UPSC Prelims 2003 Q45: Science & Technology – Chemistry
Consider the following statements
The purpose of adding sodium sulphate and sodium silicate to the detergent in a washing powder
is
1. To keep the washing powder dry
2. To maintain the alkalinity of the powder
Which of these statements is/are correct?
- (a) Only 1
- (b) Only 2
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (c) Both 1 and 2
Explanation
Sodium sulphate and sodium silicate in washing powder
| Statement | Verdict |
|---|---|
| 1. To keep the powder dry | True — sodium sulphate is a filler that absorbs moisture |
| 2. To maintain the alkalinity | True — sodium silicate (and carbonate) keep the wash alkaline |
Both statements are correct.
Answer: (c) Both 1 and 2.
Why each option is right or wrong
- (a) Incorrect. Statement 2 is also correct.
- (b) Incorrect. Statement 1 is also correct.
- (c) CORRECT. Both statements are correct.
- (d) Incorrect. Both statements are correct.
Key point
Detergent powder: surfactant, builder (sodium tripolyphosphate), sodium silicate, sodium sulphate filler.
Remember
Sodium sulphate keeps the powder dry and sodium silicate keeps it alkaline.
Common mistakes
- Thinking sodium sulphate is the cleaning agent.
- Forgetting the buffering role of the silicate.
- Mixing up soaps with synthetic detergents.
Exam tip
Fillers keep powders free flowing and dry.
Sources
- NCERT Class XII Chemistry — Chemistry in Everyday Life
- Bureau of Indian Standards — IS 4955: Household laundry detergent powders — Specification