Chemistry 2025 Oct/Nov | Past Paper

Q1

Short Answer 1 mark

The thiosulfate ion, S , decomposes when an acid is added.

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S(s) + SO

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+ H O

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The rate of this reaction can be investigated by measuring how long it takes for the solid sulfur forming to obscure the print on the insert. You will investigate how the concentration of the thiosulfate ion af fects the rate of the reaction. Note: A small amount of sulfur dioxide gas may be formed in the experiment. It is very important that you avoid inhaling any fumes. As soon as each experiment is complete, add the reaction mixture to the quenching bath and rinse the beaker thoroughly. FA 1 is 0.100 mol dm sodium thiosulfate, Na FA 2 is 2.00 mol dm hydrochloric acid, HCl.

Q1(a)

Structured 8 marks

Method Experiment 1 of FA 1 into the 100 cm beaker. measuring cylinder to measure 10.0 cm of FA 2. Experiment 2 of FA 1 into the 100 cm beaker. of distilled water into the same beaker. measuring cylinder to measure 10.0 cm of FA 2. Experiments 3-5 affects the reaction time. Note: the combined volumes of FA 1 and distilled water must always be 40.00 cm Do not use a volume of FA 1 that is less than 15.00 cm Record all your results in a table. You should include the volume of FA 1, the volume of distilled water, the reaction time and the reaction rate for each of your five experiments. The rate of reaction can be calculated using the following formula. rate = 1000 reaction time Results

Q1(b)

Short Answer 1 mark

(i) On the grid in Fig. 1.1, plot the rate (y-axis) against the volume of FA 1 (x-axis). Start each axis at the origin (0, 0). Ring any anomalous points. Draw a line of best fit.IIIVII VIII * 0000800000004 * [3] III * 0000800000005 *

Q1(ii)

Short Answer 2 marks

Use your graph in Fig. 1.1 to determine the time it would take for the print to be obscured if 7.50 cm of FA 1, 32.50 cm of water and 10.0 cm of FA 2 had been used. Show clearly on the graph how you worked out your answer. time for printing to be obscured = s

Q1(c)

Short Answer 1 mark

A student carries out the same method as given in

Q1(c)(a)

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but using a dif ferent concentration of acid. The student's calculated values for the rate are plotted on the grid in Fig. 1.2. 0.00 5.0010.0015.0020.0025.00 volume of FA 1 rate vs volume of FA 1 30.0035.0040.0045.00 rate State whether the student' s results show that the rate is directly proportional to the volume of FA 1 used. Explain your answer . [Total: 15] * 0000800000006 * BLANK PAGE * 0000800000007 *

Q2

Short Answer 1 mark

When hydrated sodium thiosulfate is dissolved in water the temperature of the liquid changes. You will carry out an experiment to determine the enthalpy change, ΔH, when one mole of hydrated sodium thiosulfate dissolves in water. FA 3 is hydrated sodium thiosulfate, Na

Q2(a)

Structured 4 marks

Method beaker. measuring cylinder to transfer 30.0 cm of distilled water into the cup. Results

Q2(b)

Short Answer 1 mark

Calculations

Q2(i)

Short Answer 1 mark

Calculate the amount, in mol, of hydrated sodium thiosulfate added. amount of Na O = mol

Q2(ii)

Short Answer 1 mark

Calculate the energy change, in J, in your experiment. energy change = J [1]III IV * 0000800000008 *

Q2(iii)

Short Answer 1 mark

Calculate the enthalpy change, ΔH, in kJ mol , when 1.00 mol of hydrated sodium thiosulfate dissolves in water. Show your working. ΔH = kJ mol sign value

Q2(c)

Short Answer 1 mark

The value calculated in (b)(iii) can be used to determine the enthalpy change, ΔH , for the following reaction.

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+ 5H O

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Outline the method of one further experiment you would need to carry out to obtain the data necessary to calculate the value of ΔH Show how you would use your results from this experiment and

Q3

Short Answer 1 mark

Half-fill the 250 cm beaker with water and place it on a tripod and gauze. Heat the water until boiling then switch of f your Bunsen burner . This will be your hot water bath for use in (b)(i). Start

Q3(a)

Short Answer 1 mark

(i) while the water is heating.

Q3(a)

Short Answer 1 mark

FA 4 is an aqueous solution containing three ions. One ion is not listed in the Qualitative analysis notes. FA 5 is an aqueous solution containing two ions. The cation in FA 5 is listed in the Qualitative analysis notes. The anions in both FA 4 and FA 5 contain sulfur.

Q3(i)

Structured 5 marks

Carry out the following tests using a 1 cm depth of either FA 4 or FA 5 in a test-tube. Record your observations in Table 3.1. * 0000800000010 * Table 3.1 test observations FA 4 FA 5 Test 1 Add aqueous sodium hydroxide. Test 2 Add aqueous ammonia. Test 3 Add aqueous sodium carbonate. Test 4 Add aqueous barium chloride or aqueous barium nitrate. Test 5 Add acidified aqueous potassium manganate(VII).

Q3(ii)

Short Answer 1 mark

From your observations in (a)(i), deduce the identities of the ions present in FA 4 and FA 5. Give the formula of each ion in Table 3.2. If you are unable to identify an ion write 'unknown'. Table 3.2 ions present FA 4 FA 5 cations anions [3] * 0000800000011 *

Q3(b)

Short Answer 3 marks

(i) Both FA 6 and FA 7 are one of propan-1-ol, propan-2-ol, methanoic acid or ethanoic acid. You will carry out tests to investigate the identities of FA 6 and FA 7. For each test use a 1 cm depth of FA 6 or FA 7 in a test-tube. Record your observations in Table 3.3. Table 3.3 test observations FA 6 FA 7 Test 1 Add a few drops of acidified aqueous potassium manganate(VII), then place the test-tube in the hot water bath. Test 2 Add a 2 cm depth of aqueous iodine followed by drops of aqueous sodium hydroxide until the colour just disappears. If no reaction is visible, place the test-tube in the hot water bath. Test 3 Add aqueous sodium carbonate.

Q3(ii)

Short Answer 1 mark

From your observations in (b)(i) deduce the identities of FA 6 and FA 7. Give reasons for your answers. FA 6 is reasons FA 7 is reasons [2] * 0000800000012 *

Q3(c)

Short Answer 1 mark

A student carrying out a similar set of tests identifies two unknown compounds to be ethanol and propanoic acid. W rite an equation for the reaction between these two compounds. [Total: 14] * 0000800000013 * Qualitative analysis notes 1 Reactions of cations cation reaction with NaOH(aq) NH

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aluminium, Al

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white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH

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no ppt. ammonia produced on warming barium, Ba

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faint white ppt. is observed unless [Ba

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] is very low no ppt. calcium, Ca

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white ppt. unless [Ca

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] is verylow no ppt. chromium(III), Cr

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grey-green ppt. soluble in excess giving dark green solution grey-green ppt. insoluble in excess copper(II), Cu

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pale blue ppt. insoluble in excesspale blue ppt. soluble in excess giving dark blue solution iron(II), Fe

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green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron(III), Fe

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red-brown ppt. insoluble in excessred-brown ppt. insoluble in excess magnesium, Mg

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white ppt. insoluble in excesswhite ppt. insoluble in excess manganese(II), Mn

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off-white ppt. rapidly turning brown on contact with air insoluble in excess off-white ppt. rapidly turning brown on contact with air insoluble in excess zinc, Zn

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white ppt. soluble in excess white ppt. soluble in excess 2 Reactions of anions anion reaction carbonate, CO liberated by dilute acids chloride, Cl

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gives white ppt. with Ag

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(soluble in NH

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) bromide, Br

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gives cream / off-white ppt. with Ag

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(partially soluble in NH

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) iodide, I

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gives pale yellow ppt. with Ag

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(insoluble in NH

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) nitrate, NO

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NH liberated on heating with OH

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and Al foil nitrite, NO

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NH liberated on heating with OH

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and Al foil; sulfate, SO

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gives white ppt. with Ba

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(insoluble in excess dilute strong acids); gives white ppt. with high [Ca

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gives white ppt. with Ba

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(soluble in excess dilute strong acids); thiosulfate, S

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gives off-white/pale yellow ppt. slowly with H + * 0000800000014 * 3 Tests for gases gas test and test result ammonia, NH turns damp red litmus paper blue carbon dioxide, CO gives a white ppt. with limewater hydrogen, H 'pops' with a lighted splint oxygen, O relights a glowing splint

Q4

Short Answer 1 mark

Tests for elements element test and test result iodine, I gives blue-black colour on addition of starch solution Important values, constants and standards molar gas constant R = 8.31 J Kmol Faraday constant F = 9.65 × 10 C mol Avogadro constant L = 6.02 × 10mol electronic charge e = -1.60 × 10-19 molar volume of gas V = 22.4 dmmol at s.t.p. (101 kPa and 273 K) = 24.0 dmmol at room conditions ionic product of water K = 1.00 × 10-14mol (at 298 K (25 °C)) (4.18 J g ) * 0000800000015 * To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Group The Periodic Ta ble of Elements hydrogen 1.0 helium 4.0 12 13 14 15 16 17 18 3456789 10 11 12 lithium 6.9 beryllium 9.0 atomic number atomic symbolKey name relative atomic mass sodium 23.0 magnesium 24.3 potassium 39.1 calcium 40.1 rubidium 85.5 strontium 87.6 caesium 132.9 barium 137.3 francium radium boron 10.8 aluminium 27.0 gallium 69.7 indium 114.8 thallium 204.4 carbon 12.0 silicon 28.1 germanium 72.6tin 118.7 lead 207.2 titanium 47.9 zirconium 91.2 hafnium 178.5 rutherfordium vanadium 50.9 niobium 92.9 tantalum 180.9 dubnium chromium 52.0 molybdenum 95.9 tungsten 183.8 seaborgium manganese 54.9 technetium rhenium 186.2 bohrium iron 55.8 ruthenium 101.1 osmium 190.2 hassium cobalt 58.9 rhodium 102.9 iridium 192.2 meitnerium nickel 58.7 palladium 106.4 platinum 195.1 darmstadtium copper 63.5 silver 107.9 gold 197.0 roentgenium zinc 65.4 cadmium 112.4 mercury 200.6 copernicium flerovium livermorium nitrogen 14.0 phosphorus 31.0 arsenic 74.9 antimony 121.8 bismuth 209.0 oxygen 16.0 sulfur 32.1 selenium 79.0 tellurium 127.6 polonium fluorine 19.0 chlorine 35.5 bromine 79.9 iodine 126.9 neon 20.2 argon 39.9 krypton 83.8 xenon 131.3 radon nihonium moscovium tennessine oganesson scandium 45.0 yttrium 88.9 57-71 lanthanoids 89-103 actinoids lanthanum 138.9 lanthanoids actinoids actinium cerium 140.1 thorium 232.0 praseodymium 140.9 protactinium 231.0 neodymium 144.2 uranium 238.0 promethium neptunium samarium 150.4 plutonium europium 152.0 americium gadolinium 157.3 curium terbium 158.9 berkelium dysprosium 162.5 californium holmium 164.9 einsteinium erbium 167.3 fermium thulium 168.9 mendelevium ytterbium 173.1 nobelium lutetium 175.0 lawrencium - * 0000800000016 *

Board	CAIE
Level	A Level
Subject	Chemistry
Code	`9701`
Year	2025
Session	Oct/Nov
Q&A	59 questions

Chemistry 2025 · Oct/Nov

Questions & Model Answers 59 Qs

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