Alkene

Objectives:

1.        define the electrophiles and nucleophiles.

2.        Explain the mechanism of electrophilic addition in alkenes.

3.        Explain the chemistry of alkenes as exemplified by the reaction with :

        Hydrogen, hydrogen bromide, bromine in CCl₄, bromine water, water and concentrated sulphuric acid.

 

Activity 1 :

Electrophile : An electron deficient species that can accept a pair of electrons. Examples : AlCl₃, BF₃, NO₂⁺, H⁺

Nucleophile : An electron rich species that can donate a pair of electrons. Example : H₂O, NH₃, OH^-, Cl^-

1.   The p bond in alkenes is electron rich and hence, alkenes are more reactive than alkanes. 
2.  The electrophile attacks the electron rich centre at the C=C forming a carbonium ion (carbocation) as an intermediate.
3.  This carbonium ion then combines with a nucleophile to form a product. Hence, alkenes undergo electrophilic addition reactions.

Activity 2:

1.        Hydrogenation

        CH₂=CH₂ + H₂  à CH₃CH₃                                  catalysts : Ni, Pd or Pt

        Uses : catalytic hydrogenation is used in industry to convert liquid vegetable oil to semi-solid fats in the 
             manufacture of margarine.

2.        Addition of hydrogen halides à Electrophilic addition reaction.

 

4.        Markovnikov’s rule : When hydrogen halides are added to unsymmetric alkenes, the hydrogen atom is added to the carbon atom with a higher number of hydrogen atoms.

       

      CH₃ – CH=CH₂ + HBr à CH₃ – CH – CH₂

Bromination of Alkene

Bromination of Alkenes in water
The reaction between bromine water and ethene follows a similar mechanism as in CCl₄. A brominium ion is also formed but there are now two nucleophiles involved ; a bromide ion and a water molecule.

Q: Why is 2-bromoethanol the major product ?  Water is in excess in the reaction.

Addition of water to alkenes

Addition of sulphuric acid

How to study chemistry

Hi... here are some advise for you
BooNBoX wrote,

You know what, there's an old legend in secondary school. Normally you hear this story when you are about to enter Form 4.

"Bio, Physics, Chemistry... the difference between these three pure science subjects is that, all three require different brain usage in a different percentage... In Biology, where you need 75% of MEMORIZING skill and 25% UNDERSTANDING of your text. Mean while for Physics, it's the other way round where you need only 25% MEMORIZING skill (my friend derives the formulae other than memorizes it!!) and 75% understanding. Chemistry is some way in the middle and should be the easy for all ... ... you need half memory and half understanding, i.e. you are not only memorize the formulae and concept, you need to apply them as well ..."

To be honest, for the first monthly test in my chemistry, i was about to fail ... ... i did even know how to get the numbers of atoms in a mole of oxygen gas ... ... becoz I couldn't see the concept and i did understand it... i could not imagine the concept... so.. the most important thing is .. YOU NEED TO UNDERSTAND AND ACCEPT THE CONCEPT...

then... you learn the basic, how to balance an equation... this is the most basic AND useful skill in chemistry... even in STPM, sometimes you really scratching your head til bleeding but still couldn't figure out the meaning and the question... all you need to do is to balance the equation and you will get the concept for that particular situation/condition... then you are half way to the answer...

the question is .. HOW TO LEARN TO BALANCE THE EQUATION ?? well... ... this is different for every individual... it's more or less like Maths... ... someone good in Maths (and understand what is Maths) could normally do better in balancing the equation... ... just take it as a simple Maths equation and maybe you will get a clearer picture ... ... break the molecules into simple element... ... ... take it simple and think simple .. then it will be...

HOW TO SCORE OK (WELL MAYBE) IN CHEMISTRY ... the most important key is ... ... go through every chapter and learn the basic concept... then... understand its concept but doing some practice questions ... ... doing questions will let you know how to apply this concept ... ...

e.g. : you study about thermochemistry... you know it's about heat produced/asorbed in a chemical reaction... ... but you won't be able to do the questions if you never done it before ... ... becoz you don't know how to apply the concept !

With the concepts in your mind... you should be able to do most questions ... but ... what if you want to do ALL QUESTIONS ??

HOW TO SCORE WELL IN CHEMISTRY then comes in your memorizing skill ... ... you need to memorize examples... ... you need to memorize the colours of elements... ... formulae... ...

you probably know about daniel cell... how to draw the cell and know which way the current going around the circuit... ... but if the question ask you to give an example ??? what if the questions asking you to build an experiment to know what element contain in an unknown substances ??

so to score very well, you will need this.

that's all i wanted to tell you all based on my personal experience. Some might feel not comfortable with my way, I understand that becoz i believe every individual got its own way to excel. Hopefully you can benefits the best from my opinion other than following it blindly.



Taken from: http://malaysian-students.blogspot.com/2006/06/scoring-1a-in-spm-chemistry.html

Terima kasih

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Sekian. Terima kasih

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Selamat Menjawab peperiksaan percubaan STPM 2010

Saya mengambil kesempatan ini untuk mengucapkan selamat menjawab peperiksaan percubaan kepada semua pelajar tingkatan 6 yang akan menghadapinya pada bulan ini. Pesan untuk anak-anakku, percayalah bahawa kimia bukanlah satu matapelajaran yang susah. Ia cuma memerlukan usaha yang berterusan dan kepercayaan kepada kebolehan sendiri dan doa berterusan kepada pencipta kita iaitu Tuhan yang Esa. Kita sebenarnya dilahirkan hebat dan perlu menambahkan kehebatan dengan memperbaiki kelemahan dari masa ke semasa. Di sini saya sertakan link yang amat berguna untuk rujukan anak-anak sekalian. Tingkatkan usaha dan saya doakan anda semua berjaya dunia dan akhirat.
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Selamat Datang ke Blog Kimia STPM

Assalamualaikum dan salam 1 Malaysia. Alhamdulillah pada hari bertuah ini sempena perayaan 1 Malaysia blog Kimia tingkatan 6 SMK Tinggi Melaka dapat dibina dan dapat dikongsi untuk seluruh rakyat Malaysia. Saya selaku ketua panitia Kimia tingkatan 6 MHS 2010 berharap agar blog ini dapat dimanfaatkan oleh semua pihak untuk berkongsi idea dan bahan-bahan yang berfaedah untuk mempertingkatkan kemahiran dan menambahkan ilmu dalam bidang kimia. Terima Kasih