Question 117 marks
Question
You are going to investigate the reaction between two different solutions, A and B, of aqueous potassium manganate(VII) and solution C. Read all the instructions carefully before starting the experiments. Instructions You are going to do three experiments. (a) Experiment 1 ●● Fill the burette up to the 0.0 cm3 mark with solution A. ●● Use the 25 cm3 measuring cylinder to pour 25 cm3 of solution C into the conical flask. ●● Add about 1 cm3 of solution A to the conical flask and swirl the conical flask. ●● Continue to add solution A to the conical flask until the mixture just turns permanently pink. ●● Record the burette readings in the table and complete the table. ●● Pour about 2 cm3 of the contents of the conical flask into a test-tube. ●● Pour away the rest of the contents of the conical flask and rinse the conical flask with distilled water. Keep the test-tube from Experiment 1 to use in Experiment 3. Experiment 1 final burette reading / cm3 initial burette reading / cm3 volume used / cm3 [2] (b) Experiment 2 ●● Pour away the contents of the burette and rinse the burette with distilled water. ●● Rinse the burette with solution B. ●● Fill the burette up to the 0.0 cm3 mark with solution B. ●● Use the 25 cm3 measuring cylinder to pour 25 cm3 of solution C into the conical flask. ●● Add about 1 cm3 of solution B to the conical flask and swirl the conical flask. ●● Continue to add solution B to the conical flask until the mixture just turns permanently pink. ●● Record the burette readings in the table and complete the table. Experiment 2 final burette reading / cm3 initial burette reading / cm3 volume used / cm3 [2] (c) Experiment 3 (i) Add aqueous sodium hydroxide to about 2 cm3 of solution C in a test-tube. Record your observations. . …… [1] (ii) Add aqueous sodium hydroxide to the reaction mixture in the test-tube saved from Experiment 1. Record your observations. . …… [1] Which solution of potassium manganate(VII), solution A or solution B, is the more (d) (i) concentrated? Explain your answer. . …… . …… [2] (ii) How many times more concentrated is this solution of potassium manganate(VII)? . …… [1] (e) (i) Predict the volume of solution B that would be used if Experiment 2 were repeated using 50 cm3 of solution C. Explain your answer. . …… . …… [2] (ii) Suggest a practical problem that using 50 cm3 of solution C could cause. How could this problem be solved? . …… . …… [2] (f) Give one advantage and one disadvantage of using a measuring cylinder rather than a pipette for solution C. advantage of using a measuring cylinder …… . …… disadvantage of using a measuring cylinder …… . …… [2] (g) What conclusions can be drawn about solution C from Experiment 3? . …… . …… [2] [Total: 17] 2 You are provided with two substances, solution D and solid E. Do the following tests on the substances, recording all of your observations at each stage. tests on solution D Divide solution D into five approximately equal portions in five test-tubes. (a) Test the pH of the first portion of solution D. pH = …… [1] (b) Add a strip of magnesium ribbon to the second portion of solution D. Shake the mixture. Test the gas produced. Record your observations. . …… . …… . …… [3] (c) Add a few drops of dilute nitric acid and about 1 cm3 of aqueous silver nitrate to the third portion of solution D. Record your observations. . …… [1] (d) Add a few drops of dilute nitric acid and about 1 cm3 of aqueous barium nitrate to the fourth portion of solution D. Record your observations. . …… [1] Keep the fifth portion of solution D for the test in (g). tests on solid E (e) Describe the appearance of solid E. . …… [1] (f) (i) Use a spatula to place half of solid E into a hard-glass test-tube. Heat the solid gently and then more strongly. Leave the hard-glass test-tube to stand for five minutes to cool. Record your observations. . …… [1] (ii) Now add about 2 cm3 of distilled water to the residue in the hard-glass test-tube. Test the pH of the mixture. pH = …… [1] (g) Add the rest of solid E to the fifth portion of solution D. Test the gas produced. Record your observations. . …… . …… . …… [3] Keep the solution from the test in (g) for the test in (h). (h) Add an approximately equal volume of distilled water to the solution from the test in (g) and shake the mixture. Add an excess of aqueous sodium hydroxide to the mixture. Record your observations. . …… [1] (i) Identify solution D. . …… [2] (j) What conclusions can you draw about solid E? . …… [2] [Total: 17]
Mark scheme
1(a) Table of results for Experiment 1 1 Initial, final volumes and differences completed correctly All readings to 1 dp Comparable to supervisor’s 1 1(b) Table of results for Experiment 2 1 Initial, final volumes and differences completed correctly All readings to 1 dp Comparable to supervisor’s 1 1(c)(i) Green precipitate 1 1(c)(ii) Red-brown precipitate 1 1(d)(i) Solution A 1 Smaller volume / less (of potassium manganate used) / solution A 1 1(d)(ii) 2 × (times) as concentrated 1 1(e)(i) 2 × (times) value from table for Experiment 2 1 Double volume (of C) used 1 1(e)(ii) Volume of potassium manganat 1 e solution added > 50 cm3 Use more than one burette / refill burette 1 1(f) Advantage easy to use / quick 1 Disadvantage not as accurate owtte 1 1(g) (Solution C) contains iron(II) (ions) / Fe2+ 1 Reference to oxidation / (iron(II)) → iron(III) / Fe3+ 1 Tests on solution D