Cambridge A Level Chemistry 9701 — 2019 May/June Paper 3 · Variant 2

1 Amidosulfonic acid is a monoprotic acid with the formula HSOxNH2. In this experiment you will determine the value of x in the formula by titration with an alkali. FB 1 is amidosulfonic acid, HSOxNH2. You are supplied with approximately 3.0 g. FB 2 is 0.110 mol dm–3 sodium hydroxide, NaOH. thymolphthalein indicator (a) Method Preparing a solution of amidosulfonic acid ●● Weigh the empty beaker. Record the mass. ●● Add 2.50 –2.70 g of FB 1 to the beaker. Weigh the beaker and its contents. Record the mass. ●● Calculate and record the mass of FB 1 used. ●● Add approximately 100 cm3 of distilled water to the beaker and stir to dissolve FB 1. ●● Transfer the solution to the 250 cm3 volumetric flask. ●● Rinse the beaker twice with approximately 20 cm3 of distilled water each time and add to the volumetric flask. ●● Add distilled water to the volumetric flask to make 250 cm3 of solution. ●● Shake the volumetric flask to mix the solution thoroughly and label it FB 3. Titration of FB 3 ●● Fill the burette with FB 2. ●● Pipette 25.0 cm3 of FB 3 into a conical flask. ●● Add a few drops of thymolphthalein to the conical flask. ●● Carry out a rough titration. ●● Record your burette readings and the rough titre in the space below. The rough titre is .............................. cm3. ●● Carry out as many accurate titrations as you think necessary to obtain consistent results. ●● Make sure any recorded results show the precision of your practical work. ●● Record all of your burette readings and the volume of FB 2 added in each accurate titration. I II III IV V VI VII [8] II (b) From your accurate titration results, obtain a suitable value for the volume of FB 2 to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FB 3 required .............................. cm3 of FB 2. [1] (c) Calculations (i) ive your answers to (ii), (iii), (iv) and (v) to the appropriate number of significant figures. [1] (ii) Calculate the number of moles of sodium hydroxide, NaOH, in the volume of FB 2 calculated in (b). moles of NaOH = .............................. mol [1] (iii) One mole of sodium hydroxide neutralises one mole of amidosulfonic acid. Complete the equation for the reaction of amidosulfonic acid with sodium hydroxide. Include state symbols. ......NaOH...... + ......HSOxNH2...... ................................. + ................................. State the number of moles of amidosulfonic acid that reacted with the number of moles of NaOH calculated in (ii). moles of HSOxNH2 = .............................. mol [1] (iv) Use your results on page 2 and your answer to (iii) to calculate the relative formula mass, Mr, of amidosulfonic acid. Mr of amidosulfonic acid = .............................. [1] (v) Calculate the value of x in the formula of amidosulfonic acid, HSOxNH2. x = .............................. [1] (d) The salts produced from amidosulfonic acid are called amidosulfonates. You are to carry out an experiment using FB 1 to find out if barium amidosulfonate is soluble in water. ●● Describe your experiment. ●● Record your observation(s) and conclusion. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] [Total: 16] Question 2 starts on the next page.

Mark scheme: 1(a) I: All the following data is recorded, with ‘g’ units • three masses with unambiguous headings (not ‘weight’) • both weighings recorded to same number of d.p. (one or more) • mass of FB 1 is correctly subtracted • mass of FB 1 used is between 2.5 and 2.7 g 1 II: All the following data is recorded • rough titration: both burette readings and the rough titre • initial and final burette readings for two (or more) accurate titrations (i.e. a 2 × 2 ‘box’) Headings and units are not required for this mark 1 III: Correct headings and units given in the accurate titration table • initial / start and (burette) reading / volume • final / end and (burette) reading / volume • titre or volume / FB 2 and used / added (not ‘amount’) • unit: / cm3 or (cm3) or in cm3 (for each heading) or cm3 unit given for each volume recorded 1 IV: All accurate burette readings are recorded to the nearest 0.05 cm3. 1 V: The final accurate titre recorded is within 0.10 cm3 of any other accurate titre 1 Award VI, VII and VIII if δ ≤ 0.10 (cm3 g–1) 1 Award VI and VII if 0.10 < δ ≤ 0.20 1 Award VI, only if 0.20 < δ ≤ 0.40 1 Question Answer Marks 1(b) Candidate calculates the mean correctly. • Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm3. • Working / explanation must be shown. • the mean should be quoted to 2 d.p., and be rounded to nearest 0.01 cm3. 1 1(c)(i) Significant figures The answers to (ii), (iii) and (iv) must all be expressed to 3 or 4 sig. fig. 1 1(c)(ii) Correctly calculates no of moles NaOH No. of moles of NaOH used = 0.110 × mean titre / 1000 1 1(c)(iii) Equation balanced with state symbols correct. NaOH(aq) + HSOxNH2(aq) → NaSOxNH2(aq) + H2O(l) and correct answer: no. of moles of FB 3 = ans (ii) 1 1(c)(iv) Correct use of M r of FB 1 = mass of FB 1 weighed out / 10 × no of moles of FB 3 (from (iii)) 1 1(c)(v) Correct expression and gives the answer as an integer x = [ans (iv) – 49.1] / 16 1 Question Answer Marks 1(d) Method: Dissolve FB 1 in water or use FB 3 and add (aqueous) BaCl 2 / Ba(NO3)2 or (aqueous) barium chloride / barium nitrate 1 Observation: no reaction / no precipitate / solution stays colourless and Deduction: barium amidosulfonate is soluble in water 1

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2 When hydrated copper hydroxycarbonate, CuCO3.Cu(OH)2.yH2O is heated, it decomposes as shown. CuCO3.Cu(OH)2.yH2O(s) 2CuO(s) + CO2(g) + (1 + y)H2O(g) In this experiment, you will heat hydrated copper hydroxycarbonate to decompose it. You will use your results to investigate the value of y. FB 4 is hydrated copper hydroxycarbonate, CuCO3.Cu(OH)2.yH2O. (a) Method ●● Weigh the crucible with its lid and record the mass. ●● Add all the FB 4 from the container into the crucible. ●● Weigh the crucible and lid with FB 4 and record the mass. ●● Place the crucible and contents on the pipe-clay triangle. ●● Heat the crucible and contents gently for approximately two minutes with the lid on. ●● Use tongs to remove the lid and heat strongly for approximately three minutes. ●● Replace the lid and leave the crucible and residue to cool for several minutes. While the crucible is cooling, you may wish to begin work on Question 3. ●● When the crucible is cool, reweigh it with its lid and contents. Record the mass. ●● Calculate and record the mass of FB 4 and the mass of residue obtained. Results I II III IV State the observations made while the decomposition of FB 4 was taking place. .................................................................................................................................................... .................................................................................................................................................... [4] (b) Calculations (i) Calculate the number of moles of copper oxide, CuO, obtained as residue. moles of CuO obtained = .............................. mol [1] (ii) Use your results to calculate the relative formula mass, Mr, of hydrated copper hydroxycarbonate, CuCO3.Cu(OH)2.yH2O. Mr of CuCO3.Cu(OH)2.yH2O = .............................. [2] (iii) Use the Periodic Table to calculate the relative formula mass of CuCO3.Cu(OH)2. Mr of CuCO3.Cu(OH)2 = .............................. Use your answer to (ii) and this Mr to comment on the value of y in the formula of hydrated copper hydroxycarbonate. ............................................................................................................................................. ............................................................................................................................................. [2] (c) State one way to improve the accuracy of the experiment, using the same mass of FB 4. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 10] Qualitative Analysis Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. At each stage of any test you are to record details of the following: ● colour changes seen; ● the formation of any precipitate and its solubility in an excess of the reagent added; ● the formation of any gas and its identification by a suitable test. You should indicate clearly at what stage in a test a change occurs. If any solution is warmed, a boiling tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests for ions present should be attempted.

Mark scheme: 2(a) I: Table / list of data, to include values and correct headings and units: • Mass of crucible (and lid) • Mass of crucible, (lid) + FB 4 (or ‘contents before heating’) • Mass of crucible, (lid) + residue / CuO / contents after heating • Mass of FB 4 (used) • Mass of residue / CuO (obtained) 1 Accuracy (Q) marks in 2(a) • To assess accuracy, check the masses of FB 4 used and of CuO obtained by the supervisor and by the candidate. • Work out the ratio mass of FB4 / mass of CuO for the supervisor (to 2 d.p.) • Work out ratio (mass FB 4: mass CuO) for the candidate (2 d.p.) • Calculate δ, the difference between these two ratios. Award II and III if δ ⩽ 0.05 1 Award III if 0.05 < δ ⩽ 0.10 1 IV: Observations made during heating (Solid changes from) green / turquoise / cyan / blue-green to black (both colours required) or black solid / residue (formed) 1 2(b)(i) Correctly calculated no. of moles of CuO • No. of moles CuO = mass of residue / 79.5 • Answer must be correct and expressed to 2, 3 or 4 sig. fig. 1 Question Answer Marks 2(b)(ii) Correct use of mole ratio 1 : 2 • No. of moles of FB 4 = answer (i) / 2 1 Correctly uses n to calculate Mr of copper hydroxycarbonate, • M r = mass of FB 4 used / no. of moles of FB 4 • Answer (for M r) must be expressed to 2, 3 or 4 sig. fig. • Some working must be shown to access the second mark 1 2(b)(iii) M r = 221 1 Appropriate comment on the value of y • If answer 2(b)(ii) is less than 221, candidate should state that y is negative, so the experiment has been inaccurate • If answer 2(b)(ii) is between 213 and 229, then (within experimental error) there is no water of crystallisation • If answer 2(b)(ii) is greater than 221, candidate should calculate the value of y and state that it should be an integer 1 2(c) Heat to constant mass (or description of procedure) 1

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3 (a) FB 5 contains one cation and one anion from those listed in the Qualitative Analysis Notes. (i) Transfer a small spatula measure of FB 5 into a hard-glass test-tube. Heat gently at first and then heat strongly, until no further change occurs. Record all your observations. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [3] (ii) To a 1 cm depth of dilute hydrochloric acid in a test-tube, add a small spatula measure of FB 5. Record your observations. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (iii) Deduce the formula of FB 5. ........................................... [1] (b) FB 6 is a solution of a compound containing one cation from those listed in the Qualitative Analysis Notes. (i) Carry out the following tests using a 1 cm depth of FB 6 in a test-tube for each test. test observations Add two drops of Universal Indicator solution. Add an equal volume of aqueous manganese(II) chloride. Add an equal volume of dilute sulfuric acid. Add a few drops of aqueous silver nitrate, then add aqueous ammonia. Add a few drops of aqueous copper(II) sulfate, then add excess dilute hydrochloric acid. [4] (ii) What can be determined about FB 6 from its reaction with manganese(II) chloride? ....................................................................................................................................... [1] (iii) Give the ionic equation for the reaction between FB 6 and sulfuric acid. Include state symbols. ....................................................................................................................................... [1] (iv) When aqueous copper(II) sulfate was added to FB 6, two precipitates were formed. Deduce the identity of the two precipitates. ................................................................... and .................................................................. Explain the observation you made when you added excess dilute hydrochloric acid in the final test of (b)(i). ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. [2] [Total: 14] Qualitative Analysis Notes 1 Reactions of aqueous cations reaction with ion NaOH(aq) NH3(aq) aluminium, white ppt. white ppt. Al 3+(aq) soluble in excess insoluble in excess ammonium, no ppt. – NH4+(aq) ammonia produced on heating barium, faint white ppt. is nearly always no ppt. Ba2+(aq) observed unless reagents are pure calcium, white ppt. with high [Ca2+(aq)] no ppt. Ca2+(aq) chromium(III), grey-green ppt. grey-green ppt. Cr3+(aq) soluble in excess insoluble in excess copper(II), pale blue ppt. blue ppt. soluble in excess Cu2+(aq) insoluble in excess giving dark blue solution green ppt. turning brown on contact green ppt. turning brown on contact iron(II), with air with air Fe2+(aq) insoluble in excess insoluble in excess iron(III), red-brown ppt. red-brown ppt. Fe3+(aq) insoluble in excess insoluble in excess magnesium, white ppt. white ppt. Mg2+(aq) insoluble in excess insoluble in excess off-white ppt. rapidly turning brown off-white ppt. rapidly turning brown manganese(II), on contact with air on contact with air Mn2+(aq) insoluble in excess insoluble in excess zinc, white ppt. white ppt. Zn2+(aq) soluble in excess soluble in excess

Mark scheme: 3(a)(i) Observations when heating FB 5: • gas / ammonia turns (red) litmus blue 1 Any of the following score one mark each: • condensation produced or water droplets (at top of tube); • white smoke / steam / steamy fumes produced; • solid sublimes / solid forms at the top of the tube; • no residue at the end of the expt. / solid changes to a gas / solid disappears 2 3(a)(ii) Both observations required for first mark • fizzing / bubbling / effervescence • solid dissolved or colourless solution formed or (reaction is) rapid / vigorous 1 Gas tested: gas / carbon dioxide turns lime water milky / cloudy white / white ppt / chalky 1 3(a)(iii) (NH4)2CO3 1 Question Answer Marks 3(b)(i) Award one mark for every two correct observations (*) test observations + U.I. violet / blue / dark blue / purple * + Mn2+ off-white / pale brown / buff / beige precipitate * turns (darker) brown / dark on standing * + H2SO4 white precipitate * + Ag+ brown / grey precipitate * + NH3 (brown / grey ppt) soluble (in excess) / ppt disappears / forms colourless solution or white ppt forms (on standing) * + Cu2+ (gives a) blue precipitate * + HCl precipitate becomes paler or white / off-white precipitate / solid * 4

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