12.1 Domestic/Household Chemistry

Various chemical substances are commonly used in households, such as table salt, baking powder, vinegar, and soft drinks.

Table Salt or Edible Salt

• Source: Table salt is primarily sodium chloride (NaCl). It is found in large quantities in sea water and underground minerals.

• Extraction Process: In coastal areas, salt is extracted from sea water through a process known as salt harvesting. Dams are constructed in square or rectangular land plots, and when tidal water enters, it is contained. The water evaporates under the heat of the sun, leaving visible salt crystals.

• Purification: The collected salt contains sand. When mixed with water, the salt dissolves while the sand settles at the bottom. The salt-water solution is separated through filtration. Upon heating, the water evaporates, leaving the salt behind.

• Processing: The processed salt is then packed and sent to markets for sale.

• Importance: Sodium ions (Na+) are essential for body functions. If there is a deficiency of sodium, it can be replenished by consuming NaCl with water.

• Uses of NaCl:

1. Enhances flavor in food, such as curry with rice.

2. Used in industries to produce sodium hydroxide (NaOH).

3. Used in pharmaceutical industries to prepare saline solutions for treating diarrhea or dehydration.

Baking Powder

• Baking Soda: The chemical name for baking soda is sodium hydrogen carbonate (NaHCO₃) or sodium bicarbonate. It is commonly used in baking, particularly in cake preparation.

• Preparation of Baking Powder:

• Baking powder is made by mixing tartaric acid (C₄H₆O₆) with baking soda (NaHCO₃).

• Baking Soda Preparation: Sodium bicarbonate (baking soda) is prepared by reacting sodium chloride (NaCl), ammonia gas (NH₃), and carbon dioxide (CO₂).

1. A saturated solution of NaCl is prepared.

2. Ammonia gas is bubbled through the solution, followed by CO₂.

3. This reaction forms ammonium hydrogen carbonate (NH₄HCO₃), which then reacts with NaCl to produce sodium hydrogen carbonate (baking soda).

4. The chemical reactions are:

• CO₂ + NH₃ + H₂O → NH₄HCO₃

• NH₄HCO₃ + NaCl → NaHCO₃ + NH₄Cl

• Tartaric acid is then mixed with the baking soda to create baking powder.

• Reaction in Baking: When baking powder is added to cake flour and heated, it reacts with tartaric acid, producing sodium tartrate (C₄H₆Na₂O₆), CO₂ gas, and water (H₂O). The CO₂ gas causes the cake to rise.

• The chemical reaction:

• 2NaHCO₃ + C₄H₆O₆ → C₄H₆Na₂O₆ + 2CO₂ + 2H₂O

• Yeast as an Alternative: In baking, yeast is used to cause the dough to rise. Yeast ferments sugar in a warm environment, producing CO₂ through aerobic respiration, which helps bread or cakes swell.

Vinegar

• Definition: Vinegar is a liquid solution of ethanoic acid (CH₃COOH), usually 4% to 10% in concentration. It is commonly used for making pickles.

• Preparation: Vinegar is produced by introducing oxygen gas (O₂) into ethanol, in the presence of an acetic acid bacteria (Acetobacter), at temperatures between 25°C and 35°C. The chemical reaction is:

• CH₃CH₂OH + O₂ → CH₃COOH + H₂O

• Role in Food Preservation: Vinegar preserves food, especially pickles, by preventing bacterial growth. The acid in vinegar damages bacterial proteins, making it difficult for bacteria to thrive. As a result, food remains safe from bacterial contamination.

Soft Drinks

• Preparation: Soft drinks are made by dissolving carbon dioxide gas (CO₂) into water under cold temperatures and high pressure, forming carbonic acid (H₂CO₃).

• Usage: Soft drinks are consumed for their refreshing taste and are often thought to aid digestion. However, there is no strong scientific evidence that they help digestion.