Question

What are the retarding agents of Plaster of Paris?
(A) Cold water
(B) Warm water
(C) Acetic acid
(D) Alcohol
(E) Salt
Choose the correct answer from the options given below:

• A. (A), (C) and (D) only
• B. (A), (D) and (E) only
• C. (A) and (E) only
• D. (B) and (D) only

Hint:

To remember plaster chemistry: "Heat and salt make it fast, cold and acid make it last."

Answer 1

The Correct Option is A

Step 1: Define retarding agents and accelerators for plaster. A retarding agent slows down the chemical reaction that causes plaster to set (harden). An accelerator speeds it up.
Step 2: Classify each substance.

(A) Cold water: Lowers the temperature of the reaction, slowing down the setting time. It is a retarder.
(B) Warm water: Increases the temperature of the reaction, speeding up the setting time. It is an accelerator.
(C) Acetic acid (like vinegar): Acids interfere with the crystal formation of the gypsum, slowing the setting time. It is a retarder.
(D) Alcohol: Acts as a retarder by disrupting the hydration process.
(E) Salt (Sodium Chloride): Acts as an accelerator, speeding up the setting time.

Step 3: Identify the group of retarders. The retarding agents are Cold water, Acetic acid, and Alcohol. This corresponds to (A), (C), and (D).