Identification of hydrocarbons Essay

Length: 1255 words

The product of alkenes in this test is an akyl hydrogensulphate. Alkenes are capable of various reactions because of its unsaturation. II. Introduction In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon, Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls. Aromatic hydrocarbons (arenes), alkanes, alkenes, alcohol, esters and alkyne-based compounds are different types of hydrocarbons. The majority of hydrocarbons found naturally occur In crude 011. ere decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can catenate to form seemingly limitless chains. Hydrocarbons are divided Into two classes known as aliphatic compounds and aromatic compounds. Aliphatic hydrocarbons are divided into three classes: alkanes have only single bonds, and are said to be saturated; alkenes and alkynes have carbon-carbon double or triple bonds, and are said to be unsaturated. Aromatic hydrocarbons are cyclic compounds whose structure is related to that of benzene, with six -electrons in a six-member ring.

Aliphatic Hydrocarbons such as Alkanes are relatively inert to chemical oxidizing agents such as neutral or alkaline permanganate, where alkenes are readily oxidized at room temperature. The change in color can be used as a test

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for a double bond, provided the molecule contains no easily oxidizable group. Alkanes react slowly or not at all with bromine at room temperature in the dark, but in the presence of sunlight, substitution is fairly rapid: R-H + Br2 ‘light R-Br + HBr (a substitution reaction) X2 ‘light The reaction is easily detected by loss of the bromine color and by evolution of hydrogen bromide.

On the other hand. romine adds rapidly at room temperature to the bromine is rapidly decolorized when added to an alkene. Aromatic Hydrocarbons such as toluene will be used in each of the following experiments. Although formally unsaturated, C6H6CH3 in the sense that it has multiple carbon-carbon double bonds, toluene does not give the usual reactions expected of an alkene. It is not easily oxidized, and preferably undergoes substitution rather than addition reactions. Permanganate converts cyclohexene into a diol.

Since a syn-hydroxylation takes place, the reaction is thought to involve the formation of an intermediate cyclic anganate ester, which is readily hydrolyzed under the reaction conditions to yield the glycol. In the course of the reaction purple permanganate is reduced to brown manganese dioxide (Mn02). Also this reaction is used as a qualitative test for the presence of an alkene (Baeyer’s Test). This decolourization of bromine water is often used as a test for a carbon-carbon double bond. The addition of bromine to cyclohexene gives a racemic trans product.

Since the product is colourless, the bromine is rapidly decolorized when added to an alkene. This experiment aims to identify hydrocarbons and determine their properties. Ill. Methodology The physical and chemical properties of hydrocarbons were tested. First was the physical property; water solubility. Approximately 1 ml of chloroform, benzene, iodobenzene and toluene was placed into each test tube, and then water was added. A layer was formed in immiscible mixtures. For the chemical properties, reactions with bromine, potassium permanganate (KMn04) and sulphuric acid (H2S04) were tested.

In the reaction with bromine, reactants were placed in different test tubes. Drops of bromine were added, but not more than 10 drops. The numbers of drops needed to have the color persist were ecorded. A negative reaction would show a different color. Again, a new set of reactants in a test tube were prepared for the reaction with KMn04. Drops of it were placed into the reactants. A reaction occurred when a brown precipitate was formed. For the reaction with H2S04, another set of reactants were prepared. The formation of layers and the change in colour was observed. ‘V.

Discussion of results In this experiment, all of the tests conducted are a success. Thus, hydrocarbons different hydrocarbons are used which are chloroform, benzene, iodobenzene and toluene. A. Water solubility Chloroform, benzene, iodobenzene and toluene were the starting material in the reaction. The following are the results when water was added to each of them: Reactants Solubility Density Chloroform Not soluble Denser 3enzene Lass dense Iodobenzene Toluene Less dense In the results, no reactant was soluble in water. Chloroform and iodobenzene are denser than water while benzene and toluene are less dense than water.

B. Reaction Nith bromine 3romine is used to determine whether an alkane, alkene, or aromatic hydrocarbon is present. If the substance is an alkene it will react with the bromine, indicating the compound is unsaturated. When the colour of bromine disappears it indicates the substance is unsaturated and a reaction has occurred. Reactants No. of drops Appearance 10 Most blur More blur Clear Results are positive, no other color was produced and reaction took place. Products are colourless, though blurriness was observed. The process that took place light or sunlight as it is a photochemical reaction.

However, there are reactions in test tube placed under the sunlight. For the alkane (chloroform) that almost has yellowish solution in the test tube will be colourless as the hydrogen atom will be replaced with bromine atom if placed under the sunlight. Alkene contain double bonds making it possible to add Br so its colour disappears rapidly leaving a clear solution. C. Reaction with potassium permanganate (Baeyer’s test) Potassium permanganate does not react with alkanes because they are saturated. Nhen it is added to alkanes the purple color does not change.

However, when it is added to an alkene, the purple color slowly disappears and a brown Mn02 precipitate forms. The appearance of the brown precipitate indicates a positive test for unsaturation. Reactants Result Negative Positive Iodobenzene is the only one that showed a positive result even though toluene nd benzene are also an alkene. There are no double bonds in benzene despite the common drawing of it, electrons are delocalized in the pi system of the 6 carbons (pi orbitals of each carbon overlap with each other) and since there are no double bonds the permanganate does not react.

Although formally unsaturated, toluene in the sense that it has multiple carbon-carbon double bonds, it does not give the usual reactions expected of an alkene. It is not easily oxidized, and preferably undergoes substitution rather than addition reactions. D. Reaction with sulphuric acid Alkanes do not react with H2S04 while alkenes react by addition. Alkyl sulfonic acids form as products and are soluble in H2S04. Reactants Colourless layers Light green lower layer Dark green lower layer Alkanes (chloroform) are not reactive as this reaction is an addition reaction.

Hence the solution remains colourless but there is a double layer that formed on the surface of the solution. For alkenes, the solution turns cloudy and there is heat released. Alkene reacts with concentrated sulphuric acid to produce alkyl hydrogensulphates. v’. Conclusion In the experiment, the properties and the differences between an alkane and alkene is identified. It can be seen from the tests conducted that alkene is much more reactive than alkane. This is due to its carbon-carbon double bond since it is an unsaturated hydrocarbon.

Alkenes undergo a lot of addition reaction while alkane does not undergo any addition reaction in the experiments conducted. For the bromine test, alkane did not react because it contains only single C-C bonds which cannot add the bromine, while alkenes have carbon-carbon double bonds that can react with the bromine. In the baeyer’s test, only iodobenzene showed a reaction although toluene and benzene are also alkenes. This is because benzene has pi rbitals of each carbon overlapping each other.

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