Chemistry 0620/53 May/June 2022: question paper and mark scheme

Question

You are going to investigate the reaction between aqueous sodium hydroxide and two different solutions of dilute hydrochloric acid with different concentrations, labelled Q and R, using two different indicators. Read all of the instructions carefully before starting the experiments. Instructions You are going to do three experiments. (a) Experiment 1 ● Fill the burette with dilute hydrochloric acid Q. Run some of the dilute hydrochloric acid out of the burette so that the level of the dilute hydrochloric acid is on the burette scale. Record the burette reading in the table. ● Use a measuring cylinder to pour 25 cm3 of the aqueous sodium hydroxide for Question 1 into a conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add dilute hydrochloric acid from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the burette reading in the table and complete the table. Experiment 1 final burette reading / cm3 initial burette reading / cm3 volume of dilute hydrochloric acid Q added / cm3 Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Rinse the burette with distilled water and then with dilute hydrochloric acid R. ● Repeat Experiment 1 using dilute hydrochloric acid R instead of dilute hydrochloric acid Q. Experiment 2 final burette reading / cm3 initial burette reading / cm3 volume of dilute hydrochloric acid R added / cm3 Experiment 3 ● Empty the conical flask and rinse it with distilled water. ● Repeat Experiment 2 using thymolphthalein indicator instead of methyl orange indicator. Experiment 3 final burette reading / cm3 initial burette reading / cm3 volume of dilute hydrochloric acid R added / cm3 [6] (b) Determine the simplest whole number ratio of the volumes of dilute hydrochloric acid R used in Experiment 2 and Experiment 3. …… [1] (c) Use your ratio in (b) to deduce the volume of dilute hydrochloric acid Q needed when Experiment 1 is repeated using thymolphthalein indicator instead of methyl orange indicator. volume of hydrochloric acid Q = …… [2] (d) Compare the concentration of dilute hydrochloric acid Q used in Experiment 1 to the concentration of dilute hydrochloric acid R used in Experiment 2. Explain your answer. …… [3] (e) State how the results change, if at all, if the aqueous sodium hydroxide is warmed before adding the dilute hydrochloric acid. Give a reason for your answer. effect on results …… reason …… [2] (f) State the advantage of using a pipette instead of the measuring cylinder in these experiments. …… [1] (g) Explain why a white tile is used in these experiments. …… [1] (h) At the start of Experiment 2 the burette was rinsed with distilled water and then with dilute hydrochloric acid R. (i) State what was removed from the burette when it was rinsed with distilled water. . …… [1] (ii) State what was removed from the burette when it was rinsed with dilute hydrochloric acid R. . …… [1] (iii) Explain why the burette does not need to be rinsed at the start of Experiment 3. . …… . …… [1] (i) After the burette was filled with dilute hydrochloric acid at the start of Experiment 1, some of the acid was run out of the burette. One reason for running the acid out of the burette is to make sure the level of the hydrochloric acid is on the scale. Give one other reason why it is important to run some acid out of the burette after it has been filled for the first time in an experiment. …… [1] [Total: 20]

Question

You are provided with solid S. Do the following tests on solid S, recording all of your observations at each stage. tests on solid S To the boiling tube containing solid S add about 20 cm3 of distilled water. Stopper the boiling tube and shake the mixture to dissolve solid S and form solution T. Divide solution T into six approximately equal portions in six test-tubes. (a) State the colour change that occurred when distilled water was added to solid S to form solution T. from solid S …… to solution T …… [1] (b) Test the pH of the first portion of solution T. pH = …… [1] (c) To the second portion of solution T, add the strip of magnesium ribbon. Record your observations. …… [2] (d) (i) To the third portion of solution T, add the aqueous potassium iodide. Keep the product for use in (ii). Record your observations. . …… [1] (ii) To the product from (i) add the aqueous sodium thiosulfate. Gently shake the test-tube. Record your observations. . …… [1] (e) To the fourth portion of solution T, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. …… [1] (f) To the fifth portion of solution T, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. …… [1] (g) To the sixth portion of solution T, add aqueous ammonia dropwise and then in excess. Record your observations. …… [3] (h) Identify solid S. …… [3] [Total: 14]

Question

When solution A and solution B are mixed they react slowly to form iodine. Starch solution is added to the mixture to act as an indicator. When a certain amount of iodine is made there is a sudden colour change to blue-black. Plan an investigation to find the effect of temperature on the rate of the reaction between solution A and solution B. You are provided with solution A, solution B, starch solution 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