Chemistry 0620/52 February/March 2023: question paper and mark scheme

Question

You are going to investigate the solubility of ammonium chloride in water at different temperatures. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments. 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 the 5.25 g sample of ammonium chloride in the boiling tube. ● Clamp the boiling tube at an angle, as shown in Fig. 1.1. clamp solid ammonium chloride water Fig. 1.1 ● 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. Do not allow the solution to boil. ● Continuously stir the solution with the thermometer while it cools. ● As soon as the solution starts to become cloudy and a solid starts to form, measure the temperature of the solution and record the temperature in Table 1.1. ● Keep the contents of the boiling tube for Experiment 2. 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. 1.1. ● 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. Do not allow the solution to boil. ● Continuously stir the solution with the thermometer while it cools. ● As soon as the solution starts to become cloudy and a solid starts to form, measure the temperature of the solution and record the temperature in Table 1.1. ● Keep the contents of the boiling tube for the next experiment. Experiment 3 ● Repeat Experiment 2 by using the burette to add another 0.5 cm3 of distilled water to the mixture in the boiling tube from Experiment 2. Experiment 4 ● Repeat Experiment 2 by using the burette to add another 0.5 cm3 of distilled water to the mixture in the boiling tube from Experiment 3. Experiment 5 ● Repeat Experiment 2 by using the burette to add another 0.5 cm3 of distilled water to the mixture in the boiling tube from Experiment 4. (a) Complete Table 1.1. Table 1.1 mass of total volume temperature when a solid experiment ammonium chloride / g of water / cm3 starts to form / °C 1 8.0 2 3 4 5 [4] (b) Complete a suitable scale on the y-axis in Fig. 1.2 and plot your results from Experiments 1 to 5 on Fig. 1.2. 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 / cm3 Fig. 1.2 [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. 1.2 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

You are provided with two solutions: solution C and solution D. Do the following tests on the solutions, recording all of your observations at each stage. Tests on solution C (a) Carry out a flame test on solution C. Record your observations. …… [1] Divide the remaining solution C into three approximately equal portions in one boiling tube and two test‑tubes. (b) To the first portion of solution C in a boiling tube, add aqueous sodium hydroxide dropwise until it is in excess. Keep the product for the test in (c). Record your observations. dropwise …… in excess …… [2] (c) (i) Transfer about 2 cm depth of the product from (b) into a clean boiling tube. Add a piece of aluminium foil. Warm the mixture gently. Test any gas produced. Record your observations. . …… . …… [2] (ii) Identify the gas produced in (c)(i). . …… [1] (d) To the second portion of solution C, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. …… [1] (e) To the third portion of solution C, add about 1 cm depth of aqueous sodium carbonate. Record your observations. …… [1] (f) Identify solution C. …… [2] tests on solution D Divide solution D into three approximately equal portions in three test-tubes. (g) Test the pH of the first portion of solution D. pH = …… [1] (h) To the second portion of solution D, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. …… [1] (i) To the third portion of solution D, add a spatula full of solid sodium carbonate. Test any gas produced. Record your observations. …… [2] (j) Identify the two ions in solution D. …… [2] [Total: 16]

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