Chemistry 0620/51 May/June 2019: question paper and mark scheme

Question

You are going to investigate the reaction between aqueous sodium carbonate and aqueous barium nitrate. Read all the instructions carefully before starting the experiment. Instructions You are going to do one experiment. ●● Fill the burette up to the 0.0 cm3 mark with the aqueous sodium carbonate. ●● Label the test-tubes 1, 2, 3, 4, 5 and 6 and place them in order in the test-tube rack. ●● Use the measuring cylinder to pour 6 cm3 of the aqueous barium nitrate into each of the six test-tubes. ●● dd 1.0 cm3 of aqueous sodium carbonate from the burette to test-tube 1. A ●● Add 2.0 cm3 of aqueous sodium carbonate from the burette to test-tube 2. ●● Add 4.0 cm3 of aqueous sodium carbonate from the burette to test-tube 3. ●● Add 5.0 cm3 of aqueous sodium carbonate from the burette to test-tube 4. ●● Add 6.0 cm3 of aqueous sodium carbonate from the burette to test-tube 5. ●● Add 7.0 cm3 of aqueous sodium carbonate from the burette to test-tube 6. Using the glass rod, carefully stir the contents of each of the test-tubes. Leave the contents of the test-tubes to stand for at least 10 minutes. You should start Question 2 while you are waiting for the solid formed in the test‑tubes to settle. (a) After 10 minutes, use a ruler to measure the height of the solid formed in each test-tube. Record your results in the table. test-tube volume of aqueous height of solid number sodium carbonate / cm3 / mm 1 2 3 4 5 6 [4] (b) Plot your results on the grid. Draw a line of best fit. height of solid / mm 0 1 2 3 4 5 6 7 8 volume of aqueous sodium carbonate / cm3 [3] (c) From your graph, deduce the height of the solid formed when 3.0 cm3 of aqueous sodium carbonate is added to 6 cm3 of aqueous barium nitrate. Show clearly on the grid how you worked out your answer. . …… [3] (d) Describe the trend in the heights of the solids formed in test-tubes 1–6. . …… . …… [1] (e) Explain one improvement you could make to the experiment to obtain more accurate results for the heights of the solid formed. improvement . …… explanation …… . …… [2] (f) Suggest a different method to measure the amount of solid formed during the experiment. . …… . …… . …… . …… [3] (g) Suggest how the reliability of the results could be checked. . …… . …… [1] (h) What type of chemical reaction occurs when aqueous sodium carbonate reacts with aqueous barium nitrate? . …… [1] [Total: 18] Question 2 starts on the next page.

Question

You are provided with two substances, solution F and solid G. Do the following tests on the substances, recording all of your observations at each stage. tests on solution F Divide solution F into five approximately equal portions in five test-tubes. (a) Test the pH of the first portion of solution F. pH = …… [1] (b) Add a strip of magnesium ribbon to the second portion of solution F. Shake the mixture. Test the gas produced. Record your observations. . …… . …… [2] (c) Add a few drops of dilute nitric acid and about 1 cm3 of aqueous silver nitrate to the third portion of solution F. 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 F. Record your observations. . …… [1] Keep the fifth portion of the solution F for the test in (f). tests on solid G (e) Describe the appearance of solid G. . …… [1] (f) Add the fifth portion of solution F to solid G. Test the gas produced. Record your observations. . …… . …… . …… [3] Add about 2 cm3 of distilled water to the solution formed in the test in (f) and shake the mixture. Divide the solution formed into two approximately equal portions in two test-tubes for the tests in (g) and (h). (g) Add aqueous sodium hydroxide to the first portion of the solution until no further change occurs. Record your observations. . …… [2] (h) Add an excess of aqueous ammonia to the second portion of the solution. Record your observations. . …… [1] (i) Identify solution F. . …… [2] (j) Identify solid G. . …… [2] [Total: 16]

Question

Steel nails rust in the presence of air and water. Plan an investigation to: ●● show that coating steel nails with paint helps to protect the nails from rusting ●● show that coating steel nails with zinc helps to protect the nails from rusting ●● determine which coating is more effective at protecting steel nails from rusting. You are provided with: ●● uncoated steel nails ●● steel nails coated with paint ●● steel nails coated with zinc ●● common laboratory 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