Chemistry 0620/52 May/June 2019: question paper and mark scheme

Question

You are going to investigate the rate of reaction between magnesium ribbon and solutions of dilute hydrochloric acid of different concentrations, solutions H, I, J and K. The dilute hydrochloric acid is in excess in all experiments. Read all the instructions carefully before starting the experiments. Instructions You are going to do five experiments. Experiment 1 ●● Use the 50 cm3 measuring cylinder to pour 30 cm3 of solution H into the beaker. ●● Add a 5.0 cm length of magnesium ribbon to solution H in the beaker and start the timer immediately. Stir the mixture constantly. ●● Measure the time taken for all of the magnesium ribbon to react and to disappear completely. ●● Record the time taken in the table. ●● Rinse out the beaker with distilled water. Experiment 2 ●● Repeat Experiment 1 but use solution I instead of solution H. Record the time taken in the table. Experiment 3 ●● Repeat Experiment 1 but use solution J instead of solution H. Record the time taken in the table. Experiment 4 ●● Repeat Experiment 1 but use solution K instead of solution H. Record the time taken in the table. (a) Record your results from Experiments 1–4 in the table. concentration of time taken for the experiment solution hydrochloric acid magnesium ribbon to in mol / dm3 disappear completely / s 1 H 2.0 2 I 1.5 3 J 1.0 4 K 0.8 [3] (b) Experiment 5 Add about 3 cm3 of solution J to a 5.0 cm length of magnesium ribbon in a test-tube. Test the gas produced with a lighted splint. Record your observations. . …… . …… . …… [3] (c) Plot your results for Experiments 1–4 on the grid. Draw a smooth line graph. time taken for the magnesium ribbon to disappear completely / s 0.0 0.5 1.0 1.5 2.0 2.5 3.0 concentration of hydrochloric acid in mol / dm3 [3] (d) From your graph, deduce the time taken for the magnesium ribbon to disappear completely if a solution of hydrochloric acid of concentration 2.5 mol / dm3 were used. Show clearly on the grid how you worked out your answer. . …… [3] (e) (i) Why was the same length of magnesium ribbon used in Experiments 1–4? . …… [1] (ii) Suggest the effect on the results if Experiments 1–4 were repeated using 2.5 cm lengths of magnesium ribbon instead of 5.0 cm lengths of magnesium ribbon. Explain your answer. . …… . …… [1] (f) Suggest a different method which could be used to investigate the rate of reaction between magnesium ribbon and dilute hydrochloric acid. State the apparatus you would use and the measurements you would take. apparatus . …… . …… measurements . …… . …… . …… [3] (g) Use your observations from Experiment 5 to answer these questions. (i) What type of chemical reaction occurs when magnesium ribbon reacts with dilute hydrochloric acid? . …… [1] (ii) Identify the gas produced. . …… [1] [Total: 19] Question 2 starts on the next page.

Question

You are provided with solid L, which contains two cations and one anion. Do the following tests on solid L, recording all of your observations at each stage. tests on solid L (a) Describe the appearance of solid L. . …… [1] Use a spatula to divide solid L into two approximately equal portions. (b) Heat the first portion of solid L in a hard‑glass test‑tube. Test any gas produced with blue cobalt(II) chloride paper. Record your observations. . …… . …… [3] Add the second portion of solid L to about 10 cm3 of distilled water in a boiling tube. Stopper the boiling tube and shake the mixture to dissolve solid L and form solution L. Divide solution L into five approximately equal portions in five test-tubes. (c) Test the pH of the first portion of solution L. pH = …… [1] (d) (i) Transfer the second portion of solution L into a boiling tube. Add about 3 cm3 of aqueous sodium hydroxide. Record your observations. . …… [1] (ii) Gently warm the mixture from (d)(i) and test the gas produced. Record your observations. . …… . …… [2] (e) Add an excess of aqueous ammonia to the third portion of solution L. Record your observations. . …… [1] (f) Add a few drops of dilute nitric acid and about 1 cm3 of aqueous silver nitrate to the fourth portion of solution L. Record your observations. . …… [1] (g) Add a few drops of dilute nitric acid and about 1 cm3 of aqueous barium nitrate to the fifth portion of solution L. Record your observations. . …… [1] (h) What does the test in (b) tell you about solid L? . …… [1] (i) Identify the three ions in solid L. . …… [3] [Total: 15]

Question

Azurite is an ore of copper which contains copper(II) carbonate. Azurite contains no other metal ions. Plan an experiment to show how a sample of copper could be obtained from large lumps of azurite. Your answer should include: ●● descriptions of the reactions involved ●● the expected observations. You are provided with a large lump of azurite and common laboratory chemicals and apparatus. . …… . …… . …… . …… . …… . …… . …… . …… . …… [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate (CO32–) add dilute acid effervescence, carbon dioxide produced chloride (Cl –) acidify with dilute nitric acid, then add white ppt. [in solution] aqueous silver nitrate bromide (Br –) acidify with dilute nitric acid, then add cream ppt. [in solution] aqueous silver nitrate iodide (I–) acidify with dilute nitric acid, then add yellow ppt. [in solution] aqueous silver nitrate nitrate (NO3–) add aqueous sodium hydroxide, then ammonia produced [in solution] aluminium foil; warm carefully sulfate (SO42–) acidify, then add aqueous white ppt. [in solution] barium nitrate sulfite (SO32–) add dilute hydrochloric acid, warm sulfur dioxide produced gently and test for the presence of will turn acidified aqueous sulfur dioxide potassium manganate(VII) from purple to colourless Tests for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia aluminium (Al 3+) white ppt., soluble in excess, giving a white ppt., insoluble in excess colourless solution ammonium (NH4+) ammonia produced on warming – calcium (Ca2+) white ppt., insoluble in excess no ppt., or very slight white ppt. chromium(III) (Cr3+) green ppt., soluble in excess grey-green ppt., insoluble in excess copper(II) (Cu2+) light blue ppt., insoluble in excess light blue ppt., soluble in excess, giving a dark blue solution iron(II) (Fe2+) green ppt., insoluble in excess green ppt., insoluble in excess iron(III) (Fe3+) red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc (Zn2+) white ppt., soluble in excess, giving a white ppt., soluble in excess, giving a colourless solution colourless solution Tests for gases Flame tests for metal ions gas test and test result metal ion flame colour ammonia (NH3) turns damp red litmus paper blue lithium (Li+) red carbon dioxide (CO2) turns limewater milky sodium (Na+) yellow chlorine (Cl 2) bleaches damp litmus paper potassium (K+) lilac hydrogen (H2) ‘pops’ with a lighted splint copper(II) (Cu2+) blue-green oxygen (O2) relights a glowing splint sulfur dioxide (SO2) turns acidified aqueous potassium manganate(VII) from purple to colourless