Answers section
Questions 1.9e
- Laboratory experiments normally use non-luminous flame, and not luminous flame. Explain --------------------
- Study the picture of a wire gauze, tripod stand and clay triangle which are normally used with a Bunsen flame when heating a substance.
- The arrangements for heating are typically as follows.
- Study diagram (b) showing the heating of a test tube in a Bunsen flame.
- How would you protect yourself and neighbors when heating a liquid in a test tube (or boiling tube)? -------------------------------------------------------------
- Overheating one part of a test tube can cause it to crack, especially when heating a solid. How would you protect the test tube when heating a solid in it? ---
- Suggest two reasons why a wire gauze is not used in the set-up in (c). ---------
Wire gauze edukitnetwork.com
Tripod stand
Clay triangle
(a) Heating a beaker or flask
heating-water-over-bunsen-burner
(b) Heating a substance in a test tube
(c) Strong heating of a solid in a crucible youtube.com
What property of hardened steel wire gauze do you think makes it suitable for use with hot flames as indicated in (a)? ---------------------------------------
Answers to Questions 1.9e
- Unlike a luminous flame, non-luminous flame is hot and does not produce soot that covers and soils the beaker or test tube.
- Non-uniform heating can cause glass to crack.
- Hardened steel wire gauze has a high melting point and does not burn in air.
- Directing the mouth of the test tube away from yourself and neighbours; moving the test tube gently over the flame, and totally removing it as the liquid content tends to spit out.
- Moving the test tube gently over the flame rather than holding it at one position.
- A wire gauze conducts away some heat; yet strong heating is required. Unlike glass, crucible does not easily crack when heated non-uniformly.