Written Assignment = Chemistry - Part 2 PDF

Preview

Summary

assignment...

Description

Comparison of the boiling points of 1-Hexanol, 2-Hexanone, 1-Butanol and 3-Methyl-1-butanol. Table 1.1 -BOILING POINTS AND MOLECULAR STRUCTURE

Name of Compound

Boiling points temperatures

Functional group

1-Hexanol (C6H14O)

157⁰ C

Alcohol

2-Hexanone (C6H12O)

127⁰ C

Ketone

1-Pentanol (C5H12O)

138°C

Alcohol

3-Methyl-1butanol (C5H12O)

132 °C

Alcohol

Molecular structures

Reference list for table 1.1 - Maryadele J O'Neil (2013) The Merck index an encyclopedia of chemicals, drugs, and biologicals. (See references for full referencing) As seen in table 1.1 – 1-Hexanol has the highest boiling point temperature. 1Pentanol has the second highest. 3-Methyl-1-Butanol has the second lowest temperature and 2-Hexanone has the lowest temperature. There are many chemistry laws/rules and explanations for this differences in boiling point temperature. A boiling point of a liquid is the temperature at which it corresponds to the vapour pressure of the liquid to the surround environment, causing the liquid to steam and release the vapours of the liquid into the air (Jim Clark (2003)). The molecular weight and the strength of the intermolecular forces within the structures are relative to the boiling point temperature. As the molecular weight of the compound and

the intermolecular forces increase, so does the boiling point temperature. Molecular weight is the sum of the each atoms weight in the molecule. Intermolecular forces are attractive forces that exist between molecules, which are responsible for many of the physical properties exhibited by substances. Collectively called Van der Waals forces. There are two types of Van der Waals forces, weak London Dispersion Forces, which occur in hydrocarbons, and stronger dipole-dipole forces, which are hydrogen bonding.

1-Hexanol (C6H14O), has the highest boiling point because the molecule has a greater number of carbons than 3-Methyl-1-Butanol (C5H120) and 1-Pentanol (C5H11O) and also the molecular weight is greater than all of the compounds, causing more intermolecular forces between atom to atom in the molecule, which then in turn will require more energy to break and convert its form into a gas. 1-Hexanol also has dispersion forces bonding its hydrocarbons. Dispersion forces are the weakest intermolecular forces but due to the amount of atoms present in the molecule, the sum of all of dispersion forces is greater than the other compounds. Hydrocarbons bond together through dispersion forces. Dispersion forces are temporary attractive force that results when the electrons in two neighbouring atoms occupy positions that make the atoms form temporary dipoles. (Mahaffy et al (2011)) 1-Hexanol is an alcohol, which consists of a hydroxyl group (-OH), which has strong intermolecular bonding of a hydrogen bond, which also requires more energy to break to convert the liquid into a vapour/steam. “Any molecule which has a hydrogen atom attached directly to an oxygen is capable of a strong hydrogen bond, compared to a carbon attached to a hydrogen. Such molecules will always have higher boiling points than similarly sized molecules which don't have an -O-H group.” (Jim Clark (2000)). This increases the intermolecular forces greatly, and making the structure strong and increasing the

boiling point temperature. Thus leading to have a boiling point of 157 ⁰ C (Maryadele J O'Neil (2013))

1-Pentanol (C5H11O) has the second highest boiling temperature of 138 ⁰ C. C5H11O has both dispersion forces in its hydrocarbons and a hydrogen bond in its hydroxyl group (-OH). Even though 2-Hexanone has a larger atomic weight compared to 1Pentanol, 1-Pentanol will have a higher boiling point. This is because of the ketone presented in the 2-Hexanone, which means it will convert with lower energy provided compared to 1-Pentanol, which doesn’t have a ketone functional group. Hydrogen bonds are the strongest intermolecular force, which requires greater energy than dispersion forces. 3-Methyl-1-Butanol has the same atomic weight, but because of the structure of each molecule the boiling point will differ. 1-Pentanol has 5 carbons on its chain, while 3-Methyl-1-Butanol only has 4 carbons. “Boiling point increase with the number of carbons on the chain. However when branching occurs it decreases the compounds boiling point; branched hydrocarbons cannot pack together as closely as unbranched ones, and so intermolecular forces are weaker” (William Reusch (2012)) Thus breaking/convert at a lower temperature. Therefore allowing 1-Pentanol to have a higher boiling point temperature of 138⁰ C

3-Methyl-1-Butanol has the second lowest boiling point temperature of 132 ⁰ C. This compound is an alcohol, which means it has also has a strong hydrogen bond, but due to its branching of a Methyl group of its 3 rd carbon, the intermolecular forces are much weaker than if you had a straight chain molecule. This is because “branched hydrocarbons cannot pack together as closely as unbranched ones” (William Reusch (2012)), and in turn making the intermolecular forces much weaker than the other compounds. 3-Methyl=1=Butanol has only 4 carbons on its chain, compared to the

other compounds, which contain 5-6 carbons on its chain. Hydrocarbons boiling point temperature is proportional to the number of carbons on its chain, if the number of carbons on its chain is higher, the boiling point will increase with every carbon added to its carbon chain. This is because the greater the number of carbons in its chain, the greater the sum of dispersion forces in the molecule. In the case of 3-Methyl-1-Butanol, only has 4 carbons in its main chain which compared to the other will have a much lower boiling point temperature than the other compounds. Therefore with only 4 carbon in its carbons chain, and its branch of a Methyl group, its decreases the boiling point temperature.

2-Hexanone has the lowest boiling point temperature of 127 ⁰ C 2-Hexanone has a ketone functional group, which consists of a double bond. Double bonds are relatively easy to break. Double bonds are two pairs of electrons which are share between two atoms. Due to this, they are easily manipulated with lower energy levels which then break the bonds. They are much weaker than single bonds, which is why this compound is has the lowest boiling point temperature because of the double bond. 2Hexanone consist only the weakest intermolecular forces, which are dispersion forces. There are 6 carbons in its chain which means it has same amount of carbons as 1Hexanol, which further means they have the same sum of dispersion forces in there carbon chain, but due to the different functional groups of each compound it differs greatly. Due to this, 2-Hexanone has a weak structure and requires less energy in order to convert liquid into a vapour/steam, thus leading to the compound having a lower boiling point of 127⁰ C ( Maryadele J O'Neil (2013))

In conclusion, 1-Hexanol has the highest boiling temperature due to the strong intermolecular forces of the molecule and the number of carbons present in the straight

chain, which requires most energy to convert itself into a gas form. 1-Pentanol has the second highest boiling temperature of 138 ⁰ C, due to its intermolecular forces compared to the other compounds. 3-Methyl-1-Butanol has the second lowest boiling temperature, this is because of the structure of compound and the number of carbons in its chain, hence having a much lower temperature than 1-Hexanol of 132 ⁰ C. 2Hexanone has the lowest boiling point temperature, meaning it requires the least energy to convert into a gas, this is because of its double bond present, making the structure weaker and hence allowing to break at a lower temperature...