CAIE
Chemistry
(9701)
Questions & Answers
A redox reaction takes place between hydroxylamine, NH OH, and the iron(III) ion, Fe , in acidic conditions. The iron(III) ion is reduced to an iron(II) ion, Fe . The reaction is slow at room temperature but is complete in a few minutes at 100 °C. The reaction is shown by one of the following equations. equation 1 NH OH(aq) + Fe
+ H O
equation 2 NH OH(aq) + 2Fe
+ ½N O(g) + 2H
+ ½H O
equation 3 NH OH(aq) + 3Fe
+ NO(g) + 3H
You will carry out a titration to determine which of equations 1, 2 or 3 best represents the reaction. The iron(II) ions formed in the reaction with the hydroxylamine are oxidised by manganate(VII) ions.MnO
+ 5Fe
+ 5Fe
+ 4H O
FA 1 is 0.0200 mol dm potassium manganate(VII), KMnO FA 2 is a solution prepared by boiling a 1.00 dm aqueous mixture containing 3.30 g of hydroxylamine hydrochloride, NH , and excess sulfuric acid. Any water lost by evaporation was replaced after cooling. FA 3 is dilute sulfuric acid. Assume that one mole of hydroxylamine hydrochloride gives one mole of hydroxylamine in solution.
Method of FA 2 into a conical flask. measuring cylinder to add 10 cm of FA 3 into the same conical flask. The rough titre is cm each accurate titration. Keep FA 3 for use in Question 2
. Results
From your accurate titration results, calculate a suitable mean value to use in your calculations. Show clearly how you obtain the mean value. 25.0 cm of FA 2 required cm of FA 1.
Calculations
Calculate the amount, in mol, of potassium manganate(VII) present in the volume of FA 1 in
. amount of KMnO = mol
Use your answer to (c)(i) to calculate the amount, in mol, of iron(II) ions in 25.0 cm solution FA 2. amount of Fe = mol
Calculate the amount, in mol, of hydroxylamine hydrochloride that has reacted in the FA 2 pipetted into the conical flask. Show your working. amount of NH
Use your answer to (c)(iii) to deduce which of the three suggested equations corresponds to your results. Show your working. The correct equation number is . [1] [Total: 13]IIIVII
The reaction between thiosulfate ions and hydrogen ions produces a precipitate of sulfur. When the concentration of hydrogen ions, [H
], is kept constant, the rate is proportional to one of the following:
] You will determine which relationship is correct by mixing solutions of sodium thiosulfate and sulfuric acid. You will measure the time taken for a fixed amount of sulfur to be precipitated. Throughout these experiments care must be taken to avoid inhaling any SO gas that is produced. It is very important that as soon as each experiment is complete, the contents of the beaker are emptied into the quenching bath and the beaker is rinsed thoroughly. FA 3 is 1.00 mol dm sulfuric acid, H FA 4 is 0.100 mol dm sodium thiosulfate, Na
Method Experiment 1 measuring cylinder to transfer 50.0 cm of FA 4 into the 100 cm beaker. measuring cylinder to measure 10.0 cm of FA 3. Experiment 2 measuring cylinder to transfer 30.0 cm of FA 4 into the 100 cm beaker. of distilled water to the same beaker. measuring cylinder to measure 10.0 cm of FA 3. immediately. Experiment 3 different volume of FA 4. Do not use a volume of FA 4 that is less than 20.0 cm Record your results in Table 2.1. Results Table 2.1 experiment volume / cm reaction time / s FA 3 FA 4 distilled water 1 10.0 50.0 0 2 10.0 30.0 20.0
Calculations
Complete Table 2.2. Use the following expression to calculate the rate. rate = 1000 reaction time Table 2.2 experiment concentration of FA 4 / mol dm -3 rate / s
Use data from two of your experiments to deduce which relationship for the rate is correct. Place a tick next to the statement in Table 2.3 which most accurately fits your results. Show your working. Table 2.3 The rate is proportional to [S
]. The rate is proportional to [S
] [2]III
The uncertainty in a 50 cm measuring cylinder is ±0.5 cm Calculate the maximum percentage error in the volume of FA 4 in Experiment 2. maximum percentage error in volume of FA 4 = %
Suggest improvements to your method and the processing of the results that would allow you to make a more reliable conclusion in (b)(ii). Do not suggest changes to the apparatus or to the concentrations of FA 3 and FA 4. Do not carry out any of your suggestions. [Total: 12] Qualitative Analysis For each test you should record all your observations in the spaces provided. Examples of observations include: added You should record clearly at what stage in a test an observation is made. Where no change is observed you should write 'no change'. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. If any solution is warmed, a boiling tube must be used. No additional tests should be attempted.
FA 5 is a solid mixture of two salts and contains two different anions. None of the ions present contains nitrogen. gently at first, then more strongly, for a total of approximately 2 minutes. Then allow the Record your observations.
Place a large spatula measure of FA 5 in a boiling tube. Add an approximately 3 cm depth of distilled water and shake the tube and contents. Record your observations. Keep the contents of the test-tube for use in (a)(iii). Record your observations. FA 5. Record your observations. Keep the contents of the test-tube for use in (b)(iii).
Suggest what your observations in (a)(ii) tell you about the identity of one of the cations in FA 5.
Select reagents for further tests to identify any anion present in FA 5. Carry out your tests and record your reagents, conditions and observations in the space below.
From your observations in
, deduce the formulae of the two anions present in FA 5. anions
Write an ionic equation for one reaction occurring in
. Include state symbols.
FA 6 is a solution of a salt. One of the two ions contains a nitrogen atom. Both ions are listed in the Qualitative analysis notes. Select reagents to identify the ion containing the nitrogen atom. Use a 1 cm depth of FA 6 in a boiling tube to carry out your tests. Record your tests, results and conclusion in the space below. [3] [Total: 15] Qualitative analysis notes 1 Reactions of cations cation reaction with NaOH(aq) NH
aluminium, Al
white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH
no ppt. ammonia produced on warming barium, Ba
faint white ppt. is observed unless [Ba
] is very low no ppt. calcium, Ca
white ppt. unless [Ca
] is verylow no ppt. chromium(III), Cr giving dark green solution copper(II), Cu
pale blue ppt. insoluble in excesspale blue ppt. soluble in excess giving dark blue solution iron(II), Fe
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 magnesium, Mg
white ppt. insoluble in excesswhite ppt. insoluble in excess manganese(II),
on contact with air insoluble in excess on contact with air insoluble in excess zinc, Zn
white ppt. soluble in excess white ppt. soluble in excess 2 Reactions of anions anion reaction carbonate, CO liberated by dilute acids chloride, Cl
gives white ppt. with Ag
(soluble in NH
) bromide, Br
(partially soluble in NH
) iodide, I
gives pale yellow ppt. with Ag
(insoluble in NH
) nitrate, NO
NH liberated on heating with OH
and Al foil nitrite, NO
NH liberated on heating with OH
and Al foil; decolourises acidified aqueous KMnO sulfate, SO
gives white ppt. with Ba
(insoluble in excess dilute strong acids); gives white ppt. with high [Ca
] sulfite, SO
gives white ppt. with Ba
(soluble in excess dilute strong acids); decolourises acidified aqueous KMnO thiosulfate, S 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
Tests for elements element test and test result iodine, I Important values, constants and standards molar gas constant R = 8.31 J Kmol Faraday constant F = 9.65 × 10 C mol Avogadro constant L = 6.022 × 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)) specific heat capacity of waterc = 4.18 kJ kg (4.18 J g Group The Periodic ble of Elements hydroge 1.0 He helium 4.0 34567893Li lithium 6.9 beryllium 9.0 atomic number atomic symbolKey name relative atomic mas sodiu 23.0 magnesium 24.319K potassium 39.1 calcium 40.1 rubidiu 85.5 38Sr strontium 87.6 caesiu 132.9 barium 137.3 87Fr francium Ra radium boron 10.813A aluminiu 27.0 galliu 69.749I indium 1 14.8 81T thallium 204.4 carbon 12.0 14Si silicon 28.1 germanium 72.6tin 18.7 82 lead 207.2 22Ti titanium 47.9 40Zr zirconium 91.2 72Hf hafniu 178.5 104 Rf rutherfordiu23V vanadium 50.9 niobiu 92.9 73Ta tantalum 180.9 105 Db dubnium 24Cr chromium 52.0 molybdenum 95.974W tungsten 183.8 106 Sg seaborgium manganes 54.9 43Tc technetium rheniu 186.2 107 Bh bohriu 26Fe iron 55.8 ruthenium 101.1 osmium 190.2 108 Hs hassium Co cobalt 58.9 rhodiu 102.977I iridiu 192.2 109 Mt meitnerium 28Ni nickel 58.7 palladiu 106.4 78Pt platinum 195.1 darmstadtium copper 63.5 Ag silver 107.9 gold 197.0 111 Rg roentgeniu zinc 65.4 cadmiu 12.4 80 mercury 200.6 coperniciu fleroviu livermorium nitrogen 14.015P phosphorus 31.0 33As arseni 74.9 antimony 121.8 83Bi bismuth 209.0 oxygen 16.016S sulfur 32.1 seleniu 79.0 52Te tellurium 127.6 polonium fluorine 19.017C chlorin 35.5 35Br bromin 79.953I iodine 126.9 85At Ne neon 20.2 18Ar argon 39.9 36Kr krypton 83.8 Xe xenon 131.3 Rn radon nihonium moscoviu tennessine oganesso 21Sc scandium 45.039Y yttrium 88.9 57-71 lanthanoids 89-103 actinoids 57La lanthanum 138.9 89Ac lanthanoids actinoids actinium Ce cerium 140.1 90Th thorium 232.0 59Pr praseodymium 140.9 protactinium 231.0 neodymium 144.492U uraniu 238.0 promethium neptuniu samarium 150.4 plutonium europium 152.0 americiu gadoliniu 157.3 Cm curium 65Tb terbium 158.9 97Bk berkeliu dysprosiu 162.5 98Cf californium holmiu 164.9 99Es einsteinium 68Er erbium 167.3 100 Fm fermium Tm thuliu 168.9 101 Md mendeleviu ytterbium 173.1 102 No nobeliu 71Lu lutetium 175.0 103 Lr lawrencium 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.