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New Way Chemistry for Hong Kong A-Level Book 41 1 Nitrogen and its Compound 43.1Introduction 43.2Unreactive Nature of Nitrogen 43.3Direct Combination.

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Presentation on theme: "New Way Chemistry for Hong Kong A-Level Book 41 1 Nitrogen and its Compound 43.1Introduction 43.2Unreactive Nature of Nitrogen 43.3Direct Combination."— Presentation transcript:

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2 New Way Chemistry for Hong Kong A-Level Book 41 1 Nitrogen and its Compound 43.1Introduction 43.2Unreactive Nature of Nitrogen 43.3Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides 43.4Ammonia 43.5Nitric(V) Acid 43.6Nitrates(V) Chapter 43

3 New Way Chemistry for Hong Kong A-Level Book Introduction (SB p.110) Nitrogen (first member of Group VA): Electronic configuration: 1s 2 2s 2 2p 3 Complete octet by forming diatomic molecules N  N Non-metal, colourless and odourless gas Very low melting and boiling points Slightly soluble in water and does not support combustion Covalent radius (nm)0.074 Melting point (°C)–210 Boiling point (°C)–196 Bond enthalpy (kJ mol –1 )+944 First ionization enthalpy (kJ mol –1 ) Electron affinity (kJ mol –1 ) +3 Electronegativity3.0 Some information about nitrogen

4 New Way Chemistry for Hong Kong A-Level Book Introduction (SB p.110) Nitrogen Mainly as free N 2 molecules in the atmosphere (78% by volume) Combine with other elements in the form of proteins in all living things Liquid N 2 is used as coolant Raw material for Haber process (manufacture of ammonia) Ammonia is the major component of nitrogenous fertilizers

5 New Way Chemistry for Hong Kong A-Level Book 44 4 Nitrogen in gaseous state As diatomic molecules (N 2 ) which are held by weak van der Waals’ forces 2 atoms are joined by extremely strong triple covalent bonds Bond enthalpy of the triple bond = +944 kJ mol –1 Due to extremely strong covalent bonds and absence of bond polarity  Nitrogen molecule is very unreactive 43.2 Unreactive Nature of Nitrogen (SB p.111)

6 New Way Chemistry for Hong Kong A-Level Book Unreactive Nature of Nitrogen (SB p.111) Bond Bond enthalpy (kJ mol –1 ) Bond Bond enthalpy (kJ mol –1 ) N  N O = O H – H C – C S – S Cl – Cl P – P F – F Bond enthalpies of some common covalent bonds

7 New Way Chemistry for Hong Kong A-Level Book 46 6 Reactions involving nitrogen usually have high activation energies and unfavourable equilibrium constants e.g.At 25°C N 2 (g) + O 2 (g)2NO(g)K c = 4.5  10 –31 The presence of catalyst and high temperature and pressure may be required for nitrogen to react N 2 (g) + 3H 2 (g)2NH 3 (g) 400 – 500°C, 300 – 1000 atm Fe as catalyst 43.2 Unreactive Nature of Nitrogen (SB p.111)

8 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.112) N 2 will not react at room temperature due to high bond enthalpy At high temperature, N 2 shows some reactions with other elements ∵ sufficient energy to break N  N triple bond At high temperature, N 2 (g) + O 2 (g) 2NO(g) 

9 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.112) The electric discharge in lightning provides sufficient energy to break the N  N triple bond and then react with O 2 N 2 (g) + O 2 (g)  2NO(g) 2NO(g) + O 2 (g)  2NO 2 (g) lightning colourless Reddish brown (poisonous) colourless

10 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.112) The above reactions are very important in nature The NO 2 formed dissolves in rainwater to produce nitric(V) acid and nitric(III) acid 2NO 2 (g) + H 2 O(l)  HNO 3 (aq) + HNO 2 (aq)

11 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.112) At high temperatures in car engines, N 2 & O 2 react to form NO(g) which emitted into air with exhausted gas The NO formed will be oxidized to NO 2 The NO 2 absorbs sunlight and breaks down into NO and O atom NO 2 (g)  NO(g) + O(g) These leads to formation of photochemical smog sunlight

12 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.113) In laboratory, we use the apparatus shown on the right to convert N 2 into NO 2 When current is switched on, electric discharges occur in the gap between the electrodes NO is formed and followed by NO 2

13 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.113) Other than NO and NO 2, N 2 can form other oxides e.g. 2 NO 2 molecules (brown) can combine to form a N 2 O 4 molecule (yellow) NO 2 & N 2 O 4 exist in equilibrium in gas phase 2NO 2 (g) N 2 O 4 (g)  H = –58 kJ mol –1 brown yellow

14 New Way Chemistry for Hong Kong A-Level Book 413 The formation of N 2 O 4 is exothermic  N 2 O 4 predominantes at low temperatures  NO 2 predominantes at high temperatures  the colour of mixture fades on cooling, darkens on warming 43.3 Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.113) NO 2 (left) and N 2 O 4 (right) predominate in hot water and ice water respectively

15 New Way Chemistry for Hong Kong A-Level Book 414 Check Point 43-1 (a)Draw the structures of the following compounds. (i)Dinitrogen monoxide (ii)Nitrogen monoxide (iii)Dinitrogen trioxide (iv)Nitrogen dioxide (v)Dinitrogen tetraoxide (vi)Dinitrogen pentaoxide Answer 43.3 Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.114) (a)(i)Dinitrogen monoxide (ii)Nitrogen monoxide

16 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.114) (iii)Dinitrogen trioxide (iv)Nitrogen dioxide

17 New Way Chemistry for Hong Kong A-Level Book Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.114) (v)Dinitrogen tetraoxide (vi)Dinitrogen pentaoxide

18 New Way Chemistry for Hong Kong A-Level Book 417 Check Point 43-1 (b)Arrange N 2, O 2 and F 2 in an ascending order of reactivity. Explain the order briefly. Answer (b) The ascending order of reactivity is: N 2 < O 2 < F 2. The reactivity of diatomic molecules depends on the bond enthalpy of covalent bonds. The bond enthalpy of N  N is greater than that of O = O, which in turn is greater than that of F – F. Therefore, the breakage of N  N bond requires the greatest amount of energy, whereas the breakage of F – F bond requires the least amount of energy Direct Combination of Nitrogen and Oxygen leading to Formation of Nitrogen Oxides (SB p.114)

19 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.114) Ammonia colourless, pungent gas polar molecules trigonal pyramidal shape with a lone pair of electrons on nitrogen extremely soluble in water and easy to condense to liquid due to hydrogen bonds good solvent for ionic compounds weakly alkaline NH 3 (aq) + H 2 O(l)NH 4 + (aq) + OH – (aq) K b = 1.8  10 –5 mol dm –3

20 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.114) Ammonia one of the most fundamental raw materials for modern industries important source of fertilizers and 85% of ammonia is used to make nitrogenous fertilizers (e.g. (NH 4 ) 2 SO 4, NH 4 NO 3 ) making fibres and plastics (rayon, nylon) making nitric(V) acid (used to make fertilizers, dyes) making household cleaners making detergents

21 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.115) Percentages of ammonia used in different industries

22 New Way Chemistry for Hong Kong A-Level Book 421 Manufacture of Ammonia by the Haber Process 43.4 Ammonia (SB p.115) NH 3 is manufactured industrially by the Haber Process, named after the German chemist Fritz Haber The process involves direct combination of N 2 and H 2 under special conditions N 2 (g) + H 2 (g)2NH 3 (g)  H = –92 kJ mol –1 Fritz Haber (1868 – 1934)

23 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.116) Flow diagram for the Haber process

24 New Way Chemistry for Hong Kong A-Level Book 423 Process of Haber Process: N 2 is obtained from fractional distillation of liquid air H 2 is obtained from methane, naphtha or mixture by steam reforming CH 4 (g) + H 2 O(g)  CO(g) + 3H 2 (g) CH 4 (g) + air  CO(g) + 2H 2 (g) + N 2 (g) Ni 900°C Ni 900°C 43.4 Ammonia (SB p.116)

25 New Way Chemistry for Hong Kong A-Level Book 424 Mixture of CO & H 2 O is mixed with steam and passed over a heated catalyst CO(g) + H 2 O(l)  CO 2 (g) + H 2 (g) The CO 2 formed is dissolved in water under pressure The gases (N 2 & H 2 ) are purified before proceeding to the next stage ∵ Compounds of oxygen and sulphur will poison the catalyst 43.4 Ammonia (SB p.116)

26 New Way Chemistry for Hong Kong A-Level Book 425 Purified N 2 & H 2 are mixed in ratio of 3 : 1 by volume  Compressed to 200 – 1000 atm and heated in the heat exchanger  Hot gaseous mixture is passed over iron in the catalytic chamber  Gases contain 10 – 15% of NH 3 and unreacted N 2 and H 2 when leaving the chamber  The gases are cooled after passing through the heat exchanger  NH 3 is liquefied under pressure and unreacted gases are recycled 43.4 Ammonia (SB p.116)

27 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.117) Physico-chemical principles: Synthesis of ammonia is an exothermic and reversible reaction N 2 (g) + H 2 (g)2NH 3 (g)  H = –92 kJ mol –1 According to Le Chatelier’s principle, (1)high pressure will increase the yield (2)low temperature will increase the yield

28 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.117) Apart from increasing yield, the reaction rate should be fast  Low temperatures would lower the rate of reaction ∴ optimum temperature is around 500°C which is high enough for reaction to proceed quickly but low enough to give satisfactory yield Catalyst is used to increase the reaction rate  poisoned by CO, CO 2, H 2 S  Gases entering the catalytic chamber should have high purity!!

29 New Way Chemistry for Hong Kong A-Level Book 428 Chemical Properties of Ammonia 43.4 Ammonia (SB p.118) As a base NH 3 partly ionizes in water to give NH 4 + and OH – ions ∴ NH 3 (aq) is alkaline NH 3 (g) + H 2 O(l) NH 4 + (aq) + OH – (aq) K b = 1.8  10 –5 mol dm –3 ∴ NH 3 (aq) is a weak base

30 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.118) Reaction with Acids NH 3 neutralizes acids to give ammonium salts e.g.2NH 3 (aq) + H 2 SO 4 (aq)  (NH 4 ) 2 SO 4 (aq) NH 3 (aq) + HNO 3 (aq)  NH 4 NO 3 (aq) ammonium sulphate(VI) ammonium nitrate(V) Filter paper soaked with NH 3 Filter paper soaked with HCl Formation of NH 4 Cl by reacting NH 3 with HCl NH 3 (aq) + HCl(aq)  NH 4 Cl(s)

31 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.118) Reaction with Metal Salts NH 3 precipitates the hydroxide of many metals from solutions of their salts CaSO 4 (aq) + 2NH 3 (aq) +2H 2 O(l)  Ca(OH) 2 (s) + (NH 4 ) 2 SO 4 (aq) ZnSO 4 (aq) + 2NH 3 (aq) +2H 2 O(l)  Zn(OH) 2 (s) + (NH 4 ) 2 SO 4 (aq) Pb(NO 3 ) 2 (aq) + 2NH 3 (aq) +2H 2 O(l)  Pb(OH) 2 (s) + 2NH 4 NO 3 (aq) CuSO 4 (aq) + 2NH 3 (aq) +2H 2 O(l)  Cu(OH) 2 (s) + (NH 4 ) 2 SO 4 (aq) FeSO 4 (aq) + 2NH 3 (aq) +2H 2 O(l)  Fe(OH) 2 (s) + (NH 4 ) 2 SO 4 (aq) Fe 2 (SO 4 ) 3 (aq) + 6NH 3 (aq) +6H 2 O(l)  2Fe(OH) 3 (s) + 3(NH 4 ) 2 SO 4 (aq) white blue dirty green reddish brown

32 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.119) Pb(OH) 2 (s)Cu(OH) 2 (s)Fe(OH) 2 (s)Fe(OH) 3 (s)

33 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.119) Some metal hydroxides (e.g. Zn(OH) 2 & Cu(OH) 2 ) redissolve in excess NH 3 solution and form complex compounds Zn(OH) 2 (s) + 4NH 3 (aq)  [Zn(NH 3 ) 4 ] 2+ (aq) + 2OH – (aq) Cu(OH) 2 (s) + 4NH 3 (aq)  [Cu(NH 3 ) 4 ] 2+ (aq) + 2OH – (aq) colourless deep blue A solution containing Cu 2+ (aq) Cu(OH) 2 (s) [Cu(NH 3 ) 4 ] 2+ (aq)

34 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.120) AgCl(s) dissolves Addition of excess NH 3 (aq) water AgCl(s) Silver(I) ions also form a complex with ammonia AgCl is insoluble in water and acids, but dissolves in excess NH 3 forming soluble complex ion [Ag(NH 3 ) 2 ] + (aq) AgCl(s) Ag + (aq) + Cl – (aq) Ag + (aq) + 2NH 3 (aq) [Ag(NH 3 ) 2 ] + (aq)

35 New Way Chemistry for Hong Kong A-Level Book 434 NH 3 does not burn in air or support combustion It burns in O 2 with a yellow flame, forming N 2 and water vapour 43.4 Ammonia (SB p.120) As a Reducing Agent Laboratory set-up for oxidation of ammonia Reaction with Oxygen 4NH 3 (g) + 3O 2 (g)  2N 2 (g) + 6H 2 O(g) 

36 New Way Chemistry for Hong Kong A-Level Book 435 In the presence of catalyst (red hot spiral coil of platinum at 800 – 900°C), NH 3 is oxidized to NO by O Ammonia (SB p.120) 4NH 3 (g) + 5O 2 (g)  4NO(g) + 6H 2 O(g) This is called catalytic oxidation of ammonia Key reaction in the preparation of HNO 3  Pt Laboratory set-up for catalytic oxidation of ammonia

37 New Way Chemistry for Hong Kong A-Level Book Ammonia (SB p.121) Reaction with Copper(II) Oxide When dry NH 3 is passed over heated black CuO, NH 3 is oxidized to N 2 and H 2 O The CuO turns from black to reddish brown as it is reduced to Cu 2NH 3 (g) + 3CuO(s)  3Cu(s) + N 2 (g) + 3H 2 O(g)  Laboratory set-up for oxidation of ammonia by copper(II) oxide

38 New Way Chemistry for Hong Kong A-Level Book 437 Check Point 43-2 (a)Write chemical equations to show how hydrogen is produced from (i)the reaction of natural gas (mainly methane) with water; (ii)the reaction of coal (mainly carbon) with water. Answer 43.4 Ammonia (SB p.121) (a) (i)CH 4 (g) + H 2 O(g)  CO(g) + 3H 2 (g) (ii)C(s) + H 2 O(l)  CO(g) + H 2 (g)  

39 New Way Chemistry for Hong Kong A-Level Book 438 Check Point 43-2 (cont’d) (b)Consider the following reversible reaction: N 2 (g) + 3H 2 (g)2NH 3 (g)  H = –92 kJ mol –1 Discuss how each of the following factors affects the above equilibrium: (i)increase in temperature (ii)decrease in pressure (iii)addition of a suitable catalyst Answer 43.4 Ammonia (SB p.121)

40 New Way Chemistry for Hong Kong A-Level Book 439 (b)(i) The forward reaction is exothermic. According to Le Chatelier’s principle, exothermic reactions are favoured at low temperatures. Therefore, an increase in temperature will favour the backward reaction, and thus decrease the yield of ammonia. (ii) According to Le Chatelier’s principle, a high pressure will increase the yield of ammonia as the forward reaction is accompanied by a decrease of volume from four to two volumes of the gas. Therefore, a decrease in pressure will decrease the yield of ammonia. (iii) Addition of a suitable catalyst will increase the rate of both forward and backward reactions to the same extent. As it does not change the position of the equilibrium, the yield of ammonia remains constant Ammonia (SB p.121)

41 New Way Chemistry for Hong Kong A-Level Book 440 Check Point 43-2 (cont’d) (c)Ammonia reacts with oxygen in two different ways. Give equations for both of these reactions and explain how one of them is used industrially to produce nitric(V) acid. Answer 43.4 Ammonia (SB p.121)

42 New Way Chemistry for Hong Kong A-Level Book 441 (c)In the absence of catalyst, ammonia burns to give molecular nitrogen and water vapour. 4NH 3 (g) + 3O 2 (g)  2N 2 (g) + 6H 2 O(g) Industrially, in the presence of red hot platinum-rhodium at about 850°C, ammonia is catalytically oxidized to nitrogen monoxide. 4NH 3 (g) + 5O 2 (s)4NO(g) + 6H 2 O(g) The nitrogen monoxide formed then reacts with oxygen from the air to give nitrogen dioxide. 2NO(g) + O 2 (g)  2NO 2 (g) The nitrogen dioxide reacts with excess air and water to produce aqueous nitric(V) acid. 4NO 2 (g) + O 2 (g) + 2H 2 O(l)  4HNO 3 (aq) H 2 O(l) + 3NO 2 (g)  2HNO 3 (aq) + NO(g) The NO(g) is recycled and subsequently combines with more oxygen and water to give more nitric(V) acid. Finally, the product is distilled to give concentrated nitric(V) acid (containing 68% HNO 3 ) Ammonia (SB p.121) Pt – Rh 850°C

43 New Way Chemistry for Hong Kong A-Level Book 442 Nitric(V) acid a very strong acid turns yellow on storage as the formation of dissolved NO 2 from decomposition of some acid 4HNO 3 (l)  4NO 2 (aq) + 2H 2 O(l) +O 2 (g) keep in brown bottles as light will speed up decomposition used to make explosives, nylon, fertilizers and dyestuff synthesis 43.5 Nitric(V) Acid (SB p.121)

44 New Way Chemistry for Hong Kong A-Level Book 443 Manufacture of Nitric(V) Acid from the Catalytic Oxidation of Ammonia 43.5 Nitric(V) Acid (SB p.122) Most of the ammonia formed is converted to nitric(V) acid by Ostward process Ostward process is divided into 3 stages: 1.Mixture of ammonia and excess air is passed over Pt-Rh catalyst at around °C under low pressure 4NH 3 (g) + 5O 2 (g)4NO(g) + 6H 2 O(g) Pt-Rh 850°C

45 New Way Chemistry for Hong Kong A-Level Book The NO formed then reacts with O 2 to form NO 2 2NO(g) + O 2 (g)  NO 2 (g) 3.The NO 2 reacts with excess air and water to give aqueous HNO 3 4NO 2 (g) + O 2 (g) + 2H 2 O(l)  4HNO 3 (aq) 43.5 Nitric(V) Acid (SB p.122)

46 New Way Chemistry for Hong Kong A-Level Book 445 Nitric(V) Acid as an Oxidizing Agent HNO 3 is a strong oxidizing agent, especially when concentrated NO 3 – acts as an electron acceptor when H + ions are present HNO 3 can be reduced to different nitrogen compounds with different oxidation states, depending on 1.the conc. of HNO 3 2.nature of substance being oxidized 43.5 Nitric(V) Acid (SB p.122)

47 New Way Chemistry for Hong Kong A-Level Book 446 If dilute or moderately concentrated HNO 3 is reduced, NO will be formed 4HNO 3 (aq) + 3e –  3NO 3 – (aq) + 2H 2 O(l) + NO(g) or NO 3 – (aq) + 4H + (aq) + 3e –  NO(g) + 2H 2 O(l) If concentrated HNO 3 is reduced, NO 2 will be formed 2HNO 3 (aq) + e –  NO 3 – (aq) + NO 2 (g) + H 2 O(l) or NO 3 – (aq) + 2H + (aq) + e –  NO 2 (g) + H 2 O(l) The electrons are supplied by the reducing agent in the reaction 43.5 Nitric(V) Acid (SB p.122)

48 New Way Chemistry for Hong Kong A-Level Book 447 Cu reacts with warm dilute HNO 3 to give NO 3Cu(s) + 8HNO 3 (aq)  3Cu(NO 3 ) 2 (aq) + 4H 2 O(l) + 2NO(g) The NO formed reacts with atmospheric O 2 to give NO 2 2NO(g) + O 2 (g)  2NO 2 (g) 43.5 Nitric(V) Acid (SB p.123) Reaction with Copper

49 New Way Chemistry for Hong Kong A-Level Book 448 Conc. HNO 3 (~14 M) reacts with Cu to give NO 2 and a blue solution of Cu(NO 3 ) 2 Cu(s) + 4HNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2H 2 O(l) + 2NO 2 (g) 43.5 Nitric(V) Acid (SB p.123)

50 New Way Chemistry for Hong Kong A-Level Book 449 Conc. HNO 3 oxdizes green Fe 2+ ions to brown Fe 3+ ions while itself reduced to NO 3Fe 2+ (aq) + NO 3 – (aq) + 4H + (aq)  3Fe 3+ (aq) + NO(g) + 2H 2 O(l) The NO formed reacts with atmospheric O 2 to form NO 2 2NO(g) + O 2 (g)  NO 2 (g) 43.5 Nitric(V) Acid (SB p.123) Reaction with Iron(II) Ion

51 New Way Chemistry for Hong Kong A-Level Book 450 Hot concentrated HNO 3 oxidizes sulphur to give sulphuric(VI) acid and brown fumes of NO 2 S(s) + 6HNO 3 (aq)  H 2 SO 4 (aq) + 6NO 2 (g) + 2H 2 O(l) 43.5 Nitric(V) Acid (SB p.123) Reaction with Sulphur

52 New Way Chemistry for Hong Kong A-Level Book 451 Check Point 43-3 Account for the following observation by giving a balanced equation. (a)Nitrogen monoxide turns brown when exposed to air. Answer 43.5 Nitric(V) Acid (SB p.123) (a)Nitrogen monoxide reacts with atmospheric oxygen to give brown nitrogen dioxide gas. 2NO(g) + O 2 (g)  2NO 2 (g)

53 New Way Chemistry for Hong Kong A-Level Book 452 Check Point 43-3 (cont’d) Account for the following observation by giving a balanced equation. (b)Nitric(V) acid turns yellowish brown on standing. Answer 43.5 Nitric(V) Acid (SB p.123) (b)Nitric(V) acid turns yellowish brown on standing because of the dissolved nitrogen dioxide formed from the decomposition of some of the acid. 4HNO 3 (aq)  4NO 2 (aq) + 2H 2 O(l) + O 2 (g)

54 New Way Chemistry for Hong Kong A-Level Book 453 Check Point 43-3 (cont’d) Account for the following observation by giving a balanced equation. (c)Silver dissolves in dilute nitric(V) acid, yielding a colourless gas. Answer 43.5 Nitric(V) Acid (SB p.123) (c)Dilute nitric(V) acid is reduced by silver to form colourless nitrogen monoxide gas. 3Ag(s) + 4HNO 3 (aq)  3Ag + (aq) + 3NO 3 – (aq) + 2H 2 O(l) + NO(g)

55 New Way Chemistry for Hong Kong A-Level Book 454 Check Point 43-3 (cont’d) Account for the following observation by giving a balanced equation. (d)The nitrate of a metal ion decomposed on heat to give the metal. Answer 43.5 Nitric(V) Acid (SB p.123) (d)Both mercury nitrate(V) and silver nitrate(V) decompose on heating to give the corresponding metal. Hg(NO 3 ) 2 (s)  Hg(s) + 2NO 2 (g) + O 2 (g) 2Ag(NO 3 ) 2 (s)  2Ag(s) + 2NO 2 (g) + O 2 (g)  

56 New Way Chemistry for Hong Kong A-Level Book Nitrates(V) (SB p.124) Metal nitrates(V) can be prepared by reacting very dilute nitric(V) acid with metals, metal oxides, hydroxides or carbonates e.g.Mg(s) + 2HNO 3 (aq)  Mg(NO 3 ) 2 (aq) + H 2 (g) CuO(s) + 2HNO 3 (aq)  Cu(NO 3 ) 2 (aq) + H 2 O(l) NaOH(aq) + HNO 3 (aq)  NaNO 3 (aq) + H 2 O(l) Na 2 CO 3 (aq) + 2HNO 3 (aq)  2NaNO 3 (aq) + H 2 O(l) + CO 2 (g) very dilute

57 New Way Chemistry for Hong Kong A-Level Book Nitrates(V) (SB p.124) Metal nitrates(V) can be prepared by reacting metals with concentrated nitric(V) acid e.g.Mg(s) + 4HNO 3 (aq)  Mg(NO 3 ) 2 (aq) + 2H 2 O(l) + 2NO 2 (g) concentrated

58 New Way Chemistry for Hong Kong A-Level Book 457 Action of Heat on Nitrates(V) When metal nitrates(V) in solid form are strongly heated, they decompose differently according to their thermal stability 43.6 Nitrates(V) (SB p.124) Metal oxide, nitrogen dioxide and oxygen 2Ca(NO 3 ) 2 (s)  2CaO(s) + 4NO 2 (g) + O 2 (g) 2Mg(NO 3 ) 2 (s)  2MgO(s) + 4NO 2 (g) + O 2 (g) 4Al(NO 3 ) 3 (s)  2Al 2 O 3 (s) + 12NO 2 (g) + 3O 2 (g) 2Zn(NO 3 ) 2 (s)  2ZnO(s) + 4NO 2 (g) + O 2 (g) 2Fe(NO 3 ) 2 (s)  2FeO(s) + 4NO 2 (g) + O 2 (g) 2Pb(NO 3 ) 2 (s)  2PbO(s) + 4NO 2 (g) + O 2 (g) 2Cu(NO 3 ) 2 (s)  2CuO(s) + 4NO 2 (g) + O 2 (g) Calcium Magnesium Aluminium Zinc Iron Lead Copper Metal nitrate(III), oxygen 2KNO 3 (s)  2KNO 2 (s) + O 2 (g) 2NaNO 3 (s)  2NaNO 2 (s) + O 2 (g) Potassium Sodium ProductReactionNitrate of         

59 New Way Chemistry for Hong Kong A-Level Book Nitrates(V) (SB p.124) Dinitrogen oxide and water NH 4 NO 3 (s)  N 2 O(g) + 2H 2 O(l) Ammonium ion Metal, nitrogen dioxide and oxygen Hg(NO 3 ) 2 (s)  Hg(s) + 2NO 2 (g) + O 2 (g) 2AgNO 3 (s)  2Ag(s) + 2NO 2 (g) + O 2 (g) Mercury(II) Silver ProductReactionNitrate of Cont’d   

60 New Way Chemistry for Hong Kong A-Level Book 459 Brown Ring Test for Nitrate(V) Ions The brown ring test is used to detect nitrate(V) ions in aqueous solutions 43.6 Nitrates(V) (SB p.125) Procedure: 1.Mix a freshly prepared FeSO 4 solution with a solution suspected of containing nitrate(V) ions in a test tube 2.Conc. H 2 SO 4 is added carefully along the side to the bottom of the test tube with the test tube tilted Laboratory set-up for brown ring test

61 New Way Chemistry for Hong Kong A-Level Book 460 Formation of a brown ring confirms the presence of nitrate(V) ions in the solution 43.6 Nitrates(V) (SB p.125)

62 New Way Chemistry for Hong Kong A-Level Book Nitrates(V) (SB p.125) Reactions involved in the brown ring test: Nitrate(V) ions react with conc. H 2 SO 4 to give HNO 3 NO 3 – (aq) + H 2 SO 4 (l)  HNO 3 (aq) + HSO 4 – (aq) The nitric(V) acid oxidizes some FeSO 4 to Fe 2 (SO 4 ) 3 and is itself reduced to NO HNO 3 (aq) + 3Fe 2+ (aq) + 3H + (aq)  NO(g) + 3Fe 3+ (aq) + 2H 2 O(l) Finally, NO reacts with unreacted FeSO 4 to form a brown complex FeSO 4 (aq) + NO(g)  FeSO 4 NO(aq) Brown complex

63 New Way Chemistry for Hong Kong A-Level Book 462 Check Point 43-4 Give the name of the ion responsible for the following observation. (a)An ion produces a blue precipitate with ammonia solution. The blue precipitate redissolves in excess ammonia solution to give a clear deep blue solution. Answer (a)Copper(II) ion 43.6 Nitrates(V) (SB p.125)

64 New Way Chemistry for Hong Kong A-Level Book 463 Check Point 43-4 (cont’d) Give the name of the ion responsible for the following observation. (b)An ion produces a dirty green precipitate with ammonia solution. Answer (b)Iron(II) ion 43.6 Nitrates(V) (SB p.125)

65 New Way Chemistry for Hong Kong A-Level Book 464 Check Point 43-4 (cont’d) Give the name of the ion responsible for the following observation. (c)An ion gives a positive result in the brown ring test. Answer (c)Nitrate(V) ion 43.6 Nitrates(V) (SB p.125)

66 New Way Chemistry for Hong Kong A-Level Book 465 The END


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