Chemistry 0620/51 October/November 2019: question paper and mark scheme

Question

You are going to investigate the reaction between dilute hydrochloric acid and three different concentrations of aqueous sodium hydroxide, labelled R, S and T. Read all the instructions carefully before starting the experiments. Instructions You are going to do three experiments. Experiment 1 ●● Fill the burette up to the 0.0 cm3 mark with dilute hydrochloric acid. ●● Use the measuring cylinder to pour 20 cm3 of solution R into the conical flask. ●● Add six drops of methyl orange indicator to the conical flask. ●● Add dilute hydrochloric acid from the burette to the conical flask, 1.0 cm3 at a time, while swirling the conical flask, until the solution just changes colour. ●● Record the burette readings in the table. ●● Empty the conical flask and rinse it with distilled water. Experiment 2 ●● Repeat Experiment 1 using solution S instead of solution R. ●● Record the burette readings in the table. Experiment 3 ●● Repeat Experiment 1 using solution T instead of solution R. ●● Record the burette readings in the table. (a) Complete the table. Experiment 1 Experiment 2 Experiment 3 burette reading / cm3 using solution R using solution S using solution T final burette reading initial burette reading volume used [4] (b) What colour change is observed in the conical flask at the end-point? from …… to …… [2] (c) Suggest why Universal Indicator is not a suitable indicator to use in these experiments. . …… . …… [1] (d) (i) Complete the sentences. Experiment …… needed the smallest volume of dilute hydrochloric acid to change the colour of the methyl orange indicator. Experiment …… needed the largest volume of dilute hydrochloric acid to change the colour of the methyl orange indicator. [1] (ii) Determine the simplest whole number ratio of volumes of dilute hydrochloric acid used in Experiments 1 and 2. Experiment 1 …… : …… Experiment 2 [1] (iii) Deduce the order of concentrations of the solutions of aqueous sodium hydroxide, R, S and T. most concentrated . …… . …… least concentrated . …… [1] (e) What would be the effect on the results, if any, if the solutions of aqueous sodium hydroxide were warmed before adding the dilute hydrochloric acid? Give a reason for your answer. effect on the results …… reason . …… [2] (f) Suggest how the reliability of the results could be checked. . …… . …… [2] (g) Suggest a different method, not involving an indicator, of finding the order of concentrations of the solutions of aqueous sodium hydroxide, R, S and T. . …… . …… . …… [3] [Total: 17]

Question

You are provided with solid U and liquid V. Do the following tests on solid U and liquid V, recording all of your observations at each stage. tests on solid U (a) Do a flame test on a small sample of solid U. Record your observations. . …… [1] Add the rest of solid U to about 10 cm3 of distilled water in a boiling tube. Stopper the boiling tube and shake the mixture to dissolve solid U and form solution U. (b) Describe the colour of solution U. . …… [1] Divide solution U into three approximately equal portions in three test‑tubes. (c) (i) Add a few drops of aqueous sodium hydroxide to the first portion of solution U. Record your observations. . …… [1] (ii) Now add an excess of aqueous sodium hydroxide to this mixture. Record your observations. . …… [1] (d) (i) Add a few drops of aqueous ammonia to the second portion of solution U. Record your observations. . …… [2] (ii) Now add an excess of aqueous ammonia to this mixture. Record your observations. . …… [1] (e) Add a few drops of dilute nitric acid and about 1 cm3 of aqueous barium nitrate to the third portion of solution U. Leave to stand for 5 minutes. Record your observations. . …… [2] (f) Solid U contains three different ions. What conclusions can you draw about the ions present in solid U? . …… . …… [3] tests on liquid V (g) Describe the appearance of liquid V. Record your observations. . …… [1] (h) Use a teat pipette to place a few drops of liquid V onto a watch‑glass. Put the stopper back into the test‑tube of liquid V. Use a lighted splint to touch the surface of liquid V carefully. Record your observations. . …… [1] (i) Use a spatula to transfer a small crystal of iodine carefully into the rest of liquid V in the stoppered test‑tube. Put the stopper back into the test‑tube and shake the test‑tube. Record your observations. . …… . …… [2] (j) Draw one conclusion about liquid V. . …… [1] [Total: 17]

Question

Potassium nitrate and ammonium chloride are two salts. The energy change when they each dissolve in water is endothermic. Plan an experiment to show which of these two salts produces the larger endothermic energy change per gram. Your answer should include: ●● any measurements you would take and record ●● how the results could be used to draw a conclusion. You are provided with potassium nitrate and ammonium chloride, distilled water and 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