F.3 Chem -- Section Two Handling Chemicals

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

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

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

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

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

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

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

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

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

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

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

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

Exercise Draw a labelled diagram for preparation of gas

Heating Technique Use of Bunsen Burner Bunsen flame Heating liquids

Use of Bunsen burner Construction of a Bunsen burner

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

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.

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

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.

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.

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.

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

Heating liquids

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

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

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.

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.

End of Section Two