iGCSE chemistry Section 2 lesson 5

1. iGCSE chemistrySection 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 • The Periodic Table • Group 1 Elements • Group 7 Elements • Oxygen and Oxides • Hydrogen and Water • Reactivity Series • Tests for ions and gases

4. g) Tests for ions and gases 2.37 describe tests for the cations: i Li+, Na+, K+, Ca2+ using flame tests ii NH4+, using sodium hydroxide solution and identifying the ammonia evolved iii Cu2+, Fe2+ and Fe3+, 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 SO42-, using dilute hydrochloric acid and barium chloride solution iii CO32-, 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. Lesson 5 g) Tests for ions and gases

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

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

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

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

9. Sodium ions, Na+, and Magnesium ions, Mg2+, are examples of cations

10. Sodium ions, Na+, and Magnesium ions, Mg2+, are examples of cations Group 1 metals form monovalent cations Eg. Lithium forms Li+

11. Sodium ions, Na+, and Magnesium ions, Mg2+, are examples of cations Group 2 metals form divalent cations Eg. Calcium forms Ca2+

12. Sodium ions, Na+, and Magnesium ions, Mg2+, are examples of cations Group 3 metals form trivalent cations Eg. Aluminium forms Al3+

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

14. Chloride ions, Cl-, and oxide ions, O2-, are examples of anions

15. Chloride ions, Cl-, and oxide ions, O2-, are examples of anions Group 6 elements form divalent anions Eg. sulphide forms S2-

16. Chloride ions, Cl-, and oxide ions, O2-, are examples of anions Group 7 elements form monovalent anions Eg. fluoride forms F-

17. Common cations

18. Common anions

19. g) Tests for ions and gases 2.37 describe tests for the cations: i Li+, Na+, K+, Ca2+ using flame tests ii NH4+, using sodium hydroxide solution and identifying the ammonia evolved iii Cu2+, Fe2+ and Fe3+, 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 SO42-, using dilute hydrochloric acid and barium chloride solution iii CO32-, 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. Lesson 5 g) Tests for ions and gases

20. Li+, Na+, K+, Ca2+ using flame tests

21. Li+, Na+, K+, Ca2+ using flame tests • Instructions for a flame test: • 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+, Ca2+ using flame tests • Instructions for a flame test: • Clean the flame test metal loop wire by dipping it into hydrochloric acid and then holding it in a hot Bunsen flame. • Repeat this until the wire doesn't produce any colour in the flame.

23. Li+, Na+, K+, Ca2+ using flame tests • Instructions for a flame test: • Clean the flame test metal loop wire by dipping it into hydrochloric acid and then holding it in a hot Bunsen flame. • 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+, Ca2+ using flame tests Instructions for a flame test: 4. Place the wire back in the flame again.

25. Li+, Na+, K+, Ca2+ 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+, Ca2+ 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+, Ca2+ using flame tests

28. Li+, Na+, K+, Ca2+ using flame tests Flame test results:

29. NH4+, using sodium hydroxide solution and identifying the ammonia produced

30. NH4+, using sodium hydroxide solution and identifying the ammonia produced NH4+ is the ammonium ion. Although not a metal, it is classified as a cation because it forms a positively charged ion.

31. NH4+, using sodium hydroxide solution and identifying the ammonia produced Test for NH4+ : All ammonium salts react with dilute alkalis, such as sodium hydroxide, to give ammonia. NH4Cl(aq) + NaOH(aq) NaCl(aq) + H2O(l) + NH3(g)

32. NH4+, using sodium hydroxide solution and identifying the ammonia produced Test for NH4+ : All ammonium salts react with dilute alkalis, such as sodium hydroxide, to give ammonia. NH4Cl(aq) + NaOH(aq) NaCl(aq) + H2O(l) + NH3(g) Because it is an alkaline gas, ammonia will turn red litmus blue

33. NH4+, using sodium hydroxide solution and identifying the ammonia produced

34. Cu2+, Fe2+ and Fe3+ using sodium hydroxide solution

35. Cu2+, Fe2+ and Fe3+ using sodium hydroxide solution When an iron(II) salt is added to sodium hydroxide, a dirty green precipitate of iron(II) hydroxide is formed.

36. Cu2+, Fe2+ and Fe3+ 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 FeSO4 + 2NaOH  Fe(OH)2 + Na2SO4

37. Cu2+, Fe2+ and Fe3+ 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. Cu2+, Fe2+ and Fe3+ 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. Cu2+, Fe2+ and Fe3+ 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. Cu2+, Fe2+ and Fe3+ 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 CuSO4 + NaOH  Cu(OH)2 + Na2SO4

41. g) Tests for ions and gases 2.37 describe tests for the cations: i Li+, Na+, K+, Ca2+ using flame tests ii NH4+, using sodium hydroxide solution and identifying the ammonia evolved iii Cu2+, Fe2+ and Fe3+, 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 SO42-, using dilute hydrochloric acid and barium chloride solution iii CO32-, 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. Lesson 5 g) Tests for ions and gases

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

43. Cl-, Br- and I- using dilute nitric acid and silver nitrate solution 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 + AgNO3 AgCl + NaNO3

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 + AgNO3 AgBr + NaNO3

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 + AgNO3 AgI + NaNO3

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

48. SO42- , using dilute hydrochloric acid and barium chloride solution

49. SO42- , using dilute hydrochloric acid and barium chloride solution STANDARD PROCEDURE: Dilute hydrochloric acid is added to a solution of the sulphate and then barium chloride solution is added.

50. SO42- , using dilute hydrochloric acid and barium chloride solution RESULT: A white precipitate shows the presence of a sulphate BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)