CAIE
Chemistry
(9701)
Questions & Answers
Bleach is made by reacting chlorine with a cold solution of sodium hydroxide. This reaction produces sodium chlorate( O
In this experiment you will determine the concentration of sodium chlorate( I) in a sample of bleach, FA 1. To do this, you will react an acidified dilute solution of the bleach with iodide ions, I . This reaction produces iodine, I
+ H O
The amount of iodine produced will then be determined by titration with thiosulfate ions, S
FA 1 is a solution of bleach. FA 3 is dilute sulfuric acid, H potassium iodide, K I. sodium thiosulfate, Na starch indicator
Method Dilution volumetric flask. of solution and shake the flask thoroughly. Titration of FA 2 into a conical flask. of FA 3 to the conical flask. of FA 4 to the conical flask. The solution will turn brown as iodine is produced. The rough titre = cm FA 5 added in each accurate titration. Keep FA 4 and FA 5 for use in Question 3.
From your accurate titration results, obtain a value for the volume of FA 5 to be used in your calculations. Show clearly how you obtained this value. of FA 2 required cm of FA 5. [1]IIIVII
Calculations
Give your answers to
to the appropriate number of significant figures.
Use your answer to
and the relevant equation on page 2 to calculate the number of of FA 2 reacted with FA 4. moles of I = mol
Calculate the concentration of sodium chlorate( I) in FA 1. Show your working. [2] of FA 2. Use your answer to (c)(ii) to show by calculation that the potassium iodide is in excess.
A student carries out the same method but the concentration of the potassium iodide solution is not stated. What change to the practical procedure could the student make to check that the potassium iodide is in excess? Explain your answer. [Total: 15]
In this experiment you will determine the value of x in the formula for hydrated sodium thiosulfate, O. In this formula x is an integer. FA 6 is hydrated sodium thiosulfate, Na
Method beaker. of distilled water into the cup. so that the bulb of the thermometer is fully covered.
Calculations
Calculate the heat energy change in the reaction. of solution by 1.0 °C.) heat energy change = J [1]III
Use your answer to (b)(i) to calculate the relative formula mass, M , of hydrated sodium thiosulfate. hyd , for Na O is under the conditions of your experiment. Show your working. of Na O =
Use your answer to
? Explain your answer. [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: 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.
FA 7 is a salt containing one cation and one anion, both of which are listed in the Qualitative Analysis Notes. and then more strongly. Record all your observations. distilled water. Use a sample of this solution to test for the cation present in FA 7. Record your tests and observations in the space below. Keep the solution for use in (a)(iii). [3] Record your observations.
Suggest the ions present in FA 7. cation anion
FA 8 is acidified aqueous iron( Carry out the following tests and record your observations. test observations Test 1 add starch indicator. Test 2 Allow to stand until there is no further change, then add starch indicator. [3] beaker with water. Place the beaker on a gauze supported on the tripod FA 9, FA 10 and FA 11 are each one of the following. hydrochloric acid, HCl methanoic acid, HCOOH sodium sulfite, Na test observations FA 9 FA 10 FA 11 Test 1 magnesium. Test 2 Add a few drops of aqueous acidified potassium manganate( VII).
Identify each of the solutions. FA 9 is . FA 10 is . FA 11 is . [2] [Total: 15] Qualitative analysis notes 1 Reactions of aqueous cationsion reaction with NaOH(aq) NH
aluminium,
white ppt. soluble in excess white ppt. insoluble in excess ammonium,
no ppt. ammonia produced on heating barium,
faint white ppt. is nearly always observed unless reagents are pure no ppt. calcium,
white ppt. with high [Ca
] no ppt. chromium( III),
grey-green ppt. soluble in excess grey-green ppt. insoluble in excess copper( II),
pale blue ppt. insoluble in excess pale blue ppt. soluble in excess giving dark blue solution iron( II),
green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron( III),
red-brown ppt. insoluble in excess red-brown ppt. insoluble in excess magnesium,
white ppt. insoluble in excess white ppt. insoluble in excess manganese( II),
R?ZKLWHSSWUDSLGO\WXUQLQJEURZQ on contact with air insoluble in excess R?ZKLWHSSWUDSLGO\WXUQLQJEURZQ on contact with air insoluble in excess zinc,
white ppt. soluble in excess white ppt. soluble in excess 2 Reactions of anions ion reaction carbonate, liberated by dilute acids chloride,
gives white ppt. with Ag
(soluble in NH
) bromide,
gives cream ppt. with Ag
(partially soluble in NH
) iodide,
gives yellow ppt. with Ag
(insoluble in NH
) nitrate,
liberated on heating with OH
and Al foil nitrite,
liberated on heating with OH
and Al foil sulfate,
gives white ppt. with Ba
(insoluble in excess dilute strong acids) VXO?WH
gives white ppt. with Ba
(soluble in excess dilute strong acids) 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 (ppt. dissolves with excess CO chlorine, Cl bleaches damp litmus paper hydrogen, H ?pops? with a lighted splint oxygen, O relights a glowing splint 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 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 caesiu m 132. 9 barium137.3 franciu m radium boron 10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 thallium204.4 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 hafnium 178. 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 technetiu m rhenium 186. 2 107 Bh bohrium iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium Co cobal t58.9 45 Rh rhodium 102.9 iridium192.2 109 Mt meitnerium nicke l58.7 46 Pd palladium 106. 4 platinum 195.1 110 Ds darmstadtiu m copper 63.5 47 Ag silver 107. 9 79 Au gold 197. 0 111 Rg roentgenium zinc 65.4 48 Cd cadmiu m 112.4 80 Hg mercury 200. 6 112 Cn copernicium fleroviu m livermorium nitrogen 14.0 phosphorus 31.0 33 As arseni c 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 argon 39.9 36 Kr krypto n 83.8 54 Xe xenon 131. 3 86 Rn radon 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