EXP CHM ( Reactions OF Hydrocarbon) PDF

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OBJECTIVE 1. To investigate the reactions of hydrocarbons which are hexane, cyclohexene and toluene. DISCUSSION In this experiment, to see the reactions of these organic compounds, we used combustion, saturation test, and oxidation. Combustion is one of the most significant uses of organic compounds, especially hydrocarbons. Hexane was used to represent the saturated hydrocarbons in the reactions we conducted in this experiment, meanwhile cyclohexene as an unsaturated hydrocarbon, and toluene as an aromatic hydrocarbon. Based on the video, compared to cyclohexene, hexane produced less colour strength and less soot produced during the combustion test. This is because hexane is a saturated hydrocarbon and because of the presence of a double bond, cyclohexene is an unsaturated hydrocarbon. During the combustion test, both hydrocarbons contain carbon dioxide and water. The result will be carbon monoxide and water when oxygen is reduced. Owing to the higher percentage of carbon compared to hexane, cyclohexene burns and creates more soot. F  or toluene, since it was an aromatic compound, with a higher carbon-to-hydrogen ratio than non aromatic compounds, it burned with a more sooty flame as a result of unburned carbon particles being present. Hydrocarbons are found in fuels such as natural gas and petrol, which are just hydrogen and carbon compounds. For saturation test, as shown in the video, after bromine water was dropped in a test tube that contained cyclohexene, it made bromine water decolourise with an orange solution. It is because alkenes are unsaturated, meanwhile alkanes are saturated and did not react with water from bromine, so the colour of orange remained. Since bromine is a brown-reddish color and all of the other compounds are colourless in these reactions, so the red-brown colour dissipates rapidly, often almost immediately, when bromine is applied to the alkene. The presence of the double bond C=C allows alkenes to react in ways that are not possible for alkanes. An addition reaction is undergone by alkenes with bromine. A single bond became the double bond of an alkene, and one bromine atom was bound to each of the carbons that shared the double bond. As the alkene and bromine simply add together, no other product is made, which is why it is called an addition reaction. Alkanes are much less reactive than alkenes and, in the presence of UV light, can only react with bromine water. Under these conditions, alkanes undergo halogen substitution reactions and can decolorize bromine water slowly. Lastly, we used an oxidation test to study the reactions of hydrocarbons. In this experiment, we used potassium permanganate as an oxidising agent that reacts with aliphatic hydrocarbons that were unsaturated but did not react with alkanes or hydrocarbons that were aromatic. As shown in the experiment, the dilute potassium permanganate, KMnO4 solution had a deep purple colour and there was no change in colour when there was no reaction. When it reacts with cyclohexene, a brown precipitate is formed. The alkene is oxidised to a diol when a purple solution of the oxidising agent KMnO4 is added to the alkene and the

KMnO4 is changed to brown MnO2. Thus, when the purple colour changed to brown in this reaction, it indicates a positive reaction. The diol formed has two alcohol groups adjacent to it. As for aromatic hydrocarbons, just like with alkanes, toluene was also unreactive to potassium permanganate. Based on the experiment, there were no major errors. However, it is important to take precautions while handling the experiment. As a precaution during these experiments, because hydrocarbons are extremely flammable, it is necessary to be extremely cautious. Each of these combustion tests should be conducted either in the hood or on the stainless steel lip of the hood by positioning the evaporating dish. Other than that, bromine solution should be dispensed cautiously and go into a small test tube under the hood. As bromine is an extremely strong oxidising agent, it is crucial to be very careful not to spill any of the bromine on the hands. In my opinion, the links given were very helpful as it helps me understand more about the experiment even without conducting it myself especially during this online lab. The videos were conducted well and the data shown were accurate. CONCLUSION In conclusion, hydrocarbons reactions can be investigated by combustion, saturation test and oxidation. Except under special conditions or catalysts such as exposure to UV light, alkanes are unreactive to bromine and unreactive to potassium permanganate. Since this experiment does not occur in the absence of ultraviolet light or heat, the reddish-brown colour of the bromine remained when the bromine is applied to the alkane. Alkenes are readily reactive to bromine and if alkenes are added with KMnO4, their double bonds can be quickly broken by addition reaction, as well as being relatively similar. Aromatic compounds are unreactive since they are typically stable and, if given a catalyst, can only be reacted. In this experiment, the data supports the research hypothesis.

LAB ASSIGNMENT 1. Test

Observations Hexane

Cyclohexene

Toluene

Combustion

Less colour strength and less soot produce

Produce more soot ot flames

Produce more sooty flames

Saturation Test

No change with bromine water

Bromine water decolourised

Colour become lighter

Oxidation

Bromine water : No change

Bromine water : Decolourise

Bromine water: No change

KMnO4: No colour change

KMnO4: - Changes from purple to brown - Presence of purple precipitate

KMnO4: - No colour change - Dark precipitate sink to the bottom of the test tube

QUESTIONS 1. What is bromine test? The bromine test is a qualitative test for the existence of unsaturation, phenols and anilines (carbon-to-carbon double or triple bonds). 2. Write balance equation for the combustions of : Compounds

Balance chemical equation

Hexane

2C6H14 + 19O2 → 6CO2 + 7H2O

Cyclohexene

2C6H10 + 17O2 → 12CO2 + 10H2O

Toluene

C7H8 + 9O2 → 7CO2 + 4H2O

3. Why alkane does not react with bromine?

Alkanes are much less reactive than alkenes and in the presence of UV light, can only react with bromine water. Under these conditions, alkanes undergo halogen substitution reactions and can decolorize bromine water slowly.

REFERENCES Alexandra Corrigan. 2015. Reaction of Hexane and Hexene with Br and KMnO4. Retrieved November 10, 2020, from https://www.youtube.com/watch?v=5VO0Jwx0C2w Jim Clark. 2020. Reactions of Alkenes with Bromine. Retrieved November 11, 2020, from https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organi c_Chemistry)/Reactions/Addition_Reactions/Electrophilic_Addition_Reactions/Reactions_of _Alkenes_with_Bromine Joice San L. 2013. Hydrocarbons. Retrieved November https://www.slideshare.net/joicesanluis/hydrocarbons-27066904

11,

2020,

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Mr D. 2020. Reactivity of cyclohexane, cyclohexene and toluene. Retrieved November 10, 2020, from h ttps://www.youtube.com/watch?v=mmMBzvIn7sk Prof Kemistry. 2016. Combustion of cyclohexane and cyclohexene. Retrieved November 10, 2020, from https://www.youtube.com/watch?v=1M4XqEsWh8s Science Marshal. 2013. Identifying Alkenes with Bromine Water. Retrieved November 10, 2020, from h ttps://www.youtube.com/watch?v=vBMGNzRYngk SolaWildlife. 2017. Methanol, Acetone, Hexane, Cyclohexanol, and Toluene combustion reactions. Retrieved November 10, 2020, from https://www.youtube.com/watch?v=bWX36oKBSmQ Susan Cull. 2018. Reaction of Hydrocarbons with Bromine. Retrieved November 10, 2020, from https://www.youtube.com/watch?v=OSaQJJf8pRQ...