Chem Lab Viva Questions PDF

Q.3. How will you identity the presence of carboxylic COOH group in the organic compound ? Ans. By litmus solution test and sodliùm bicarbonate test. Q.4. What are phenols ? Ans. These are aromatlc hydroxy compounds and contain C-OH group. 5. Name the te...

Q.3. How will you identity the presence of carboxylic COOH group in the organic compound ? Ans. By litmus solution test and sodliùm bicarbonate test. Q.4. What are phenols ? Ans. These are aromatlc hydroxy compounds and contain C-OH group. 5. Name the tests which are generally employedfor the identification of phenollc OH group. Ans. (9 Blue litmus paper test () Ferric chloride test (i) Dye test. Q.6. Can litmus paper test be used for detection of alcoholic group ? Ans. No, because alcohols are a.7. Name the neutral to litmus. chemical tests for detecting unsaturation, Ans. Bromine test and alkaline KMnO4 test. Q.8. What is the difference between alcoholic -OH group anid phenolic -OH group? Ans. Phenolic - OH group is acidic while alcoholic - OH group is neutral in character. a.9. How carbonyl Ans. It is identified group is identifled ? by () 2, 4-Dinitrophenylhydrazine test and () sodium bisulphite test G.10. Name two tests used to distinguish between aldehydes and ketones. Ans. Tollen's reagent test and Fehling's sólutlon test. Q.11. How is Schiff's reagent Ans. It is prepared ? dilute solution of p-rosanline hydrochloride in the water, pnk colour of which is decolourised by passing S02 throught. Q.12. What is Tollen's reagent ? Ans. It is ammonical silver nitrate solution and. contains diammine silver (). lon: [Ag(NHs)2]*. Aldehydes glve slver mirror or black ppt. with Tollen's reagent. It is used to detect the presence of aldehyde. Q.13. What is Fehling's solution? Ans. It Is an alkaline solution of CuSO% and contains Cu lons complexed with tartrate ions. With aldehydes it produces red ppt. of Cu20. Ketones do not give this test. Q.14. What is Fehling's solution A? Ans. It is 7% copper sulphate solution. Q.15. What is Fehling's solution 8? Ans. It is alkaline solution of sodlum potasslum tartrate (Roschell's salt). a.16. What will happen when aldehyde is treated with Fehling solution? Ans. A red precipitate of cuprous oxide is formed. Q.17. Can you write chemical a equation for the above reaction ? Ans. RCHO +2Cu* +5OH RCOO + Cu20 +3H20 From febling solution (Red ppt.) Q.18. Is dye test given by aliphatic amines? Ans. No. Q.19. Is carbylamine test given by all amines? Ans. No, it is only reliable in case of primary amines. Q.20. What is the formula of sodium nitroprusside ? Ans. Na2Fe(CN)sNO]. Q.21. Name a phenol that decomposes sodium bicarbonate. Ans. 2, 4, 6-Trinitrophenol decomposes sodium blcarbonate. - Dinesh Practieal Chemistry XII 55  www.ww.oAWNA Questions fron NCERT Lab Manual- wAwwWNwwwwwwwwww* Q.1. Why do alkenes and alkynes decolourise bromine water and alkaline KMnO4? CaUSe alkenes and alkynos are unsaturated compoundswith alkenes having carbon-carbon double bonds and alkynes having carbon-carbon triple bonds. Q.2 Explain why for the confirmatlon of unsaturatlon in a compound both the tests namely bromine water and test with Bayers reagent should be test with Ans. performed ? Certain compounds lke aniline, phenof etc. whlch otherwise behave as saturated compounds, also decolourise bromine water. This ls b>cause these compounds undergo brominatlom under the reaction conditions. On the other hand, easily oxidisable compounds like aldehydes, whlch otherwise behave as saturated compounds, also decolourise Bayers reagent. This is because aldehydes are easlly oxldised to their corresponding carboxyiic acids thus decolourising alkalline KMnO4 solution [Bayers reagent). Thus both the tests for unsaturation should be performed to confrm-Its presence in the given organic compound. Q.3. Why does phenoi decolourise bromine water? Ans. Because phenol undergoes electrophilic substitution reaction with bromine wate, as follows : OH OH Br r Phenol +3 Bra (a9 O +3HBT 2,4,6Triöroruopheool As bromine is used up in the reaction, the reddish orange colour of bromlne water disappears a:4. How will you distinguish between phenal.and benzoicacic2 Ans. Only benzoic acid gives effervescence with sodium hydrogencarbonate solution. Q.5. Whydoes benzene not decofourise bromine water althought it is highly'unsaturated? Ans. Due to resonance, benzene with three carbon-carbon doublé bonds beñaves as a saturated compounds a.6. Why does formic acid glve a positive test with Tollen's reagent? Ans. Because formic acid is easily oxidised to carbon dioxlde and water. HCoOH + CO2 + H0o Formic acid (From Tollen's reagent) Q.7. Outline the principle of testing glucose in a sample of urine in a pathological laboratory? Ans. Presence of glucose in a sample of urine is tested either with Fehling's solutlon or with Benedict's reagent. Both these reagents contain Cu ion complexed elther with tartarate lons (Fehling's solution) or citrate ions (Benedict's reagent). When any of these reagent is warmed with urine in which some glucose is present, Cu lons are reduced to brick red coloured Cuz0. This ls due to the presence of -CHO group inglucose, which is oxidised to -COOH group during the reactton. Formation of brick red coloured ppt. indicates the presence of glucose in the urine sample. Q.8. Why is Benedicts reagent more stable than Fehling's reagent? Ans. Because Cuf*-citrate complex present in Benedicts reagent Is more stable than CuT-tartarate complex present in Fehling's reagent Q.9. How would you mixture of phenol and benzoic acid in the separate a laboratory by using chemical method of separation? Ans. Shake the mixture with an aqueous solutlon of sodium hydrogencarbonate when only benzolc acid will dissolve. It is due to the formation of its sodium salt. 56 -Dinesh Practical Chemlstry XI  CgH COOH+NaHCO CHscoONa+C02 +H20 Use a separating funnel to separate phenol and sodium benzoate solutlon. Add'any ackd (say diltice) to aqueous layer, when benzoic acid preclpitates out. CHsCOONa(aq) + HCI (aq) CgHgCOOH(s) + NatCi (aq)D Q.10. How can you distinguish between hexylamine (CeH13NH2} and aniline ? Ans. By dye test. Only aniline -an aromatic azo 1° amine will give positlve azo dye test after diazotisation and coupling with alkaline B-naphtho. G.11..How you distinguish between ethylamine and diethylamine ? can Ans. By carbylamina test. Only 1 amines like ethylamine give this tast. Dlethyamine (a2 amine) wil not give this test. Q.12. How can CHaOH and CaHsOH be distinguished chemically ? Ans. By iodoform test. Only CH3CH2OH will give positive lodoform test (yellow ppt. with I2 + NaOH). It is due OH to the presence of CH3-CH- groupin CH3CH20H Q.13. Whý is-solution of iodine prepared in potassium.iodide(aq) and not in pure water? Aris. Solid.iodíne is mote solubleinKt (ag) than in pure'water. Ifls due to the formation of l5 lon. K ag) +l (s- Kag. Q.14. Howe.can you distinguísh.tie compounds. CHs--CaHs and CaHs--Cais by simple chemical tes: It Ans. By iodofom test. Only CHa-C-C2Hs.will give posit+ve iodoform test [yellow ppt. with l2 +NaOH (aq)}}. ** is due to the presence of CHa-C group in CH3-C-C2Hs.  given sample contains 5. Xanthoprotein Add two Adeep yellow colour formed. test. The drops of conc. HNO3 to the proteins sample in a dry test tube. Shake| for some time and keep aside. Result. The given sample contains starch (carbohydrates) and protelns. Experiment 9(d) Aim: Test for the presence of carbohydrates, tats and proteins in ground nuts. fats and proteins: Test for carbohydrates with Molsch test, Iheory. Ground nuts contain carbohydrates, test. iodine solution test for fat with spot test, solubility test, acrolein test and for proteins with Xanthoproteln Procedure. Crush the ground nuts and perform various test as explained in Experiment 9 (c) Result. Groundnut contains carbohydrates, fats and proteins ORAL QUESInnSADnGnSHIERS Q. 1. What is food ? otherwise taken into the body to sustaln life. Ans. Food is nourishing substance that is eaten or a Q. 2. What is the main function ofcarbohydrates? Ans. Carbohydrates provide energy. Q. 3. Which constituents of food are mainly essential for growth of tissues? Ans. Fats and proteins. a. 4. What are the differences between oils and fats ?_ Oi is a liquid while fât is a solid or a semi solild at room Ans. Oils are unsaturated while fats are more saturated!.. temperature: Q. 5. Name atleast two carbohydrates which cannot be represented by the general formula Ca(H20)y. Deoxyribase (CsHio0a). Ans. Ahamnose (CsH120s), Bioinonosa (CeH100s; ? when carbohydrates aretested by Molish's reagent Q.6. What is the purple ring formed to furfural or lits derivatives which then reacts with a naphthol Ans. Conc. H2S04 converts carbohydrates into give a purple product. formed in Fehling's test for carbohydrates ? Q. 7. What is the red precipitate Ans. Mainly cuprous oxide (Cu20). a. 8. Name one reducing sugar ? Ans. Glucose, fructose. a.9. Name one non-reducing sugar Ans. Sucrose, starch. Q. 10. Is Fehling's test given by all sugars? Ans. No. It is given by reducing sugars only. Q. 11. What is Molish's reagent ? Ans. It is a 1% ethanolic solution of a-naphthol. Q. 12. What is Bauodouin tests used for ? oil in Vana:pati ghee and therefore distinguishing between Vanaspatl ghee and Ans. For detecting seasame Desi ghee. -Dinesh Practical Chemistry Xl 60  Q. 13. Name the end products of hydrolysis of proteins ? Ans. Amino acids. Q. 14. What is the colour obtained, in the Ninhydrin test for proteins ? Ans. Blue. Q. 15. Name three foods which contain carbohydrates and protein. Ans. Pulses, groundnut and milk. a. 16. Name a food stuff which contain carbohydrates, fats as well as proteins? Ans. Milk. a. 17. Are proteins polymers ? If so what are their monomeric unit ? Ans. Yes, Amíno aclds.are the monomeric units. a. 18. What are amino acíds? Ans. Fhese arë the compounds containing an amno group as well as a carboxyi group. Q. 19. What is peptide linkage? Ans. The linkage -co-NH- which links one amino acld with another is called peptide linkage. Q. 20. What are oils and fats ? Ans. Olis and fäts are triesters of glycerolwith higherfatty acids. They are also called triglycerides. a. 21. Conc. HNO3, when'äccidently comes in'contact with the skin of your hand, turns it yellow. What does t Indicate 2 Ans. Skin of our hand consists of proralis.n Xanthoprotei test, conc: HNO3 gives ai yllow colour with proteins. Questions fronm NCERT Lab Manual G. T. How wilf you distinguish.between suerose and glicose? Ans. Only glucose will give positve Fehling's/Benedlct's or Tllen's test. This is because sucrose is not a reducing sugar. a. 2: Explain why, does fructose reduce Fehling's solution and Tollen's reagent inspite of the presence of ketonic group ? Ans. Fructase contains a-hydroxy ketone group which in alkaline medium changes to aldehydic group. Both Fehling's sofution and Tollen's reagent are alkaline in nature. As such in alkaline medium, fructose, also acts asa sugar and give pasitve test with these reagents. Q. 3. reducing What is the role of tartarate -and ctrate ions in Fehling's reagent and Benedict's reagent respectively? Ans. These tests are carried out in alkallne medium. In alkaline medium CufT lons are precipltated Cu(OH)2. as To overcome this problem Cuft ions are ccmplexed with tartarate or citrate ions as both these complexes are soluble in alkaline medium.  i) Do not blow out the last drop of the solutlon from the jet end of the pipette. )Do not lorget to add one test tube of 1 M HSO4 to the titration flask before starting the titration. a. 1. Define URRL QUGSEIQDSANDARSUERS volumetric analysis. Ans. It deals with the measurements of volumes of solutions involved in a chermical reactlon 1.8. t leaos determinatlon of the amount of constituents present in the glven unknown solutions. Q. 2. Volumetric analysis is a qualitative or quantitative analysis ? Ans. It is quantitative analysis. a. 3. What is quantitative analysis ? Ans. It involves the estimation of a substance in a solutlon or sample. Q. 4. What is molarity of a solution? Ans. It is the number of gram-moles of solute present in one litre of the solutian. Q.5. What is a molar solution ? Ans. Asolution which contains 1 g mole of a solüte dissoived in one litre of solutiton is called a molar solution..6. What is a redox reàction? Ans. Reaction between an oxidising agent and a reducing agent is called a redax reaction. Q.7. Which is an oxidising agent and reducing agentin a reactionbetween KMnO, and Fe$O4 ? Ans. KMn04 acts as an oxidising agent and FeSO4 acts as a reducing agent a.8. What do you understand by redox titrations ? Ans. It includes all those varleties oftitrations where one reactant is oxtdised and other is reduced. Redax titrations involves redox reactions. Q.9. Will you read upper or lower meniscus-of KMnO4 solution in a burette? Ans. Upper meniscus. a. 10. Why will you read upper meniscus of KMnO4 solution? Ans. KMnO4 Solution is dark purple in colour and t is easy to read. Q. 11. What is the indicator used in KMnO4 titration ? Ans. No indicator is used because it is self indicator. a. 12. Why does KMnOs act itself as an indicator? KMn04 reacts with reducing agent (oxalic acid or ferrous Ans. In the presence of dlute sulphuric acid, sulphate) as follows. 2KMnO 3H,SO4 + K SO + 2MnSO +3H0+ 5 (Oxidation) When all the reducing agent (oxalic acid or ferrous The products of this reaction are almost colourless. KMnO4 not decomposed and imparts its pink colour to the is sulphate) has been oxidised the excess of solution. Q. 13. What is the end point in KMnO4 titrations ? Ans. From colourless to light pink. standard over ferrous sulphate in volumetric analysis ? Q. 14. Why is Mohr's salt preferred as primary a Ans. This is because of the fact that; to ferrlc not readily oxidised by air. Ferrous sulphate gets easily oxidised ( Mohr's salt is stable and is sulphate by atmospheric oxygen. (i) It is readily soluble in water. and its composition does not change. (i) It does not give effervescence -Dinesh Practieal Chemistry X 68  of Mohr's the standard solution of dilute sulphuric acid added while preparing.15. Why are a few drops salt ? ns. Few drups of dil. H2SO4 are added in order to prdvent the hydrolysis of ferrous sulphate. ? in KMnOs titratlons , 16. Why a burette with rubber pinch cock should not be used Ans. KMnO4 being a strong oxldising agent attacks rubber..17. Sometimes a brown turbidity is observed in KMnO4 titrations. Why ? to is formed due actd. Brown coloured ppt. (Mn02. H20) Ans. it is due to insuficient quantity of dil. sulphuric the incomplete oxidation of KMnO4. would happen ? 18. Suppose you torget to add dil. H2S04. What detected A brown ppt. af hydrated MnO2 is formed and end point is not properly Ans. 2KMnO + HO 2KOH+2MnO2 +3 (Brown ppt.) in the burette ? 19. Why KMnO4 solution should be taken burette the end point can be detected easily and readily Just for accuracy. By taking KMnO4 in the ns in KMnO4 titration ? 20 Why a larga amountof KMnOs should not be added at.a time ns. By doing so, abrownish precipitate of hydrated MnO2 is produced.. :3**. 21. What do you mean by concordant set of readings? them is called a have. a difference of -05 mi or less, between any two of ins. A set of readings which concordant set of readings, r. t to about 60-70°C:sofut+on ? 22. Why shouid youn heat the oxalic acid solution to the slw liberation of Mn* lons. Oxallc acid is heated to speed up n s. In cold, the reaction is very stow due the réaction, thus the reaction proceed rapidly. Alsa the liberation of Mn ions whichi then autocatalysis this is done to expell the carbon dioxide evolveddurlng-the reaction 23. How will you check that the solution is heated by 60-70°C in permanganate titrations ? attain aa n s. Byjust touching the conical flask, if it is unbearable to touch by hand it means that the solution temp. to about 60°-70°C. 24. Will you heat Mohr's salt solution before titrating it with KMnO4? and KMnO4 gets reduced by ferrous ammonium ns. No. This is because the reaction in cold is quite vigorous sulphate. 25. What is the formula of Mohr's salt ? ns. It is FeSO4. (NH4)2S04.6H20. 26. Which mineral acid is most suitable for carrying out KMn04 titrations ? ns. Dilute sulphuric acid. 27. Why dil, H2SO4 is suitable for KMnO4 tltrations ? ns. Under the titration conditions, it does not react with potassium permanganate or the reducing agent used. 28. cannot HCI be used in place of dil. HzS04 acid ? Why ns. Because hydrochlorlc acid reacts with KMnO4 to evolve chlorine gas. 2KMnO + 16HCI 2KCI +2MnCl, +8H,O+5Cl 29. Can we usenitric acid in place of dilute HaS04 acid in KMnO4 titration ? ns. No. 30. Why can't we use HNOa in KMnO4 titrations? ns. Nitrlc acid itself is an oxidising agent which reacts with reducing agent. Thus, a smaller amount of KMnO4 will be consumed in redox titration and hence introduces an error. Dinesh Practical Chemistry XII 69  PRACTICAL CHEMISTRY APPROACH TO MODERN 30lution ? 200 gives effervescence with 5% NaHCO, Q.3. Which compound and ajdehydes? Ans. Carboxylic acid. acids, phenbls are present in carboxylic What functional groups Q. 4..H and C- O ortho position benz COOH.COH group at Ans. earboxylic and hydroxyl contains both carboxylic acid Q.5. Which coOH - OH Ans. Salicylic acid compounds ? test with. diazonium hydroxy compound gives dye Which Q. 6. Ans. Phenols. for which compounds ? hydrazine test is. specific Q. 7. 2, 4-dintrophenyl ketones> C 0. :ompound, aldehydes CHO. and Ans. Carbonyl test 2 hydroxylamine Q.8. Which compound gives Ans. Esters. NaOH ? a m m o n i a on heating with aq. Which compounds give Q. 9. Ans. Amides. carbylamine test ? offensive smell. Q. 10What is on heating with alcoholic KOH and chloroform give Primary amines Kns. group ? compound is ci Q. h a t is functional properties of a a chemical that detemines the group of atoms Ans. An atom or functional group. What is u n s a t u r a t i o n ? called unsaturation. 9A2. triple bond in a.compound is Ans. Presence of double (> C = C ), gas Ans. SO. gas reduces Cr (VI) (II), which is green in colour. to Cr rotten evolves a gas with 6. a n o u guesS tthe radical present in a mixture, if it eges smeli with dil. H,SO,2 EsYes. it may be sulphide. sodium bromide with cone. H,>l), h i c h gas is evolved on treatment of brown bromine gas. bromide which oxidation converts to on aerial ris. Hydrogen carbonate extract for wet tcsis of ay S i necessary to prepare sodium anons? interference soluble in water and removing It is prepared for making insoluble salt Ans. etc. in the tests. of basic radicals like mercury, barium of nitrate? of the ring in the test 29. What causes the formation Ans. It is due to formation of FeSO,NO complex. brown or violet of Br and I, why does only organic layer acquire 30. in the tests colour? solvents. formed are soluble in organic Ans. Because Br, and I, chloride test? and iodides not give chromyl 31. Why do bromides iodide are not stable. Because bromide and chromyl chromyl Ans. for SO, be acidified before testing should sodium carbonate extract before addition of 32. Why and if it is not decomposed extract contains C0, Ans. Sodium carbonate which may be mistaken as BaS0 white precipitate of BaCO, is formed BaCl a the BaCl, test of SO,2 HCl not be used in may be 33. Why should conc. therefore, white insoluble BaCl, is less in conc. HCI, Ans. Solubility of BaCl, even in the absence of SO inferred as BaSO, in place of BaCl, for testing SO,2 solution be used 34. Can Ba(NO), and form white precipitate of the Ba2* ions which interact with sO, Ans. Yes, since it is BaSO name of yellow precipitate in ammenium molybdate test chemical 35. What is the ofPO,? Ans. Ammonium phosphomolybdate. radical on a solution is positive. molybdate test applicd for PO, 36. Ammonium How does it happen? does not contain PO. but the solution arsenic then also the test will be positive. contains arsenate salt of Ans. If the solution identitication solution" of the salt for of preparing *original 37. What is the need of its basic radicals? is based on the reaction of these identification scheme of basic radicals Ans. Because radicals in solution. solution? for preparing the original 38. Can H,SO, he used of the cations and some sulphates such because H,SO will produce sulphates Ans. No, insoluble. are etc. as PbsO, BasO, SrSO, QUALITATIVE ANALYSIS 167  9, Can the solution he As. passing H,S gas? acidified with HNO, in place of HCI in (roup Il before No, HNO, the analysisbeing oxidising in nature, complicated. oxidises H,S to colloidal sulphur which makes 40. What can it be, if the original in cold water? sulbstance is soluble in hot water and Ans. Plumbous insoluble chloride (Lead chloride). 41. Why lead is placed in Ans. This is due to fact both, Groups and II? that lead is not A part of it completely precipitated in first group as PbCl goes into the filtrate meant for PbS. Group II and gets precipitated there as 42. Can conc. HCI be used Ans. No, because as group reagent in place of dil. HCI for group 1? PbCI, gets into solution due to formation of chloroplunmbous complex by conc. HCI 43. Why is HCl added to the solution in Ans. To avoid the Group II before passing H,S gas? precipitation of Group IV cations (for Theory see text). 44. What is the function of adding nitric acid before the precipitation of Group II? Ans. It is added to oxidise ferrous salts to ferric salts. It also helps in removal of HS gas. 45. Why is it essential to boil off H,S gas before precipitation of Group U? Ans. If H,S would not be boiled off, Group IV cations also get precipitated along with Group II radicals. 46. Why is it essential to oxidise ferrous salts to ferric salts before precipitation of Group ? Ans. Because ferrous salts are not completely precipitated as Fe(OH), in presence of NH CI on addition of NH OH and as a result iron will interfere in Group IV analysis. 47. Why is NH CI added in Group I1? Ans. To prevent the precipitation ofradicals other than Group II as hydroxides by common ion effect. 48. Can we add NH,OH first? Ans. No, then purpose of adding NH,CI will be defeated and radicals of Groups IV, V, get precipitated along with Group Il. VI will also other ammonium salt in Group ll1? 49. Can NH,CI be replaced by any ammonium sulphate cannot be used. Ans. Yes, NH,NO, can be used but 50. Why NaOH cannot be used? its ionization cannot be suppressed. Moreover, Ans. NaOH being a very strong electrolyte, and Cr* as a result of formation of Al0,, CO2- it dissolves precipitates of A1* complexes. in precipitation of Group IV cations as 51. How does addition of NH,OH help sulphides? those of Group I of Group IV sulphides are greater than Ans. Solubility product ions are required to precipitate concentration of S radicals. Therefore, a higher H* ions of HS, ions of NH,OH unite with Group IV radicals as sulphides. OH LABORATORY MANUAL CHEMISTRY-XI! 168