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Handling Chemicals

F.3 Chem -- Section Two. Handling Chemicals. Handling Chemicals. From reagent bottle. Use a clean and dry spatula or spoon. 1. Solids. Never return unused chemicals to the reagent bottle. Transfer a liquid. (a) Pouring a liquid from a reagent bottle to a test tube.

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Handling Chemicals

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

  2. Handling Chemicals From reagent bottle Use a clean and dry spatula or spoon 1. Solids 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. 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 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 barrel collar air hole jet towngas base How to light a Bunsen burner? • 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 Large air-hole Small air-hole Non-luminous flame Turn the collar to adjust the size of the air-hole Luminous flame or air hole is closed

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

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

  22. Precaution: Striking back Gas burns at the jet instead of the mouth of the barrel. What is ‘striking back’? 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 Heat the upper part of the liquid first in a test tube Use test-tube holder Use a small non-luminous flame 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

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