Sekolah Rendah SK Seksyen 6

Assalamualaikum...

Harini Faiz ada melawat sekolah Faiz dekat Seksyen 6. Nama sekolah tu SK Seksyen Enam. Banyak kenangan kat sini. Macam2 la. Ponteng kelas la, sorok report laporan la, mengada2 nak ada kakak angakat sedangkan dah ada ada kakak sendiri & macam-macam la. Hahaha..., pergi melawat dalam pukul 3 petang camtu. Nak masuk tadi ingatkan dapat jumpa cikgu Fatimah tapi tak dapat sebab dah pencen. Last2, baru tahu yang jiran rumah kami kat Ken Rimba ni adik kepada Cikgu Fatimah. Kenangan aku ngan cikgu Fatimah ni satu je yang ingat. Cikgu Fatimah rajin bagi aku gula free. Baik kot. Um, time datang tadi, tengok surrounding sekolah almost 70% sama macam aku sekolah kat situ dulu. Aku sekolah kat situ 3 tahun je sekitar tahun 2001-2003. Ingat lagi kenangan lepas habis pekse. Dulu setiap kali habis exam, mesti ada kawan2 yang bawa gameboy konon2nya nak bagi aku cemburu. Tapi memang betulpun aku cemburu. Nak beli gameboy memang tak mampu. Dengan ibu ngan ayah faizpun garang semacam je. Dah besar panjang ni, baru dapat rasa bukan senang tau nak jadi ibu ngan ayah ni. Hope korang jaga diorang elok2 ye.


Sekolah ni, walaupun kejap dalam 3 tahun gitu, memang banyak mengimbau kenangan tau. Aku ingat lagi, time darjah satu, aku takut giler ngan tandas jenis flash yang kat atas. Tak tahu kenapa. Mungkin sebab tinggi kot. Dulu sanggup nak balik jumpa ibu semata-mata nak buang air besar kat rumah tau. Dulu korang pernah tak dapat air milo free? Alaa...,setiap kali kunjungan Lori Milo, Vitagen & lain2 nak promote kat murid2 kat sekolah tuk beli barang diorang & testing product diorang. Aku suka gila setiap kali lori Milo datang. Dulu setahun bukan sekali datang, Dalam 3 kali datang kalau xsilap. Hahaha..., aku dulu suka main curi2 air. Maksud aku curi tu, time budak2 lain xnak minum air milo...,faiz suruh jela diorang ambil air & then bagi faiz. Kira Faiz tukang minum jelakan. Jangan pelik pulak tau, diorang yang tak minum air ni sebab diorang alergic apa tah. Aku serius tak ingat.

Nie gambar sepanjang aku melawat tu...

Dulu kat sinilah kami suka tangkap belalang. Macam2 keturunan belalang kami jumpa. Hehehe

Surau sekolah. Setiap hari sebelum masuk ke kelas, mesti nampak abang & kakak hensem cantik tengah gardening kat situ.

Pemandangan Dari atas. Cantikkan? Sekolah ni dah lama kot. Faham2lah ye.

Koperasi Sekolah. Dulu, aku geram dulu bila ayah ajak teman beli buku. Mana taknya, ajak hari sabtu atau ahad. Faiz dah la nak tengok Dragon Ball ngan pokemon. Hahaha,

Dulu area belakang sejolah ni sempit tau. Sekarang dah advance dah. Luas kot sekolah ni.

Setiap kali rehat, wajib singgah sini. Rajin sebab suka tengok air kat taman ni.

Pejabat Sekolah. Dulu rajin datang pejabat sebab nak balik rumah. Aku tak suka toilet sekolah ni. Dulu jela,sekarang aku dah boleh adapt. Time aku masuk sekolah ni, terkejut jugak aku tengok. Toilet siap ada kipas. Korang hado? 

Tak berubah sampai sekarang kantin ni. Dulu ingat lagi, aku suka gila tarik tudung buduk perempuan. Takde keje memanglah. Namanya Afiqah. Die memang pandai kot. Yang sorang lagi namanya Fatihah. Si Afiqah & Fatihah ni selalu compete nak dapat no.1. Hahaha...., terlebih story pulak.

Padang ni banyak berjasa dengan aku. Aku dapat banyak pingat emas darjah 2 & 3 sebab aku geram ngan sorang budak kalau tak silap aku namanya Nazrin. Hope I can find him & ngeteh with him one day. Um, jangan ingat lembut disangka lembut. Hahaha.

Nak jumpa kawan2 lama memang susah. Kalau jumpapun, ada ke diorang aku. Akupun xberapa ingat nama. Setakat nama Rauf, Nazreen ngan Naufal jelah yang aku. But seriuously, chance nak cari diorang adalah 0.1%. Thats all from today. Juz sharing moment. K bye

Angah Oh! Angah

Assalamualaikum...

Harinie aku rasa macam rindu seseorang sangat2...Rindu sangat2 angah. Macam manalah kesihatan dia sekarang. Dulu time study kat Unimas selalu kehulu kehilir bersama-sama... Ingat lagi, selalu pergi FSTS tengok akasia slot kat tonton.com.my . Hurm..., harap dia sihat2 je. Banyak gambar dia yang aku simpan...Aku nak contact die,tapi ada masalah keluarga la pulak. Mana satu aku kena ikut. Takpe, Allah adakan...Bangah doakan angah elok2 ye. Yang penting selalu ingat bangah. Kita dulu susah bersama-sama kot... nak chow la.

Angah & Aku..

Sekian

Kenangan Steamboat

Assalamualaikum...

Best giler today..dapat makan ngan kwn2 sekelas.Walau diantaranya diorang,aku paling senyap. However diorang layan je aku. Sedih la today. Tak sampai hati nak bagitahu diorang minggu ni aku last ngan diorang. Tapi aku xde mood nak study. Banyak fikir masalah.Hidup aku xsempurna macam2 kawan aku. Tapi aku percaya rezeki Allah. Mungkin aku susah sekarang, hope Allah bagi kekuatan untuk meneruskan perjuangan hidup ni. Haha..., nak sharing sikit. Arini kitorang makan steamboat kat Capsicum kat area Seksyen 30, Shah Alam. Pergh, cara diorang makan steamboat mengalahkan aku sebagai lelaki... Lagi2 Tiqa Simi, makan xhingat dunia. Boleh die sumbat segala macam makanan dalam perut. Aq tengok je. Ni ha gambar kitorang.. Love diorang;

Masing2 dah lapar lettuw tengok makanan...

Terkezut aku tengok imran tetiba tangkap gambar.. naki, tengok cameralah. haha

TOO DELICIOUS... Korang kena cuba semua makan ni...

Cera, Elyani, Alyaa', Amal Azhar, Fatin & Tiqah Hasimi

Alahai..,cover2 senyum pulop..hahaha

cer tengok yang paling kiri sekali... bitch sangat. hahaha.. Yang tak boleh tengok cera macam miss doll tercongok kat tengah2.. Lol

Joe, Imran, Elyani, Tiqa Simi, Amal, Fatin, Alyaa', Cera, Naki, Zakhuan & Aku

Bagi aku,setiap hari yang terjadi adalah kenangan...susah aku nak tinggalkan diorang. Nak cakap yang aku ambil cuti khaspun kat diorangpun segan. Aku layan diorang buat kelakar. Release tension kot. Tapi dalam otak aku ni, biasalah banyak sangat fikir. Lagi2 fikir duit... Hope nanti aku dah tak ade, diorang still ingat kat aku. Aku akan tengok. Kalau diorang tak ingat..., aku bagi CURSE. hahaha.... Btw, nak pergi steamboat lagilah...tapi bersama kawan2 satu kelas...Hope aku sempat. 

Bagi sesiapa yang nak merasai steamboat kat Capsicum..., refer google maps ni ye. Thorbaik tau.

                                                                          Sekian.

Preparation of 1-bromobutane

     ORGANIC CHEMISTRY    

OBJECTIVE 

1) To prepare1-bromobutane
2) To find the percentage yield calculation of 1-bromobutane
3) To observe the boiling point and literature boiling point of 1-bromobutane

    INTRODUCTION
       In this experiment, nucleophilic substitutions are one of the most useful of synthetic organic reactions.     It introduces the class of reaction which is second order nucleophilic substitution.
     The class of reactions requires three things consist of a nucleophiles, an electrophile and free radical   group. In order for the reaction to proceed via substitution mechanism, the nucleophile should be in goodrange so that an electrophile must be unhindered (methyl or 1^o), and the leaving group should also in the good range. This is the reaction that refer to that criteria where water is the leaving group in acid. We can see that the first two are satisfied where bromide ion is an excellent nucleophile and the electrophile is a 1o alkyl group and the hydroxide ion is a poor leaving group.


                         CH₃CH₂CH₂CH₂-OH^- + Br^- --->  CH₃CH₂CH₂CH₂-Br + H₂O 

     We will carry out a reaction with the specific purpose of making a new compound which is it is a synthetic reaction. It is our responsibility to read the procedure and technique that required when conduct this experiment. We must understand the procedure well enough to be able to go to then lab, get set up and execute the necessary steps quickly, efficient and accurately. In this experiment, sodium bromide and 1-butanol are dissolved in water. Sulfuric acid is added cautiously which generates hydrobromic acid which in turn reacts with the alcohol upon heating to make 1-bromobutane.

MATERIALS
100 mL round-bottom flask
25 mL round bottom flask
Pasteur pipets
Ice bath
Boiling stones
Distillation setup
Reflux apparatus and trap
125 mL separatory funnel
125 mL Erlenmeyer flask
Weighing flask

APPARATUS
17.0 g sodium bromide, NaBr
10.0 mL of n-butyl alcohol (1-butanol, molecular weight= 74.1 g mol^-1, density= 0.81 g mL^-1
17.0 mL distilled water
14.0 mL of concentrated sulfuric acid, H₂SO₄
14.0 mL of 9 M H₂SO₄
14.0 mL distilled water
14.0 mL saturated aquoues sodium bicarbonate, NaHCO₃
1.0 g anhydrous calcium chloride, CaCl₂

PROCEDURE
Safety Consideration
1-butanol and 1-bromobutane are both flammable liquids and irritants where no flame cannot be conduct within this week experiment. We had to wear mask and gloves while handling it. Concentrated sulfuric acid is strongly corrosive and toxic while sodium bromide, sodium bisulfite and calcium chloride are all irritants.
17.0 g of sodium bromide, 17.0 mL of water and 10.0 mL of 1- butanol were placed into the 100 mL round-bottom flask. That round-bottom flask was swirled and place in the ice-water bath. Then, 14.0 mL of concentrated sulfuric acid to the reactants of the flask and swirl gently to mix the contents after each addition.
     The flask was assembled into a reflux apparatus using the condenser tube attached to the flask. A trap is attached to the top opening of the condenser to trap HBr gas which is produced during the reaction. The trap consists of a filter funnel connected to a rubber hose and attached to the top opening of the condenser. The filter funnel is clammed upside down at the stem so that its mouth just touches the surface of the water contained in a beaker. A boiling chip was added to avoid bumping.
     The mixture was refluxed for 1 hour. The heat was turned off when the reflux is over and allow the condensate in the condenser to drain back into the flask. The mixture was transferred to a separatory funnel after the reflux setup is cooled. Two layered was formed and the lower layer was discarded. 14 mL of 9 M H₂SO₄ was added to the funnel and shake that funnel. The lower layer was drained into the beaker after two layered is formed for second time. The lower layer inside the beaker was transferred into the empty separatory funnel. After that, 14 mL of saturated sodium bicarbonate solution was added and shaked for 1 minutes. The lower layer was drained into an Erlenmeyer flask. The product was dried woth 1.0 g anhydrous calcium chloride to remove the cloudiness and removes water moisture. The flask was swirled until the liquid is clear.
     The 1-bromobutane was purified using simple distillation. The liquid was pipetted into a 50 mL round-bottom flask and be careful to not let it any solid crystal inside the distillation flask. A few boiling stone were added and the distillation was started. The sample that distills above 90-95^oC was collected while any forerun was discarded. Collect the 1-bromobutane up to its boiling point about 101^oC. That distillate was weighed and measured to get the mass and volume of the product.

DATA/ RESULT:
Mass of 100 mL of empty round-bottom flask= 56.3478 g
Mass of sodium bromide= 17.0047 g
Mass of anhydrous CaCl₂= 1.0063 g
Mass of 1-bromobutane= (Mass of 100 mL of empty round-bottom flask + 1-bromobutane) -                 
                     Mass of 100 mL of empty round-bottom flask
                   = 56.3478 g – 54.3770 g = 1.9708 g
Melting point = 99^oC
Molecular Mass 1-butanol= 74.1224 g mol^-1
Molecular Mass 1-bromobutane= 137.0191 g mol^-1
Number of mol of 1-butanol= 17.0047 g/ 137.0191 g mol^-1 = 0.1241 mol
CH₃CH₂CH₂CH₂-OH^- + Br^-    CH₃CH₂CH₂CH₂-Br + H₂O
1 mol of 1-butanol ≡ 1 mol of Br^-
0.1241 mol of 1-butanol ≡ 0.1241 mol of 1-butanol
Theoretical yield= 0.1241 mol * 137.0191g mol^-1= 17.0041 g
Actual Yield= 1.9708 g
Percent Yield(%) = (Experimental Yield/ Theorertical Yield) x 100
=  1.9708 g  x 100 = 11.5901 %
  17.0041 g

DISCUSSION
CH₃CH₂CH₂CH₂-OH^- + Br^-    CH₃CH₂CH₂CH₂-Br + H₂O
SN₂ mechanisms was shown as above. SN₂ reaction always occur in with inversion configuration at the substrate carbon. The nucleophile approaches the substrate carbon from the back side with respect to the leaving group. In this experiment we are using water as a solvent because it has a hydrogen atom which it attached to a strongly to electronegative element. Hydrogen bonding encumbers a nucleophile and hinders its reactivity in a substitution reaction. The boiling point of our product is 99˚C, so the boiling point is nearly to 1-bromobutane which has 101˚C as it boiling point. As we know alcohol do not undergo nucleophilic substitution reactions because hydroxide ion is strongly basic and poor leaving group. The leaving group is a group of atom which depart with the electron pair used to bond them with the substrate. However, alcohols readily undergo SN₂ because the sulfuric acid was added which protonate the hydroxyl group in the presence of the bromide ion which changes the leaving group from hydroxide to water and allows bromide ions to react with it in the same mixture.
           
     The sulfuric acid serves as two purposes which is to increases the amount of protonated alcohols present in the reaction mixture and to help tie up the water molecules generated in the reaction shifting the equilibrium in favor of the alkyl bromide. From the calculation, the percentage yield for this experiment is 11.5901 %. It is because when doing the experiment, I had broken the separatory funnel near the sink. I do not want to blame my partner. However, I can estimate the product by helping other group. When conduct the experiment, we need to wear gloves while doing an experiment because 1-butanol and 1-bromobutane are flammable fluid which can irritate our skin. Sulfuric acid also very concentrated acid which can affect our skin. Make sure we wash our hand and gloves after handling the substances.


CONCLUSION
11.5901% percent yield was calculated, which 1.9708 g of 1-bromobutane was produced experimentally. The 1-bromobutanol was prepared well from 1-butanol. The melting point is 99^oC where nearly to the exact boiling point of 1-bromobutane which is 101^oC . The nucleophilic substitution mechanism that involved in the reaction was kept in mind.


REFERENCE
1)        Martin S. Silberberg, Patricia G. Amateis, “CHEMISTRY: THE MOLECULAR NATURE OF MATTER AND CHANGE “, 7^th edition, McGraw-Hill Education, Inc. N.Y 2015, page 617-651
2)        http://chemistry.csudh.edu/faculty/noel/CHE317L/Preparation%20of%201-bromobutane.htm
3)        http://myweb.brooklyn.liu.edu/swatson/Site/Laboratory_Manuals_files/Exp7.pdf

QUESTIONS
1)        Explain why the upper phase, after reflux contained the 1-bromobutane, even though its expected density is 1.276 g/cm³, and the density of water is ~1.00 g/cm³. Think what is in the aqueous solution. (e.g., what is the density of salt water?)
= Maybe it contain some of the hydroxide ions (OH^-) and bromobutane ions.
2)        Why does the alkyl halide layer from the top to the bottom layer at the point where water is used to extract the organic layer?
= Because the alkyl halide is denser compared to the water.
3)        Aqueous sodium bicarbonate was used to wash the crude 1-bromobutane. What is the purpose of this wash?
= The 1-bromobutane was formed by the addition of bromine or hydrogen bromide to 1-butene, then the bicarbonate neutralizes any unreacted bromide. This prevents the formation of polybrominated butanes from the addition of any more bromine to the 1-bromobutane. The bicarbonate reacts with the unreacted bromides to form CO₂ and sodium bromide.


4)        What is the purpose of the anhydrous CaCl₂? Why is it important that none of the solid CaCl₂ be included in the final distillation of your 1-bromobutane?
= The purpose of the anhydrous CaCl₂ is to remove the moisture before the distillation step. In this experiment, we had to remove the cloudiness that indicates the water and alcohol removal. It is important that none of the solid CaCl₂ be included in the final distillation of your 1- bromobutane because it can cause contamined our product and change our reading of melting point.(^oC)

Preparation Of 4-Methylcyclohexene

ORGANIC CHEMISTRY

OBJECTIVE

1)        To learn the distillation technique

2)        To understand the mechanism involved in the reaction

3)        To produce 4-methylcyclohexene through the acid-catalyzed elimination of water from 4-methylcyclohexanol

INTRODUCTION

In this experiment, 4-methylcyclohexanol undergoes acid-catalyzed dehydration to give 4-methylcyclohexene. The product is distilled from the reaction flask along with the water generated. The distillate is washed with salt solution, dried and distilled.

     The hydration of alcohols using strong mineral acids, such as sulfuric acid or phosphoric acids, as a catalyst is a general laboratory method for preparing alkenes. The reaction is conducted in a distillation apparatus. As the reaction mixture is heated, the lower boiling products (cyclohexene with boiling point= 83^oC and water boiling point= 100^oC distilled out and are collected out in the receiving flask. Any unreacted cyclohexanol (the starting material) and phosphoric acid (the catalyst) are left in the distilling flask because of their high boiling points (161^oC and 213^oC). However, a small amount of phosphoric acid still appears in the receiving flask, the product is washed with aqueous sodium carbonate to neutralize the acid. As we know, cyclohexene is insoluble in water and it is not lost during the crude cyclohexene by drying the liquid over anhydrous sodium sulfate. Sodium sulfate is a salt which forms a hydrate. Final purification is achieved by simple distillation.

     This week experiment, 4-methylcyclohexanol undergoes acid-catalyzed dehydration to give 4-methylcyclohexene. The product is distilled from the reaction flask along with water generated. Then, the distillate is washed with salt solution, dried and distilled.

MATERIALS

7.5 mL of 4-methylcyclohexanol (molecular weight=114.2; boiling point= 171-173^oC), 2.0 mL of 85% phosphoric acid, 30 drops (0.4 mL) of concentrated sulfuric acid, saturated sodium chloride solution, granular anhydrous sodium sulfate, bromine test reagent, potassium permanganate test reagent

APPARATUS

50 mL round bottom flask, 25 mL round bottom flask, Erlenmeyer flask, glass stirring rod, Pasteur pipets, boiling stones, distillation apparatus, ice-water bath, heating mantle, weighing balance

PROCEDURE

Safety Consideration

Phosphoric and sulfuric acids are very corrosive. We are not allowed to touch our skin. The experiment have strong odors because have many of compound so that we was used caution when smelling them. In addition, the sample was kept away from flames unless testing small amounts for behavior when heated. We were reminded all the times to place

all discarded in the waste bottle in fume hood.

·         Apparatus assembly

The apparatus for simple distillation was set up first. 50 mL round bottom flask was used as distilling flask and a 25 mL round bottom flask as a receiver. An ice bath was placed around the receiver to reduce the loss of product by evaporation. An empty 50 mL round-bottom flask was weighed. 7.5 mL of 4-methylcyclohexanol was placed in that round bottom-bottom flask using graduated pipets.

·         Dehydration

The distillation temperature was maintained below 100^oC. We was continued until only 0.5-0.6 mL of the residue remains in the distillation flask or the mixture begins to smoking or bumping.

·         Isolation and drying of the product

The distillate was transferred to a separatory funnel with the aid of 3ml saturated sodium chloride solution. (We don’t have to use centrifuge tube and Pasteur pipette)

·         Distillation

Drying agent was prevented before starting with distillation process. The 25ml round-bottom flask was used as a receiver that should be pre-weighed. The temperature range which is most of the product distills is the boiling point of our 4-methylcyclohexene.

·         Spectroscopy

We are reminded by our supervisor to not do this part

·         Unsaturation test

This test must be done and our result was recorded and explained in discussion

DATA/ RESULT:

Weight of empty round-bottom flask= 46.3255 g

Weight of empty round-bottom flask + 4-methylcyclehexanol= 56.2991 g

Weight of 4-methylcyclohexanol= 47.2991 g - 46.3255 g = 9.9736 g

Weight of empty Erlenmeyer flask= 51.1172 g

Weight of empty Erlenmeyer flask= 53.8272 g

Weight of 4-methylcyclohexene= 2.71 g

Melting point range for experimental= 174^oC

Melting point range for literature= 102^OC

Percent Yield = % ?

From The Reaction,

1 mol of 4-methylcyclohexanol = 1 mol of 4-methylcyclohexene

Molecular Mass 4-methylcyclohexanol= 114.2 g mol^-1

Molecular Mass 4-methylcyclohexene= 96.2 g mol^-1

n(mol) of 4-methylcyclohexanol l= 9.9736 g/ 114.2 g mol^-1 = 0.0873 mol

Thus, 0.0873 mol of 4-methylcyclohexanol was produced.

Mass of cyclohexene = 0.0873 mol X 96.2 g mol^-1 = 8.39826 g

= 8.3983 g

Percent Yield(%) = (Experimental Yield/ Theorertical Yield) x 100

=  2.71 g   x 100 = 32.2684 %

   8.3983 g

DISCUSSION

Elimination reactions involve the loss of a small molecule (H-X) from adjacent carbon atoms, resulting in pi-bond formation. Elimination reactions are good synthetic methods for producing alkene. These reactions occur through a process called heterolytic bond cleavage. Heterolytic bond cleavage occurs when one atom leaves a compound with both electrons of the original bond, resulting in the formation of ions. The leaving group departs with both electrons from the original C-X bond. The electrons in the adjacent C-H bond form the new pi bond of the alkene, with the loss of the proton.

The elimination of water (H-OH) from 4-methylcyclohexanol in this experiment is called a dehydration reaction. In many cases, alcohol dehydration is an acid-catalyzed reaction that proceeds by an elimination mechanism.

The mechanism is a cyclohexyl cation, which can undergo substitution as well as elimination. In this experiment, the substitution reaction are the use of strong acids with anions that are relatively poor nucleophiles and a high reaction temperature, which favors elimination. The anion of phosphoric acids in this experiment is a poor nucleophile, while substitution reactions are not favored. The first step of dehydration is a proton transfer from the acid catalyst to the oxygen atom of the alcohol. This protonation forms a oxonium ion, the conjugate acid of the alcohol. Weak base are good leaving groups, so changing the leaving group from hydroxide to water favours the reaction. The second step of the dehydration reaction is loss of water from the oxonium ion forming a positively charged secondary carbocation. This step of the mechanism is rate determining. The third and final step, a molecule of water deprotonates the carbocation at either of the adjacent carbons.  The remaining electrons flow towards the positive charge producing a sigma–bond between the carbons and forming a double bond.

Precaution steps that must we cared are phosphoric acids and 4-methylcyclohexene. Phosphoric acids are strong, corrosive acids. If any acid is splashed on your skin or clothing, wash immediately with copious amounts of water. 4-methylcyclohexene are not particularly dangerous but are highly flammable. Both are quite painful if splashed in the eyes and must be removed by extensive eye washing. Last but not least, remaining 4-methylcyclohexene should be disposed of in the fume-hood sink because 4-methylcyclohexene vapors are heavier than air where they will accumulate in the sink.

CONCLUSION

32.2684 % percent of theoretical yield was calculated, which 2.71 g of 4-methylcyclohexene was produced experimentally. We has produce 4-methylcyclohexene through the acid-catalyzed elimination of water well. And mechanism that involved in the reaction was understood in mind.

REFERENCE

1)        Martin S. Silberberg, Patricia G. Amateis, “CHEMISTRY: THE MOLECULAR NATURE OF MATTER AND CHANGE “, 7^th edition, McGraw-Hill Education, Inc. N.Y 2015, page 617-658

QUESTIONS

1)        The preparation of cyclohexene from cyclohexanol, what is basic type of reaction?

= Elimination Reaction

2)        Why is the receiving flask supposed to be kept on ice during the preparation of cyclohexene?

=In order to lower the temperature and condense it. Furthermore, it can minimize losses because the product is semisolid material at room temperature and solidifies completely when kept in a refrigerator.

Acid-Base Extraction

Salam..., sekadar nak berkongsi sahaja.

ORGANIC CHEMISTRY LAB

OBJECTIVE

1)        To separate a mixture of an acid, base and and a neutral compound into its individual components

2)        Purify the unknown by re-crystallization

3)        Analyze and identify the compound by melting point determination

INTRODUCTION

Extraction is a process of transferring a solute from one solvent to another. It is used to separate one or more components from a mixture. Extraction is like distillation and recrystallization. However, extraction, unlike recrystallization or distillation, rarely gives a pure products. Recrystallization may be needed to purify a crude product extracted from a mixture. Another use of extraction is to wash the solution of an organic solute in an organic solvent free of inorganic impurities. Extraction is accomplished by shaking a solution in a separatory funnel with a solvent that is immiscible with the one in which the desired substance is dissolved and in which the desired substance is more soluble. Two liquid layers are formed which can be separated from each other by draining the lower layer through the stopcock of the separatory funnel. Immiscible is used to describe two phases that do not dissolve each other.

     For example, a reaction is carried out in aqueous solution and the desired product is an organic compound. The reaction mixture is then shaken with a small amount of an organic solvent such as ether where upon the organic solute, being more soluble in the organic solvent than in water transfer primarily to the organic layer. Then, the undesired aqueous layers is drawn off resulting organic solution is shaken with a small amount of distilled water to wash the organic solution to remove inorganic impurities. The new aqueous layer containing inorganic impurities is then discarded. The organic solution that remains is now ready for further treatment to isolate the desired product.

     If two solutes are both soluble in an organic solvents but insoluble in water, they can separated by extraction if one of the solutes can converted to a water-soluble salt. For example, a mixture of benzoic acid and naphthalene (neutral hydrocarbon) can be separated as follows. Dissolve the mixture in a small amount of ether. Then, pour the mixture into a separatory funnel. Add a small amount of diluted NaHCO₃ solutions. The NaHCO₃ is a base and reacts with the benzoic acid to form a water-soluble salt. The naphthalene being a neutral which is remains in the ether. After that, the aqueous layer can be separated from the ether layer by opening the separatory funnel’s stopcock and draining the aqueous solution into a separate container.

MATERIALS

0.24 g of an unknown (Triphenylmethanol or 1,2,4,5-tetrachlorobenzene), 10.0 mL ether, 10.0 mL of 1.0mL NaOH, 6M hydrochloric acid, 5.0mL saturated NaCl and Na₂SO₄

APPARATUS

125 mL Erlenmeyer flask, 125 mL separatory funnel, weighing balance, hot water bath/ steam bath, Melting point apparatus, litmus/ pH paper and Pasteur pipet

PROCEDURE

1.        Extraction:

i.      0.24 g of unknown sample and 0.12 g of benzoic acid was weight and placed in a test tube.

ii.    10 mL of ether was added to the mixture and was shaked to dissolve the mixture.

iii.  The solution then transferred to the separatory funnel and 5 mL of 1M NaOH was added, capped tightly and the layers was mixed by swirling and shaking about 30 minutes. Pressure was vent by titling the funnel and opening the stop cork.

iv.  It was shakes again after closed the stop cock. The mixture was leaved to stand and allow the layers to separate. The aqueous layer was drain into the Erlenmeyer flask and was labeled as first extraction NaOH.

v.    5 mL of the 1M NaOH solution was added to the ether layer in the funnel and the step (i)-(iv) was repeated and labeled as second extraction NaOH. 

2.        Filtration:

i.      The flask was taken to the hood and by using a glass rod slowly stirring when 6M HCl was added into each Erlenmeyer flask until the solution was acidic by using blue litmus paper.

ii.    Then, the flask was taken to cool in an ice bath for about 15 minutes or until thoroughly chilled.

iii.  The solid benzoic acid was collected using Buchner funnel and filter flask.

iv.  2-3 mL water was used to wash and allowing the suction to continue for five minutes to get solid as dry as possible.

v.    It was scraped gently into a watch glass and was put into an oven for complete dryness.

vi.  The solid was weight and obtain melting point.

3.        Remove NaOH

i.      5 mL of saturated solution of sodium chloride was added to the ether layer in separatory funnel to remove any trace of NaOH solution.

ii.    The layer was separated like before,capped, mixed and vent.

iii.  The ether layer was transfer into and Erlenmeyer flask and 1g of anhydrous sodium sulfate was added to remove the moisture inside.

iv.  The stop cork was closed and swirled and was leaved to stand for 10 minutes

v.    While the ether layer was drying, a small beaker or Erlenmeyer was weighted.

vi.  The dried ether layer was transfer using a Pasteur filter pipet into a beaker. The beaker then brought to a steam bath in the fume hood to evaporate the ether.

vii.                        After evaporated, the beaker was cooled down at room temperature and reweighing to determine the yield of two unknown sample.

viii.                      The melting point was obtained and compared to the two chemicals given

DATA/ RESULT:

Actual weight of benzoic acid= 0.1264 g

Weight of benzoic acid recovered= 0.0941 g

Percent recovery of unknown sample= (0.0941 g/ 0.1264 g) *100 = 74.45%

Actual weight of unknown sample= 0.2927 g

Weight of unknown sample recovered= 0.2007 g

Percent recovery of unknown sample= (0.2007 g / 0.2927 g) * 100= 68.59%

Observed melting point of unknown sample:

Literature melting point of triphenylmethanol= 163^o C

Literature melting point of 1,2,4,5-tetrachlorobenzene= 140^o C

~White precipitate of benzoic acid and white precipitate of unknown sample was formed.

DISCUSSION

When executing experimentation of this lab, it is crucial to understand the potential results from the acid-base of the compounds. A successful extraction can then occur as long as those concepts are understood. We had to know which compounds dissolve into distinct solutions. The compounds in the mixture all dissolved in the ether solution but were insoluble in the aqueous layer until further conditions allowed for solubility. Water is a poor solvent of covalent molecules but rapidly dissolves ionic compounds.

The order of extraction occurred chronologically starting with benzoic acid substance. The melting point readings indicated that benzoic acid, which re-crystallized was indeed pure and the melting point matched the known melting range of benzoic acid. Both triphenylmethanol and the 1,2,4,5-tetrachlorobenzene had melting ranges that proved inconsistent with known melting ranges for both compounds. Since triphenylmethanol 1,2,4,5-tetrachlorobenzene substance were extracted after the benzoic acid, it is possible that the layers could have mixed and contaminated the extracted layer from the pipette.

     A procedure known as backwashing was used in an effort to remove any possible contaminates from both the substance and any solutions. Any contaminates present will transfer to the ether layer and then can be removed via pipette. Though the experiment only called for a single backwash, multiple attempts would have resulted in a more pure solution. This could have gained closer accuracy in melting ranges and reflected a more pure substance.

The precision required to pipette a specific layer out of a reaction tube becomes more accurate with experience. Some level of contamination can be anticipated when multiple lab technicians are participating in this procedure which results in an experiment with a lower degree of control. In addition, glassware from the micro-lab kit utilized during experimentation could have contaminated samples of phenol and the neutral substance. Such contamination could have fluctuated melting point ranges from the expected temperature readings.

CONCLUSION

This report has discussed the separation a mixture of an acid, base and a neutral compound into its individual components, purify the unknown by re-crystallization and identify the compound by melting point determination. The objectives of this lab were to develop the necessary hardware and software to have the HC11 measure temperature and indicate whether that temperature fell outside of prescribed limits. That objectives were met. The Percent recovery of unknown sample is 63.3998%.

QUESTIONS

1)        List four water-immiscible liquids other than ether could be used to extract organic compounds from aqueous solution.

Ø  Cyclohexane

Ø  Chloroform (trichloromethane)

Ø  Carbon tetrachloride (tetrachloro-methane)

Ø  Methylene chloride (dichloromethane)

2)        Why is it wrong to leave a bottle of anhydrous sodium sulfate or calcium chloride open?

When open the bottle of anhydrous, the air contains of water which is it expose the anhydrous to absorb the water particles in the air. This will affect the anhydrous effectiveness during the experiment.

3)        Draw the structure of the product when benzoic acid reacts with sodium hydroxide. Why is the product of this reaction easily extracted into H₂O, while the original benzoic acid is not easily extracted into H₂O?

=It is because the more OH^- that remove a hydrogen H⁺ to form a salt, the polar salt is soluble in aqueous solution, where both OH^- and benzoate are bases, the stronger base takes the H⁺ to form the weaker base.  

4)        Why does a benzoic acid precipitate out when the aqueous layer is acidified with HCl?

=Benzoic ion is stronger bases than Cl^-, so each one takes H⁺ from the HCl,the acid forms are not  water soluble, so they precipitate out from the solution.

5)        Develop a procedure for isolating a neutral compound from a mixture containing a basic impurity by drawing a flowchart as on page 20.