HOW TO GET 100% MARKS IN CHEMISTRY

secure  100%  marks

Chemistry is a scoring subject and students can obtain higher marks in this subject by putting in little hard work. Chemistry is a very important subject for both board exam and various competitive exams. One can score 95+ marks in this subject in board exam by investing little bit of time. Nowadays different competitive exams are conducted within one month after the completion of class 12 board exam. If you have command over this subject then you can really perform well in different competitive exams too.

Why students face difficulty in chemistry?

Many students fail to score good marks in this subject. The only reason behind it is that they fear from chemistry. If you really want to perform better in this subject then try to remove chemistry-phobia from your mind. Believe me, chemistry is one of the most easy subjects in the science stream provided you study this subject with full concentration and consistently. You must read chemistry regularly or you will fail to prepare it well for the board exam. Try to consult your teacher and friends when you find any topic difficult to understand. 

If you want to secure 95+ marks then you need to concentrate equally on all chapters of chemistry. Forweak students who want to get magical 23 marks i.e. passing marks or more, it’s important that they prepare selective but important topics. First of all thoroughly learn last three chapters of chemistryBiomolecules, Polymers and Chemistry in Everyday Life. These three chapters together carry 10 marks. Prepare all above mentioned topics of Organic chemistry

In Inorganic Chemistry, p-Block Elements and d-Block Elements together constitute 13 marks. Though it a tough ask to mug up both the chapters in a quick time, it would be ideal to study the notes of these chapters. The questions from the inorganic chemistry are directly asked. Students should practice the structures of different chemical compounds of p-block elements properly because they are often asked in the board exam. In summary, inorganic chemistry should be read in discrete manner and regularly. Because irregular study of inorganic chemistry can cost you very much and you tend to forget even the already learned topic too.

 The last three chapters like Biomolecules, Polymer and Chemistry in Everyday life should be prepared really well. They together constitute 10 marks and students often dare to take these chapters lightly and it really affects their final marks in Chemistry.

 Physical Chemistry should be read in appropriate manner. First of all, each formula from each chapter should be learned. Students should then try to solve related problems based on those formulas. Theory part should also be learned from those chapters as they are often asked in the exam.

 Try to solve sample paper on every Sunday at least. It will help you in time management and would give you an idea of which question should be attempt first.

 If you tend to forget the learned topics then do not take much stress. It happens with every student. Prepare a time table and take out at least 2 hours daily for revising the learned topic. A regular revision can help you in securing higher marks in Chemistry.

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STATE OF MATTER

STATES  OF  MATTER  AND  FORCES :

Water exists in three state i.e. solid (ice), liquid (portable water), gas (steam, vapors).

·       In these three states water has different physical properties but same chemical composition i.e. H₂O

·       Also characteristics of these states of water depend on the molecular energy and how molecules aggregate.

·       As molecules change its physical state (from liquid to gas, gas to liquid, solid to gas etc.) there is no change in chemical properties of the substance but some changes may occur in rate of chemical reaction.

Intermolecular Forces:

                             These are forces of attraction and/or repulsion between the interacting particles i.e. atom or molecules.

Dutch Scientist J. Van der Waals (1837-1923) explains deviation of the real gases from ideal behavior with intermolecular forces, so intermolecular forces are also called as van der waals forces.

Example: Hydrogen bonding which is strong dipole-dipole interaction.

Dispersion Forces: 

                             If an atom gets instantaneous dipole (i.e. Atom has more electron density in right or left hand side) then its nearby atom become induced dipole, so these two temporary dipole attract each other. This attraction force is known as dispersion forces.

·       As these forces were first proposed by F. London so these forces are also known as London forces.

Dipole-Dipole Forces: 

                                    This type of force act between the molecules which have permanent dipole. Dipole of these molecule possess some partial charges (denoted by delta  that is delta positive or delta negative)

Example: HCl molecule, where H possess delta positive and Cl possess delta negative.

Dipole-Induced Dipole Forces: 

                                             These attractive forces act between polar and non-polar molecules where polar molecules have permanent dipole, which induced the dipole and non-polar molecule by deforming electronic cloud of non-polar molecule.

·       As polarisability increases, strength of the attractive interaction also increases.

Hydrogen-Bond:  

                           It is a type of dipole-dipole interaction present in molecules with high polar N-H, O-H and H-F bonds.

Thermal Energy: 

                           It is the energy of the body arise due to the motion of its atoms and molecules.

·       Thermal energy is directly proportional to temperature of the substances.

Intermolecular forces v/s Thermal interactions

·       Intermolecular forces make molecules of the substance keep together.

·       While thermal energy of the substance make molecules keep apart.

·       These two (thermal energy and intermolecular forces) decides collectively the states of matter.

·       If intermolecular forces predominance then

                                      Gas->Liquid->Solid

·       If thermal energy predominance then

                                      Solid->Liquid->Gas

What is Troposphere: 

                                   It is the lowest layer of the atmosphere held to surface of the earth by gravitational forces where we live. It contains O₂, CO₂, N₂ and water vapors etc.

Gaseous State: 

                     Only 11 elements ( H, O, N, F, Cl, He ,Ne, Ar, Kr, Xe, Rn exists in gaseous state under normal conditions.

Characteristic Physical Properties Of Gases

·       Gases are highly compressible.

·       Gases exert the equal pressure in all direction.

·       As compared to solid and liquids, gases have much lower density.

·       Gases don’t have definite (fix) shape and volume.

·       Gases mix completely and evenly in all proportions.

The following table illustrates different states of matter and their physical properties.

	Property	States of matter
		Solid	Liquid	Gas(Vapor)
i)	Shape	definite	indefinite	indefinite
ii)	Volume	definite	definite	indefinite
iii)	Molecular Bonding	very strong	strong	Weak
iv)	Examples	NaCl ZnSO4	H2O Petrol	H2 , CO2 LPG

The Molecular mode of Solids, Liquids, Gases

Plasma : This is the fourth state of matter. It is a type of gas containing positively and negatively charged particles in approximately equal numbers and present in the sun and most stars.

EXAM TIPS

TIPS  FOR   EXCELENT  PERFORMANCE  IN YOUR  EXAMS  

Good Time Table

Before starting with the studies, students should design their own time-table which directs all the material that has to be covered and tells them how much is needed to be studied each day. A schedule of every subject should be made with different priorities. Tough subjects and the ones in which a student is weak should be given more hours, and easier ones should be given less hours with sufficient intervals between each subject. The timetable should very importantly have breaks in between.

Loose that Fear

Fear and stress are one of the major factors which tend to become an obstacle in getting high percentage. One should loose all the fear and free his mind.

Approximating a certain score to achieve is beyond our control .This fact also needs to be understood by parents, who should not pressurize their children but rather boost up their confidence.

Don't Cram, Make Notes

Students should let go off the cramming part as it is not a good method of studying. Instead of this, they should make short notes while studying. Cramming everything can result in forgetting everything and making brief notes can help in remembering all points while revising the subject.

Where to Study?

If the big question of where to study confuses you, the answer to it is very simple-study in a place where you feel comfortable, relaxed and where you can concentrate properly. If you can, study early morning, head to a library or any place where you find a quiet ambience.

Trust God and Yourself

Students should meditate or pray well before the exam as it helps in relaxing their mind and also provides immense energy and peace to the mind. And it is much important that you are confident about yourself of producing splendid result.

Sleep and Eat Well

The biggest mistake students commit during exam time is that they don't sleep and eat well. They think sleeping is a waste of time. They should believe in the fact that they need to sleep between 6-8 hours a day. They also need to take care of their diet. They should try and avoid eat junk food, and instead include food which supplies continuous energy to their brain for a longer period of time.

Time to Study

Time is possibly the most important factor. According to a research conducted, human brain is in its most active state between 5 am to 8 am in the morning and in the evening between 7 pm to 11 pm. Therefore, students who study during these timings have the maximum retention power in comparison with others.

Use Creative Techniques

If students find their subjects boring, they can convert their chapters into various types of games such as repetition, flash cards and mnemonics. Students should sit with their notebook and write over and over, draw flash cards with information on them and go over them regularly, design funny rhymes or word associations to help remember the points.

Never Cheat in Exam Hall

Students should always be advised by their parents as well their teachers as to not use any kind of malpractice in exam hall as it may prove to be harmful for them and their future. If an answer is not known by them, they shouldn't attempt it as they have to prove no one but themselves. 

Write Neat and Present Well

When students write neatly and present their answer sheet in a proper way, they have more chances of securing high marks. Many times the teacher is not able to read all the answers but if she gets impressed by the way it has been presented then it would definitely lead to less deduction of marks.


 SOME  OTHER  USEFUL TIPS FOR  YOUR EXAMS.....................................................................................................................

Create your own study guide.

While many teachers provide a study guide, creating your own can help you understand the material better. Outlining the important information you need to learn can be helpful, both in creation and to refer to during your studies.

 Ask questions.

Your professors and TA’s are there to help! Ask them questions regarding the material and the exam so that you’re prepared when exam time arrives.

 Attend the review session.

Review sessions offer vital information on exam format, what will be on the exam and key concepts you should be focusing your studies on.

 Start early.

If you always start ahead of schedule, you’ll never be cramming the night before an exam. You’ll almost always perform better in doing so!

 Organize a group study session.

It can be helpful to study in groups – sometimes. Evaluate whether or not studying with others will be beneficial to the subject as well at your learning process.

 Study things not on the study guide.

Study guides aren’t always comprehensive – they’re just suggestions of the main concepts to learn. Use your study guide for its intended purpose: a guide. Be sure to fill in the blanks with related information.

 Take breaks.

You won’t be able to memorize or comprehend all the material at once. Balance is key – ensure that you reward learning with break times to recharge and relax.

 Stay well-rested.

There’s a lot to be said about a good night’s sleep. Make sure you’re well-rested so that you can be fully focused during your exams.

 Create a study schedule – and follow it.

Splitting the material into chucks you can actually achieve can be very beneficial. That way, you can keep track of what you’ve accomplished instead of looking at the big picture and getting overwhelmed.

 Prioritize your study time.

Some exams will be more difficult than others, some you may find easier to study for. Some may be worth more of your grade than others. Make sure to evaluate all of your exams to consider and determine all of the involved factors so you can study accordingly.

 Study for the style of exam.

If it’s multiple choice, you’ll need to know definitions and concepts. For essay exams, focus on your understanding of all the concepts presented, with examples in mind.

 Quiz yourself.

If you think about and create actual exam questions, you will likely become more familiar with what you need to study and, in the meantime, familiarize yourself with the type of language that will be on the exam. Draft potential exam questions and quiz yourself so that you can set expectations of what you need to focus on.

 Meet with your professor or TA.

Often times, meeting with an instructor, whether it’s a professor or a TA, can give you helpful hints for what to study and ways to prepare for the exam.

 Reorganize your notes.

Evaluate and reorganize your notes into what’s important, outlining important concepts, formulas dates and definitions so they’re easy to understand.

Pace yourself.

Make sure you stay focused and don’t burn yourself out. A great way to do so is to pace yourself rather than opting for the dreaded all-nighter. You can easily pace yourself by following tips like starting early, creating a study schedule and taking breaks when necessary!

 Teach classmates.

Learning by teaching is a method that really works! If you work with a study buddy and explain concepts to one another, you’re re-learning the material all over again. It’s a great way to reinforce what you’ve learned and help someone in the meantime!

 Revolve your focus.

Switching up your subjects is a helpful way to learn everything for your exams while preventing burnout on one topic. Make sure to switch it up before your eyes glaze over! That way, you can keep studying for longer periods of time while maintaining your focus.

 Color code it.

Create a system that allows you to color code material that’s going to be on the exam by what’s most important, less important, etc. This will help you focus on the most pertinent information and prioritize the material.

 Visualize.

If you’re a visual learner, it can help to create mind maps or diagrams to visualize how the concepts you’re learning relate to one another. This is especially beneficial when learning concepts that build upon the understanding of one another, like in science courses.

 Make it fun.

It’s easier to focus if you adapt to studying by quizzing yourself, creating acronyms or rewarding yourself for a job well done. Create a game plan – literally – that allows you to accomplish tasks and be rewarded for each.

FRIEDEL CRAFT REACTION

Friedel-Crafts alkylation

The Friedel-Crafts reactions, discovered by French alkaloid chemist Charles Friedel and his American partner, James Crafts, in 1877, is either the alkylation or acylation of aromatic compounds catalyzed by a Lewis acid. They are very useful in the lab for formation of carbon-carbon bonds between an aromatic nucleus and a side chain.

Source of electrophile

Friedel-Crafts alkylation is an example of electrophilic substitution in aromatic compounds. The electrophile is formed in the reaction of an alkyl halide with a Lewis acid. The Lewis acid polarizes the alkyl halide molecule, causing the hydrocarbon part of it to bear a positive charge and thus become more electrophilic.

CH₃—Cl + AlCl₃ → CH₃⁺ + AlCl₄⁻

or

CH₃Cl + AlCl₃ → CH₃^δ+Cl⁺Al⁻Cl₃

(The carbon atom has a slight excess of positive charge, as the electronegative chlorine atom draws electron density towards itself. The chlorine atom has a positive charge, as it has formed a sub-ordinate bond with the aluminium atom. In effect, the Cl atom has lost an electron, while the Al atom has gained an electron. Therefore, the Al atom has a negative charge.)

Mechanism of alkylation

The polarized, electrophilic molecule then seeks to saturate its electron deficiency and forms a π-complex with the aromatic compound that is rich in π-electrons. Formation a π-complex does not lead to loss of aromaticity. The aromaticity is lost however in the σ-complex that is the next stage of reaction. The positive charge in the σ-complex is evenly distributed across the benzene ring.

C₆H₆ + CH₃⁺ → C₆H₆⁺Br → C₆H₅Br + H⁺

The σ-complex C₆H₆⁺Br can be separated (it is stable at low temperatures), while the π-complex can not.

RestrictionS

• Deactivating functional groups, such as nitro (-NO₂), usually prevent the reaction from occurring at any appreciable rate, so it is possible to use solvents such as nitrobenzene for Friedel-Crafts alkylation.

• Primary and secondary carbocations are much less stable than tertiary cations, so rearrangement typically occurs when one attempts to introduce primary and secondary alkyl groups onto the ring. Hence, Friedel-Crafts alkylation using n-butyl chloride generates the n-butylium cation, which rearranges to the t-butyl cation, which is far more stable, and the product is exclusively the t-butyl derivative. This may, in some cases, be circumvented through use of a weaker Lewis acid.

• The Friedel-Crafts reaction can not be used to alkylate compounds which are sensitive to acids, including many heterocycles.

• Another factor that restricts the use of Friedel-Crafts alkylation is polyalkylation. Since alkyl groups have an activating influence, substituted aromatic compounds alkylate more easily than the original compounds, so that the attempted methylation of benzene to give toluene often gives significant amounts of xylene and mesitylene. The usual workaround is to acylate first (see the following sections) and then reduce the carbonyl group to an alkyl group.

Friedel-Crafts acylation

Friedel-Crafts acylation, like Friedel-Crafts alkylation, is a classic example of electrophilic substitution.

Source of electrophile]Reacting with Lewis acids, anhydrides and chloranhydrides of acids become strongly polarized and often form acylium cations.

RCOCl + AlCl₃ → RC⁺O + AlCl₄^-

Mechanism of acylation                                                                                                                      The mechanism of acylation is very similar to that of alkylation.

C₆H₆ + RC⁺O → C₆H₆—CO—R + H⁺

The ketone that is formed then forms a complex with aluminum chloride, reducing its catalytic activity.

C₆H₆—CO—R + AlCl₃ → C₆H₆—C⁺(R)—O—Al⁻Cl₃

Therefore, a much greater amount of catalyst is required for acylation than for alkylation.

QUESTIONS  RELATED WITH TOPIC :

Which is most reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 2

Which is least reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 3

Which gives a meta nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 4

Which is most reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 5

Which is least reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 6

Which gives a meta nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 7

Which will be the main product upon chlorination of m-nitrotoluene with Cl2/AlCl3?

a) 

b) 

c) 

d) 

Question 8

Which is obtained as the main mononitration product upon reaction of m-t-butylanisole (1-t-butyl-3-methoxybenzene) with HNO3-H2SO4?

a) 

b) 

c) 

d) 

Question 9

Which of the following statements regarding Friedel-Crafts reactions is wrong?

a) Alkylation of benzene with an alkyl chloride requires only a catalytic amount of a Lewis acid such as aluminum chloride.

b) Alkylation of benzene with an alcohol requires only a catalytic amount of a Brønsted acid such as phosphoric acid.

c) Acetylation of benzene with acetyl chloride requires only a catalytic amount of a Lewis acid.

d) Acetylation of benzene with acetic anhydride requires more than one equivalent of a Lewis acid.

Question 10

Which of the following statements regarding electrophilic aromatic substitution is wrong?

a) Acetyl and cyano substituents are both deactivating and m-directing.

b) Alkyl groups are activating and o,p-directing.

c) Ammonio groups are m-directing but amino groups are and o,p-directing.

d) Chloro and methoxy substituents are both deactivating and o,p-directing.

Question 11

Which is most reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 12

Which is least reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 13

Which gives a para nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 14

Which gives a meta nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 15

Which of (a)-(d) does not give isopropylbenzene as a product upon reaction with benzene?

a) (CH3)2CHCl/AlCl3

b) CH3CH2CH2Cl/AlCl3

c) CH3CH=CH2/H3PO4

d) (CH3)2C=CH2/H3PO4

Question 16

Which combination of reagents used in the indicated order with benzene will give m-nitropropylbenzene?

a) 1) HNO3/H2SO4, 2) CH3CH2CH2Cl/AlCl3

b) 1) CH3CH2CH2Cl/AlCl3, 2) HNO3/H2SO4

c) 1) CH3CH2COCl/AlCl3, 2) HNO3/H2SO4, 3) H2NNH2/NaOH

d) 1) HNO3/H2SO4, 2) CH3CH2COCl/AlCl3, 3) H2NNH2/NaOH

Question 17

Which pair of compounds are the most probable main products of the following reaction?
 

a) 

b) 

c) 

d) 

Question 18

Which pair of compounds are the most probable main products of the following reaction?
 

a) 

b) 

c) 

d) 

Question 19

Which will be the main product upon bromination of phenyl benzoate with Br2/AlBr3?

a) 

b) 

c) 

d) 

Question 20

Which of the following statements regarding electrophilic aromatic substitution is wrong?

a) Sulfonation of toluene is reversible.

b) Friedel-Crafts alkylation of benzene can be reversible.

c) Friedel-Crafts alkylation with primary alkyl chloride may involve rearrangement.

d) Friedel-Crafts acylation of nitrobenzene readily gives a meta substitution product.