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: Determine retarders and accelerators for plaster. A retarder delays plaster hardening; an accelerator hastens it.
Step 2: Categorize each substance.

(A) Cold water: Slows the reaction, extending setting time. It's a retarder.
(B) Warm water: Speeds the reaction, reducing setting time. It's an accelerator.
(C) Acetic acid (e.g., vinegar): Acids hinder gypsum crystal formation, delaying setting. It's a retarder.
(D) Alcohol: Functions as a retarder by impeding hydration.
(E) Salt (Sodium Chloride): Acts as an accelerator, accelerating setting.

Step 3: List the retarders. The retarders are Cold water, Acetic acid, and Alcohol, corresponding to (A), (C), and (D).