt. Beds of rock salt were formed when seas of bygone ages dried up. Rock salt is mined like coal.

Common salt — a raw material for chemicals

The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda and bleaching powder.

Let us see the uses of these materials mentioned above.

1 . Sodium hydroxide

When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. This process is called the chloro-alkali process.

 

 

2 . Bleaching Powder

Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2]. Bleaching powder is represented as CaOCl2.

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Uses of bleaching powder:

  1. It is used in textile industries, paper factories and laundry for bleaching cotton and linen, wood pulp and washed clothes respectively.
  2. It is used as an oxidizing agent in chemical industries.
  3. It is used as disinfectant in drinking water to make it germs free.

3 . Baking soda

The soda that is commonly used in kitchen for making tasty food like cakes. The chemical name of the compound is sodium hydrogen carbonate (NaHCO3). It is produced using sodium chloride.

NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3

It is a mild non-corrosive basic salt.

Uses of sodium hydrogen carbonate

  1. It is used as soda-acid fire extinguishers.
  2. Is used as an ingredient in antacids.
  3. It is used in food industry for baking purpose.

4 . Washing Soda

Washing soda is obtained from sodium carbonate. It is represented as Na2CO3.10H2O.

Na2CO3 + 10H2O → Na2CO3.10H2O

   (Soda ash)   (Water)     (Washing soda)

Uses of washing soda

  1. It is used in glass, soap and paper industries.
  2. It is used in the manufacture of sodium compounds such as borax.
  3. It can be used as a cleaning agent for domestic purposes.
  4. It is used for removing permanent hardness of water.