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15 0 SELECTED Problems in Chemistry 15 0 SELECTED Problems in Chemistry Ranjeet Shahi ARIHANT PRAKASHAN (Series), MEERUT Arihant Prakashan (Series), Meerut All Rights Reserved © Author No part of this publication may be re-produced, stored in a retrieval system or distributed in any form or by any means, electronic, mechanical, photocopying, recording, scanning, web or otherwise without the written permission of the publisher Arihant has obtained all the information in this book from the sources believed to be reliable and true However, Arihant or its editors or authors or illustrators don’t take any responsibility for the absolute accuracy of any information published and the damages or loss suffered there upon All disputes subject to Meerut (UP) jurisdiction only Administrative & Production Offices Regd Office ‘Ramchhaya’ 4577/15, Agarwal Road, Darya Ganj, New Delhi -110002 Tele: 011- 47630600, 43518550; Fax: 011- 23280316 Head Office Kalindi, TP Nagar, Meerut (UP) - 250002 Tele: 0121-2401479, 2512970, 4004199; Fax: 0121-2401648 Sales & Support Offices Agra, Ahmedabad, Bengaluru, Bhubaneswar, Bareilly, Chennai, Delhi, Guwahati, Hyderabad, Jaipur, Jhansi, Kolkata, Lucknow, Meerut, Nagpur & Pune ISBN : 978-93-12147-38-2 For further information about the books published by Arihant log on to www.arihantbooks.com or email to info@arihantbooks.com PREFACE This work is the result of my teaching the JEE aspirants over the post decade and a half Often I have found that the students mess up with the chemical reactions given in the problem and get themselves entangled into them The reason is that they are not able to distinguish the relationships between the various chemical principles and concepts This book is an effort to make them master the fundamentals of Chemistry through problems-solving, and apply them intelligently to arrive at a correct solution The problems included in the book with their solutions, aim to give you the mastery required for solving the intricate problems asked in the exams such as JEE Critical analysis of the situation is required whatever be format of the questions This book just gives emphasis on this, and it is hoped that it will give a boost to all the meritorious and hard-wroking students I shall like to thank Mr Yogesh Chand Jain, Chairman, Arihant Group, for bringing the book in this nice form Suggestions for further improvement of the book are welcome Ranjeet Shahi CONTENTS Mole Concept Acid-Base Titration Redox Titration 12 Gaseous State 16 Thermochemistry 20 Thermodynamics 26 Atomic Structure 33 Chemical Bonding 36 Chemical Equilibrium 39 10 Ionic Equilibrium 47 11 Electrochemistry 57 12 Chemical Kinetics 67 13 Colligative Properties 75 14 Solid State 78 15 Surface Chemistry 80 16 Reaction Mechanism 81 17 Stereochemistry 95 18 Hydrocarbons 103 19 Alkyl Halides 120 20 Alcohols and Ethers 133 21 Aldehydes and Ketones 161 22 Carboxylic Acids and Its Derivatives 193 23 Amines 213 24 Aromatic Compounds 216 25 Carbohydrates, Amino Acids and Polymers 264 26 Miscellaneous 265 27 Qualitative Analysis 271 28 Co-odination Compounds 278 29 Representative Elements 285 30 Metallurgy 292 Solutions 295 Problems in Chemistry MOLE CONCEPT PROBLEM A crystalline hydrated salt on being rendered anhydrous, loses 45.6% of its weight The percentage composition of anhydrous salt is: Al = 10.5%, K = 15.1%, S = 24.8% and O = 49.6% Find the empirical formula of the anhydrous and crystalline salt PROBLEM How much quantity of zinc will have to be reacted with excess of dilute HCl solution to produce sufficient hydrogen gas for completely reacting with the oxygen obtained by decomposing 5.104 g of potassium chlorate? PROBLEM A 1.85 g sample of mixture of CuCl and CuBr was dissolved in water and mixed thoroughly with 1.8 g portion of AgCl After reaction, the solid which now contain AgCl and AgBr was filtered, dried and weighed to be 2.052 g What was the % by weight of CuBr in the mixture? PROBLEM 1.0 g of a sample containing NaCl, KCl and some inert impurity is dissolved in excess of water and treated with excess of AgNO solution A 2.0 g precipitate of AgCl separate out Also sample is 23% by mass in sodium Determine mass percentage of KCl in the sample PROBLEM A one gram sample containing CaBr , NaCl and some inert impurity was dissolved in enough water and treated with excess of aqueous silver nitrate solution where a mixed precipitate of AgCl and AgBr weighing 1.94 g was obtained Precipitate was washed, dried and shaken with an aqueous solution of NaBr where all AgCl was converted into AgBr The new precipitate which contain only AgBr now weighed to be 2.4 g Determine mass percentage of CaBr and NaCl in the original sample PROBLEM Sulphur combines with oxygen to form two oxide SO and SO If 10 g of S is mixed with 12 g of O , what mass of SO and SO will be formed, so that neither S nor oxygen will be left at the end of reaction? PROBLEM An aqueous solution of ethanol has density 1.025 g/mL and it is 8.0 M Determine molality m of this solution PROBLEM An aqueous solution of acetic acid has density 1.12 g/mL and it is 5.0 m Determine molarity (M) PROBLEM Octane is a component of gasoline Incomplete combustion of octane produces some CO along with CO and H 2O, which reduces efficiency of engine In a certain test run, 1.0 gallon of octane is burned and total mass of CO, CO and H 2O produced was found to be 11.53 kg Calculate efficiency of the engine, density of octane is 2.65 kg/gallon PROBLEM 10 The formula of a hydrated salt of barium is BaCl ⋅ xH 2O If 1.936 g of this compound gives 1.846 g of anhydrous BaSO upon treatment with H 2SO , calculate x PROBLEM 11 A mixture of CuSO ⋅ 5H 2O and MgSO ⋅ 7H 2O was heated until all the water was driven-off If 5.0 g of mixture gave g of anhydrous salts, what was the percentage by mass of CuSO ⋅ 5H 2O in the original mixture? PROBLEM 12 A sample of clay contain 15% moisture, and rest are CaCO and non-volatile SiO This on heating loses part of its moisture, but CaCO is completely converted into CaO The partially dried 280 Problems in Chemistry precipitate on treatment with excess AgNO solution whereas an aqueous solution of B containing same amount of salt gave 28.7 g of precipitate on treatment with excess of AgNO solution Identify A and B [Atomic mass : Pt = 195, Ag =108, Br = 80] PROBLEM 1444 A, B and C are three complexes of chromium (iii) with their formula H12O 6Cl 3Cr Complex A does not react with concentrated H 2SO solution whereas complexes B and C loses 6.75% and 13.5% of their weight, respectively, on treatment with concentrated H 2SO solution Deduce formula of A, B and C PROBLEM 1445 An aqueous solution of titanium chloride, when subjected to magnetic measurement, measured zero magnetic moment Deduce formula of complex assuming it to be octahedral in aqueous solution PROBLEM 1446 A cobalt (ii) salt when dissolved in excess of concentrated HCl, it forms an octahedral complex whose magnetic moment was found to be 3.87 Bm Predict shape of complex PROBLEM 1447 How [Co(NH ) ][Cr(NO ) ] and [Co(NO ) ][Cr(NH ) ] can be distinguished by electrochemical method? PROBLEM 1448 How [Cr(NH ) ][Cr(NO ) ] and [Cr(NH ) (NO ) ][Cr(NH ) (NO ) ] can be distinguished from conductivity measurement in their aqueous solution? PROBLEM 1449 Two complexes of chromium have empirical formulae corresponding to Cr(NH ) (NO ) In aqueous solution, one of these is non-conducting while other is electrolytic What is the lowest possible formula weight of conducting reagent? What is the highest possible formula weight of non-conducting reagent? PROBLEM 1450 Write formula of all possible polymerization isomers of Pt(NH ) (NO ) PROBLEM 1451 A metal complex having composition Cr(NH ) Cl Br has been isolated in two forms A and B A reacts with AgNO producing a white precipitate which was soluble in dilute ammonia solution B reacts with AgNO producing a pale-yellow precipitate soluble in concentrated ammonia solution Write formula of A and B and state hybridization of chromium in each Also calculate their magnetic moment (spin only) PROBLEM 1452 A metal complex having composition Cr(NH ) ClBr ⋅ H 2O has been isolated in three forms A, B and C Heating 16.7 gram of either A or C loses 0.9 gram of its weight whereas no weight loss was observed on heating B Adding 35.35 g of A to a concentrated solution of AgNO resulted in 14.35 gram of precipitate whereas adding same amount of C to a concentrated AgNO solution resulted in 18.8 g of precipitate In another experiment, when 6.67 gram of complex B was added to a concentrated aqueous solution of AgNO , when 7.52 gram precipitate was formed Deduce formula of complexes A, B and C PROBLEM 1453 An octahedral complex of cobalt has its composition Co(NH ) (H 2O) (SO )(NO ) and it exists in four isomeric forms A, B, C and D Simple heating of either A or B loses 5.6% of its original weight whereas similar treatment on C causes 11.2% loss in its original weight D did not lose any weight on simple heating Either A or C did not result in any precipitation if treated with aqueous BaCl solution, whereas B and D resulted a white precipitate when treated with aqueous BaCl solution Also C does not conduct electricity in its aqueous solution Deduce formula of A, B, C and D PROBLEM 1454 An octahedral complex of platinum has its composition Pt(NH ) Cl Br and exist in three isomeric forms A, B and C A 4.94 gram of compound A on treatment with excess of aqueous Problems 281 AgNO gave 3.76 g of precipitate 2.47 gram of B on treatment with excess of AgNO solution gave 1.66 gram of precipitate while 9.88 gram of C gave 5.74 gram of precipitate with aqueous AgNO Deduce structural formula of A, B and C (Atomic weight Pt =195, Br = 80, Ag = 108) PROBLEM 1455 A complex of cobalt has composition Co(NH ) (H 2O) ClBr and exist in two isomeric forms A and B A on simple heating loses 5.3% of its weight whereas B does not lose any weight on simple heating A on treatment with excess of AgNO solution gives off precipitate that is 42% by mass of the complex Similar treatment of B gives off another precipitate which is 110% by mass of the complex Deduce structures of A and B PROBLEM 1456 A solution was prepared by dissolving 0.5 g CrCl ⋅ 6H 2O in sufficient water and volume made upto 100 mL A 10.0 mL position of this solution when treated with excess of AgNO , gave a precipitate, filtered dried and weighed to be 0.538 gram Deduce structural formula of the complex PROBLEM 1457 A complex [CoA ]3+ is red coloured while [CoB6 ]3+ is green coloured (a) Which ligand produces the lager crystal field splitting (b) Which complex is expected to be more easily oxidised PROBLEM 1458 In which complex [Cu(H 2O) ]2+ or [Cu(NH ) ]2+ , are the bonds from acceptor to the donor atoms stronger? PROBLEM 1459 Which complex is more stable [Cr(NH ) ]3+ or [Cr(en) ]3+ ? PROBLEM 1460 Why are complexes of Ti 4+ and Zn 2+ are typically white? PROBLEM 1461 Accounts for the followings : 2– is paramagnetic (a) Ni(CN) 2− is diamagnetic but [NiCl ] (b) [Ni(CO) ] is tetrahedral (c) [Ni(NH ) ]2+ is an outer orbital complex PROBLEM 1462 Why [CuCl ]2– exist but [CuI ]2− does not? 3+ PROBLEM 1463 Both Fe(CN) 3− and Fe(H 2O) are colourless in aqueous medium, explain PROBLEM 1464 Calculate the magnetic moment of K [Mn(CN) ] and K [MnBr ] and explain the geometries of these complexes PROBLEM 1465 Select the complexes which will absorb in visible range : (a) [Ti(H 2O) ]Cl (b) [VF4 ] (c) [Cu(NH ) ]+ (d) [Cu(NH ) ]2+ (e) [Ni(CN) ]2− (f) [Ni(CO) ] PROBLEM 1466 CoF63− is paramagnetic while Co(CN) 3− is diamagnetic, explain PROBLEM 1467 Use an orbital diagram to show the electron distribution in 3d-orbitals of the central metal ion in each of the following complex ion If more than one distribution seems possible, indicate whether you expect low-spin or high-spin state to be favoured and determine spin-only magnetic moment (d) [Mn(CN) ]3– (c) [CoCl ]2– (b) [FeCl ]3– (a) [Cr(H 2O) ]3+ 282 Problems in Chemistry PROBLEM 1468 Of the following two complexes: [Cr(H 2O) ]Cl and [Cr(NH ) ]Cl , one is yellow coloured while other is violet Identify them PROBLEM 1469 Of the following two complexes : [Fe(H 2O) ] (NO ) and K [Fe(CN) ] ⋅ 3H 2O, one is green coloured while other is yellow Identify them PROBLEM 1470 Explain why one of the cis-trans isomers of [CoCl (en) ] exhibit optical isomerism and other does not PROBLEM 1471 Would you expect to find optical isomerism in either of the hypothetical tetrahedral complexes : [ZnA2 B ]2+ and [ZnABCD ]2+ ? Explain PROBLEM 1472 The complex [Pt(NH ) Cl ] displays cis-trans isomerism but [ZnCl (NH ) ] does not Why you suppose these two cases are different? PROBLEM 1473 The magnetic properties of octahedral complex ion [CrL ]3+ are independent of identity of the ligand L How you account for this fact? PROBLEM 1474 Four structures are shown in the accompanying sketch Indicate whether any of these structures are identical, geometrical isomers or optical isomers: en Cl Co Cl 3+ Co Cl en Cl en 3+ Cl en 3+ Co en Cl 3+ en Co Cl en en Cl (a) (b) (c) (d) PROBLEM 1475 When ethylene diamine is added to a solution of cobalt chloride hexahydrate in concentrated HCl, a blue crystalline solid separate out Analysis of this complex shows : N = 14%, C =12%, H = 5%, Cl = 53.25% The magnetic moment of the solution was found to be 3.9 Bm Determine structural formula and shape of this complex PROBLEM 1476 Addition of TiCl to an aqueous solution of urea followed by addition of KI gives a deep blue crystals of octahedral complex containing Ti, urea and iodine with this magnetic moment (spin-only) =1.76 Bm Also 1.0 g of this complex on heating in excess of oxygen gives 0.12 g TiO Deduce structures of complex PROBLEM 1477 (a) Explain why dissolution of a chromium (III) salt produces an acidic solution? (b) Explain why the slow addition of hydroxide ions to a solution of Cr(III) ions first produces a gelatinous precipitate that subsequently dissolves with further addition of hydroxide ion PROBLEM 1478 Name the following complex ions: (c) [Pt(NH )Cl ]– (a) [Zr(OX ) ]4– (b) [CuCl (H 2O) ]2– (d) [Mo(CN) (OH) ]4– PROBLEM 1479 By considering electronic configuration, suggest a reason why iron (III) compounds are readily prepared from iron (II), but conversions of Ni(II) and Co(II) to Ni(III) and Co(III) are much more difficult? 283 Problems PROBLEM 1480 Suggest a chemical test for distinguishing between: (a) [Ni(SO )(en) ]Cl and [NiCl (en) ]SO (c) [Ni(en) I ]Cl and [NiCl (en) ]I PROBLEM 1481 (a) Sketch the orbital energy-level diagrams for [MnCl ]4– and [Mn(CN) ]4– (b) Which complex is expected to transmits the longer wavelengths of incident electromagnetic radiations? PROBLEM 1482 The complex [Co(CN) ]3– is pale yellow (a) Is short or long wavelength visible light absorbed? (b) How many unpaired electrons are available? (c) If ammonia molecules are substituted for cyanide ions as ligands, will the shift in absorbance of radiation be towards the blue or red region of electromagnetic radiation? PROBLEM 1483 Explain why high spin complex Mn 2+ are only faintly coloured PROBLEM 1484 The relative thermodynamic stability of two complexes can be predicted from a comparison of their standard potentials Determine which complex of the following pair is the more stable? (i) (ii) [Co(NH ) ]3+ + e → [Co(NH ) ]2+ [Co(H 2O) ] 3+ + e → [Co(H 2O) ] 2+ E ° = 0.11 V E ° =1.81 V PROBLEM 1485 (a) When excess of AgNO is added to a 0.001mol Cr(III) chloride, 0.001 mol AgCl is formed (b) When excess of AgNO is added to a 0.001 mol Cr(III) chloride, 0.003 mol of AgCl is formed Discuss the structure of complex based on above information PROBLEM 1486 Identify the type of isomers represented by the following pairs : (a) [Cu(NH ) ][PtCl ] and [Pt(NH ) ][CuCl ] (b) [Cr(OH) (NH ) ] Br and [CrBr(OH)(NH ) ]OH (c) [Co(NCS)(NH ) ]Cl and [Co(SCN)(NH ) ]Cl (d) [CrCl(H 2O) ]Cl ⋅ H 2O and [CrCl (H 2O) ]Cl ⋅ 2H 2O PROBLEM 1487 Following is a chelating ligand called nitrilotriacetic (NTA) acid It act as a tetradentate ligand Sketch the structures of [Co(NTA)(H 2O) ]3+ ion and propose type of isomerism if present any : N(CH 2COOH) : Nitrilotriacetic acid PROBLEM 1488 The complex shown below is called diethylenetriamine (dien) : •• •• •• H N CH 2CH NH CH 2CH NH (a) Sketch the structure of complex [Co(dien) ]3+ (b) Which complex would be expected to be more stable in aqueous solution, [Co(dien) ]3+ or [Co(NH ) ]3+ ? PROBLEM 1489 Arrange the following complexes in order of increasing wavelength of visible light absorbed by them : (a) [Cr(H 2O) ]3+ (b) [CrCl ]3– (c) [Cr(en) ]3+ (d) [Cr(CN) ]3– (e) [Cr(NH ) ]3+ 284 Problems in Chemistry PROBLEM 1490 Which complex should be expected to absorb light of highest frequency [Cr(H 2O) ]3+ , [Cr(en) ]3+ or [Cr(CN) ]3– ? PROBLEM 1491 Which complex should absorb light at longer wavelength? (b) [Mn(CN) ]3– or [Mn(CN) ]4– (a) [Fe(OH ) ]2+ or [Fe(CN) ]4– PROBLEM 1492 Sketch the structures of the following complexes indicating any cis-trans or optical isomerism: (b) [Pt(NH )(Py)(Cl)(Br)] square planar, Py = Pyridine (a) [Pt(H 2O) Br ] square planar (c) [Zn(NH ) Cl]+ (d) [Ni(H 2O) Cl ] (e) [Co(C 2O ) Cl ]3– PROBLEM 1493 Draw diagrams for any cis-trans and optical isomers that could exist for the following complexes: (c) [Cr(NH ) (H 2O) Br ]+ (b) [Co(en) Cl ]+ (a) [Co(en) NO (Cl)]+ 3+ (d) [Pt(NH ) Cl ] (e) [Cr(en) ] PROBLEM 1494 Determine the spin only magnetic moment: (c) [Mn(CN) ]3– (b) [Co(en) ]3+ (a) [CoF6 ]3– (d) [MnCl ]4– PROBLEM 1495 If trimethylphosphene is added to solution of Ni(II) chloride in acetone, a blue compound of molar mass 280 is isolated This compound on analysis gave the following composition : Ni = 21.5%, Cl = 26%, and (CH ) P = 52.5% This blue compound does not have any isomeric forms What are the geometry and molecular formula of this blue complex? Also determine magnetic moment (spin-only) of the complex PROBLEM 1496 The complex Na [Ni(CN) Br ] has zero magnetic moment Predict geometry and draw shape of the complex PROBLEM 1497 Draw all geometrical isomers of the following complexes: (a) [Co(NH ) Cl ]– (b) [Co(NH ) Cl ] PROBLEM 1498 Draw structures of all the geometrical and optical isomers of each of the following complex: (c) [Co(C 2O ) ]3– (b) [Co(NH ) Cl]2+ (a) [Co(NH ) ]3+ PROBLEM 1499 The [Ni(CN) ]2– ion is diamagnetic while [Ni(Cl) ]2– ion is paramagnetic Explain with the help of crystal field splitting diagram PROBLEM 1500 Transition metal complexes containing cyanide (CN – ) ligands are often yellow in colour, whereas those containing H 2O ligands are often green or blue in colour Explain PROBLEM 1501 The absorption maximum for complex ion [Co(NH ) ]3+ occurs at 470 nm Determine the crystal field splitting energy PROBLEM 1502 For each of the following pair, choose the complex that absorbs light of longer wavelengths (b) [FeF6 ]3– and [Fe(CN) ]3– (a) [Co(NH ) ]3+ and [Co(H 2O) ]3+ (c) [Cu(NH ) ]2+ and [CuCl ]2– 285 Problems PROBLEM 1503 A solution made by dissolving 0.875 g of compound Co(NH ) 4⋅Cl in 25 g of water freezes at −0.56° C Deduce structural formula of complex if cryoscopic constant of water is 1.86 K kg mol –1 PROBLEM 1504 Oxalic acid H 2C 2O is sometimes used to clean rust stains from bathtubs Explain the chemistry underlying the cleaning action PROBLEM 1505 When aqueous potassium cyanide is added to a solution of Cu(II) sulphate, a white precipitate is formed in the beginning which dissolves on adding excess of reagent No precipitate is formed when H 2S( g ) is bubbled through this solution at the point Explain PROBLEM 1506 A concentrated aqueous copper (II) chloride solution is bright green in colour When diluted with water, the solution becomes light blue Explain PROBLEM 1507 In dilute nitric acid solution, Fe 3+ forms a dark-red complex with thiocyanate ion (SCN – ) according to following reaction : [Fe(H 2O) ]3+ + SCN – H 2O + [Fe(H 2O) NCS]2+ In one experiment,1.0 mL of 0.20 M Fe(NO ) was mixed with1.0 mL of a10 −3 M KSCN solution and mL dilute nitric acid was added Final concentration of [Fe(H 2O) (SCN)]2+ was found to be 7.3 ×10 –5 M Calculate formation constant of complex PROBLEM 1508 A student has prepared a cobalt complex that has one of the following three structures : [Co(NH ) ]Cl , [Co(NH ) Cl]Cl or [Co(NH ) Cl ]Cl Explain how the student would distinguish between these possibilities by an electrical conductance experiment At the student’s disposal are three strong electrolytes—NaCl, MgCl and FeCl PROBLEM 1509 Aqueous solution of CoCl are generally either light pink or blue Low concentrations favour the pink form while high concentration favours blue form Adding HCl to a pink solution of CoCl causes the solution to turn blue; the pink colour is restored by addition of HgCl Account for these observations PROBLEM 1510 Suggest a method that would allow you to distinguish between cis-Pt(NH ) Cl and trans-Pt(NH ) Cl PROBLEM 1511 You are given two solutions containing FeCl and FeCl at same concentrations One solution is light yellow and the other is brown Identify these solutions based on their colours REPRESENTATIVE ELEMENTS PROBLEM 1512 Write equations for the following process : (a) B2O + Mg (b) The result of the addition of aqueous NaOH to a mixture of solid Al 2O and Fe 2O (c) CO + Na[Al(OH) ]( aq ) → 286 Problems in Chemistry PROBLEM 1513 Explain how, during dimerization, each BH molecule acts both a Lewis base and a Lewis acid PROBLEM 1514 Suggest likely products for the following reactions: (a) BF3 + EtOH → (b) BCl + PhNH → (c) BF3 + KF → PROBLEM 1515 Comment on the following observations: (a) AlF3 is almost insoluble in anhydrous HF but dissolves if KF is present Passage of BF3 through the resulting solution causes AlF3 to reprecipitate (b) Borazine is similar to benzene in some ways but dissimilar in other ways PROBLEM 1516 (a) Suggest why trimethylamine is pyramidal while trisilylamine is planar (b) Suggest reasons why, at 300 K, CO and SiO are not isostructural PROBLEM 1517 Write equations for : (a) the reaction of SiCl with aqueous NaOH (b) the hydrolysis of SiH 3Cl, (c) the hydrolysis of SiF4 PROBLEM 1518 What would you expect to form when: (a) Sn is heated with concentrated NaOH, (b) SO is passed over PbO , (c) SiH 2Cl is hydrolysed, (d) 4ClCH 2SiCl + 3Li[AlH ] → PROBLEM 1519 Discuss the bonding in BeH in its solid state PROBLEM 1520 Write balanced equations for the following reactions: (a) NaH + H 2O → (b) NaN + Heat → (c) KO + H 2O → (d) NaF + BF3 → PROBLEM 1521 Write balanced equations for the following reactions: (a) Thermal decomposition of [NH ]2 [BeF4 ] (b) The reaction between NaCl and BeCl (c) The dissolution of BeF2 in water PROBLEM 1522 (a) Suggest a likely structure for the dimer of BeCl , present in the vapour phase What hybridization scheme is appropriate for the Be centers? (b) Suggest structure of BeCl in diethyl ether PROBLEM 1523 How anhydrous CaCl and CaH function as drying agents? PROBLEM 1524 Among NaF and NaCl, NaF has higher melting point instead of its lower molecular weight while reverse trend is there between CF4 and CCl , justify PROBLEM 1525 Be and C11 are positron emitter while C14 is beta emitter, explain PROBLEM 1526 Determine nuclear binding energy of He Problems 287 PROBLEM 1527 Lithium ion being smallest in its group, is expected to have highest ionic mobility and hence solution of its salts would be expected to have a higher conductivity than solution of cesium salts Explain, why this is not so PROBLEM 1528 Ionization energy suggest that Cs should be the most reactive metal but the standard reduction potential suggest that Li is most reactive Reconcile these two observations PROBLEM 1529 Discuss the colour of alkali metal solution in liquid ammonia PROBLEM 1530 0.35 g of a metal ( A ) was dissolved in dilute HNO This solution gave a red colouration to a non-luminous Bunsen-burner flame and on evaporation gave 0.75 g of metal oxide ( B ) A also reacted with hydrogen forming C On reacting 0.16 g of C with water, a gas D was evolved and a sparingly soluble compound E was formed, which gave a strongly alkaline reaction and required 200 mL 0.1 M HCl for neutralization Identify A to E PROBLEM 1531 Which is more heavily hydrated LiCl or MgCl ? PROBLEM 1532 Why Be salts seldom contain more than four molecules of water of crystallization? PROBLEM 1533 An element ( A ) reacts quitely with water librating a colourless, odourless gas and a solution of ( B ) Passing CO gas through B yields a while precipitate (C ) which dissolves on passing excess CO gas Precipitate C effervesced with dilute HCl and gave a deep red colouration to a Bunsen burner flame Heating C gave a caustic white compound ( D ) which when further heated with carbon at 1000°C, gave a solid ( E ) of immense commercial importance Identify A to E PROBLEM 1534 A white salt ( A ) evolves a colourless gas (B ) when treated with dilute HCl Bubbling ( B ) through lime water, a precipitate (C ) formed initially which dissolved forming a clear solution on further passing the gas A small sample of A was moistened with concentrated HCl, placed on a platinum wire and introduced into a Bunsen burner flame where it caused a green flame colouration On strong heating, A decomposed giving a white solid ( D ) which turned red litmus blue Identify A to D PROBLEM 1535 SnCl is a good reducing agent but PbCl is stable, explain PROBLEM 1536 AlCl exist as dimer in benzene While in aqueous solution it remains in the form of hydrated ions, explain PROBLEM 1537 Discuss the reaction of B2 H with NH under following conditions: (a) Excess ammonia at low temperature (b) Excess ammonia at high temperature (c) NH and B2 H in :1 ratio at high temperature PROBLEM 1538 Complete the following inorganic reactions: (a) B3 N H + HCl → (b) B2 H + H 2O → (c) B2 N H + H 2O → (d) B2 H + EtOH → (e) B2 H + LiH → (f) B2 H + HCl → (g) B2 H + Cl → PROBLEM 1539 An yellowish-white, deliquescent substance ( A ) has its vapour density 133.5 A reacts quickly with water forming a solution B A sample of B gave a curdy white precipitate (C ) on addition of dilute HNO and AgNO solution, but this readily dissolved on addition of dilute NH 4OH, though a 288 Problems in Chemistry white gelatinous precipitate ( D ) was formed in its place D dissolves in a concentrated solution of NaOH, but passage of CO gas through this solution results in reprecipitation of D Also compound ( A ) dissolved unchanged in dry diethyl ether and when this solution was reacted with excess of LiH, a new compound E was formed Identify A to E PROBLEM 1540 (a) How SiCl is prepared from SiO ? (b) How SiC is prepared from SiO ? PROBLEM 1541 Complete the following reactions: (a) Al 4C + H 2O → (b) CaC + H 2O → 1100°C (c) CaC + N → O (d) SiC + NaOH → (e) Mg 2C + H 2O → PROBLEM 1542 Synthesize a linear chain silicones starting with SiCl and ethylmagnesium chloride PROBLEM 1543 How R 3SiCl acts to control the molecular weight in preparation of polysilicones PROBLEM 1544 Draw the structures of: 12– (a) tri cyclo-dimethyl siloxane (b) Si 3O 6− (c) Si 6O18 (d) Pyroxene (e) Amphiboles PROBLEM 1545 Complete the following reactions: (a) P4 + NaOH → (b) CaNCN + H 2O → (c) N H + I → (d) N 2O + NaNH → PROBLEM 1546 Discuss, how superphosphate and triple superphosphate fertilizers are manufactured? PROBLEM 1547 Complete the following reactions: (a) N 2O + NaCl → (b) N 2O + Na → (c) N 2O + H 2O → (d) NO + Cl → (e) NO + HCl → PROBLEM 1548 Explain why nitrogen exist as diatomic molecule while phosphorus exist as tetra atomic (P4 ) molecule PROBLEM 1549 Why NF3 is stable while NCl and NI are explosive? PROBLEM 1550 Draw the shapes of P4O and P4O10 PROBLEM 1551 (a) How nitric acid is prepared by Ostwald’s method (b) Give one example of each in which HNO acts as an oxidising agent and reducing agent PROBLEM 1552 Explain the following observations: (a) Liquid oxygen sticks to the pols of magnet but liquid nitrogen does not (b) The N—O + ion has a shorter bond than does NO PROBLEM 1553 Describe method how H 2O is prepared by electrolysis of H 2SO Draw structure of H 2O Write balanced equations for the reaction of H 2O with: (a) an acidified solution of KMnO , (b) an acidified solution of K 2Cr 2O , (c) aqueous HI, (d) an acidic solution of K [Fe(CN) ] 289 Problems PROBLEM 1554 Draw shapes of the following oxyacid of sulphur and indicate oxidation states of sulphur (b) H 2S 2O (c) H 2S 2O (d) H 2S 2O (a) H 2SO (g) H 2S 2O (e) H 2S 2O (f) H 2SO PROBLEM 1555 How sulphuric acid is manufactured by contact process? PROBLEM 1556 Provide two method by which sodium thiosulphate is synthesized Why thiosulphuric acid can’t be made by adding acid to aqueous solution of thiosulphate salt? PROBLEM 1557 Complete the following chemical reactions: (a) F2 + H 2O → (b) Cl + CO → (c) Cl + NH (excess) → (d) Cl + NaOH → (e) SiO + HF → PROBMEL 1558 Complete the following reactions: (a) Cl 2O + NaOH → (b) HClO + P4O10 → (c) ClO + NaOH → (d) KBrO + F2 + KOH → (e) Cl 2O + NaOH → (f) Cl 2O + HF → PROBLEM 1559 Why it is not possible to produce F2 by electrolysis of aqueous NaF, aqueous HF or anhydrous HF? PROBLEM 1560 (a) Draw structures of OF2 , Cl 2O, O F2 and I 2O (b) Explain bond angle in OF2 and give a reason why it is different in Cl 2O (c) Why are the OF bond in O F2 longer than in OF2 while O—O bond in O F2 is short compared with that in H 2O PROBLEM 1561 Complete the following reactions: (a) XeF2 + HCl → (b) (c) XeF4 + SF4 → (d) (e) XeF4 + H 2O → (f) (g) XeF6 + XeO → (h) XeF4 + KI → XeF2 + H 2O → XeF6 + H 2O → XeO + XeOF4 → PROBLEM 1562 Ferric bromide (FeBr ) when dissolved in water, converted into Fe 2+ evolving Br ( g ) while no chlorine gas is evolved when FeCl is dissolved in water Justify PROBLEM 1563 When Cl ( g ) is mixed with F2 ( g ), ClF3 ( g ) is produced not the FCl ( g ) Explain PROBLEM 1564 Explain why nitrogen forms extra-ordinary stable N at room temperature but phosphorus forms P2 only at very high temperature PROBLEM 1565 Explain sulphur forms compounds such as SF4 , SF6 , etc while oxygen, of the same group forms only OF2 ? PROBLEM 1566 In laboratory, HF and HCl can be prepared by reacting the metal fluorides and chlorides with concentrated H 2SO but HBr can’t be prepared by the same procedure Explain PROBLEM 1567 Discuss the acidic behaviour shown by boric acid in water and explain why it can’t be titrated satisfactorily by NaOH Why does glycerol or other such syn vicinal diols/triols enhances its acidic properties? 290 Problems in Chemistry PROBLEM 1568 Explain why CCl is unaffected by water while SiCl is rapidly hydrolyzed? In CCl unreactive towards superheated steam? PROBLEM 1569 Explain the difference between temporary and permanent hardness in water PROBLEM 1570 What is “Boiler-scale” and how it is formed? PROBLEM 1571 Describe the role of Li 2CO and BaSO in medicinal chemistry PROBLEM 1572 Sodium hydroxide has lower melting point (322°C) than sodium chloride (801°C), electrolysis of NaCl is the primary source of Na-metal not NaOH Explain PROBLEM 1573 Complete the diagram below indicating the reagents and special reaction conditions needed to produce each substance, using MgCO as the starting material [E ] [F ] [D ] [A] [C ] [B] Mg(NO ) ← Mg(OH) ← MgO ← MgCO → MgCl → Mg → Mg N [G] MgHPO PROBLEM 1574 Consider the following sequence of actions and observations (1) A small chunk of dry ice is added to an aqueous Ca(OH) solution and a white precipitate forms initially (2) After a short time, precipitate redissolve Write chemical equations to explain the observations PROBLEM 1575 Although, both boric acid and phosphoric acid have three hydroxy groups, phosphoric acid is a weak tribasic acid while boric acid is a weak monobasic acid PROBLEM 1576 Provide missing reagents below: [A] [B] [C ] [D ] Na B4O ⋅ 10H 2O → B(OH) → B2O → BCl → B [E ] → BF3 PROBLEM 1577 A typical baking powder contain baking soda and alum NaAl(SO ) as its active ingredients During process, baking powder undergoes a reaction that yields CO Write a plausible equation for this reaction PROBLEM 1578 What is the principle that underlies the fact that thallium forms both +1and + ions while aluminium forms only + ion? PROBLEM 1579 Why can’t aluminium cookware be used in cooking strongly acidic food? PROBLEM 1580 In the use of aluminium sulphate in water treatment, the water to be treated is usually kept between pH and pH Why you suppose this is the case? PROBLEM 1581 Complete the following reactions: (a) N H ( aq ) + HCl → (b) NO( g ) + O ( g ) → (c) NO ( g ) + H 2O( l) → (d) NH ( g ) + O ( g ) → 200°C (e) NH NO ( l) → PROBLEM 1582 Write balanced chemical equation for the following reactions: (a) Action of Al over Fe 2O in presence of electric spark (b) Action of water over Na 2O (c) Oxidation of Pb 2+ (aq.) to PbO in acidic medium, by ozone 291 Problems PROBLEM 1583 Write an equation to represent: (a) The formation of oxygen by the action of water over KO (b) Oxidation of Cl – to ClO –3 by ozone in acidic solution PROBLEM 1584 How BF3 is prepared from borax? PROBLEM 1585 You have available with you elemental sulphur, chlorine gas, sodium metal and water Using these materials, prepare (a) Na 2SO (b) Na 2SO (c) Na 2S 2O PROBLEM 1586 Why is it that NF3 has no donor properties, but PF3 forms many complexes with metals? Give one example of such complexes PROBLEM 1587 Substance (A) is a gas with vapour density 8.5 On oxidation at high pressure and temperature with a platinum catalyst, it gave a colourless gas (B), which rapidly turned brown in air forming a gas (C) B and C were condensed together to give substance (D), which reacted with water forming a compound (E) E turned blue litmus paper red On treatment of E with acidified solution of KI, gas B was evolved, but when E was treated with a solution of NH 4Cl, a stable, colourless gas (F) was evolved F did not support combustion, but magnesium continued to burn in it However, F reacted with calcium-carbide in an electric furnace, forming a solid (G), which was slowly hydrolyzed by water, forming a solution of substance A Identify A to G PROBLEM 1588 Explain why P—O bond length in POCl is 1.45 Å whereas the sum of the single bond covalent radii of phosphorus and oxygen is 1.83 Å? PROBLEM 1589 Suggest a reason why PF5 is known but PH is not PROBLEM 1590 HCl (g) can be prepared from NaCl and H 2SO HBr and HI can’t be made in a similar way from NaBr and NaI Explain why this is so? PROBLEM 1591 Write Lewis structure for each of the followings: (a) HCP (b) PH +4 (c) P2 H (d) PO 3– (e) PF5 PROBLEM 1592 Complete and balance each of the followings: (a) P4 + Al → (b) P4 + F2 → (c) P4 + Na → (d) P4 + Se → (e) P4 + Cl → (f) P4 + O → PROBLEM 1593 Oxygen forms double bond in O , but sulphur forms single bond in S Explain PROBLEM 1594 Explain why at room temperature fluorine and chlorine are gases while bromine is liquid and iodine is solid at room temperature PROBLEM 1595 (a) XeO F2 Suggest shapes of the following species: (d) XeO 4– (c) XeF3+ (b) XeF + (e) XeO F2 PROBLEM 1596 Sodium hydroxide is hygroscopic–that is it absorbs moisture when exposed to the atmosphere A student placed a pellet of NaOH on watch glass A few days later, she noticed that the pellet was covered with a white solid What is the identity of this solid? PROBLEM 1597 PROBLEM 1598 Discuss the reactivity of white P4 Complete the following reactions: Red hot CuO (a) NH → Heat (b) (NH ) Cr 2O → 292 Problems in Chemistry PROBLEM 1599 Aqueous Cu(II) sulphate is blue coloured When aqueous potassium fluoride is added to CuSO solution, a green precipitate is formed If aqueous KCl is added instead, a bright green solution is formed Explain, what happens in each case PROBLEM 1600 Write balanced chemical reaction: Heat (a) H PO → (c) HI + HNO → (b) Li 4C + HCl → (d) H 2S + Cl → PROBLEM 1601 Arrange the following species in increasing order of indicated property: (a) PCl , SiCl , CCl , BCl : Ionic character (b) F – , C 4– , N 3– , O 2– : Ionic radii (c) F, Cl, Br, I: Ionisation energies (d) H 2O, SiO , CO : Acidic character METALLURGY PROBLEM 1602 Discuss the principle involved in extraction of Mg from sea water PROBLEM 1603 Discuss the method of extraction of Mg from its dolomite ore PROBLEM 1604 Why extraction of magnesium is impractical by chemical reduction of its salt? PROBLEM 1605 Mg 2+ ion being smaller than Na + instead, Mg 2+ has very low ionic mobility and electrical conductivity compared to Na + in their aqueous solution Explain PROBLEM 1606 (a) How Epsom salt (MgSO ⋅ 7H 2O) is obtained? What is its use? (b) Write a balanced chemical reaction of Mg metal with dilute nitric acid PROBLEM 1607 How Na 2CO is manufactured by Solvay process? Why this method fails in preparation of K 2CO ? PROBLEM 1608 Discuss the principle of purification of bauxite Al 2O ⋅ 2H 2O by the following processes : (a) Baeyer’s process (b) Hall’s process (c) Serpek’s process PROBLEM 1609 How Al is extracted from bauxite ore? Describe thermite welding PROBLEM 1610 Write the reaction of Al metal with dilute HCl, H 2SO and NaOH Why concentrated nitric acid render Al passive? PROBLEM 1611 Discuss the reactions involved in polymerization of ethene using Zeigler catalyst PROBLEM 1612 Discuss the principle involved in extraction of iron from its oxide ore, by carbon reduction method PROBLEM 1613 Discuss the principle of rusting of iron and methods of its protection 293 Problems PROBLEM 1614 What happens when iron is treated with: (a) Steam (e) Dilute HNO (b) Dilute HCl (f) Concentrated HNO (g) Boiling sulphur (c) Concentrated H 2SO (d) Anhydrous Cl ( g ) PROBLEM 1615 How ferrous ammonium sulphate hexahydrate (Mohr’s salt) is prepared in laboratory What are the advantages of using Mohr’s salt as analytical standard of ferrous ion over ferrous sulphate? PROBLEM 1616 How anhydrous and hydrated ferric chloride is prepared in laboratory What happens when anhydrous ferric chloride is (a) heated above 500°C (b) dissolved in water PROBLEM 1617 How tin is extracted by carbon reduction method? PROBLEM 1618 What happens when Sn is reacted with: (a) Cl ( g ) (b) dilute HNO (c) conc HNO (d) conc H 2SO (e) NaOH PROBLEM 1619 How copper is obtained from copper pyrite, by self-reduction technique? PROBLEM 1620 When copper is exposed to atmosphere for a longer time, a green mass deposits on its surface Discuss the chemical reaction involved PROBLEM 1621 Why copper is passive in dilute HCl or dilute H 2SO PROBLEM 1622 Discuss the action of pure oxygen gas over copper metal at high temperature PROBLEM 1623 What happens when copper is reacted with: (Write complete balanced reaction) (a) dil HNO , (b) warm HCl in presence of oxygen, (c) warm H 2SO in presence of oxygen, (d) concentrated HNO , (e) with aqueous Fe (SO ) , PROBLEM 1624 How Pb is extracted from galena (PbS) by self-reduction method? PROBLEM 1625 Discuss the reactions involved in action of (i) air and (ii) pure oxygen on lead PROBLEM 1626 Lead react with hot concentrated sulphuric acid in the begining but reaction ceases after some time Explain PROBLEM 1627 What happens when lead is reacted with: (a) dilute HNO (b) concentrated HNO (c) NaOH (d) CH 3COOH PROBLEM 1628 How silver metal is extracted from its sulphide ore? PROBLEM 1629 Discuss the role of AgBr in photography How does it react with Na 2S 2O solution? PROBLEM 1630 Silver ornament gets tarnished when exposed to atmosphere for a long time, why? PROBLEM 1631 Complete the following chemical reactions: Heat (a) Ag + Concentrated HNO → (b) Ag + Concentrated H 2SO → (c) AgBr + NaCN( aq ) → (d) AgCl + NH 4OH → 294 Problems in Chemistry PROBLEM 1632 How gold is obtained from its ore by cyanide process? PROBLEM 1633 How does Au react with aqua-regia? PROBLEM 1634 Both copper and silver forms monovalent ion like alkalimetal but alkali metals are highly reactive while Cu and Ag are almost inert What are the reasons for this difference in reactivity? PROBLEM 1635 How KMnO is manufactured from MnO ? PROBLEM 1636 How K 2Cr 2O is manufactured industrially from chrome-iron? PROBLEM 1637 Complete the following reactions: Heat (a) K 2Cr 2O → (b) K 2Cr 2O + KOH → Heat (c) K 2Cr 2O + KCl + H 2SO (concentrated) → PROBLEM 1638 (a) KMnO (b) KMnO (c) KMnO (d) KMnO Write the balanced chemical reaction for the followings: + K 2C 2O + H 2SO → + O + H 2SO → + FeC 2O + H 2SO → + HCl → PROBLEM 1639 Draw shape of FeCl in (a) gaseous state (b) ether (c) water PROBLEM 1640 FeCl and FeBr are well known, but FeI has doubtful existence, explain PROBLEM 1641 How potash alum is prepared? What is its major application? ... strength of original NaOH solution PROBLEM 56 A complex of cobalt with ammonia is analyzed for determining its formula, by titrating it against a standardized acid as follows: Co(NH ) x Cl ( aq ) + HCl... ? ?a? ?? PROBLEM 109 A gas mixture containing 5% by mass of butane and 95% by mass of Ar (40) is to be prepared by allowing gaseous butane to fill an evacuated 40 L cylinder at 1.0 atm and 27°C Calculate... reversible isothermal expansion followed by reversible adiabatic expansion so that the final state is attained and calculate work done by the system in attaining the final state C vm = 3/ R PROBLEM 199