Presentation on theme: "1. Solids Never return unused chemicals to the reagent bottle From reagent bottle Use a clean and dry spatula or spoon."— Presentation transcript:
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 controlled Prevent the gas escaping from the funnel
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
How to prevent sucking back? The delivery tube must be removed from water before heating is stopped.
For gases having densities much smaller than air. Examples: hydrogen, ammonia
For gases having densities much larger than air. Examples: carbon dioxide, chlorine
For collecting all kinds of gases Can be used to measure volume of the gas Precaution 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
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 town gas base jet collar 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; or leave 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 zone Luminous zone Dark 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 zone Green-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 liquid A 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.