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Air & Oxygen

Air & Oxygen. RAG Sheet & WordBank. Red Amber Green (No idea) (Some clue) (Know it) . What is the difference between the two methods you could use to find the % oxygen in air?. The Atmosphere. Mixture of gases which forms a blanket around the earth.

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Air & Oxygen

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  1. Air & Oxygen

  2. RAG Sheet & WordBank Red Amber Green (No idea) (Some clue) (Know it)

  3. What is the difference between the two methods you could use to find the % oxygen in air?

  4. The Atmosphere • Mixture of gases which forms a blanket around the earth

  5. Composition of Air • Investigate the % of oxygen in the air, using a night light (MP) • Main steps • Floating night light, lit, graduated cylinder over it • Water rises • Allow to cool, measure volume of gas left • Not very accurate, air is  oxygen

  6. Issues with experiment • Night light goes out without all oxygen being used up • Graduated cylinder does not measure volume as accurately as gas syringe

  7. Composition of Air • To measure % oxygen in air using gas syringe (MP) • Main steps

  8. Composition of air • Reaction: Copper + Oxygen  Copper oxide • Start with 100cm3 of air (100%) • Volume at end of reaction 79cm3 (79%) • Volume of oxygen reacted with copper = 21cm3  21% oxygen

  9. Why it’s more accurate • More oxygen removed from air • Gas syringe is more accurate at measuring volume

  10. Practical worksheet

  11. What is the difference between the two methods you could use to find the % oxygen in air?

  12. What is the significance of:cobalt chloridelimewaterlitmusglowing splinta lighting splint going out?

  13. Composition of Air

  14. Composition of Air • To show that carbon dioxide & water vapour are present in air (MP) • Cobalt chloride paper goes from blue to pink in presence of water • Limewater goes milky/cloudy in presence of CO2

  15. Practical worksheet

  16. Preparation of oxygen Decomposition of hydrogen peroxide Word equation Hydrogen peroxide  water + oxygen Chemical equation (HL) 2H2O2  2H2O + O2 • This reaction requires a catalyst • Substance which speeds us a chemical reaction but is not used up in the reaction itself • Catalyst in this reaction is manganese dioxide/MnO2 • MnO2

  17. Preparation of Oxygen (MP) • Main steps • H2O2 dropped on to catalyst • Oxygen produced is collected over water as it is only slightly soluble

  18. Properties of oxygen (MP) • Oxygen is neutral • No change in colour of red litmus or blue litmus paper • Oxygen relights a glowing split

  19. Practical worksheet

  20. Properties of oxygen (MP) • Burning carbon in oxygen • Another name for burning is combustion • Rxn: Carbon + oxygen  carbon dioxide • C + O2  CO2 • Limewater turns milky • Carbon dioxide + water turns blue litmus paper red  acidic gas • Carbon dioxide quenches a burning split • Denser then air

  21. Practical worksheet

  22. Properties of Oxygen (MP) • Burning magnesium in oxygen • Burns much brighter in oxygen then in air • Magnesium + oxygen  magnesium oxide

  23. Properties of Oxygen (MP) • Magnesium oxide and water Word equation: Magnesium oxide + water  magnesium hydroxide • Red litmus turns blue  a base is formed

  24. Properties of Oxygen - summary

  25. Summary of reactions with O2

  26. What is the significance of:cobalt chloridelimewaterlitmusglowing splinta lighting splint going out?

  27. Uses of Oxygen • Breathing • Stored in cylinders • Used in hospitals and by mountain climbers • Burning and welding • Acetylene in O2 reaches 3000C • Flame can cut through melting or melt metal and join them together • Space rockets • Need to bring own oxygen to space for combustion

  28. RAG Sheet & WordBank Red Amber Green (No idea) (Some clue) (Know it)

  29. Worksheet • Exam questions • Mindmap

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