Plaster of Paris is stored in a moisture-proof container because it is highly hygroscopic, meaning it readily absorbs moisture from the atmosphere. Exposure to moisture can cause Plaster of Paris to undergo premature setting or hardening, rendering it unusable. Storing it in a moisture-proof container helps to maintain its dryness and extend its shelf life.

Neutralization reaction is a chemical reaction in which an acid reacts with a base to form a salt and water. Two examples of neutralization reactions are:

• Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H2O)
• Sulfuric acid (H2SO4) + Calcium hydroxide (Ca(OH)2) → Calcium sulfate (CaSO4) + Water (H2O)

Two uses of baking soda are:

• Baking soda (sodium bicarbonate, NaHCO3) is used as a leavening agent in baking to help dough rise.
• It is used as an antacid to relieve heartburn, indigestion, and upset stomach by neutralizing excess stomach acid.

Two uses of washing soda (sodium carbonate, Na2CO3) are:

• Washing soda is used as a cleaning agent and laundry detergent booster due to its alkaline properties, which help to remove stains and grease.
• It is used in water treatment processes to soften hard water by precipitating calcium and magnesium ions.

A milkman adds a small amount of baking soda to fresh milk to shift the pH of fresh milk from 6 to slightly alkaline because alkaline conditions inhibit the growth of bacteria and help to preserve the freshness of milk. Baking soda (sodium bicarbonate) acts as a buffer, helping to maintain the pH of milk and prolong its shelf life.

Acids do not show acidic behavior in the absence of water because the characteristic properties of acids, such as the donation of hydrogen ions (H+) and the ability to react with bases, depend on the presence of water molecules to facilitate proton transfer reactions. In the absence of water, acids cannot ionize and exhibit their acidic properties.