1. F.3 Chem -- Section Two
Handling Chemicals

2. Handling Chemicals 1. Solids From reagent bottle
Use a clean and dry spatula or spoon
Never return unused chemicals to the reagent bottle

3. Transfer a liquid
(a) Pouring a liquid from a reagent bottle to a test tube
Place the stopper upside down on the bench.
Mouths of test-tube and reagent bottle are at the eye level.
Never return unused chemicals to the reagent bottle

4. Pouring a liquid from a beaker
Pour the liquid along the spout of the beaker.
spout of the beaker
Mouths of test-tube and beaker are at the eye level

5. Produce and collect a gas
Use gas generator
Produce and collect a gas
It can produce a large amount of gas
easily control the flow of the product gas

6. Use of gas generator What are the advantages of using tap funnel?
Rate of addition of liquid can be controlled
Prevent the gas escaping from the funnel

7. Collection of Gases 1. Displacement of water
For gases that do not dissolve in water

8. Precaution: Sucking back
It a gas is produced from a hot vessel and heating is stopped, water may be sucked back to the hot vessel is

9. Precaution: Sucking back
How to prevent sucking back?
The delivery tube must be removed from water before heating is stopped.

10. Collection of gas: Displacement of air
(i) upward delivery (downward displacement)
(ii) downward delivery (upward displacement)

11. Collection of gas - Upward delivery
For gases having densities much smaller than air.
Examples:
hydrogen, ammonia

12. Collection of gas - Downward delivery
For gases having densities much larger than air.
Examples:
carbon dioxide, chlorine

13. Gas syringe Two uses: For collecting all kinds of gases
Can be used to measure volume of the gas
Horizontal position
Prevent the plunger from falling out
Keep the syringe clean, dry and free from grease.
Precaution

14. Exercise
Draw a labelled diagram for preparation of gas

15. Heating Technique
Use of Bunsen Burner
Bunsen flame
Heating liquids

16. Use of Bunsen burner
Construction of a Bunsen burner

17. The use of a Bunsen burner
How to light a Bunsen burner?
air hole
towngas
base
jet
collar
barrel
Close the air hole.
Put a lighted match near the top of barrel.
Turn on the gas supply

18. The use of a Bunsen burner
How to control the size of a Bunsen flame?
by using the gas tap
When there is no immediate use of a burner, what should you do?
Turn it off; or
leave it with a small luminous flame.

19. Bunsen Flame Non-luminous flame Luminous flame Large air-hole
Turn the collar to adjust the size of the air-hole
Small air-hole
Luminous flame
or air hole is closed

20. Luminous Flame The air hole is closed completely There are 3 zones.
Non-luminous zone
Luminous zone
Dark zone
There are 3 zones.
Non-luminous zone
Luminous zone
Dark zone
This flame is not very hot.

21. Non-luminous Flame The air hole is open. There are 3 zones.
Non-luminous zone
Green-blue zone
Dark zone
There are 3 zones.
Non-luminous zone
Green-blue zone
Dark zone
This flame is hotter than luminous flame.

22. Precaution: Striking back
What is ‘striking back’?
Gas burns at the jet instead of the mouth of the barrel.
How do you know that there is ‘striking back’?
A high pitched sound will usually be heard.
Why does striking back occur?
The amount of air getting into the barrel is too much.
The gas supply is too low.

23. Precaution: Striking back
What should you do?
Turn off the gas supply immediately.
Caution!
The collar is very hot.

24. Heating liquids

25. Heating non-inflammable liquids
in a test tube
Use test-tube holder
Use a small non-luminous flame
Heat the upper part of the liquid first
How to get uniform heating?
shake the tube
move the tube around the flame

26. Heating non-inflammable liquids
Safety precaution
The tube should not be more than 1/3 full.
The tube should be pointed to open area, never to anybody

27. Heating non-inflammable liquids
in a beaker
For larger amount of liquid
A wire gauze is placed between the beaker and the flame
The beaker should not be filled more than 1/2 full.

28. Heating inflammable liquids
The liquid is heated indirectly
Oil bath may be used to achieve a higher temperature.
Why are inflammable liquids heated indirectly?
Inflammable liquids may easily catch fire.

29. End of Section Two