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Important Chemicals from Common Salt

🔄 Quick Recap​

In the previous section, we learned about:

  • What salts are and how they're formed
  • Different families of salts
  • Common salts and their uses in everyday life
  • The concept of water of crystallization in salts

Now, let's explore how common salt (sodium chloride) serves as a raw material for many important industrial chemicals!

📚 Common Salt: A Valuable Resource​

Common salt or sodium chloride (NaCl) is one of the most abundant natural resources on Earth. It is found in seawater and as rock salt deposits. Beyond its use as a food additive, sodium chloride is a key raw material for producing various chemicals that are essential in our daily lives.

📚 The Chlor-Alkali Process​

The chlor-alkali process is an industrial process that uses the electrolysis of sodium chloride solution (brine) to produce chlorine gas and sodium hydroxide (caustic soda). The process is named "chlor-alkali" because chlorine and an alkali (sodium hydroxide) are the two main products.

How Does It Work?​

When electricity is passed through a brine solution (concentrated sodium chloride solution), it decomposes to form chlorine gas, hydrogen gas, and sodium hydroxide:

2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
  • Chlorine gas (Cl₂) is released at the anode (positive electrode)
  • Hydrogen gas (H₂) is released at the cathode (negative electrode)
  • Sodium hydroxide (NaOH) is formed near the cathode

Products of the Chlor-Alkali Process​

  1. Chlorine Gas (Cl₂)
  2. Sodium Hydroxide (NaOH)
  3. Hydrogen Gas (H₂)

All three products are valuable industrial chemicals with numerous applications.

📚 Sodium Hydroxide (NaOH)​

Sodium hydroxide, also known as caustic soda, is a strong base produced in the chlor-alkali process.

Uses of Sodium Hydroxide​

  1. Soap and detergent manufacturing

    • Saponification reaction (converting oils and fats into soap)

  2. Paper and pulp industry

    • Breaking down wood fibers
    • Removing ink from recycled paper

  3. Textile industry

    • Mercerizing cotton to improve strength and luster
    • Processing fibers

  4. Aluminum production

    • Extracting aluminum from bauxite ore

  5. Chemical manufacturing

    • Production of other sodium compounds
    • Neutralizing acids in various processes

📚 Bleaching Powder​

Bleaching powder is produced by passing chlorine gas (from the chlor-alkali process) through dry slaked lime (calcium hydroxide).

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Bleaching powder is represented as CaOCl₂, though its actual structure is more complex.

Uses of Bleaching Powder​

  1. Bleaching

    • Textiles and paper pulp
    • Stain removal in laundry

  2. Water treatment

    • Disinfection of drinking water
    • Treatment of swimming pool water

  3. Sanitation

    • Disinfecting surfaces
    • Use in public health for disinfection during epidemics

  4. Chemical industry

    • As an oxidizing agent in various chemical processes

📚 Baking Soda (Sodium Hydrogen Carbonate)​

Baking soda (NaHCO₃) is produced using sodium chloride, ammonia, and carbon dioxide through the Solvay process:

NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl

Uses of Baking Soda​

  1. Cooking

    • Leavening agent in baking
    • When heated, it decomposes: 
      2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
    • The CO₂ released causes the dough to rise

  2. Baking powder

    • Mixture of baking soda and a mild edible acid (like tartaric acid)
    • When mixed with water: 
      NaHCO₃ + H⁺ → CO₂ + H₂O + Sodium salt of acid

  3. Medicine

    • Antacid for relief from acidity
    • Neutralizes excess stomach acid: 
      NaHCO₃ + HCl → NaCl + H₂O + CO₂

  4. Fire extinguishers

    • Produces CO₂ when heated or reacted with acid
    • CO₂ smothers the fire by displacing oxygen

📚 Washing Soda (Sodium Carbonate)​

Washing soda (Na₂CO₃·10H₂O) is produced by heating baking soda:

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

The anhydrous sodium carbonate can absorb water to form the hydrated washing soda:

Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O

Uses of Washing Soda​

  1. Laundry and cleaning

    • Removes grease and oil stains
    • Softens hard water by precipitating calcium and magnesium ions: 
      Na₂CO₃ + Ca²⁺ → CaCO₃↓ + 2Na⁺

  2. Glass manufacturing

    • Essential component in glass production
    • Lowers the melting point of the silica mixture

  3. Paper industry

    • Used in pulp processing
    • Removes lignin from wood

  4. Water treatment

    • Adjusts pH in water treatment processes
    • Softens hard water in industrial settings

📚 Plaster of Paris​

While not directly produced from common salt, Plaster of Paris is an important calcium-based compound related to our study of salts.

Plaster of Paris (CaSO₄·½H₂O) is produced by heating gypsum (CaSO₄·2H₂O) at 373K:

CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O

When water is added to Plaster of Paris, it forms gypsum again, setting into a hard solid:

CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O

Uses of Plaster of Paris​

  1. Medical applications

    • Making casts for broken bones
    • Dental impressions

  2. Art and decoration

    • Making statues and decorative items
    • Making molds for ceramics

  3. Construction

    • Creating smooth wall finishes
    • Decorative ceiling designs

  4. Fire protection

    • Fire-resistant coatings
    • When heated, the water of crystallization is released, absorbing heat

🧪 Activity Time! Making a Soda-Acid Fire Extinguisher​

Materials needed:

  • Baking soda (sodium bicarbonate)
  • Vinegar (acetic acid)
  • A bottle with a narrow mouth
  • A cork with a hole for a straw
  • A straw

Steps:

  1. Put about 2 tablespoons of baking soda in the bottle
  2. Add about 50 mL of vinegar
  3. Quickly put the cork with the straw in the bottle's mouth
  4. Direct the straw towards a small candle flame (set up in advance)
  5. Observe what happens

The reaction between baking soda and vinegar produces carbon dioxide gas:

NaHCO₃ + CH₃COOH → CH₃COONa + H₂O + CO₂

The carbon dioxide is heavier than air and flows down the straw, smothering the flame by displacing oxygen.

✅ Solved Example​

Problem: Calculate the mass of washing soda (Na₂CO₃·10H₂O) that can be obtained from 100 g of anhydrous sodium carbonate (Na₂CO₃). (Atomic masses: Na = 23, C = 12, O = 16, H = 1)

Solution:

Step 1: Calculate the molar masses. Molar mass of Na₂CO₃ = (2 × 23) + 12 + (3 × 16) = 106 g/mol Molar mass of Na₂CO₃·10H₂O = 106 + (10 × 18) = 106 + 180 = 286 g/mol

Step 2: Calculate the number of moles of Na₂CO₃. Moles of Na₂CO₃ = 100 g / 106 g/mol = 0.943 mol

Step 3: Apply the stoichiometric relationship. According to the equation: Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O 1 mol of Na₂CO₃ produces 1 mol of Na₂CO₃·10H₂O

Step 4: Calculate the mass of washing soda. Mass of Na₂CO₃·10H₂O = 0.943 mol × 286 g/mol = 269.7 g

Therefore, 100 g of anhydrous sodium carbonate can produce 269.7 g of washing soda.

🎮 Fun Facts​

  1. Origin of "Plaster of Paris": The name "Plaster of Paris" originates from the large gypsum deposits in Montmartre, Paris, which were extensively mined to produce the plaster used in building the city.

  2. Historical significance of salt: Salt was so valuable in ancient times that Roman soldiers were sometimes paid with it. This is where the word "salary" comes from (Latin: "salarium").

  3. Chlorine in swimming pools: The distinctive smell of swimming pools isn't actually chlorine—it's chloramines, which form when chlorine reacts with organic compounds (like sweat or urine) in the water.

💡 Key Points to Remember​

  • Common salt (NaCl) is a valuable raw material for many important chemicals
  • The chlor-alkali process produces chlorine, sodium hydroxide, and hydrogen
  • Bleaching powder is made by passing chlorine through slaked lime
  • Baking soda is used in cooking, medicine, and fire extinguishers
  • Washing soda is used for cleaning, glass making, and water softening
  • Plaster of Paris is made by partially dehydrating gypsum

🤔 Think About It!​

  1. How has the industrial production of chemicals from salt changed society?
  2. What environmental concerns might be associated with the chlor-alkali industry?
  3. Can you think of ways to make the production of these chemicals more environmentally friendly?

🔜 What Next?​

Now that we've explored acids, bases, salts, and the important chemicals derived from common salt, in the next section we'll summarize all the key points from this chapter to help you review and retain the information.