Acids, Bases and Salts · Lesson 10 of 12
Chemicals From Common Salt
“One pinch of common salt has a surprisingly ambitious chemical career.”
• Explain why sodium chloride is an important raw material. • Describe the chlor-alkali process and its products. • Explain the preparation and uses of bleaching powder. • Explain the preparation, properties and uses of baking soda. • Explain the formation and uses of washing soda.
Common salt may look chemically simple, but it is the starting material for several important substances used in homes and industries. Sodium hydroxide, chlorine, hydrogen, bleaching powder, baking soda and washing soda are all connected directly or indirectly with sodium chloride.
Common Salt — A Raw Material For Chemicals
Sodium chloride is obtained from seawater and from underground deposits of rock salt. Rock salt crystals may appear brown because of impurities. Once purified, sodium chloride becomes a valuable raw material for many chemical processes.
Sodium Hydroxide
Brine is a concentrated aqueous solution of sodium chloride.
The Chlor-Alkali Process is the electrolysis of brine to produce chlorine, hydrogen and sodium hydroxide.
| Location | Product |
|---|---|
| Anode | Chlorine gas |
| Cathode | Hydrogen gas |
| Solution near cathode | Sodium hydroxide |
Bleaching Powder
Chlorine produced during the chlor-alkali process reacts with dry slaked lime to produce bleaching powder. Bleaching powder is represented by the formula Ca(ClO)₂ in the simplified treatment.
| Use | Purpose |
|---|---|
| Textile processing | Bleaching cotton and linen |
| Paper industry | Bleaching wood pulp |
| Laundry | Bleaching washed clothes |
| Chemical industry | Oxidising agent |
| Water treatment | Helping make drinking water free from germs |
Baking Soda
Baking Soda is sodium hydrogencarbonate, NaHCO₃, a mild non-corrosive basic salt.
Uses Of Baking Soda
Baking powder contains baking soda and a weak edible acid such as tartaric acid. When heated or mixed with water, carbon dioxide is produced. Gas bubbles expand inside dough or batter, making bread and cakes soft and spongy.
Tartaric acid also helps neutralise the sodium carbonate that may form from baking soda, preventing an unpleasant basic taste.
Because sodium hydrogencarbonate is mildly basic, it can neutralise excess stomach acid and is used in some antacid preparations.
Sodium hydrogencarbonate is also used in soda-acid fire extinguishers, where carbon dioxide generation helps suppress fire.
Washing Soda
Washing Soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O.
Sodium carbonate obtained by heating baking soda can be recrystallised with water to form washing soda.
| Use Of Washing Soda | Application |
|---|---|
| Manufacturing | Glass, soap and paper industries |
| Chemical manufacture | Preparation of sodium compounds such as borax |
| Domestic cleaning | Cleaning agent |
| Water treatment | Removal of permanent hardness |
Quiz
Which gas is produced at the anode during the electrolysis of brine?
Which gas forms at the cathode during electrolysis of brine?
What is the chemical name of baking soda?
Why does baking powder help cakes become soft and spongy?
Practice Problems
- Write the balanced equation for the chlor-alkali process.
- State the products formed at the anode and cathode during electrolysis of brine.
- Explain how bleaching powder is prepared from chlorine and slaked lime.
- Write the reaction that occurs when baking soda is heated and explain how the released gas helps in baking.
- State four important uses of washing soda.
Key Takeaways
• Sodium chloride is an important raw material for many useful chemicals. • Electrolysis of brine produces sodium hydroxide, chlorine and hydrogen. • Chlorine forms at the anode and hydrogen forms at the cathode during the chlor-alkali process. • Bleaching powder is prepared using chlorine and dry slaked lime. • Baking soda is sodium hydrogencarbonate and releases carbon dioxide when heated. • Washing soda is sodium carbonate decahydrate and has important domestic and industrial uses.