Question

xamination, Long Question 2 2.1 The purity of a sample of solid potassium cyanide is determined as follows: • 5.00 g of impure potassium cyanide is weighed off and transformed into to a 100.00 ml. volumetric flack, dissolved and made up to the mark. • A 10.00 ml. portion of this solution is pipetted into a conical flask, and titrated with 0.700 M KMnO solution • The average titrwtion value wa 20,69 ml of the KM The reaction stoichiometry is as follows 2KMnO, (aq) + 3KCN (aq) + H2017 - 2Mn0,(s) + 3KOCN(aq) + 2OH(aq) 211 Determine the percentage purity of the potassium cyanide 171 2.1.2 To what final volume should you dilute 10:00 ml. of the 0.200 M KMICO solution above, to ensure that 500 ml of the diluted solution contains 60 KM OP 141 2.2 Referring to the same reaction as above suppose that the MnO, that is obtained is filed of and dried. When 159 g of this MnO, then reacts with excess pure hydrochloric acid, a certain volum of chlorine yas is produced this is collected over water at 13 C and a barometr gree of 751.0 mm Hg The vapour pressure of water is 21 mmHg under these conditions Ô NH 206 L4 11 The si cutant mol Determine the volume in stof Cla collected The action society is as follows Mno, island Mncca 200 C

Answer 1

Solution (2 (2-1) MoQorib 4 км,0м = 0:2 09 (1) Volymace of krinau used = 20.6gine. volume KCN Solestion used for titration som Moles of knnoy Ins94 vih x 604 0.2 00 х 20 68 с Ч: 38 т. — Reaction involved: 2 килом + 3. Ксм + 10 — 2 Мh02 +3 Focy + 2Kah from the stoichiometry of reaction IX moles of km noy 1/2 x males of KCN 3 хуло 04 4 k Плоч — —1 Malej of kan (~ | — — 3х ч")38 п.) moles of KCH 6. 20 mnog. This is the males of ken in some of salution, moles of kon in loome of solution 1 ox 6. 267 мгло 62.07 { . = 62-07х10 м.4. - 3

Molar mass of KCN - 65.12 g) mod. goum of K CNY hole x molar mass 62.07.X1053 'mol x 65.12g mal 4.042 g mags in impure kon is Therefor of Ken 4.042 g Solution (2.1.1) percentage pusity o kwa mass of mass of sample pico 11: 4.042 X 100 5:00 11 80.84% solution (2.1.2) soome of diluted solution contains brogg Kmnou, mass Meley of knnoy modes mass 6.o.g. 158.03 g/mal. 0.03796 mal 0.03796 volyme 500mL mal diluted solution modersity of 0.0759 0.03796 500mL XIL lovom m

MIV) M2 V2 C با befor dilution after dilution 0.28 loni 0.0759 M X V2 V2 26.338 m2 Therefore you should dilute upto 26. 33.8ml to lom, 0.2oom Kmnoy solution Solution (2.2) mass of mnoz males of Mudza 0.3.59 g 0.359 g Molar mass 0.359 g 86:94 g/mol 0.004129 mal from the stoichiomety of reaction moles of MnO2 = molis of cl modes of cl 0.00412g mal. Total pressure pressure = 751.0 1.omming 1.1 mmity 21:1 Vapour pressure

= 729.9 m ART T = 23c = pressure of cl2 = (751.00-21.1 3 mming unny 729.9 mmHg x. i ahm 76omnily 0.96039 atm. PV = = 296k R=0.08206 L-am K-mal I! 23+273 296k 0.004129 mol x 0.08206 L-at kohal 0.9603) atom XV = v=0./ou4 L 0.1044 L יר Therefor volume of cl =