Organic lab. Comparison of alkanes and alkenes

5. Combustibility of hexane and hexene

Part III – Alcohols and Carboxylic acids

6. Oxidation of ethanol

7. Making esters

Data Analysis

Part I – Alkanes

1. Volatility of methane, hexane, and paraffin

• Methane

CH4 (g)

• Hexane

C6H14 (aq)

• Paraffin wax

C20H42 (s)

2. Solubility of hexane and paraffin in water

• Hexane

No reaction occurs:

C6H14 (aq) + H2O(l) → C6H14 (aq) +H2O(l)

• Paraffin wax

No reaction occurs:

C20H42 (s) + H2O(l) → C20H42 (s) +H2O(l)

3. Combustibility of methane, hexane, and paraffin wax

• Methane

CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O(g) *

• Hexane

2 C6H14 (aq) + 19 O2(g)  → 14 H2O(g) +  12 CO2 (g) *

• Paraffin wax

No combustion reaction occurred - paraffin only changes state:

C20H42 (s) + heat → C20H42 (l)

Part II – Comparison of alkanes and alkenes

4. Reaction of the double bond

• Hexane

No addition reaction occurred

                                           Concentrated  H2SO4(l) 

C6H14 (aq) + KMnO4 (aq)                                          C6H14 (aq) + KMnO4 (aq) 

• Hexene

                                         Concentrated  H2SO4(l)             

C6H12 (aq) + KMnO4 (aq)                                             C3H6O2 (aq) + KMnO2 (aq)

5. Combustibility of hexane and hexene 

• Hexane

2 C6H14 (aq) + 19 O2(g)   → 14 H2O(g) +  12 CO2 (g) *

• Hexene

C6H12 (aq) + 9 O2 (g) →6 H2O(g) +  6 CO2 (g) *

Part III – Alcohols and Carboxylic acids

6. Oxidation of ethanol

          reflux

3 CH3CH2OH(aq) + 2 K2Cr2O7 (aq) + 8 H2SO4  (aq) + heat                               3 CH₃COOH(aq) + 2 Cr₂(SO₄)₃(aq) +

                                                                       2 K₂SO₄(aq) + 11 H₂O(g)

7. 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.

2. 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).

3. 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

4. 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.   

5. 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

6. 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 (CH₃COOH). 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.

        

7. 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.