Chemistry 0620/53 May/June 2020: question paper and mark scheme

Question

You are going to investigate the temperature change when aqueous sodium hydroxide neutralises dilute hydrochloric acid. The equation for the reaction is shown. NaOH + HCl → NaCl + H2O Read all of the instructions carefully before starting the experiments. Instructions You are going to do eight experiments. Experiment 1 ●● Place the polystyrene cup into the 250 cm3 beaker for support. ●● Use a measuring cylinder to pour 5 cm3 of aqueous sodium hydroxide into the polystyrene cup. ●● Use a measuring cylinder to pour 45 cm3 of dilute hydrochloric acid into the polystyrene cup. ●● Stir the mixture in the polystyrene cup with the thermometer. Record the highest temperature reached in the table in (a). ●● Rinse out the polystyrene cup with distilled water. Experiment 2 Repeat Experiment 1 using 10 cm3 of aqueous sodium hydroxide and 40 cm3 of ●● dilute hydrochloric acid. Experiment 3 ●● Repeat Experiment 1 using 15 cm3 of aqueous sodium hydroxide and 35 cm3 of dilute hydrochloric acid. Experiment 4 Repeat Experiment 1 using 20 cm3 of aqueous sodium hydroxide and 30 cm3 of ●● dilute hydrochloric acid. Experiment 5 ●● Repeat Experiment 1 using 30 cm3 of aqueous sodium hydroxide and 20 cm3 of dilute hydrochloric acid. Experiment 6 ●● Repeat Experiment 1 using 35 cm3 of aqueous sodium hydroxide and 15 cm3 of dilute hydrochloric acid. Experiment 7 ●● Repeat Experiment 1 using 40 cm3 of aqueous sodium hydroxide and 10 cm3 of dilute hydrochloric acid. Experiment 8 Repeat Experiment 1 using 45 cm3 of aqueous sodium hydroxide and 5 cm3 of ●● dilute hydrochloric acid. (a) Complete the table. Experiment 1 2 3 4 5 6 7 8 volume of aqueous 5 10 15 20 30 35 40 45 sodium hydroxide / cm3 volume of dilute hydrochloric acid / cm3 highest temperature reached / °C [4] (b) Add a suitable scale to the y-axis. Your scale should extend by at least 2 °C above your highest temperature. Plot your results from Experiments 1 to 8 on the grid. Draw two straight lines through your points. Extend your straight lines so that they cross. highest temperature reached / °C 0 5 10 15 20 25 30 35 40 45 50 volume of aqueous sodium hydroxide / cm3 [5] (c) The point on the graph where the two straight lines cross is where all of the aqueous sodium hydroxide reacts with all of the dilute hydrochloric acid to form a neutral solution. (i) Use your graph to deduce the volume of aqueous sodium hydroxide and the volume of dilute hydrochloric acid that react together to produce a neutral solution. Show your working on the grid. volume of aqueous sodium hydroxide = …… cm3 volume of dilute hydrochloric acid = …… cm3 [3] (ii) Use your graph to determine the highest temperature reached if the volumes in (c)(i) were mixed together. highest temperature reached = …… °C [1] (iii) Which solution, aqueous sodium hydroxide or dilute hydrochloric acid, was the most concentrated? Use your answer to (c)(i) to explain why. most concentrated solution . …… explanation …… . …… [1] (d) On the graph, sketch the lines you would expect to obtain if a copper can was used instead of a polystyrene cup. [2] (e) Give one advantage and one disadvantage of using a burette, instead of a measuring cylinder, to add the dilute hydrochloric acid directly into the polystyrene cup. advantage . …… . …… disadvantage …… . …… [2] (f) How could the reliability of the results of this investigation be checked? . …… . …… [1] [Total: 19]

Question

You are provided with two solids, solid N and solid P. Do the following tests on solid N and solid P, recording all of your observations at each stage. tests on solid N (a) Describe the appearance of solid N. . …… [1] (b) Add about 10 cm3 of distilled water to the boiling tube containing solid N. Place a stopper in the boiling tube and shake the tube to dissolve solid N and form solution N. Divide solution N into two approximately equal portions in two boiling tubes. (i) To the first portion of solution N add aqueous ammonia slowly until it is in excess and no further changes are seen. Record your observations. . …… . …… . …… [2] (ii) To the second portion of solution N add aqueous sodium hydroxide slowly until it is in excess and no further changes are seen. Keep the product for (b)(iii). Record your observations. . …… . …… . …… [2] (iii) Pour about 3 cm depth of the product from (b)(ii) into a boiling tube. Add a piece of aluminium foil and warm the mixture gently. Test any gas produced. Record your observations. . …… . …… . …… [2] (c) Identify solid N. . …… . …… [2] tests on solid P (d) Carry out a flame test on solid P. Record your observations. . …… [1] (e) Place solid P in a boiling tube. Add about 10 cm3 of distilled water to the boiling tube. Place a stopper in the boiling tube and shake the tube to dissolve solid P and form solution P. Divide solution P into three approximately equal portions in three test-tubes. (i) To the first portion of solution P add about 1 cm depth of dilute nitric acid and a few drops of aqueous silver nitrate. Record your observations. . …… [1] (ii) To the second portion of solution P add about 1 cm depth of dilute nitric acid and a few drops of aqueous barium nitrate. Record your observations. . …… . …… [1] (iii) Add the third portion of solution P to the test-tube containing aqueous bromine. Record your observations. . …… . …… [1] (f) Identify solid P. . …… . …… [2] [Total: 15]

Question

Stayclean and Brightwhite are two brands of washing powder. Both contain sodium carbonate. Sodium carbonate is soluble in water and reacts with dilute sulfuric acid to produce carbon dioxide gas. Plan an investigation to determine which of the two washing powders, Stayclean or Brightwhite, contains the greatest percentage of sodium carbonate. You are provided with samples of the two washing powders and common laboratory apparatus and chemicals. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [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