Organic lab. Comparison of alkanes and alkenes Essay

1. Volatility of methane, hexane, and paraffin Substance Methane Hexane Paraffin wax Observations Colorless gas, with a smell of sweet burnt alcohol. Clear, colorless liquid. Alcoholic smell, light but pungent. White, oily (waxy) solid. Very malleable, odorless. 1. Solubility of hexane and paraffin in water Substance Hexane + water Paraffin wax + water Observations Hexane when shaken with water does not dissolve. We can tell so because even though both liquids are clear and colorless, we can see a clear line which distinguishes one liquid from the other. The hexane floats right above the water, never mixing, and we can see the line of separation. Paraffin wax when shaken with water also does not dissolve. Even when finely ground, the solid pieces of wax float throughout the liquid and eventually deposit on the bottom of the test tube, never mixing with the water. 1. Combustibility of methane, hexane, and paraffin wax Substance Methane Hexane Paraffin wax Observations When the lighted splint is inserted in the test tube filled with methane, the flame quickly extinguishes itself, with a small spurt of black smoke. Right after, water vapour coats the walls of the test tube. Therefore, combustion occurred, since the water vapour means that H2O and CO2 are produced as bi products. The combustion almost complete, but not quite, since the black smoke suggests that a small amout of noxious CO and carbon were also produced. When the lighted splint is applied to the basin full of hexane, the whole surface of the alcohol catches fire (combusts) and a big flame forms, which lasts circa 5 minutes. As the fire blazes, some black smoke rises from it, and the walls of the evaporing basin become first light brown, and then progessively a darker shade of brown. This is the soot collecting on the basin. Therefore, a incomplete combustion occurred, in which the bi products of CO and carbon were released. Indeed, the soot is the amount of carbon produced by the combustion. The lighted splint does not cause the paraffin wax to combust. When applied, the heat of the fire of the splint causes the wax to melt, but not catch fire itself. This because the wax is in the solid fase, and so does not combust. It would need a candle wick, a piece of yarn inside the candle which catches fire and helps the candle melt. Part II – Comparison of alkanes and alkenes 1. Reaction of the double bond Substance Hexane + dilute sulfuric acid + potassium permanganate Hexene + dilute sulfuric acid + potassium permanganate Observations When the fucsia potassium permanganate is added to the clear hexane and sulfuric acid, the whole solution turns fucsia, as one would expect. Since there is no color change (the fucsia just happens to be the predominant color) no reaction occurred. When the fucsia potassium permanganate is added to the clear hexane and sulfuric acid, initially the whole solution turns fucsia. However right after there is a color change and the solution goes from fucsia, to light pink, to clear again. We can tell from the color change that an addition reaction occurred. 1. Combustibility of hexane and hexene Substance Hexane Hexene Observations When the lighted splint is applied to the basin full of hexane, the whole surface of the alcohol catches fire (combusts) and a big flame forms, which lasts circa 5 minutes. As the fire blazes, some black smoke rises from it, and the walls of the evaporing basin become first light brown, and then progessively a darker shade of brown. This is the soot collecting on the basin. Therefore, a incomplete combustion occurred, in which the bi products of CO and carbon were released. Indeed, the soot is the amount of carbon produced by the combustion. When the lighted splint is applied to the basin full of hexene, the whole surface of the alcohol catches fire (combusts) and a big flame forms, which lasts circa as long as the hexane combustion. As the fire blazes, a lot of thick black smoke rises from it, and the walls of the evaporing basin become first brown, and then progessively a darker until they become almost black. This is the soot collecting on the basin. Therefore, a incomplete combustion occurred, in which the bi products of CO and carbon were released. Indeed, the soot is the amount of carbon produced by the combustion. Since the basin of the hexene was darker than that of the hexane, we can deduce that the combustion of hexene is more incomplete. Part III – Alcohols and Carboxylic acids 1. Oxidation of ethanol Substance Ethanol + potassium dichromate + dilute sulfuric acid Observations When first placed in the water bath the solution turns from orange-yellow to first a light green. The smell is quite alcoholic and strong, pungent. After 5 minutes, the solution has become a darker shade of green, an almost turquoise color. The smell is a bit like a medicine, still a bit pungent (less though) and quite sweet – like cough syrup. After other 5 minutes, the color is now an intense forest green, and the smell is very sugary sweet. 1. Making esters Substance Ethanol + ethanoic acid + concentrated sulfuric acid Observations When first placed in the water bath the solution turns from a warm yellow color to first a light blue-green. The smell is very strong, pungent and unpleasant. After 5 minutes, the solution has become a more intense and dark shade of blue-green. The smell is still acidic and tangy, but now quite sweet. It is not unpleasant anymore. After other 5 minutes, the color is now an a very dark green, almost black, and the smell is almost like lemon pie, tangy but sugary at the same time. It is a nice scent. Data Analysis Part I – Alkanes 1. Volatility of methane, hexane, and paraffin 1. Methane CH4 (g) 1. Hexane C6H14 (aq) 1. Paraffin wax C20H42 (s) 1. Solubility of hexane and paraffin in water 1. Hexane No reaction occurs: C6H14 (aq) + H2O(l) à ¯ C6H14 (aq) +H2O(l) 1. Paraffin wax No reaction occurs: C20H42 (s) + H2O(l) à ¯ C20H42 (s) +H2O(l) 1. Combustibility of methane, hexane, and paraffin wax 1. Methane CH4 (g) + 2 O2 (g) à ¯ CO2 (g) + 2 H2O(g) * 1. Hexane 2 C6H14 (aq) + 19 O2(g) à ¯ 14 H2O(g) + 12 CO2 (g) * 1. Paraffin wax No combustion reaction occurred – paraffin only changes state: C20H42 (s) + heat à ¯ C20H42 (l) Part II – Comparison of alkanes and alkenes 1. Reaction of the double bond 1. Hexane No addition reaction occurred Concentrated H2SO4(l) C6H14 (aq) + KMnO4 (aq) C6H14 (aq) + KMnO4 (aq) 1. Hexene Concentrated H2SO4(l) C6H12 (aq) + KMnO4 (aq) C3H6O2 (aq) + KMnO2 (aq) 1. Combustibility of hexane and hexene 1. Hexane 2 C6H14 (aq) + 19 O2(g) à ¯ 14 H2O(g) + 12 CO2 (g) * 1. Hexene C6H12 (aq) + 9 O2 (g) à ¯ 6 H2O(g) + 6 CO2 (g) * Part III – Alcohols and Carboxylic acids 1. Oxidation of ethanol reflux 3 CH3CH2OH(aq) + 2 K2Cr2O7 (aq) + 8 H2SO4 (aq) + heat 3 CHà ¢COOH(aq) + 2 Crà ¢(SOà ¢)à ¢(aq) + 2 Kà ¢SOà ¢(aq) + 11 Hà ¢O(g) 1. Making esters concentrated H2SO4 CH3CH2OH(aq) + CH3COOH(aq) CH3COOCH2CH3 (aq) + H2O(g) * These reactions are written as complete combustions, but in reality they were incomplete conbustions, as we can tell from the soot (carbon) left behind after the reaction. Therefore the products of these combustions would not only be CO2 and H2O (water vapour) but also the noious CO and Carbon (black smoke and soot). These equations thus do not represent fully the reaction which took place. Conclusion Part I – Alkanes 1. Volatility of methane, hexane, and paraffin The state of methane, hexane, and paraffin wax are gas, liquid, and solid at room STP, respectively. They are all alkanes, and therefore only have Van Der Waal intermolecular forces (they are non-polar, so do not have dipole dipole, and do not have any Hydrogen bonds as well), The stronger the intermolecular forces, the more energy (heat) it requires to break the bonds, the higher the MP. However, even though methane, hexane, and paraffin all have VDW forces, they have very different MP and BP, as seen from their physical state at room temperature. This is due to the difference in surface area of the three alkanes. Van Der Waal forces are stronger in molecules that have a larger surface area: indeed, paraffin wax, which can have a molecular formula of C20H42 to C40H82 which be a much longer chain than hexane (C6H14) which in turn will be longer than methane (CH4). Therefore, paraffin wax will have a higher MP than hexane, which will have a higher MP than methane. 1. Solubility of hexane and paraffin in water Since hexane did not mix with the water (there was a cler line of separation between the two substances) we can concude that hexane is not soluble in polar solutions, (water is the universal solvent for polar solutions). Therefore, hexane is non-polar, as its symmetrical structure (C6H14) would suggest (the dipole moments cancel out). Also paraffin wax did not mix with water. This is due to the fact that also paraffin wax is a alkane, and therefore will also be non polar, because of its symmetrical structure (eg: C20H42) with dipole moments which cancel out. Also, the fact that the wax was solid, and no heat was added to the solution, contrbuted probably to the insolubility of the wax in the water (even polar substances like sugar melt better when heat is applied). 1. Combustibility of methane, hexane, and paraffin wax Methane combusted when the lighted splint was applied. The flame extinguishes itself quickly, and the products CO2 and H2O are formed (water vapour). However, the combustion is not complete, because also some black smoke (Carbon and CO) are produced, since there is not enough oxygen and the carbons in the reactants are not combusted completely. Likewise, also the hexane combusts when the lighted splint is applied (a huge flame erupts). However, the hexane has a more incomplete combustion. We can tell from the substantial amount of soot (carbon) left on the evaporating basin, much greater than the thin black smoke generated from the combustion of methane. The paraffin wax, even though it is an alkane, is in its solid state and therefore does not combust. When the lighted splint is applied, the wax changes state from solid to liquid. Therefore, no reaction occurs, and the products of combustion are not formed (CO2 and H2O, and Carbon and CO). If a wollen wick were to be inserted, then combustion would occur. Part II – Comparison of alkanes and alkenes 1. Reaction of the double bond Hexane did not react with the potassium permanganate, since the color did not change. This because the alkanes are saturated (do not have any double bonds) and therefore cannot perform addition reactions. Hexene instead reacts with the potassium permanganate (KMnO4), aided by the concentrated H2SO4 to form C3H6O2 and KMnO2. We can tell see the reaction visually, for the potassium permanganate is fucsia, and therefore tinges the whole solution of a pink, but after the reaction occurs the solution becomes clear, since the products are different. This because it is an alkene, and therefore unsaturated, so other molecules can add into it to form different products. The carbon-carbon double bond is very reactive. However the alkene could not react with the potassium permanganate without the catalyst H2SO4 to facilitate the reaction. 1. Combustibility of hexane and hexene Hexane and hexene both combust when the lighted splint is applied. They both catch fire, and burn for circa 5 minutes. They both produce CO2 and H2O (water vapour is formed, and moisture is left behind after the fire extinguishes), and also Carbon and CO (black smoke rises from the flame, and soot is left behind on the basin. Therefore, there is not enough oxygen, and the hexane and hexene do not combust completely, generating these noxious, unwanted products. The main difference is that hexene has a more incomplete combustion than hexane, since it leaves behind much more dirt and soot, coloring the basin pitch black, while the hexane only leaves a bit of soot, coloring the basin of a lighter brown. Therefore, the combustion of hexene requires more oxygen than that of hexane, since the amount of oxygen in the atmosphere remains more or less constant. Part III – Alcohols and Carboxylic acids 1. Oxidation of ethanol The oxidation of ethanol is an oxidation of a primary alcohol. The reaction can occur because all the reaction conditions are present: heat, the oxidizing agent (K2Cr2O7 ) and the catalyst (H2SO4). Therefore, the alcohol (CH3CH2OH) first will form an aldehyde through distilling (low ratio of oxidizing agent to alcohol) but then through reflux it will form a carboxyllic acid (CHà ¢COOH). We can notice the reaction occurring by observing the changes in the test tube. Initially yellow-orange, the solution then turns green. Also, we notice a change in scent, from a pungent alcoholic scent, to a sweeter, more pleasant smell. 1. Making esters A reaction occurs when the ethanol and the ethanoic acid, aided by the catalyst H2SO4 and heat, form an ester CH3COOCH2CH3 and water. Also here, the reaction only occurs because the reaction conditions were present: heat and catalyst H2SO4. We can notice the reaction occurring by observing the changes in the test tube. The color changes from a warmer color, to a colder, blue-green color. Also, we notice a change in scent, from a pungent alcoholic scent, very unpleasant, to a fruity, sweet and tangy smell like lemon pie. Indeed, esters are used as artificial flavouring, replicsting the smell of fruits.