Chemistry 0620/63 October/November 2024: question paper and mark scheme

Question

When crystals of hydrated calcium ethanedioate, CaC2O4•H2O, are heated they decompose to form solid calcium carbonate, steam and carbon monoxide gas. CaC2O4•H2O(s) → CaCO3(s) + H2O(g) + CO(g) A student suggests using the apparatus shown in Fig. 1.1 to decompose hydrated calcium ethanedioate and obtain the products. hydrated calcium ethanedioate B A ice Fig. 1.1 Table 1.1 shows some information about carbon monoxide. Table 1.1 melting point boiling point density solubility safety / °C / °C compared to air in water warning carbon monoxide –205 –192 about the same insoluble toxic (a) Name the items of apparatus labelled A and B in Fig. 1.1. A …… B …… [2] (b) The apparatus shown in Fig. 1.1 will not work because there is an error in how the gas is collected. This error makes it dangerous to use the apparatus. Identify the error and explain why this error makes it dangerous to use the apparatus. error …… explanation …… [2] (c) Complete Fig. 1.2 to show how the gas could be collected safely. hydrated calcium ethanedioate ice X Fig. 1.2 [1] (d) Add one arrow to Fig. 1.2 to show where the apparatus should be heated. [1] (e) Identify the substance that collects at the point marked X on Fig. 1.2. …… [1] (f) Suggest why this experiment should be carried out in a fume cupboard. …… [1] [Total: 8]

Question

A student investigates the temperature change when solid P dissolves in water. The student does two experiments. Experiment 1 ● Use a 25 cm3 measuring cylinder to pour 20 cm3 of distilled water into a boiling tube. ● Use a thermometer to measure the temperature of the distilled water. This is the temperature 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 a 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. ● Rinse the boiling tube with distilled water. Experiment 2 ● Repeat Experiment 1 using 10 cm3 of distilled water instead of the 20 cm3 of distilled water. (a) Complete Table 2.1 by using the thermometer diagrams and 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 2.1 Experiment 1 Experiment 2 temperature temperature time thermometer temperature thermometer temperature decrease decrease /s diagram / C diagram / C / C / C 30 30 0 25 24.0 0.0 25 23.0 0.0 20 20 30 20 20 25 15 20 10 30 20 40 25 15 20 10 25 20 60 20 15 15 10 25 20 80 20 15 15 10 25 20 100 20 15 15 10 25 20 120 20 15 15 10 [5] (b) Complete a suitable scale on the y-axis and plot the results from Experiment 1 and Experiment 2 on Fig. 2.1. 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. 2.1 [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. 2.1, deduce the temperature decrease in Experiment 2 after 45 seconds. Show clearly on Fig. 2.1 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 3 starts on the next page.

Question

A student tests two substances: solid R and solid S. Tests on solid R Table 3.1 shows the tests and the student’s observations for solid R. Table 3.1 tests observations test 1 Gently heat about half of solid R in a boiling the white solid forms a colourless liquid tube. steam comes out from the boiling tube and condensation forms at the top of the boiling tube test 2 The remaining solid R is dissolved in distilled water to form solution R. Solution R is divided into four portions. To the first portion of solution R, add aqueous white precipitate forms sodium hydroxide dropwise and then in excess. the white precipitate dissolves in excess aqueous sodium hydroxide test 3 To the second portion of solution R, add white precipitate forms aqueous ammonia dropwise and then in excess. the white precipitate remains in excess aqueous ammonia test 4 To the third portion of solution R, add 1 cm3 no change of dilute nitric acid followed by a few drops of aqueous barium nitrate. test 5 To the fourth portion of solution R, add 1 cm3 cream precipitate forms of dilute nitric acid followed by a few drops of aqueous silver nitrate. (a) State the conclusion that can be made from the observations in test 1. …… [1] (b) Identify solid R. …… [2] Tests on solid S Solid S is sodium sulfite. Record the expected observations. (c) The student carries out a flame test on solid S. observations …… [1] The student dissolves the remaining solid S in distilled water to form solution S. The student divides solution S into two portions. (d) To the first portion of solution S, the student adds about 2 cm3 of aqueous sodium hydroxide. observations …… [1] (e) To the second portion of solution S, the student adds a few drops of acidified aqueous potassium manganate(VII). observations …… [1] [Total: 6]

Question

A mixture contains three solid compounds: ● aluminium oxide ● calcium carbonate ● calcium chloride. Table 4.1 gives some information about the three compounds in the mixture. Table 4.1 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