10. Chemistry of the environment
A section of Chemistry, 0620
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This question is about compounds of nitrogen. Nitrogen reacts with lithium to form lithiumnitride, Li3N. Write the chemical equation for the reaction between lithium and nitrogen. Lithiumnitride is ionically bonded. Complete the diagram to show the electronic structure of the nitride ion. Show the charge on the nitride ion. N  Nitrogen reacts with fluorine to form nitrogen trifluoride, NF3. The chemical equation can be represented as shown. N≡N + 3 F–F 2 F–N–F F Some bond energies are shown in the table. bond bond energy in kJ / mol N≡N F–F N–F Calculate the energy change for the reaction between nitrogen and fluorine, using the following steps: ● energy taken in to break bonds  kJ ● energy released when bonds are formed  kJ ● energy change during the reaction.  kJ / mol  Use your answer to to deduce whether this reaction is endothermic or exothermic. Explain your answer. Complete the dot-and-cross diagram to show the electron arrangement in a molecule of NF3. Use dots for nitrogen electrons and crosses for fluorine electrons. Show outer electrons only. F F F N  Lithiumnitride melts at 813 °C. Nitrogentrifluoride melts at –206 °C. Explain in terms of attractive forces why lithiumnitride has a much higher melting point than nitrogentrifluoride. In your answer refer to the types of attractive forces between particles and their relative strengths. Ammoniumnitrate, NH4NO3, is a compound of nitrogen. Calculate the percentage by mass of nitrogen in ammoniumnitrate.  percentage by mass of nitrogen = State a use of ammoniumnitrate in agriculture. State the name of a compound that will displace ammonia from ammoniumnitrate. Ammonia is a base which forms a weakly alkaline solution when dissolved in water. Define the term base. Suggest the pH of aqueous ammonia. 
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Paper 4, Variant 2
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