June 2012
45 posts
thestarrs asked: Where do I begin learning Chemistry from the complete ground up?
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Neighbouring Group Participation
Neighbouring Group Participation (NGP) is observed in nucleophilic substitution reactions, where a neighbouring group helps in the removal of the leaving group to form a reactive intermediate that leads to the formation of the product. Increase in the reaction rate and unexpected stereo chemical outcomes are associated in reactions involving NGP.
An atom having an unshared pair of electrons and...
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Question on Solvay Process
Na2CO3 can be manufactured by Solvay’s process, but not K2CO3. Why?
Answer:
Solvay process involves the following 3 steps.
In the second step NaHCO3 formed is insoluble in water while NH4Cl is soluble. So, the two compounds can be separated and the third reaction can be performed. If the second step is attempted with KCl in place of NaCl, the products formed will be KHCO3 and NH4Cl. Both these...
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Update
Guys, I am updating answers for many of the questions. You can check them. Also, I have changed the theme and included comments. In case, you need to discuss any answers, you can do so through comments section.
Keep reading Chemistry.
Cheers!
:)
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Ibuprofen
Ibuprofen is an anti-inflammatory drug used for relief from fever and body pain. Ibuprofen’s pain killing effect takes place almost immediately after a suitable dosage is administered while its anti-inflammatory effects take a little longer. Along with the pain killing properties Ibuprofen also comes with lots of side effects and should NOT be taken without the advice of a physician.
...
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Question on Hydrolysis
How many moles of water are required to completely hydrolyse one mole of P4O10 and convert it to H3PO4?
Answer:
6 moles of water are used in the conversion.
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Question on Reduction
Which out of (a) Clemmensen Reduction and (b) Wolff Kishner Reduction is the best suitable reduction method for the following reaction?
Answer:
Wolff Kishner Reduction is the best suitable reaction method for the given reaction. Though both Clemmensen and Wolff Kishner reduction methods bring about the same outcome, Clemmensen Reduction is not used for compounds having acid sensitive groups...
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Question on Carbonyl Compounds
An organic compound P of molecular formula C4H10O upon dehydrogenation gives a compound Q which forms phenyl hydrazone with phenylhydrazine and both the compounds P and Q respond positive to the Iodoform Test. What is the name of the compound P?
Answer:
The name of the compound P is Butan-2-ol.
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Question on Oxidation States
What is the oxidation state of P in P4, PH3 and H3PO3 respectively?
Answer:
The oxidation states are 0, -3 and + 3 respectively.
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Question on Electrochemistry
3 Faraday of electricity are passed through molten Al2O3 aqueous solution of CuSO4 and molten NaCl in three different electrolytic cells. What will be the molar ratio of Al, Cu, Na deposited at the respective cathodes?
Answer:
1 Faraday of electricity will deposit 1 equivalent of a metal. So 3 equivalents of Al, Cu & Na will be deposited which is same as 1 mole of Al, 1.5 mole of Cu and 3...
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E2 Elimination
Elimination reaction in Organic Compounds involves the removal of certain groups from the reactant molecule usually leading to the formation of an unsaturated compound as a product.
For example the reaction between an alcohol and a mineral acid at high temperature is an elimination reaction leading to formation of an alkene along with the elimination of a molecule of water.
The elimination...
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Question on Electrophilic Aromatic Substitution
Which among (a) Nitrobenzene and (b) benzene, is a suitable solvent for the Friedel - Craft alkylation of para - bromo benzene?
Answer:
Among the three aromatic compounds mentioned in the question, benzene is the most reactive towards an electrophile followed by bromo benzene and then by nitro benzene. If we want the electrophile to substitute on bromo benzene then a solvent which is less...
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Question on Equivalent Weights
Monosodium salt of oxalic acid is titrated with NaOH solution. In a second titration it is titrated with KMnO4 solution. What will the ratio of equivalent weights of monosodiumoxalate in both the titration be?
Answer:
The equivalent weight of oxalic acid in the titration with NaOH is equal to its molecular weight and in the titration with KMnO4 it is equal to half of its molecular weight. So,...
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Question on Alkenes
An alkene, “A”, with molecular formula, C6H12 on reductive ozonolysis gives two products. One of these gives a positive iodoform test but negative Tollen’s reagent test. The other product gives a positive Tollen’s reagent test but negative iodoform test. What is the name of “A”?
Answer:
2-methlypent-2-ene
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Question on Carbonyl Compounds
If the cyanohydrin of a carbonyl compound on hydrolysis gives lactic acid (CH3CH(OH)COOH), what is the name of the carbonyl compound?
Answer:
Ethanal.
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Question on Basic Strength
Is aniline is a weaker base than ethylamine? Why?
Answer:
Yes. In aniline the lone pair of electrons on the nitrogen atom will be in resonance with the benzene ring and will be less available to be donated to a proton as compared to the lone pair of electrons on the nitrogen atom of ethyl amine.
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Question on Nucleophilic Substitution
Vinyl chloride does not undergo nucleophilic substitution reaction but allyl chloride does. Why?
Answer:
In vinyl chloride due to resonance the carbon halogen bond will have a partial double bond character. Moreover, positive charge developed on the vinyl carbon will be unstable compared to positive charge on the allyl carbon.
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Question on Grignard Reagent
What is the name of the ester, having molecular formula C2H4O2, which on treatment with MeMgI, followed by hydrolysis produces acetaldehyde as the product?
Answer:
Methyl Formate
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The Scent of Rain
The scent of rain is one of the things that comes to our mind when we think about a rainy day. The smell is so intense in air that you can not miss it. Geosmin is responsible for this strong scent that is present in air when rain falls after a hot or dry weather.
Geosmin is produced by several class of microbes especially the Streptomyces. Geosmin is released when these microbes die. Geosmin...
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Question on Grignard Reagent
Ethyl acetate is treated with double molar quantity of C2H5MgBr and the reaction mixture is hydrolysed with H2O to a produce a product “P”. What is the name of “P”?
Answer:
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Hunsdiecker Reaction
Reaction: Hunsdiecker Reaction
Reagent: Br2/CCl4
Use in Chemistry: Conversion of Silver salts of carboxylic acids to alkyl halides
Reaction Examples:
Reaction Mechanism:
The widely believed mechanism involves the Silver salt of the carboxylic acid reacting with bromine to form acyl hypobromite which undergoes homolytic bond cleavage to produce bromine radical and a carboxylate radical. This...
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“Science is a great game. It is inspiring and refreshing. The playing field is...”
– Isidor Isaac Rabi - Physicist and Nobel Prize winner.
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Question on Sulphonation
What will the ascending order of the rate of sulphonation of the following molecules?
Answer:
Activating groups increase the rate of electrophilic aromatic substitution while deactivating groups decrease the rate of such reaction.
The ascending order of the rate of sulphonation of the given compounds will be (IV) < (II) < (I) < (III)
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Question on Nitration
Nitrobenzone can be prepared from benzene by using a mixture of conc. HNO3 and conc. H2SO4. In the nitrating mixture, what is the role of H2SO4?
Answer:
H2SO4 makes HNO3 act as a base and produce nitronium ion (NO2+).
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Question on Chemical Kinetics
The time required for 99.9% completion of the first order reaction is “x” times to that of its half life time. What is the value of “x”?
Answer:
10
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Question on Molecular Formula
A compound A crystallizes in a hexagonal close packing system. If the compound is made of X and Y in which X occupies all the lattice position of hcp layers and Y occupies two third of the octahedral voids, what will the formula of A be?
Answer:
X3Y2
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Question on Freezing Point
What will happen to the freezing point of an aqueous solution of potassium iodide when mercuric iodide is added to it?
Answer:
Addition of mercuric iodide to an aqueous solution of potassium iodide will form K2[HgI4] according to the following equation.
2KI + HgI2 = K2[HgI4]
So, the addition of mercuric iodide will decrease the number of ions in the solution. This will make the depression...
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Hydroxycitric Acid
Hydroxycitric acid (HCA) is a derivative of citric acid and is found in variety of tropical plants. It is found in Garcinia Indica commonly known as kokum and is used in Indian & Thai food as a flavoring agent.
Earlier experiments with HCA on mice showed that when mice were administered with HCA along with their food, it made them eat less.
If our food contains large amounts of...
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Base and Nucleophile
A negatively charged species can act both as a base and also as a nucleophile. When an alkyl halide reacts with a negatively charged species there are two possible outcomes; elimination and substitution. If the outcome is elimination the negatively charged species has played the role of a base and if the outcome is substitution then the negatively charged species has acted as a nucleophile.
If we...
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Question on Basic Strength
Is a 0.01 N solution of Ca(OH)2 more basic than a 0.01 M solution of Ca(OH)2? Why?
Answer:
No. 0.01 N solution of Ca(OH)2 is 0.005 M. SO, it will produce 0.01 M hydroxide ions while 0.01 M solution will produce 0.02 M hydroxide ions.
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Question on Chemical Equilibrium
If at 100°C, the vapour density of N2O4 is 26.8, what is the degree of dissociation of N2O4 at this temperature?
Answer:
0.72
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Question on Stoichiometry
If 3.68 g of a mixture of CaCO3 and MgCO3 when heated strongly leave 1.92 g of a white residue what is the percentage composition of the mixture?
Answer:
CaCO3 = 57.75% and MgCO3 = 42.25%
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Aspartame
Aspartame is an artificial sweetener. It is used as a substitute for sugar in food and some beverages. It is the methyl ester of the dipeptide of L-aspartic acid and L-phenyl alanine. Both L-aspartic acid and L-phenylalanine are natural amino acids. It is said that aspartame is almost 200 times sweeter than sugar. This property allows us to have the same amount of sweetness as sugar but will a...
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Question on Glucose
How many molecules of phenyl hydrazine reacts with one molecule of glucose to produce glucosazone?
Answer:
3 molecules
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Question on Molecular Structure
How many sigma bonds (a), pi bonds (b) and lone pair of electrons (c) respectively are present in the enolic form of acetone?
Answer:
It has 9 sigma bonds, 1 pi bond and 2 lone pair of electrons.
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Question on Precipitation
7-Bromo-cycloheptatriene gives a precipitate of AgBr with AgNO3. Why?
Answer:
It is because, after losing the bromide ion the remaining 7 membered ring becomes aromatic and hence becomes more stable.
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Caught Red Handed
Mr. Stanley was missing some money that he had kept in this cup board. This is the third time that he was missing money. In earlier occasions he blamed himself for having lost the money. But, this time he knew for sure that something is wrong. Someone is stealing money from him. “Who could it be?”, he asked himself. He made a list of suspects. It read 4 names. Alex, Charles, Robin and...
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Question on Copper
In moist air Copper corrodes to produce a green layer on the surface. Why?
Answer:
Copper reacts with moisture and CO2 in air to form a 1:1 molar mixture of Cu(OH)2 and CuCO3 which is green in color.
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Question on Alkenes
Compound A of molecular formula C6H12 gives a positive test with bromine in carbon tetrachloride. Reaction of A with alkaline KMnO4 yields potassium salt of an acid. What is the name of compound A?
Answer:
The name of compound A is Hex-3-ene.
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Isoelectric Point
Amino Acids have both amino group as well as a carboxylic acid group. The pKa values of both the groups are well separated that at any given pH a molecule of amino acids carries some charge. For example at a pH as low as 1, the amino group will be protonated and the net charge of the molecule will be positive and at a pH as high as 12 the acidic hydrogen atoms will be removed and the net charge on...
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Question on Chemical Bonding
Why is NF5 not known while PF5 is known?
Answer:
Nitrogen atom cannot expand its octet as Phosphorus atom as it does not have vacant d-orbitals.
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Question on Solubility
Among MgSO4 and BaSO4 which one is more soluble in water at room temperature? Why?
Answer:
MgSO4 is more soluble than BaSO4 in water at room temperature because among the sulphates of alkaline earth metals the decrease in hydration energy down the group is more rapid than the decrease in lattice energy down the group.
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Question on Acidic Strength
Out of (a) P2O5 (b) MgO (c) SiO2 and (d) Al2O3 which oxide is the most acidic?
Answer:
P2O5 is the most acidic oxide.
May 2012
21 posts
3 tags
Question on Colloids
Fog is a colloidal solution in which a liquid is dispersed in a gas. Is this statement correct?
Answer:
Correct.
