Chemistry 0620/53 October/November 2024: question paper and mark scheme

Question

You are going to investigate the temperature change when solid P dissolves in water. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Use the 25 cm3 measuring cylinder to pour 20 cm3 of distilled water into a boiling tube. ● Use the thermometer to measure the temperature of the distilled water. Record this temperature in Table 1.1 at time = 0 seconds. ● Add a 5 g sample of solid P to the distilled water in the boiling tube. At the same time start the stop-watch. ● Continually stir the contents of the boiling tube using the thermometer. ● Measure the temperature of the mixture in the boiling tube every 20 seconds for 120 seconds. Record each temperature measured in Table 1.1. ● Rinse the boiling tube with distilled water. Complete Table 1.1 by calculating the temperature decreases from the temperature at 0 seconds. For example, at 60 seconds: temperature decrease = temperature at 0 s – temperature at 60 s Table 1.1 time / s 0 20 40 60 80 100 120 temperature / °C temperature 0.0 decrease / °C Experiment 2 ● Repeat Experiment 1 using 10 cm3 of distilled water instead of the 20 cm3 of distilled water. ● Record your results for Experiment 2 in Table 1.2. Complete Table 1.2 by calculating the temperature decreases from the temperature at 0 seconds. Table 1.2 time / s 0 20 40 60 80 100 120 temperature / °C temperature 0.0 decrease / °C [5] (b) Complete a suitable scale on the y-axis and plot your results from Experiment 1 and Experiment 2 on Fig. 1.1. Draw two lines of best fit. Both of your lines of best fit must go to (0,0). Label both lines. temperature decrease / C 0 0 20 40 60 80 100 120 140 time / s Fig. 1.1 [4] (c) State whether the energy change in Experiment 1 is exothermic or endothermic. Explain your answer. …… [1] (d) Compare the maximum temperature decrease in Experiment 1 with the maximum temperature decrease in Experiment 2. …… [2] (e) From your graph in Fig. 1.1, deduce the temperature decrease in Experiment 2 after 45 seconds. Show clearly on Fig. 1.1 how you worked out your answer. temperature decrease = …… °C [2] (f) The average rate of temperature decrease in each experiment can be calculated using the equation shown. temperature decrease average rate of temperature decrease = time Calculate the average rate of temperature decrease in Experiment 1 for 120 seconds. Give units for the average rate you have calculated. average rate of temperature decrease = …… units = …… [2] (g) State two possible sources of error in these experiments. For each source of error, suggest an improvement which reduces the error. source of error 1 …… improvement 1 …… source of error 2 …… improvement 2 …… [4] [Total: 20]

Question

You are provided with two solids: solid R and solid S. Do the following tests on solid R and solid S, recording all of your observations at each stage. Tests on solid R (a) Transfer about half of solid R to a boiling tube. Gently heat the solid for about 30 seconds. Record your observations. …… [2] Transfer the remaining solid R to a boiling tube. Add about 5 cm depth of distilled water to the boiling tube and place a stopper in the boiling tube. Shake the boiling tube to dissolve solid R and form solution R. Divide solution R into three approximately equal portions in two boiling tubes and one test-tube. (b) To the first portion of solution R in a boiling tube, add aqueous sodium hydroxide dropwise and then in excess. Record your observations. …… [2] (c) To the second portion of solution R in a boiling tube, add aqueous ammonia dropwise and then in excess. Record your observations. …… [2] (d) To the third portion of solution R in the test-tube, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. …… [1] (e) Identify the two ions in solid R. …… [2] Tests on solid S (f) Carry out a flame test on solid S. Record your observations. …… [1] Transfer the remaining solid S to a boiling tube. Add about 4 cm depth of distilled water to the boiling tube and place a stopper in the boiling tube. Shake the boiling tube to dissolve solid S and form solution S. Divide solution S into two approximately equal portions in two test-tubes. (g) To the first portion of solution S, add about 2 cm depth of aqueous sodium hydroxide. Record your observations. …… [1] (h) To the second portion of solution S, add a few drops of acidified aqueous potassium manganate(VII). Record your observations. …… [1] (i) Identify solid S. …… [2] [Total: 14]

Question

A mixture contains three solid compounds: ● aluminium oxide ● calcium carbonate ● calcium chloride. Table 3.1 gives some information about the three compounds in the mixture. Table 3.1 effect of adding name of compound solubility in water aqueous sodium hydroxide aluminium oxide insoluble reacts to form a soluble compound calcium carbonate insoluble no effect calcium chloride soluble reacts to form an insoluble compound Plan an experiment to find the percentage by mass of calcium carbonate in the mixture. Your plan must include how you will calculate the percentage by mass of calcium carbonate in the mixture. You are provided with a sample of the mixture, distilled water, aqueous sodium hydroxide 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