12.5 Identification of ions and gases
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22. Describe the test and result for identifying the carbonate (CO32-) anion.
Add dilute acid and test for carbon dioxide gas; the result is effervescence and carbon dioxide is produced (turning limewater milky).
23. Describe the test and result for chloride (Cl-) ions in solution.
Acidify with dilute nitric acid, then add aqueous silver nitrate; a white precipitate is formed.
24. Describe the test and result for bromide (Br-) ions in solution.
Acidify with dilute nitric acid, then add aqueous silver nitrate; a cream precipitate is formed.
25. Describe the test and result for iodide (I-) ions in solution.
Acidify with dilute nitric acid, then add aqueous silver nitrate; a yellow precipitate is formed.
26. Describe the test for nitrate (NO3-) ions.
Add aqueous sodium hydroxide, then aluminium foil, and warm carefully; ammonia gas is produced.
27. Describe the test and result for sulfate (SO42-) ions.
Acidify with dilute nitric acid, then add aqueous barium nitrate; a white precipitate is formed.
28. Describe the test and result for sulfite (SO32-) ions.
Add a small volume of acidified aqueous potassium manganate(VII); the solution changes from purple to colourless.
29. Describe the results of testing aqueous aluminium (Al3+) with sodium hydroxide and ammonia.
With aqueous sodium hydroxide, a white precipitate forms which is soluble in excess to give a colourless solution; with aqueous ammonia, a white precipitate forms which is insoluble in excess.
30. Describe the test and result for aqueous ammonium (NH4+).
Add aqueous sodium hydroxide and warm; ammonia is produced.
31. Describe the results of testing aqueous calcium (Ca2+) with sodium hydroxide and ammonia.
With aqueous sodium hydroxide, a white precipitate forms that is insoluble in excess; with aqueous ammonia, no precipitate or a very slight white precipitate is formed.
32. Describe the results of testing aqueous chromium(III) (Cr3+) with sodium hydroxide and ammonia.
With aqueous sodium hydroxide, a green precipitate forms that is soluble in excess; with aqueous ammonia, a grey-green precipitate forms that is insoluble in excess.
33. Describe the results of testing aqueous copper(II) (Cu2+) with sodium hydroxide and ammonia.
With aqueous sodium hydroxide, a light blue precipitate forms that is insoluble in excess; with aqueous ammonia, a light blue precipitate forms which is soluble in excess to give a dark blue solution.
34. Describe the results of testing aqueous iron(II) (Fe2+) with sodium hydroxide and ammonia.
Both reagents produce a green precipitate that is insoluble in excess; the precipitate turns brown near the surface on standing.
35. Describe the results of testing aqueous iron(III) (Fe3+) with sodium hydroxide and ammonia.
Both reagents produce a red-brown precipitate that is insoluble in excess.
36. Describe the results of testing aqueous zinc (Zn2+) with sodium hydroxide and ammonia.
Both reagents produce a white precipitate that is soluble in excess to give a colourless solution.
37. Describe the test and result for ammonia (NH3) gas.
Use damp red litmus paper; it turns blue.
38. Describe the test and result for carbon dioxide (CO2) gas.
Use limewater; it turns milky.
39. Describe the test and result for chlorine (Cl2) gas.
Use damp litmus paper; it is bleached.
40. Describe the test and result for hydrogen (H2) gas.
Use a lighted splint; the gas "pops".
41. Describe the test and result for oxygen (O2) gas.
Use a glowing splint; the splint relights.
42. Describe the test and result for sulfur dioxide (SO2) gas.
Use acidified aqueous potassium manganate(VII); it turns from purple to colourless.
43. State the flame test colour for lithium (Li+).
Red.
44. State the flame test colour for sodium (Na+).
Yellow.
45. State the flame test colour for potassium (K+).
Lilac.
46. State the flame test colour for calcium (Ca2+).
Orange-red.
47. State the flame test colour for barium (Ba2+).
Light green.
48. State the flame test colour for copper(II) (Cu2+).
Blue-green.