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Salt Families: Exploring the Common Bonds of Sodium and Chloride in Chemicals
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- Salts having the same positive or negative radicals are said to belong to a family.
- Example: NaCl and Na2SO4 belong to the family of sodium salts.
- Similarly, NaCl and KCl belong to the family of chloride salts.
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pH of Acid,Bases and salts
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- Neutral: Salts of a strong acid and a strong base are neutral with a pH value of 7.
- Acidic: Salts of a strong acid and weak base are acidic with pH value less than 7 and
- Basic: Salts of a strong base and weak acid are basic in nature, with pH value more than 7.
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Common Salt :Transformation from Sodium Chloride to Everyday Chemical elements
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- Combination: The salt formed by the combination of hydrochloric acid and sodium hydroxide solution is called sodium chloride.
- Rock Salt: Deposits of solid salt are also found in several parts of the world and are often brown due to 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 is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder and many more.
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Different Substances: The Realm of Acid, Bases and Salts
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- Sodium Hydroxide: When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide.
- The process is called the chlor-alkali process because of the products formed – chlor for chlorine and alkali for sodium hydroxide.
- Chlorine gas is given off at the anode, and hydrogen gas at the cathode.
- Sodium hydroxide solution is formed near the cathode.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
- Bleaching Powder: Chlorine is produced during the electrolysis of aqueous sodium chloride (brine) and is used for the manufacture of bleaching powder.
- Bleaching powder (CaOCl2) is produced by the action of chlorine on dry slaked lime [Ca(OH)2].
Ca(OH)2 + Cl2 → CaOCl2 + H2O
- Uses of Bleaching Powder –
- For bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry;
- As an oxidising agent in many chemical industries; and
- To make drinking water free from germs.
- Baking Soda: The baking soda is commonly used in the kitchen for making tasty crispy pakoras, etc. Sometimes it is added for faster cooking.
- The chemical name of the compound is sodium hydrogen carbonate (NaHCO3).
- It is produced using sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 → NH4Cl (Ammonium chloride)+NaHCO3(Sodium Hydrogencarbonate)
- When it is heated during cooking the following reaction takes place;
2NaHCO3 → Na2CO3 (Sodium carbonate) + H2O + CO2
- For making baking powder, which is a mixture of baking soda (sodium hydrogencarbonate) and a mild edible acid such as tartaric acid.
- When baking powder is heated or mixed in water the following reaction takes place,
NaHCO3 + H+ (From any acid) → CO2 + H2O + Sodium salt of acid
Carbon dioxide produced during the reaction can cause bread or cake to rise making them soft and spongy.
- It is also an ingredient in antacids. Being alkaline, it neutralises excess acid in the stomach and provides relief.
- It is also used in soda-acid fire extinguishers.
- Washing Soda: Another chemical that can be obtained from sodium chloride is Sodium carbonate – Na2CO3.10H2O (washing soda).
- Recrystallisation of sodium carbonate gives washing soda. It is also a basic salt. The journey from sodium chloride to washing soda exemplifies the transformative influence of acid,bases and salts in our daily lives.
Na2CO3 + 10 H2O → Na2CO3.10H2O
- Sodium carbonate is used in glass, soap and paper industries.
- It is used in the manufacture of sodium compounds such as borax.
- Sodium carbonate can be used as a cleaning agent for domestic purposes.
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Hydrated Salt Dynamics: An Exploration of Water of Crystallisation in Copper Sulphate, Gypsum, and the Journey to Plaster of Paris
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- Copper sulphate crystals which seem to be dry contain water of crystallisation.
- When the crystals are heated, this water is removed and the salt turns white.
- If we moisten the crystals again with water, then the blue colour of the crystals reappears.
- Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.
- Five water molecules are present in one formula unit of copper sulphate.
- Chemical formula for hydrated copper sulphate is CuSO4.5H2O.
- Gypsum has two water molecules as water of crystallisation.
- It has the chemical formula CaSO4.2H2O.
- On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4.1/2H2O).
- This is called Plaster of Paris, the substance which doctors use as plaster for supporting fractured bones in the right position.
- Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass.
CaSO4. 1/2 H2O + 11/2 H2O → CaSO4.2H2O
- Plaster of Paris is used for making toys, materials for decoration and for making surfaces smooth.
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