Recent questions in Chemistry

Maximum amount of hydrogen bonding occurs in case of

asked Feb 2, 2017 by meena.p

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Resonance in a molecules results in

asked Feb 2, 2017 by meena.p

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Resonance energy of benzene is about so much $Kcal/mol$

asked Feb 2, 2017 by meena.p

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What is the hybridisation of central metal ion and shape of Wilkinson’s catalyst ?

asked Jan 30, 2017 by sharmaaparna1

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Give simple chemical tests to distinguish between the following pairs of compounds (i) Propanal and Propanone (ii) Acetophenone and Benzophenone (iii) Phenol and Benzonic acid

asked Dec 29, 2016 by meena.p

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(i) Halogen acids (HX) readily combine with alkenes to form addition products but fail to react with carbonyl compounds. Explain (ii) Why HCOOH does not give HVZ reaction but $CH_3COOH$ does?

asked Dec 29, 2016 by sharmaaparna1

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Name the following compounds according to IUPAC system of nomenclature $(i)CH_3CH(CH_3)CH_2CH_2CHO \\ (ii)CH_3CH_2COCH(C_2H_5)CH_2CH_2Cl \\ (iii) CH_3CH = CHCHO \\ (iv) CH_3COCH_2COCH_3 \\ (v) CH_3CH(CH_3)CH_2C(CH_3)_2COCH_3 \\ (vi) (CH_3)_3CCH_2 COOH \\ (vii) OHCC_6H_4CHO-P$

asked Dec 29, 2016 by meena.p

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Describe a method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reactions involved.

asked Dec 29, 2016 by sharmaaparna1

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How will you convert: (i) Ethanoic acid into methanamine (ii) Hexanenitrile into 1-aminopentane (iii) Methanol to ethanoic acid

asked Dec 29, 2016 by sharmaaparna1

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Arrange the following compounds in the increasing order of their boilling points : $CH_3CH_2CH_2CHO,CH_3CH_2CH_2CH_2OH,H_5C_2-O-C_2H_5,CH_3CH_2CH_2CH_2CH_3$

asked Dec 29, 2016 by meena.p

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(a) What does it mean for a molecule or a ligand to be "chiral"? What properties does chirality impart to a molecule? (b)What is the difference between a heterogeneous and a homogeneous catalyst? What are some of the advantages of homogeneous catalysts?

asked Dec 29, 2016 by sharmaaparna1

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(a) How is granular zinc & zinc dust obtained ? (b) Explain why thermit process is quite useful for repairing the broken parts of a machine ?

asked Dec 29, 2016 by sharmaaparna1

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(a) The actinoids exhibit more number of oxidation states and give their common oxidation states. (b)A wellknown orange crystalline compound (A) when burnt impart violet colour to flame. (A) on treating (B) and conc. $H_2SO_4$ gives red gas (C) which gives red yellow solution (D) with alkaline water. (D) on treating with acetic acid and lead acetate gives yellow p. pt. (E). (B) sublimes on heating. Also on heating (B) with NaOH gas (F) is formed which gives white fumes with HCl. What are (A) to (F) ?

asked Dec 29, 2016 by sharmaaparna1

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How do you account for the following ? Hydrazones of aldehydes and ketones are not prepared in a highly acidic medium

asked Dec 29, 2016 by meena.p

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Consider the electrochemical cell :$Zn (s) / Zn^{2+} (aq) // Cu^{2+} (aq) / Cu.$ It has an electrical potential of 1.1 V when concentration of $Zn^{2+}$ and $Cu^{2+}$ ions is unity.State the direction of flow of electrones and also specify if Zinc and Copper aredeposited or dissolved at their respective electrodes. When :(a) an external opposite potential of 0.8 V is applied.(b) an external opposite potential of 1.1 V is applied.(c) an external opposite potential of 1.4 V is applied.

asked Dec 29, 2016 by sharmaaparna1

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How will you test aldehydes and ketones with (i) Tollens' reagent (ii) Fehiling's solution . Give equation

asked Dec 29, 2016 by meena.p

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(i) In a cell reaction, the equilibrium constant K is less than one. Is E° for the cell positive or negative ? (ii) What will be the value of K of $E^{\circ}$ cell = 0 ?

asked Dec 29, 2016 by sharmaaparna1

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How much ethyl alcohol must be added to 1 litre of water so that the solution will freeze at $14^{\circ}F$ ? ($K_f$ for water = $1.86^{\circ}C/mol)$

asked Dec 29, 2016 by sharmaaparna1

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Out of (a) 200 ml of 2 M NaCl Soln and (b) 200 ml of 1 M glucose Soln. which one has higher osmotic pressure ?

asked Dec 29, 2016 by sharmaaparna1

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An ether A $(C_5H_{12}O)$ when heated with excess of hot concentrated $HI$ produced two alkyl halides which on hydrolysis from compounds B and C. Oxidation of B gives an acid D whereas oxidation of C gave a ketone E. Deduce the structures of A, B, C, D and E.

asked Dec 29, 2016 by meena.p

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An alcohol A $(C_4H_{10}O)$ on oxidation with acidified potassium dichromate gives carboxylic acid B $(C_4H_8O_2)$. Compound A when dehydrated with conc. $H_2SO_4$ at $443 \;K$ gives compound C. Treatment of C with aqueous $H_2SO_4$ gives compound D $(C_4H_{10}O)$ which is an isomer of A. Compound D is resistant to oxidation but compound A can be easily oxidised. Identify A, B, C and D and write their structures

asked Dec 29, 2016 by meena.p

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An organic compound A having molecular formula $C_6H_6O$ gives a characteristic colour with aqueous $FeCl_3$ . When A is treated with $NaOH$ and $CO_2$ at $400\;K$ under pressure, compound B is obtained. Compound B on acidification gives compound C which reacts with acetyl chloride to form D which is a popular pain killer. Deduce the structure of A, B, C and D. What is the common name of Drug D?

asked Dec 29, 2016 by meena.p

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Explain the reason behind a colour of some gem stone with the help of example.

asked Dec 28, 2016 by meena.p

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How $t_{2g}$ and eg orbitals are formed in an octahedral complex ?

asked Dec 28, 2016 by meena.p

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A, B and C are three complexes of Chromioum with the empirical formula $H_{12}O_{6}Cl_3Cr$. All the three complexes have $Cl$ and $H_2O$ molecules as the ligands. Complex A does not react with conc. $H_2SO_4$. Complexes $B$ and $C$ lose $6.75\%$ and $13.5\%$ of their original weight respectively on heating with conc. $H_2SO_4$. Identify A, B and C.

asked Dec 28, 2016 by meena.p

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The Species that does not contain peroxide ions is

asked Nov 30, 2016 by meena.p

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There is no S-S bond in

asked Nov 30, 2016 by meena.p

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Bond energy is highest for

asked Nov 30, 2016 by meena.p

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Amongst $H_2O,H_2S,H_2Se$ and $H_2T_e$ the one with highest boiling point is

asked Nov 30, 2016 by meena.p

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Which among the following is peroxic acid of sulphur ? $(i) H_2SO_3 \\ (ii)H_2SO_4 \\ (iii)H_2S_2O_8 \\ (iv)H_2sO_4$

asked Nov 30, 2016 by meena.p

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The true statement for the acids of phosphorus , $H_3PO_2,H_3PO_3$ and $H_3PO_4$ is

asked Nov 30, 2016 by meena.p

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The number of S-S bonds is cyclic trimer of sulphur trioxide $(S_3O_3)$ is

asked Nov 30, 2016 by meena.p

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The correct order of acidic strength is

asked Nov 30, 2016 by meena.p

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The number of P_O_P linkages in pyrophosphopric acid is

asked Nov 30, 2016 by meena.p

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Which one of the following oxides is neutral

asked Nov 30, 2016 by meena.p

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(a)Which of the following is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene and why?

asked Nov 29, 2016 by meena.p

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(i) A chemical reaction $2A \to 4B + C$ in gas phase occurs in a closed vessel. The concentration of $B$ is found to increase by $5 \times 10^{-3}\; mol L^{-1}$ in $10$ seconds, Calculate (a) the rate of appearance of B (b) the rate of disappearance of A. (ii)The activation energy of first order reaction at $300\;K$ is $60 kJ/mol$ . In the presence of a catalyst, the activation energy gets lowered to $50 kJ/mol$ at $300K$. How many times the reaction rate changes in presence of a catalyst at the same temperature?(iii) Define Threshold energy and activation energy. How they are related?

asked Nov 29, 2016 by meena.p

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Explain giving reasons: (i) Transition metals and many of their compounds show paramagnetic behaviour. (ii) The enthalpies of atomisation of the transition metals are high. (iii) The transition metals generally form coloured compounds. (iv) Transition metals and their many compounds act as good catalyst.

asked Nov 29, 2016 by meena.p

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The chemistry of the actinoid elements is not so smooth as that of the Lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.

asked Nov 29, 2016 by meena.p

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Explain the following observations: (i) The boiling point of ethanol is higher than that of methoxy methane. (ii) Phenol is more acidic than ethanol (iii) O-and -P - nitrophenols are more acidic than phenol . (iv) Phenol is an acid but does not react with sodium bicarbonate solution .

asked Nov 29, 2016 by meena.p

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(i) Why are complexes of the d-block elements coloured ? (ii) Why are scandium and Zinc not counted as transition metals even though they belong to the d-block? (iii)When a brown compound of manganers (A) is treated with $Hcl$ it gives a gas (B) . The gas taken in excess , reacts with $Nh_3$ to give an explosive compound A and B

asked Nov 29, 2016 by meena.p

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Distinguish between rate expression and rate constant of a reaction. (ii) Can a reaction have zero activation energy ? explain (iii) Is the enthalpy of a reaction altered by a catalyst

asked Nov 29, 2016 by meena.p

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Drugs containing carboxylic Acid organic acids characterized by the presence of at least one carboxylic group. The general formula of a carboxylic acid is $R-COOH$. The carboxylic acids find a use in the manufacture of many useful drugs.one Such important drug is aspirin Answer the following (i) What is the IUPAC name of the drugs ? Name the functional groups present in the drug . (ii) Can the drug be prepared in the lab ? (iii) A person goes to the shop keeper to get aspirin pills without doctors presoription . The chemist is reluctant to give him pills with out doctor's prescription . (iv) Which values are reflected in chemists approach ?

asked Nov 28, 2016 by meena.p

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Rahul observed that families from nearby localities bring loads of laundry to wash in the river practically every day, while others bring their cars, taxis and rickshaws and wash them clean by using water from the river. The same water was being consumed by people living downstream.When he tried to stop people from washing clothes and cleaning vehicles.Nisar Khadim a local resident objected. “It makes no difference if we wash our cars and clotheshere. It is a gift from nature,” he said ,Answer the following question a)Who do you think is right Rahul or the taxi driver?Give a reason for your answer. b) What are the values associated with the answer?

asked Nov 28, 2016 by meena.p

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A survey revealed that most of the industries in Najafgarh area have not installed smoke precipitators in the chimneys. a) What is the use of smoke precipitators? b) Why do you feel that it should be mandatory for industries to install smoke precipitators?

asked Nov 28, 2016 by meena.p

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famous sweet in hyderabad , Rishi bought some sweets . He requested the sales boy to put the sweets in a polythene bag.The sales boy refused to do so, instead he kept the sweet box in a paper bag. After reading the above passage answer the following questions. (i) Why did the sales boy refuse to put the sweet box in a polythene bag? (ii) As a student of chemistry, why would you advocate the use of paper bags instead of polythene bags?Which values are promoted through the use of paper bag? (iii) Suggest two activities to promote these values.

asked Nov 28, 2016 by meena.p

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Ethyl alcohol to which another liquid has been added to make it unfit for use as beverage is called denatured alcohol. Ethyl alcohol denatured by adding methyl alcohol, is highly poisonous. Answer the following questions: (i) Mention another way by which alcohol is denatured. (ii) Explain why methanol is highly toxic to human beings? (iii) How is methanol prepared on large-scale? Give its two important uses.

asked Nov 28, 2016 by meena.p

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Purification of drinking water is a big problem. In your locality, vendors of various companies are promoting RO units for purification of water for domestic use irrespective of whether it is required or not. Answer the following questions: (i) What is the meaning of RO? (ii) Would you recomend the installation of RO units in all the areas? (iii) Support your views with reasons.

asked Nov 28, 2016 by meena.p

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Earth receives enormous amount of energy from sunlight. The problem of shortage of power can be solved if we could convert solar energy into electricity. A device which generates electrical power from sunlight is called solar cell or photovoltaic cell. Solar cells are made up of silicon doped with arsenic and silicon doped with boron. Answer the following questions: (i) When silicon is doped with arsenic, what type of semiconductor is obtained? Explain. (ii) What type of semiconductor is obtained by doping silicon with boron? (iii) Give any two applications (other than solar cells) of semiconductors.

asked Nov 28, 2016 by meena.p

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A boy baths in the first shower of rainfall during rainy season and his body gets yellowish brown colour patches on the whole body for which he was medicated. Answer the following questions: (i) Why the skin of the boy got yellowish brown patches. (ii) As a student of chemistry what do you think could be reason and the term you would use to explain it? (iii) Which values are promoted through this activity? (iv) Suggest two activities to promote these values.

asked Nov 28, 2016 by meena.p

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