9701 Chemistry November 2025 Question Paper 53

1 The concentration of aqueous chloride ions can be found by titration with aqueous silver nitrate, AgNO3(aq). Ag+(aq) + Cl –(aq) AgCl(s)

The indicator used is aqueous potassium chromate(VI), K2CrO4(aq).

As AgNO3(aq) is added to aqueous chloride ions, a white precipitate of AgCl(s) is formed.

When all the chloride ions have reacted, further addition of AgNO3(aq) leads to the formation of a red precipitate of silver chromate(VI), Ag2CrO4(s). The first appearance of the red precipitate shows the end-point of the titration.

A student carries out an experiment to determine the number of molecules of water of crystallisation, x, in hydrated barium chloride, BaCl 2•xH2O(s).

(a) The student makes 250.0 cm3 of 0.0500 mol dm–3 AgNO3(aq) to use for the titration.

(i) Calculate the mass of solid silver nitrate, AgNO3(s), needed to make 250.0 cm3 of 0.0500 mol dm–3 AgNO3(aq).

Give your answer to two decimal places.

mass of AgNO3(s) = g [1]

(ii) Describe how the student should make 250.0 cm3 of 0.0500 mol dm–3 AgNO3(aq) starting from the mass of AgNO3(s) calculated in (a)(i) in a 50 cm3 beaker.

Give the name and size of any key apparatus used.

Write your answer using a series of numbered steps [3] , ,

(b) The student uses the following method. step 1 Dissolve 1.58 g of BaCl 2•xH2O(s) to form 250 cm3 of aqueous solution. Label this solution A. step 2 Transfer 20.0 cm3 of solution A into a conical flask. step 3 Add aqueous sodium sulfate, Na2SO4(aq), to the flask and swirl the mixture to remove barium ions from the solution. step 4 Add 2–3 drops of K2CrO4(aq) indicator to the flask. step 5 Titrate the contents of the flask against 0.0500 mol dm–3 AgNO3(aq). step 6 Repeat steps 2 to 5 to collect sufficient data for analysis.

(i) Suggest a suitable piece of apparatus for transferring 20.0 cm3 of solution A in step 2 [1]

(ii) Suggest why barium ions are removed in step 3 before performing the titration [1]

(iii) Suggest why chemically resistant gloves should be worn to carry out step 4 [1]

(c) The student’s results are shown in Table 1.1. Table 1.1 rough titration titration 1 titration 2 titration 3 burette reading (final) / cm3 20.10 40.55 20.75 20.90 burette reading (initial) / cm3 0.00 20.25 0.05 0.30 titre / cm3 20.10 20.30 20.70 20.60

The student uses the titres from titrations 2 and 3 shown in Table 1.1 to calculate a mean titre value of 20.65 cm3.

(i) Explain why only these two values are used [1] , ,

(ii) Calculate the percentage error in the titre volume for titration 3.

Show your working.

percentage error = [1]

(d) The equation for the reaction of silver nitrate with barium chloride is shown. 2AgNO3(aq) + BaCl 2(aq) Ba(NO3)2(aq) + 2AgCl(s)

(i) Calculate the amount, in mol, of AgNO3(aq) in the mean titre of 20.65 cm3.

amount of AgNO3 = mol [1]

(ii) Calculate the amount, in mol, of BaCl 2(aq) in 250 cm3 of solution A.

amount of BaCl 2 = mol [1]

(iii) Calculate the value of x in the formula BaCl 2•xH2O.

x = [2] , ,

(e) Another student uses a different experimental method to check the value of x obtained by the method described in (b).

Give a brief description of another method, not involving titration, that could be used to determine the value of x in the formula BaCl 2•xH2O(s). Write your answer using a series of numbered steps.

Your plan should include details of the following: • the apparatus and method you would use • the measurements you would make.

You are provided with standard laboratory apparatus [3]

[Total: 16] , ,

2 Effusion is the process in which a gas escapes through a small hole.

A student investigates the relationship between rate of effusion and relative molar mass of a gas using the apparatus shown in Fig. 2.1. gas syringe side-arm tube plunger gas being tested three-way tap aluminium foil with small hole Fig. 2.1

The following method is used: step 1 Turn the tap and remove any gas from the syringe through the side-arm tube, by pushing in the plunger. step 2 Add 50 cm3 of the gas being tested to the syringe through the side-arm tube. step 3 Remove the gas from the syringe, through the side-arm tube, by pushing in the plunger. step 4 Add 70 cm3 of the gas being tested to the syringe through the side-arm tube. step 5 Turn the tap to connect the syringe to the tube with the aluminium foil and small hole. step 6 Allow the syringe plunger to fall and start a timer when the volume of gas in the syringe reaches 60 cm3. step 7 Stop the timer when the volume of gas in the syringe reaches 10 cm3. Record the time taken. step 8 Repeat steps 1 to 7 with different gases. , ,

(a) Suggest why the student adds 50 cm3 of the gas being tested to the syringe in step 2 and then removes this gas in step 3 [1]

(b) The student’s results are shown in Table 2.1. Table 2.1 gas hydrogen, H2 helium, He neon, Ne argon, Ar krypton, Kr relative molar mass, M 2.0 4.0 20.2 39.9 83.8 M 1 time taken / s 10.8 15.3 34.5 39.7 70.4 rate of effusion / cm3 s–1 rate of effusion = volume of gas time taken

(i) Complete Table 2.1.

Give the values for M 1 to three significant figures.

Give the values for rate of effusion to two decimal places. [2]

(ii) Identify the dependent variable in this experiment [1]

(iii) Identify a variable, other than temperature, that is controlled when carrying out this experiment [1] , ,

(c) Plot a graph on the grid in Fig. 2.2 to show the relationship between rate of effusion and M 1 . Use a cross (×) to plot each data point. Draw a suitable line of best fit. 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.5 1.0 1.5 2.0 te of fusion m3 s–1 2.5 3.0 3.5 4.0 4.5 5.0 M 1 Fig. 2.2

[2] , ,

(d) Circle one point on the graph in Fig. 2.2 which you consider to be most anomalous.

Suggest one reason for this anomaly. Assume there is no error in M 1 [1]

(e) Graham’s law of effusion can be expressed as: the rate of effusion of a gas is proportional to M 1 .

State whether or not the student’s results support Graham’s law of effusion.

Explain your answer, using the graph in Fig. 2.2 [1]

(f) Suggest how the position of the plotted points relative to the line of best fit in Fig. 2.2 is related to the reliability of the results [1]

(g) The student then repeats this method to determine the value of M of a sample of natural gas.

The time recorded in step 7 is 31.6 s.

(i) Use the graph in Fig. 2.2 and the student’s result to calculate the value of M for this sample.

M = [2]

(ii) Natural gas is a mixture of mainly methane, CH4, with small amounts of other gases.

Suggest what your calculated value of the M of natural gas in (g)(i) tells you about the other gases in the mixture [1] , ,

(h) The experiment described in (g) is repeated at a higher temperature.

Suggest how the rate of effusion for this sample of natural gas would change, if at all.

Explain your answer. effect on the rate of effusion explanation [1]

[Total: 14] Important values, constants and standards molar gas constant R = 8.31 J K–1 mol–1 Faraday constant F = 9.65 × 104 C mol–1 Avogadro constant L = 6.02 × 1023 mol–1 electronic charge e = –1.60 × 10–19 C molar volume of gas Vm = 22.4 dm3 mol–1 at s.t.p. (101 kPa and 273 K) Vm = 24.0 dm3 mol–1 at room conditions ionic product of water Kw = 1.00 × 10–14 mol2 dm–6 (at 298 K (25 °C)) specific heat capacity of water c = 4.18 kJ kg–1 K–1 (4.18 J g–1 K–1) , , Group The Periodic Table of Elements 1 H hydrogen 1.0 2 He helium 4.0 1 2 13 14 15 16 17 18 3 4 5 6 7 8 9 10 11 12 3 Li lithium 6.9 4 Be beryllium 9.0 atomic number atomic symbol Key name relative atomic mass 11 Na sodium 23.0 12 Mg magnesium 24.3 19 K potassium 39.1 20 Ca calcium 40.1 37 Rb rubidium 85.5 38 Sr strontium 87.6 55 Cs caesium 132.9 56 Ba barium 137.3 87 Fr francium – 88 Ra radium – 5 B boron 10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 81 Tl thallium 204.4 6 C carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sn tin 118.7 82 Pb lead 207.2 22 Ti titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium 178.5 104 Rf rutherfordium – 23 V vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium – 24 Cr chromium 52.0 42 Mo molybdenum 95.9 74 W tungsten 183.8 106 Sg seaborgium – 25 Mn manganese 54.9 43 Tc technetium – 75 Re rhenium 186.2 107 Bh bohrium – 26 Fe iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium – 27 Co cobalt 58.9 45 Rh rhodium 102.9 77 Ir iridium 192.2 109 Mt meitnerium – 28 Ni nickel 58.7 46 Pd palladium 106.4 78 Pt platinum 195.1 110 Ds darmstadtium – 29 Cu copper 63.5 47 Ag silver 107.9 79 Au gold 197.0 111 Rg roentgenium – 30 Zn zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200.6 112 Cn copernicium – 114 Fl flerovium – 116 Lv livermorium – 7 N nitrogen 14.0 15 P phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 83 Bi bismuth 209.0 8 O oxygen 16.0 16 S sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium – 9 F fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 53 I iodine 126.9 85 At astatine – 10 Ne neon 20.2 18 Ar argon 39.9 36 Kr krypton 83.8 54 Xe xenon 131.3 86 Rn radon – 113 Nh nihonium – 115 Mc moscovium – 117 Ts tennessine – 118 Og oganesson – 21 Sc scandium 45.0 39 Y yttrium 88.9 57–71 lanthanoids 89–103 actinoids 57 La lanthanum 138.9 89 Ac lanthanoids actinoids actinium – 58 Ce cerium 140.1 90 Th thorium 232.0 59 Pr praseodymium 140.9 91 Pa protactinium 231.0 60 Nd neodymium 144.2 92 U uranium 238.0 61 Pm promethium – 93 Np neptunium – 62 Sm samarium 150.4 94 Pu plutonium – 63 Eu europium 152.0 95 Am americium – 64 Gd gadolinium 157.3 96 Cm curium – 65 Tb terbium 158.9 97 Bk berkelium – 66 Dy dysprosium 162.5 98 Cf californium – 67 Ho holmium 164.9 99 Es einsteinium – 68 Er erbium 167.3 100 Fm fermium – 69 Tm thulium 168.9 101 Md mendelevium – 70 Yb ytterbium 173.1 102 No nobelium – 71 Lu lutetium 175.0 103 Lr lawrencium – , ,