Chemistry 0620/61 May/June 2024: question paper and mark scheme

Question

A student carries out a titration to find the concentration of a sample of dilute hydrochloric acid. The student: ● adds 25.0 cm3 of aqueous potassium hydroxide to the apparatus labelled A in Fig. 1.1 B 25.0 cm3 aqueous potassium hydroxide A Fig. 1.1 ● adds a few drops of a suitable indicator to the apparatus labelled A ● uses a burette to add dilute hydrochloric acid to the aqueous potassium hydroxide and indicator mixture in the apparatus labelled A. (a) Name the items of apparatus labelled A and B in Fig. 1.1. A …… B …… [2] (b) The student adds the indicator after the volume of the 25.0 cm3 of aqueous potassium hydroxide has been measured. (i) Explain why the student adds an indicator to the aqueous potassium hydroxide. . …… [1] (ii) Name a suitable indicator. . …… [1] (c) Describe how the student can determine the volume of dilute hydrochloric acid used in this titration. …… [2] (d) The student observes the colour changes that occur as they add dilute hydrochloric acid from the burette. State one other thing the student should do as they add the dilute hydrochloric acid to the aqueous potassium hydroxide. …… [1] [Total: 7]

Question

A student investigates the temperature change when magnesium reacts with dilute sulfuric acid. The student does five experiments. Experiment 1 ● Use a 25 cm3 measuring cylinder to pour 20 cm3 of dilute sulfuric acid into a boiling tube. ● Use a thermometer to measure the initial temperature of the acid in the boiling tube. Record the initial temperature. ● Add a coiled 5 cm length of magnesium ribbon to the acid in the boiling tube. At the same time start a timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture in the boiling tube. Record this temperature. ● Rinse the boiling tube with distilled water. Experiment 2 ● Use the 25 cm3 measuring cylinder to pour 20 cm3 of dilute sulfuric acid into the boiling tube. ● Use a 10 cm3 measuring cylinder to add 2.0 cm3 of distilled water to the acid in the boiling tube. ● Place a bung in the boiling tube and invert the tube to mix the acid and water. ● Use the thermometer to measure the initial temperature of the contents of the boiling tube. Record the initial temperature. ● Add a coiled 5 cm length of magnesium ribbon to the contents of the boiling tube. At the same time start a timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture. Record this temperature. ● Rinse the boiling tube with distilled water. Experiment 3 ● Repeat Experiment 2, adding 4.0 cm3 of distilled water instead of 2.0 cm3. Experiment 4 ● Repeat Experiment 2, adding 6.0 cm3 of distilled water instead of 2.0 cm3. Experiment 5 ● Repeat Experiment 2, adding 10.0 cm3 of distilled water instead of 2.0 cm3. (a) Use the information in the description of the experiments and the thermometer diagrams to complete Table 2.1. Table 2.1 volume of volume of thermometer initial temperature temperature dilute distilled diagram experiment temperature after 45 s increase sulfuric acid water after 45 s / °C / °C / °C / cm3 / cm3 / °C 40 1 25.0 35 30 40 2 25.5 35 30 40 3 25.5 35 30 35 4 26.0 30 25 35 5 26.0 30 25 [5] (b) (i) State which Experiment, 1, 2, 3, 4 or 5, had the smallest temperature change. . …… [1] (ii) Explain why the temperature change was smallest in the experiment you have given in (b)(i). . …… . …… [1] (c) Complete a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on Fig. 2.1. Draw a line of best fit. temperature increase / C 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 volume of distilled water / cm3 Fig. 2.1 [4] (d) Use your graph in Fig. 2.1 to deduce the temperature increase when Experiment 2 is repeated with 7.5 cm3 of distilled water instead of 2.0 cm3. Show clearly on Fig. 2.1 how you worked out your answer. …… °C [2] (e) The average rate of temperature increase in each experiment is calculated using the equation shown. temperature increase average rate of temperature increase = 45 seconds Calculate the average rate of temperature increase in Experiment 1. Give units for the rate you have calculated. average rate of temperature increase = …… units = …… [2] (f) (i) Explain why the results of the experiment are more accurate if the boiling tube is wrapped in cotton wool. . …… . …… . …… [2] (ii) Explain why a 25.0 cm3 volumetric pipette cannot be used to accurately measure the volume of the distilled water added. . …… . …… [1] (iii) State one other way in which the apparatus can be changed to give more accurate results. . …… . …… . …… [1] (g) Sketch on Fig. 2.1 the graph you would expect if all of the experiments were repeated using a 2 cm length of magnesium ribbon instead of the 5 cm length. Label your line g. [1] [Total: 20]

Question

A student tests two substances: solution E and solid F. Tests on solution E Solution E is aqueous chromium(III) bromide. Solution E is divided into two portions. Record the expected observations. (a) To the first portion of solution E, the student adds aqueous sodium hydroxide dropwise and then in excess. observations adding dropwise …… observation in excess …… [2] (b) To the second portion of solution E, the student adds about 1 cm3 of dilute nitric acid and a few drops of aqueous silver nitrate. observations …… …… [1] Tests on solid F Table 3.1 shows the tests and the student’s observations for solid F. Table 3.1 tests observations test 1 Heat about half of solid F in a boiling tube until the white solid forms a colourless liquid, there is no further change. steam comes out from the boiling tube and condensation is seen at the top of the boiling tube, after a while the colourless liquid becomes a white solid test 2 The remaining solid F is dissolved in water to form solution F. Solution F is divided into three portions. To the first portion of solution F in a boiling no change tube, add aqueous sodium hydroxide dropwise and then in excess. Warm the product and hold damp red litmus the damp red litmus paper remains red paper at the mouth of the boiling tube. test 3 To the second portion of solution F, add 1 cm3 white precipitate of dilute nitric acid followed by a few drops of aqueous barium nitrate. test 4 To the third portion of solution F, add a the solution becomes light purple few drops of acidified aqueous potassium manganate(VII). (c) The observations in test 1 show that solid F is hydrated. Describe a chemical test to show that the condensation at the top of the boiling tube contains water. test . …… result . …… [2] (d) From the tests and observations in Table 3.1 it is not possible to identify the cation in solid F. Give another test that can be carried out to help identify the cation in solid F. …… [1] (e) Identify the anion in solid F. …… [1] [Total: 7]

Question

A mixture contains three compounds: ● liquid ethanol ● solid sodium chloride ● solid zinc carbonate. Table 4.1 gives some information about these three compounds. Table 4.1 name of compound solubility in water solubility in ethanol ethanol soluble sodium chloride soluble insoluble zinc carbonate insoluble insoluble Describe how to obtain a pure sample of each of the three compounds, ethanol, sodium chloride and zinc carbonate, from the mixture. You are provided with common laboratory apparatus. …… [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate, CO32– add dilute acid, then test for carbon effervescence, carbon dioxide dioxide gas produced chloride, Cl – acidify with dilute nitric acid, then white ppt. [in solution] add aqueous silver nitrate bromide, Br – acidify with dilute nitric acid, then cream ppt. [in solution] add aqueous silver nitrate iodide, I– acidify with dilute nitric acid, then yellow ppt. [in solution] add aqueous silver nitrate nitrate, NO3– add aqueous sodium hydroxide, ammonia produced [in solution] then aluminium foil; warm carefully sulfate, SO42– acidify with dilute nitric acid, then white ppt. [in solution] add aqueous barium nitrate sulfite, SO32– add a small volume of acidified the acidified aqueous potassium aqueous potassium manganate(VII) manganate(VII) changes colour 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 white ppt., insoluble in excess a 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 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, ppt. turns brown near surface on ppt. turns brown near surface on standing standing iron(III), Fe3+ red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc, Zn2+ white ppt., soluble in excess, giving white ppt., soluble in excess, giving a colourless solution a colourless solution Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 turns limewater milky chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium manganate(VII) from purple to colourless Flame tests for metal ions metal ion flame colour lithium, Li+ red sodium, Na+ yellow potassium, K+ lilac calcium, Ca2+ orange-red barium, Ba2+ light green copper(II), Cu2+ blue-green