1. Oxygen and oxides

2. Air is a mixture of gases which contains 4/5 nitrogen 1/5 oxygen

3. describe how experiments involving the reactions of elements such as copper, iron and phosphorus with air can be used to determine the percentage by volume of oxygen in air Experiment with copper This can be demonstrated by the reaction of a fixed amount of air with heated copper. Copper will react with oxygen in the air to form copper(II) oxide. copper + oxygen  copper(II) oxide. 2Cu (s) (pink) + O 2(g) 2CuO (s) (black)

4. A known amount of air is passed backward and forward over the heated copper. As copper(II) oxide is formed, oxygen is removed from the air and the volume of air in the syringes is seen to decrease. When the reaction is complete, only 80% of the original volume of air remains. This shows that the proportion of oxygen in the air is about 20%.

5. Experiment using iron If the original volume of air was 15cm 3 and the final volume of air is 12cm 3 then the oxygen used up measured is 3 cm 3. % of oxygen = 3/15 *100 = 20%

6. Describe the laboratory preparation of oxygen from hydrogen peroxide 2H2O2  2H2O + O2 Hydrogen peroxide Water Oxygen

7. EQUATION: Catalyst is Manganese (IV) oxide Hydrogen peroxide  Water + Oxygen 2H 2 O 2  2H 2 O + O 2 DESCRIPTION: The apparatus is set up as shown above. 10 volume hydrogen peroxide is added slowly to the flask. [CARE: If O 2 is released too quickly the cork will explode out.] Oxygen is collected by downward displacement of water. PROPERTIES: Colourless, odourless gas. Slightly soluble in water (hence fish can breathe in it). Many substances, both elements and compounds, burn in oxygen (and in air which is one fifth oxygen). TEST: Oxygen relights a glowing splint.

8. Describe the reactions of magnesium, carbon and sulphur with oxygen in air and the acid base character of the oxides produced Reaction with magnesium. What precaution you need to take? Why? Write a balanced chemical reaction for the same.

9. Reaction of these oxides with water MgO MgO + H2O  Mg(OH)2 Basic (metal oxide) CO 2 CO2 + H2O  H2CO3 Acidic (Non-metal oxide) SO 2 SO2 + H2O  H2SO3 Acidic (Non-metal oxide) Acidic solution turns litmus blue to red and show a pH lower than 7 Basic solution turns litmus red to blue and show pH higher than 7

10. Describe the laboratory preparation of carbon dioxide from calcium carbonate and dilute hydrochloric acid Adding dilute hydrochloric acid to calcium carbonate powder or chips. The carbon dioxide gas is collected by downward delivery. CaCO3 + 2HCl  CaCl2 + CO2 + H2O

11. describe the formation of carbon dioxide from the thermal decomposition of metal carbonates such as copper(II) carbonate CuCO3  CuO + CO2 (green) (black)

12. Action of heat on carbonates: Sodium carbonate and potassium carbonate on heating will make any change. Other carbonate on heating gives oxide and carbon dioxide. Na2CO3  Heat …. No change CaCO3  Heat CaO + CO2 ZnCO3  Heat ZnO + CO2 CuCO3  Heat CuO + CO2 (blue green to black)

13. Action of heat on nitrates Sodium nitrate and potassium nitrate on heating give nitrite + Oxygen gas Sodium nitrate  Heat … Sodium nitrite + Oxygen 2NaNO3  Heat 2NaNO2 + O2 Calcium to cupper nitrate on heating gives metal oxide, Nitrogen dioxide and Oxygen gas. 2Mg(NO3)2  Heat 2MgO + 4NO2 + O2 2Zn(NO3)2  Heat 2ZnO + 4NO2 + O2 Silver and gold nitrate gives metal and nitrogen and Oxygen 2AgNO3  Heat 2Ag + N2 + 3O2

14. Action of heat on hydroxides Sodium hydroxide and potassium hydroxide on heating, no change Potassium hydroxide  Heat…No change Other hydroxides on heating gives metal oxide and water Mg(OH)2  Heat MgO H2O Ammonium chloride on heating gives Ammonia gas and hydrogen chloride gas. NH4Cl  Heat NH3 + HCl