CAIE
Chemistry
(9701)
Questions & Answers
An iron compound can contain Fe ions, Fe ions or both ions. In this experiment, you will determine the percentage by mass of iron in FA 1, an unknown compound. You will first prepare a solution of the compound and then carry out a titration using acidified potassium manganate( VII), KMnO5Fe
+ MnO
+ 4H O
The end-point of the titration is when all the Fe ions have been oxidised and so unreacted potassium manganate( VII) causes the colour of the solution to become a permanent pale pink. FA 1 is a sample of the unknown compound. potassium manganate( VII), KMnO FA 3 is dilute sulfuric acid, H
Method Weighing the compound beaker. Preparing the solution of distilled water to the beaker and stir until the FA 1 has dissolved. volumetric flask. flask. Titration of FA 4 into a conical flask. of FA 3 to the conical flask. rough titre = cm results. of FA 2 added in each accurate titration.
From your accurate titration results, calculate a suitable mean value to use in your calculations. Show clearly how you obtained this value. of FA 4 required cm of FA 2. [1]IIIVII VIII
Calculations
Give your answers to (c)(ii), (c)(iii) and (c)(iv) to the appropriate number of significant figures.
Calculate the amount, in mol, of manganate( VII) ions in the volume recorded in
. amount of MnO = mol
Calculate the amount, in mol, of iron( II) ions in the weighed sample of FA 1. amount of Fe = mol
Calculate the percentage by mass of iron in FA 1. Show your working. percentage by mass of iron = %
A student carries out the same experiment as in
. The student receives a sample of FA 1 in a container with a lid. The student records the initial mass of the container with its lid and the sample of FA 1. Then the student records the mass of the container with the residue but forgets to replace the lid. How would this error alter the student's answer to
State two assumptions that have been made in calculating the percentage by mass of iron in FA 1 in (c)(iv). [Total: 17] Question 2 starts on the next page.
In this experiment you will determine the percentage by mass of magnesium in a hydrated salt, O, where X represents the anion. You will measure the loss of mass when a sample of the hydrated salt is heated to form the anhydrous salt.
Method While the crucible is cooling you may wish to begin work on Question 3. Record the mass.
Calculations
Calculate the amount, in mol, of water lost. amount of H O lost = mol [1]III
Calculate the percentage by mass of magnesium in FA 5. Show your working. percentage by mass of Mg = %
Suggest two assumptions that must be made for this experiment to give an accurate value of the percentage of Mg. [Total: 10] 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. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests should be attempted.
FA 6 is an acidified aqueous solution of a salt which contains two cations and one anion, all of which are listed in the Qualitative analysis notes.
Select a reagent or reagents for use in tests to identify the two cations. Record your observations.
The anion in FA 6 is either the sulfate ion, SO , or the sulfite ion, SO Select a reagent or reagents for use in tests to identify the anion. Record your observations.
Identify the ions present in FA 6 and give their formulae. The cations present in FA 6 are and . The anion present in FA 6 is .
Carry out the tests and record your observations. test observations Test 1 sodium sulfite, then Rinse out this test-tube thoroughly. Test 2 potassium iodide, then add a few drops of starch solution.
FA 7, FA 8 and FA 9 are aqueous solutions of sodium salts. Each solution contains one of the following ions: CO You will identify which solution contains which ion.
Carry out the tests and record your observations. test observations FA 7 FA 8 FA 9 Add a few drops of aqueous silver nitrate, then add aqueous ammonia.
If your results are insufficient to identify which anion is present in each solution, carry out a further test. Record your test and observations.
Identify which solution contains which ion. The CO ion is present in . ion is present in . ion is present in . [1] [Total: 13] 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
grey-green ppt. soluble in excess giving dark green solution grey-green ppt. insoluble in excess 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
red-brown ppt. insoluble in excessred-brown ppt. insoluble in excess magnesium, Mg
white ppt. insoluble in excesswhite ppt. insoluble in excess manganese( II), Mn
R?ZKLWHSSWUDSLGO\WXUQLQJEURZQ on contact with air insoluble in excess R?ZKLWHSSWUDSLGO\WXUQLQJEURZQ 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; GHFRORXULVHVDFLGL?HGDTXHRXV.0Q2 sulfate, SO
gives white ppt. with Ba
(insoluble in excess dilute strong acids); gives white ppt. with high [Ca
] VXO?WHSO
gives white ppt. with Ba
(soluble in excess dilute strong acids); GHFRORXULVHVDFLGL?HGDTXHRXV.0Q2 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 gives blue-black colour on addition of starch solution Important values, constants and standards Faraday constant F = 9.65 u 10 Avogadro constant L = 6.022 u 10 electronic charge e = ?1.60 u 10?19 molar volume of gas V at room conditions ionic product of water K = 1.00 u 10?14 Group The Periodic Table of Elements hydrogen 1.0 He helium 4.0 12131415161718 34567891011123Li 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 strontiu m 87.6 caesium 132. 9 barium 137.3 francium Ra radium boron10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 thallium 204.4 carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sntin 118.7 82 Pb lead 207.2 titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium178. 5 rutherfordium vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium chromium 52.0 42 Mo molybdenum 95.9 74 W tungste n 183.8 106 Sg seaborgium manganese 54.9 43 Tc technetium rhenium 186. 2 107 Bh bohrium iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium Co cobalt 58.9 45 Rh rhodium 102.9 iridium192.2 109 Mt meitnerium nicke l58.7 46 Pd palladium 106. 4 platinum 195. 1 110 Ds darmstadtium copper 63.5 47 Ag silver 107. 9 79 Au gold 197. 0 111 Rg roentgenium zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200. 6 112 Cn copernicium flerovium livermorium nitrogen 14.0 phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 bismuth 209.0 oxygen 16.0 sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 iodine 126.9 Ne neon 20.2 18 Ar argo n39.9 krypto n 83.8 54 Xe xenon131. 3 86 Rn radon nihonium moscovium tennessine oganesson scandium 45.0 yttriu m 88.9 57?71 lanthanoids 89?103 actinoids 57La lanthanum 138.9 89 Ac lanthanoids actinoids actinium Ce cerium 140.1 90 Th thoriu m232.0 praseodymium 140.9 91 Pa protactinium 231.0 neodymium 144.4 uranium 238.0 promethium neptunium samarium 150.4 94 Pu plutonium europium 152.0 95 Am americium gadolinium 157.3 96 Cm curium terbiu m158.9 97 Bk berkelium dysprosium 162. 5 californium holmium 164. 9 99 Es einsteinium erbium 167. 3 100 Fm fermium Tm thulium168. 9 101 Md mendelevium ytterbiu m 173. 1 102 No nobelium lutetium 175.0 lawrencium 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.