Chemistry 0620/62 February/March 2023: question paper and mark scheme

Question

Long-chain alkanes can be broken down into shorter chain alkanes and gaseous alkenes. Vapour from a long-chain alkane is passed over a very hot catalyst and the gases formed are collected over water. The apparatus used is shown in Fig. 1.1. aluminium oxide catalyst gaseous alkenes long-chain alkane on mineral wool delivery tube A water Fig. 1.1 (a) Name the item of apparatus labelled A in Fig. 1.1. . …… [1] (b) The catalyst is small pieces of aluminium oxide. Explain why several small pieces of aluminium oxide speed up the reaction more than one large piece of aluminium oxide. . …… . …… [1] (c) (i) Name the item of apparatus that can be used to heat the long-chain alkane and catalyst. . …… [1] (ii) Add two arrows to Fig. 1.1 to show where the apparatus should be heated. [1] (d) The gas collected is tested using aqueous bromine. Alkenes turn aqueous bromine from orange to colourless. When the first few bubbles of gas collected are tested, the aqueous bromine does not change colour. Explain why the aqueous bromine does not change colour. . …… . …… [1] (e) As soon as the experiment is over and the heating is stopped, the delivery tube must be removed from the water. Explain what happens if the delivery tube is not removed from the water as soon as the heating is stopped. . …… . …… [2] [Total: 7]

Question

A student investigates the solubility of ammonium chloride in water at different temperatures. The student does five experiments using the following instructions. Experiment 1 ● Fill a burette with distilled water. ● Run some of the water out of the burette so that the level of the water is on the burette scale. ● Use the burette to add 8.0 cm3 of distilled water to a 5.25 g sample of ammonium chloride in a boiling tube. ● Clamp the boiling tube at an angle, as shown in Fig. 2.1. clamp solid ammonium chloride water Fig. 2.1 ● Gently heat the bottom of the boiling tube while stirring the contents with a thermometer. ● Stop heating as soon as all the solid has dissolved. ● Continuously stir the solution with the thermometer while it cools. ● Measure the temperature of the solution as soon as the solution becomes cloudy and a solid starts to form. Experiment 2 ● Use the burette to add 0.5 cm3 of distilled water to the mixture in the boiling tube from the previous experiment. ● Clamp the boiling tube as shown in Fig. 2.1. ● Gently heat the bottom of the boiling tube while stirring the contents with a thermometer. ● Stop heating as soon as all the solid has dissolved. ● Continuously stir the solution with the thermometer while it cools. ● Measure the temperature of the solution as soon as the solution becomes cloudy and a solid starts to form. Experiment 3 ● Repeat Experiment 2. Experiment 4 ● Repeat Experiment 2. Experiment 5 ● Repeat Experiment 2. (a) Use the information in the description of the experiments and the thermometer diagrams to complete Table 2.1. Table 2.1 mass of thermometer temperature total volume experiment ammonium diagram when a when a solid of water / cm3 chloride / g solid starts to form starts to form / °C 80 1 8.0 75 70 70 2 65 60 65 3 60 55 60 4 55 50 50 5 45 40 [4] (b) Complete a suitable scale on the y-axis of Fig. 2.2 and plot your results from Experiments 1 to 5 on Fig. 2.2. Draw a line of best fit through your points. temperature when a solid starts to form / C 30 8.0 8.5 9.0 9.5 10.0 10.5 11.0 total volume of water / cm 3 Fig. 2.2 [4] (c) Extrapolate the line on your graph and deduce the temperature when a solid starts to form when a total volume of 10.5 cm3 of water is used. Show clearly on Fig. 2.2 how you worked out your answer. temperature when a solid starts to form = …… °C [3] (d) Solubility, in g / 100 cm3 of water, is calculated using the equation shown. mass of solid dissolved × 100 solubility = volume of water used Use this equation to calculate the solubility of ammonium chloride in Experiment 1. solubility = …… g / 100 cm3 of water [1] (e) Describe how the solubility of ammonium chloride changes as the temperature changes. . …… . …… [1] (f) In this experiment the volume of water was measured using a burette. (i) State the advantage of using a burette rather than a measuring cylinder to measure the volume of water. . …… . …… [1] (ii) State the advantage of using a burette rather than a volumetric pipette to measure the volume of water. . …… . …… [1] (g) A total volume of 2.0 cm3 of water was added to the original 8.0 cm3 of water. Explain the disadvantages of adding the 2.0 cm3 of water in 1.0 cm3 portions rather than 0.5 cm3 portions. . …… . …… [2] (h) Suggest why it would not be possible to use 6.0 cm3 of water instead of 8.0 cm3 of water in Experiment 1. . …… . …… [1] [Total: 18]

Question

A student tests two solutions: solution C and solution D. Tests on solution C Solution C is aqueous calcium nitrate. Complete the expected observations. The student divides solution C into three portions. (a) The student carries out a flame test on the first portion of solution C. observations …… [1] (b) To the second portion of solution C, the student adds aqueous sodium hydroxide dropwise until it is in excess. observations adding dropwise …… observations in excess …… [2] (c) To the product from (b), the student adds a piece of aluminium foil and warms the mixture gently. Any gas produced is tested. observations …… . …… [1] (d) To the third portion of solution C, the student adds about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. observations …… . …… [1] tests on solution D Table 3.1 shows the tests and the student’s observations for solution D. The student divides solution D into four portions. Table 3.1 tests observations test 1 Use a glass rod to transfer one drop of the first the universal indicator paper turns red portion of solution D onto a piece of universal indicator paper. test 2 To the second portion of solution D, add solid the solid sodium carbonate disappears sodium carbonate. and there is effervescence Test any gas produced. the gas turns limewater milky test 3 To the third portion of solution D, add about no change 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. test 4 To the fourth portion of solution D, add about white precipitate 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. (e) Deduce the pH of solution D. pH = …… [1] (f) Identify the gas made when sodium carbonate is added to solution D. . …… [1] (g) Identify the two ions in solution D. . …… . …… [2] [Total: 9]

Question

Cadmium, cobalt and vanadium are all metals. They react with dilute hydrochloric acid to form hydrogen gas. These reactions are exothermic. Plan an investigation to find the order of reactivity of the three metals. Your plan must make it clear how your investigation will be a fair test and how you will use your results to place the metals in order of reactivity. You are provided with powdered samples of each metal, dilute hydrochloric acid and 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