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1. Solids
Never return unused chemicals to the reagent bottle
From reagent bottle Use a clean and dry spatula or spoon
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
(a) Pouring a liquid from a reagent bottle to a test tube
Mouths of test-tube and beaker are at the eye level
Pour the liquid along the spout of the beaker.
spout of the beaker
Use gas generator
It can produce a large amount of gas
easily control the flow of the product gas
What are the advantages of using tap funnel?
Rate of addition of liquid can be controlledPrevent the gas escaping from the funnel
re ac tin g liq u id
re ac tin g so lid
ro u n d b o tto m ed fla sk
g a s o u t
ta p fu n n e l
For gases that do not dissolve in water
1. Displacement of water
It a gas is produced from a hot vessel and heating is stopped, water may be sucked back to the hot vessel is
Sucking back
g as
w a te r
W a te r is b e in g su ck ed b ack
How to prevent sucking back?The delivery tube must be removed from water before heating is stopped.
g as
w a te r
W a te r is b e in g su ck ed b ack
> (i) upward delivery (downward displacement)
> (ii) downward delivery (upward displacement)
For gases having densities much smaller than air. Examples:
hydrogen, ammonia
Up w a rd d e live ry
g a s
For gases having densities much larger than air. Examples:
carbon dioxide, chlorine
D ow nw ard de live ry
G a s
For collecting all kinds of gases
Can be used to measure volume of the gasPrecaution
•Horizontal position
•Prevent the plunger from falling out
•Keep the syringe clean, dry and free from grease.
Two uses:
Draw a labelled diagram for preparation of gas
Use of Bunsen Burner
Bunsen flame
Heating liquids
Construction of a Bunsen burner
a ir h o le
to w ng asb ase
je tco lla r
b a rre l
•Close the air hole.
•Put a lighted match near the top of barrel.
•Turn on the gas supply
How to light a Bunsen burner?
air hole
towngasbas
e
jetcollar
barrel
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; orleave it with a small luminous flame.
Turn the collar to adjust the size of the air-hole
Non-luminous flame
Luminous flame
Small air-hole
Large air-hole
or air hole is closed
The air hole is closed completely
There are 3 zones.
Non-luminous zoneLuminous zoneDark zone
Non-luminous zone
Luminous zone
Dark zone
This flame is not very hot.
The air hole is open.
There are 3 zones.
Non-luminous zoneGreen-blue zone
Dark zone
Non-luminous zone
Green-blue zone
Dark zone
This flame is hotter than luminous flame.
•The amount of air getting into the barrel is too much.
•The gas supply is too low.
How do you know that there is ‘striking back’?
Why does striking back occur?
What is ‘striking back’?
A high pitched sound will usually be heard.
Gas burns at the jet instead of the mouth of the barrel.
What should you do?
Caution!
The collar is very hot.
Turn off the gas supply immediately.
shake the tube
Use a small non-luminous flame
How to get uniform heating?
Use test-tube holder
Heat the upper part of the liquid first
move the tube around the flame
The tube should not be more than 1/3 full.
Safety precaution
The tube should be pointed to open area, never to anybody
For larger amount of liquidA wire gauze is placed between the beaker and the flame
The beaker should not be filled more than 1/2 full.
The liquid is heated indirectly
Inflammable liquids may easily catch fire.
Why are inflammable liquids heated indirectly?
Oil bath may be used to achieve a higher temperature.