Chemistry 0620/63 May/June 2024: question paper and mark scheme

Question

A sample of rock salt contains sodium chloride, sand and mud. Sodium chloride is soluble in water. Sand and mud are insoluble in water. A student obtains dry crystals of pure sodium chloride from a lump of rock salt. Fig. 1.1 shows some of the steps the student uses. step 1 step 2 step 3 Grind the rock salt into Add the rock salt to water Filter the mixture. smaller pieces. and heat while stirring with a glass rod. mud and sand A rock salt aqueous sodium chloride heat Fig. 1.1 (a) Explain why the rock salt is made into smaller pieces in step 1. . …… [1] (b) Name an item of apparatus that can be used to heat the water in step 2. . …… [1] (c) Name the apparatus labelled A in step 3. . …… [1] (d) Describe what the student must do after step 3 to obtain dry crystals of pure sodium chloride. . …… . …… . …… . …… [3] [Total: 6]

Question

A student investigates the rate at which hydrogen gas is made when magnesium ribbon reacts with dilute ethanoic acid at two different temperatures. Instructions The student does two experiments using the apparatus shown in Fig. 2.1. rubber delivery tube clamp bung inverted 100 cm3 measuring cylinder conical flask trough dilute ethanoic acid water Fig. 2.1 Experiment 1 ● Use a measuring cylinder to pour 50 cm3 of dilute ethanoic acid into a conical flask. ● Use a thermometer to measure the initial temperature of the dilute ethanoic acid and record the initial temperature. ● Set the apparatus up as shown in Fig. 2.1, ensuring the inverted measuring cylinder is full of water. ● Remove the bung from the conical flask, ensuring the delivery tube remains in the measuring cylinder. ● Add a coil of magnesium ribbon to the conical flask, immediately put the bung back into the conical flask and start the timer. If the magnesium sticks to the side of the flask, gently shake the flask so that it is washed off the side. ● Measure the volume of gas collected in the inverted measuring cylinder every 15 seconds for 150 seconds. Record the volume of gas collected. ● Use the thermometer to measure the final temperature of the mixture in the conical flask and record the final temperature. ● Rinse out the conical flask with distilled water. Experiment 2 ● Repeat Experiment 1 but warm the acid by about 15 °C after it has been poured into the conical flask and before the initial temperature is measured and recorded. (a) Use the thermometer diagrams to complete Table 2.1. Table 2.1 initial final average thermometer temperature thermometer temperature experiment temperature diagram / °C diagram / °C / °C 30 30 1 25 25 20 20 40 40 2 35 35 30 30 [3] (b) Use the diagrams of the inverted measuring cylinders to complete Table 2.2. Table 2.2 time / s 15 30 45 60 75 90 105 120 135 150 volume of gas collected in 12 22 31 37 43 48 52 56 59 62 Experiment 1 / cm3 diagram 10 20 30 40 50 50 60 70 70 70 of inverted measuring 20 30 40 50 60 60 70 80 80 80 cylinder in Experiment 2 30 40 50 60 70 70 80 90 90 90 volume of gas collected in Experiment 2 / cm3 [2] (c) Complete a suitable scale on the y-axis and plot the results for Experiments 1 and 2 on Fig. 2.2. Draw two lines of best fit. Both lines must start at (0,0). Label your lines. volume of gas collected / cm3 0 0 20 40 60 80 100 120 140 160 time / s Fig. 2.2 [4] (d) Deduce the volume of gas collected between 20 seconds and 40 seconds in Experiment 1. Show clearly on Fig. 2.2 how you worked out your answer. volume of gas collected between 20 seconds and 40 seconds …… cm3 [3] (e) Use Fig. 2.2 to explain which experiment had the faster rate of reaction. experiment with faster rate …… explanation …… . …… [1] (f) During Experiment 1, the temperature of the mixture in the conical flask changed. (i) State how this change in temperature affects the rate of the reaction. . …… [1] (ii) Describe how the apparatus could be altered to minimise the change in temperature. . …… . …… [1] (g) Some gas escapes in the short time between adding the magnesium ribbon to the conical flask and putting the bung back into the conical flask. Explain how the apparatus could be altered so that no gas escapes and the results of the experiment are more accurate. You may draw a diagram to help explain your answer. . …… . …… [2] (h) Describe one other way in which the results of Experiments 1 and 2 could be made more accurate. . …… . …… [1] (i) Sketch on Fig. 2.2 the graph you would expect when Experiment 2 is repeated using ethanoic acid with a higher concentration. Label your line X.[1] [Total: 19]

Question

A student tests two substances: solid K and solution L. Tests on solid K Solid K is copper(II) carbonate. Complete the expected observations. (a) The student adds about 5 cm3 of dilute hydrochloric acid to solid K. observations …… . …… [1] The solution made in (a) is solution M. The student divides solution M into two portions. (b) To the first portion of solution M, the student adds aqueous ammonia dropwise until it is in excess. observations …… . …… . …… [3] (c) The student carries out a flame test on the second portion of solution M. (i) State the colour the Bunsen burner flame becomes during the flame test. . …… [1] (ii) Describe how the student should carry out the flame test. . …… . …… . …… [2] Tests on solution L Table 3.1 shows the tests and the student’s observations for solution L. Solution L was divided into two portions. Table 3.1 tests observations test 1 To the first portion of solution L, add aqueous a white precipitate forms sodium hydroxide dropwise until in excess. which is insoluble in excess test 2 To the second portion of solution L, add 1 cm3 a cream precipitate forms of dilute nitric acid followed by a few drops of aqueous silver nitrate. (d) Identify solution L. . …… . …… [2] [Total: 9]

Question

Iron rusts slowly when exposed to water and air. There is an increase in mass when iron rusts as the insoluble solid hydrated iron(III) oxide forms. Cast iron, mild steel and stainless steel are all alloys that contain iron. Plan an experiment to find which of these three alloys rusts most quickly when exposed to water and air. Include in your answer how the results of the experiment will show which alloy rusts most quickly. You are provided with powdered cast iron, powdered mild steel, powdered stainless steel 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