1. IGCSE CHEMISTRY SECTION 2 LESSON 5

2. Content The iGCSE Chemistry course Section 1 Principles of Chemistry Section 2 Chemistry of the Elements Section 3 Organic Chemistry Section 4 Physical Chemistry Section 5 Chemistry in Society

3. Content Section 2 Chemistry of the Elements a)The Periodic Table b)Group 1 Elements c)Group 7 Elements d)Oxygen and Oxides e)Hydrogen and Water f)Reactivity Series g)Tests for ions and gases

4. Lesson 5 g) Tests for ions and gases 2.37 describe tests for the cations: i Li +, Na +, K +, Ca 2+ using flame tests ii NH 4 +, using sodium hydroxide solution and identifying the ammonia evolved iii Cu 2+, Fe 2+ and Fe 3+, using sodium hydroxide solution 2.38 describe tests for the anions: i Cl -, Br - and I -, using dilute nitric acid and silver nitrate solution ii SO 4 2-, using dilute hydrochloric acid and barium chloride solution iii CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved 2.39 describe tests for the gases: i hydrogen ii oxygen iii carbon dioxide iv ammonia v chlorine.

5. What’s a cation (and now we mention it, what’s an anion?)

7. Cations are positively charged ions

8. What’s a cation (and now we mention it, what’s an anion?) Cations are positively charged ions

9. Sodium ions, Na +, and Magnesium ions, Mg 2+, are examples of cations

10. Group 1 metals form monovalent cations Eg. Lithium forms Li +

11. Sodium ions, Na +, and Magnesium ions, Mg 2+, are examples of cations Group 2 metals form divalent cations Eg. Calcium forms Ca 2+

12. Sodium ions, Na +, and Magnesium ions, Mg 2+, are examples of cations Group 3 metals form trivalent cations Eg. Aluminium forms Al 3+

13. What’s a cation (and now we mention it, what’s an anion?) Anions are negatively charged ions

14. Chloride ions, Cl -, and oxide ions, O 2-, are examples of anions

15. Group 6 elements form divalent anions Eg. sulphide forms S 2-

16. Chloride ions, Cl -, and oxide ions, O 2-, are examples of anions Group 7 elements form monovalent anions Eg. fluoride forms F -

17. Common cations MonovalentDivalentTrivalent Lithium Li + Potassium K + Sodium Na + Copper(I) Cu + Silver Ag + Hydrogen H + Barium Ba 2+ Calcium Ca 2+ Magnesium Mg 2+ Zinc Zn 2+ Iron(II) Fe 2+ Tin(II) Sn 2+ Lead(II) Pb 2+ Copper(II) Cu 2+ Aluminium Al 3+ Iron(III) Fe 3+

18. Common anions MonovalentDivalentTrivalent Bromide Br - Chloride Cl - Iodide I - Hydroxide OH - Nitrate NO 3 - Oxide O 2- Carbonate CO 3 2- Sulphate SO 4 2- Sulphite SO 3 2- Sulphide S 2- Phosphate PO 4 3-

19. Lesson 5 g) Tests for ions and gases 2.37 describe tests for the cations: i Li +, Na +, K +, Ca 2+ using flame tests ii NH 4 +, using sodium hydroxide solution and identifying the ammonia evolved iii Cu 2+, Fe 2+ and Fe 3+, using sodium hydroxide solution 2.38 describe tests for the anions: i Cl -, Br - and I -, using dilute nitric acid and silver nitrate solution ii SO 4 2-, using dilute hydrochloric acid and barium chloride solution iii CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved 2.39 describe tests for the gases: i hydrogen ii oxygen iii carbon dioxide iv ammonia v chlorine.

20. Li +, Na +, K +, Ca 2+ using flame tests

21. Instructions for a flame test: 1.Clean the flame test metal loop wire by dipping it into hydrochloric acid and then holding it in a hot Bunsen flame.

22. Li +, Na +, K +, Ca 2+ using flame tests Instructions for a flame test: 1.Clean the flame test metal loop wire by dipping it into hydrochloric acid and then holding it in a hot Bunsen flame. 2.Repeat this until the wire doesn't produce any colour in the flame.

23. Li +, Na +, K +, Ca 2+ using flame tests Instructions for a flame test: 1.Clean the flame test metal loop wire by dipping it into hydrochloric acid and then holding it in a hot Bunsen flame. 2.Repeat this until the wire doesn't produce any colour in the flame. 3. When the wire is clean, moisten it again with some of the acid and then dip it into a small amount of the solid you are testing so that some sticks to the wire.

24. Li +, Na +, K +, Ca 2+ using flame tests Instructions for a flame test: 4. Place the wire back in the flame again.

25. Li +, Na +, K +, Ca 2+ using flame tests Instructions for a flame test: 4. Place the wire back in the flame again. 5. If the flame colour is weak, it is often worthwhile to dip the wire back in the acid again and put it back into the flame as if you were cleaning it. You often get a very short but intense flash of colour by doing that.

26. Li +, Na +, K +, Ca 2+ using flame tests Instructions for a flame test: 4. Place the wire back in the flame again. 5. If the flame colour is weak, it is often worthwhile to dip the wire back in the acid again and put it back into the flame as if you were cleaning it. You often get a very short but intense flash of colour by doing that. RESULT?

27. Li +, Na +, K +, Ca 2+ using flame tests

28. Flame test results: CATIONFLAME TEST COLOUR Lithium RED Sodium STRONG PERSISTENT ORANGE Potassium LILAC (PINK) Calcium ORANGE-RED

29. NH 4 +, using sodium hydroxide solution and identifying the ammonia produced

30. NH 4 + is the ammonium ion. Although not a metal, it is classified as a cation because it forms a positively charged ion.

31. NH 4 +, using sodium hydroxide solution and identifying the ammonia produced Test for NH 4 + : All ammonium salts react with dilute alkalis, such as sodium hydroxide, to give ammonia. NH 4 Cl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) + NH 3(g)

32. NH 4 +, using sodium hydroxide solution and identifying the ammonia produced Test for NH 4 + : All ammonium salts react with dilute alkalis, such as sodium hydroxide, to give ammonia. NH 4 Cl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) + NH 3(g) Because it is an alkaline gas, ammonia will turn red litmus blue

33. NH 4 +, using sodium hydroxide solution and identifying the ammonia produced

34. Cu 2+, Fe 2+ and Fe 3+ using sodium hydroxide solution

35. When an iron(II) salt is added to sodium hydroxide, a dirty green precipitate of iron(II) hydroxide is formed.

36. Cu 2+, Fe 2+ and Fe 3+ using sodium hydroxide solution When an iron(II) salt is added to sodium hydroxide, a dirty green precipitate of iron(II) hydroxide is formed. Eg. Iron + Sodium  Iron + Sodium sulphate hydroxide hydroxide sulphate FeSO 4 + 2NaOH  Fe(OH) 2 + Na 2 SO 4

37. Cu 2+, Fe 2+ and Fe 3+ using sodium hydroxide solution When an iron(III) salt is added to sodium hydroxide, a orange / brown precipitate of iron(III) hydroxide is formed.

38. Cu 2+, Fe 2+ and Fe 3+ using sodium hydroxide solution When an iron(III) salt is added to sodium hydroxide, a orange / brown precipitate of iron(III) hydroxide is formed. Eg Iron + sodium  iron + sodium chloride hydroxide hydroxide chloride Fe(Cl) 3 + 3NaOH  Fe(OH) 3 + 3NaCl

39. Cu 2+, Fe 2+ and Fe 3+ using sodium hydroxide solution When a copper(II) salt is added to sodium hydroxide, a pale blue precipitate of copper(II) hydroxide is formed.

40. Cu 2+, Fe 2+ and Fe 3+ using sodium hydroxide solution When a copper(II) salt is added to sodium hydroxide, a pale blue precipitate of copper(II) hydroxide is formed. Eg. Copper + Sodium  Copper + Sodium sulphate hydroxide hydroxide sulphate CuSO 4 + NaOH  Cu(OH) 2 + Na 2 SO 4

41. Lesson 5 g) Tests for ions and gases 2.37 describe tests for the cations: i Li +, Na +, K +, Ca 2+ using flame tests ii NH 4 +, using sodium hydroxide solution and identifying the ammonia evolved iii Cu 2+, Fe 2+ and Fe 3+, using sodium hydroxide solution 2.38 describe tests for the anions: i Cl -, Br - and I -, using dilute nitric acid and silver nitrate solution ii SO 4 2-, using dilute hydrochloric acid and barium chloride solution iii CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved 2.39 describe tests for the gases: i hydrogen ii oxygen iii carbon dioxide iv ammonia v chlorine.

42. Cl -, Br - and I - using dilute nitric acid and silver nitrate solution

43. STANDARD PROCEDURE: Add dilute nitric acid to a solution of the halide, and then add silver nitrate solution.

44. Cl -, Br - and I - using dilute nitric acid and silver nitrate solution RESULT: With a chloride solution, a white precipitate of silver chloride is formed: NaCl + AgNO 3  AgCl + NaNO 3

45. Cl -, Br - and I - using dilute nitric acid and silver nitrate solution RESULT: With a bromide solution, a pale yellow precipitate of silver bromide is formed: NaBr + AgNO 3  AgBr + NaNO 3

46. Cl -, Br - and I - using dilute nitric acid and silver nitrate solution RESULT: With an iodide solution, a yellow precipitate of silver iodide is formed: NaI + AgNO 3  AgI + NaNO 3

47. Cl -, Br - and I - using dilute nitric acid and silver nitrate solution Halide Results: Chloride Bromide Iodide

48. SO 4 2-, using dilute hydrochloric acid and barium chloride solution

49. STANDARD PROCEDURE: Dilute hydrochloric acid is added to a solution of the sulphate and then barium chloride solution is added.

50. SO 4 2-, using dilute hydrochloric acid and barium chloride solution RESULT: A white precipitate shows the presence of a sulphate BaCl 2(aq) + Na 2 SO 4(aq)  BaSO 4(s) + 2NaCl (aq)

51. SO 4 2-, using dilute hydrochloric acid and barium chloride solution Barium sulphate precipitate

52. CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved

53. STANDARD PROCEDURE: Dilute hydrochloric acid is added to a solution of the carbonate.

54. CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved RESULT: A gas, carbon dioxide, is produced which will turn limewater cloudy (then clear again)

55. CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved RESULT: CaCO 3(aq) + 2HCl (aq)  CaCl 2(aq) + H 2 O (l) + CO 2(g) Calcium + Hydrochloric  Calcium + water + carbon Carbonate Acid Chloride dioxide

56. CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved Calcium carbonate + Hydrochloric acid Limewater

57. Lesson 5 g) Tests for ions and gases 2.37 describe tests for the cations: i Li +, Na +, K +, Ca 2+ using flame tests ii NH 4 +, using sodium hydroxide solution and identifying the ammonia evolved iii Cu 2+, Fe 2+ and Fe 3+, using sodium hydroxide solution 2.38 describe tests for the anions: i Cl -, Br - and I -, using dilute nitric acid and silver nitrate solution ii SO 4 2-, using dilute hydrochloric acid and barium chloride solution iii CO 3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved 2.39 describe tests for the gases: i hydrogen ii oxygen iii carbon dioxide iv ammonia v chlorine.

58. Tests for gases You need to know these!

59. Tests for gases 1. Hydrogen Magnesium ribbon Hydrochloric acid Hydrogen gas

60. Tests for gases 1. Hydrogen Magnesium ribbon Hydrochloric acid Hydrogen gas

61. Tests for gases 1. Hydrogen Magnesium ribbon Hydrochloric acid Hydrogen gas POP!

62. Tests for gases 1. Hydrogen Magnesium ribbon Hydrochloric acid Hydrogen gas POP! To test for hydrogen, use a burning splint. The gas will explode with a squeaky ‘pop’.

63. Tests for gases 2. Oxygen Hydrogen peroxide Manganese (IV) oxide Oxygen gas

64. Tests for gases 2. Oxygen Hydrogen peroxide Manganese (IV) oxide Oxygen gas Glowing splint

65. Tests for gases 2. Oxygen Hydrogen peroxide Manganese (IV) oxide Oxygen gas Splint re-lights

66. Tests for gases 2. Oxygen Hydrogen peroxide Manganese (IV) oxide Oxygen gas Splint re-lights To test for oxygen, use a glowing splint. The gas will cause the splint to re-light.

67. Tests for gases 3. Carbon dioxide Calcium carbonate Hydrochloric acid Bubbles of carbon dioxide Delivery tube Limewater

68. Tests for gases 3. Carbon dioxide Calcium carbonate Hydrochloric acid Bubbles of carbon dioxide Delivery tube Limewater

69. Tests for gases 3. Carbon dioxide Calcium carbonate Hydrochloric acid Bubbles of carbon dioxide Delivery tube Limewater To test for carbon dioxide, bubble the gas through limewater. After a short while the limewater will go milky-white.

70. Tests for gases 3. Carbon dioxide Calcium carbonate Hydrochloric acid Bubbles of carbon dioxide Delivery tube Limewater To test for carbon dioxide, bubble the gas through limewater. After a short while the limewater will go milky-white. If carbon dioxide continues to be bubbled through limewater, the liquid will eventually go clear again.

71. Tests for gases 4. Ammonia

72. Tests for gases 4. Ammonia

73. Tests for gases 4. Ammonia Ammonia gas will turn moist litmus paper from RED to BLUE

74. Tests for gases 5. Chlorine

75. Tests for gases 5. Chlorine

76. Tests for gases 5. Chlorine Chlorine gas will turn moist litmus paper from BLUE to RED, and will then bleach it WHITE

77. Tests for gases Summary GasTest Positive result Hydrogen Burning splint Burns with a squeaky pop Oxygen Glowing splint Relights a glowing splint Carbon dioxide Bubble through Limewater Limewater turns cloudy Ammonia Moist red litmus paper Turns from red to blue Chlorine Moist blue litmus paper Bleaches the paper

78. End of Section 2 Lesson 5 In this lesson we have covered: Tests for Cations Tests for Anions Tests for the gases