Beatty 12. QA4 – 5074 Nov 2015 Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: ________________ Class: 4E___ Practical 12: QA4 – 5074 Nov 2015 You are provided with solution R and solid S. Carry out the following tests and record your observations in the table. You should test and name any gas evolved. test no. test observations 1 (a) To 1 cm depth of R in a test-tube, add a few drops of aqueous silver nitrate. (b) Add dilute nitric acid to the mixture from (a). Pale yellow ppt formed. Pale yellow ppt remained insoluble in nitric acid. [2] 2 To 1 cm depth of aqueous iron(III) chloride in a test-tube, add an equal volume of R. Yellow solution turns brown. [1] 3 (a) To 1 cm depth of R in a test-tube, add an equal volume of dilute sulfuric acid and then one or two drops of S. (b) To the mixture from (a), add an equal volume of S and allow to stand for a few minutes. Yellow solution is formed. Yellow solution turns dark brown. On standing, black ppt is formed. [2] 4 (a) To 1 cm depth of iron(II) sulfate in a boiling tube, add an equal volume of S. (b) Add aqueous sodium hydroxide to the mixture from (a) until no further change occurs. Pale green solution turns brown. Effervescence is observed. Reddish-brown ppt formed; insoluble in excess aqueous sodium hydroxide. [2] 5 To 1 cm depth of aqueous acidified potassium manganate(VII) in a test-tube, add an equal volume of S. Purple acidified KMnO4 turns colourless. [1] 6 (a) To 1 cm depth of S in a test-tube, add a small amount of copper powder. (b) Add an equal volume of aqueous ammonia to the mixture from (a). Reddish-brown solid is insoluble in S. Some reddish-brown solid dissolves to form a blue solution. Effervescence is observed. Gas produced relights a glowing splint. Gas produced is oxygen. [4] 20

2 Conclusion: Consider the results of the experiments you have performed from tests 1 to 6. (a) Identify the anion present in R. Give evidence from your observations to support your conclusion. anion iodide ion / I− evidence Based on test 1, a yellow precipitate was formed when aqueous acidified silver nitrate was added. (b) State the role of S in test 4(a) and in test 5. Explain your answer. role of S in test 4(a) oxidising agent explanation Pale green Fe2+ ions in FeSO4 has been oxidised by S to form brown Fe3+ ions. role of S in test 5 reducing agent explanation oxidising agent purple acidified KMnO 4 has been reduced to form a colourless solution Planning: (c) An aqueous solution contains the following cations – Pb2+, Ca2+, Fe2+. In the space below, briefly describe the steps to prove that all the cations are present in the mixture. To the aqueous solution, add excess dilute hydrochloric acid. If a white precipitate is formed, this would indicate the presence of Pb2+ ions in lead(II) chloride. Filter the mixture to obtain lead(II) chloride as the residue. The filtrate would contain a mixture of excess hydrochloric acid, calcium ions and iron(II) ions. To the remaining filtrate, add excess dilute sulfuric acid. If a white preci pitate is formed, this would indicate the presence of Ca 2+ ions in calcium sulfate. Filter the mixture to obtain calcium sulfate as the residue. The filtrate would then contain a mixture of excess hydrochloric acid, excess sulfuric acid and iron(II) ions. To the remaining mixture, add excess aqueous sodium hydroxide / aqueous ammonia. If a dirty-green precipitate is formed, this would indicate the presence of Fe2+ ions in iron(II) hydroxide. ………………………………………………………………………………………………………………[5]

3 Revision Exercise: The following table shows the conclusions that a student made after carrying out tests with a white crystalline salt T. Fill in the observations for each test. test observations conclusions Dissolve a portion of T in distilled water. Add a few drops of aqueous sodium hydroxide to the solution of T. Continue adding aqueous sodium hydroxide until it is in excess. Zn2+ or Pb2+ ions may be present. Zn2+ or Pb2+ ions may be present. Dissolve a portion of T in distilled water. Add a few drops of aqueous ammonia to the solution of T. Continue adding aqueous ammonia until it is in excess. Zn2+ or Pb2+ ions maybe present. Zn2+ ions are present.