Alcohols | A-level Chemistry | OCR, AQA, Edexcel
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Alcohols in a Snap! Unlock
Alcohols in a Snap!
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The key points covered in this video include:
1. What are Alcohols?
2. Classes of Alcohols
3. Trends: Boiling Points
4. Solubility of Alcohols
5. Alcohols vs. Alkanes
6. Oxidation of Alcohols
What are Alcohols?
Alcohols form a homologous series. They are saturated. Contain only single carbon to carbon bonds. They have a general formula, They have a gradiation in their physical properties, They have similar chemical properties.
Classes of Alcohols
Primary Alcohols. The -OH group is attached to a carbon with no more than 1 alkyl group. Secondary Alcohols. The -OH group is attached to a carbon with no more than 2 alkyl groups. Tertiary Alcohol. The -OH group is attached to a carbon with no more than 3 alkyl groups.
Trends: Boiling Point
As the chain length increases, the boiling point increases. As the chain length increases, the molecules get longer. As the molecules get longer, there are more surface area contacts. As there are more surface area contacts, the London Forces of attraction are stronger. As the London Forces of attraction are stronger, more energy is required to overcome these forces of attraction and the boiling point increases.
Solubility
Alcohols are soluble in polar solvents. The -OH group is polar. Water molecules are polar. Alcohol molecules can form hydrogen bonds with water molecules.
Alcohols vs. Alkanes
Higher Boiling Point than Alkanes. Unlike alkanes, alcohols are able to form intermolecular hydrogen bonds. These hydrogen bonds are the strongest type of intermolecular force. Alcohols have a higher boiling point than the corresponding alkane. Volatility. Volatility is the tendency of a substance to evaporate. As their boiling points are higher than alkanes, alcohols will be less volatile than the corresponding alkane.
Oxidation
Through the process of oxidation, alcohols lose atoms of hydrogen. These atoms of hydrogen that are lost are from: The -OH group. The carbon bonded to the -OH group. Not all classes of alcohols can be easily oxidised. Primary Alcohols, Secondary Alcohols, Tertiary Aclcohols.Does not have a H atom on the C of the C-OH group. They are not easily oxidised.
Oxidation: Primay Alcohols
Forming an Aldehyde. Conditions. Gentle Heating, Acidified Potassium. This is the oxidising agent, Acts as a source of oxygen. Immediate distilling. If we want to obtain this aldehyde we need to immediately distil the mixture. This prevents any further reaction. Observation. Colour change from orange to green. Forming a Carboxylic Acid. If we do not immediately distil the reaction mixture, further reactions will occur. The aldehyde can be further oxidised. Conditions. Heating Under Reflux. This is a process of constant boiling and condensing, This process ensures that the reaction goes to completion and minimises loss of reactants and products as vapour. Excess acidified potassium dichromate. Observation. Colour change from orange to green.
Oxidation: Secondary Alcohols
Conditions. Heat Under Reflux, Acidified Potassium Dichromate. Process. Secondary alcohols will oxidise to form ketones. No further reactions occur. Observation. Colour change from orange to green.
Oxidation: Tertiary Alcohols
Tertiary alcohols are not easily oxidised.
Summary
Alcohols form a homologous series
a. CnH2n+1OH
They can be Primary, Secondary or Tertiary
Boiling point increases as chain length increases
a. Higher than similar alkanes, due to presence of hydrogen bonding
Less volatile than similar alkanes
Alcohols are soluble in water
a. They are polar, as water molecules are
Primary and Secondary alcohols can be oxidised
a. Tertiary alcohols cannot easily be oxidised
Primary alcohols are oxidised to aldehydes then carboxylic acids
a. To fully oxidise a primary alcohol, the reaction must be carried out under reflux
b. To obtain aldehydes, they must be distilled off right away
c. Acidified potassium dichromate is used as an oxidising agent
Secondary alcohols are oxidised to form ketones
a. Acidified potassium dichromate is also used
The oxidation of primary and secondary alcohols involves a colour change from orange to green
Unlock the full A-level Chemistry course at http://bit.ly/2YtkDvv created by Ella Buluwela, Chemistry expert at SnapRevise.
SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks.
Sign up today and together, let’s make A-level Chemistry a walk in the park!
The key points covered in this video include:
1. What are Alcohols?
2. Classes of Alcohols
3. Trends: Boiling Points
4. Solubility of Alcohols
5. Alcohols vs. Alkanes
6. Oxidation of Alcohols
What are Alcohols?
Alcohols form a homologous series. They are saturated. Contain only single carbon to carbon bonds. They have a general formula, They have a gradiation in their physical properties, They have similar chemical properties.
Classes of Alcohols
Primary Alcohols. The -OH group is attached to a carbon with no more than 1 alkyl group. Secondary Alcohols. The -OH group is attached to a carbon with no more than 2 alkyl groups. Tertiary Alcohol. The -OH group is attached to a carbon with no more than 3 alkyl groups.
Trends: Boiling Point
As the chain length increases, the boiling point increases. As the chain length increases, the molecules get longer. As the molecules get longer, there are more surface area contacts. As there are more surface area contacts, the London Forces of attraction are stronger. As the London Forces of attraction are stronger, more energy is required to overcome these forces of attraction and the boiling point increases.
Solubility
Alcohols are soluble in polar solvents. The -OH group is polar. Water molecules are polar. Alcohol molecules can form hydrogen bonds with water molecules.
Alcohols vs. Alkanes
Higher Boiling Point than Alkanes. Unlike alkanes, alcohols are able to form intermolecular hydrogen bonds. These hydrogen bonds are the strongest type of intermolecular force. Alcohols have a higher boiling point than the corresponding alkane. Volatility. Volatility is the tendency of a substance to evaporate. As their boiling points are higher than alkanes, alcohols will be less volatile than the corresponding alkane.
Oxidation
Through the process of oxidation, alcohols lose atoms of hydrogen. These atoms of hydrogen that are lost are from: The -OH group. The carbon bonded to the -OH group. Not all classes of alcohols can be easily oxidised. Primary Alcohols, Secondary Alcohols, Tertiary Aclcohols.Does not have a H atom on the C of the C-OH group. They are not easily oxidised.
Oxidation: Primay Alcohols
Forming an Aldehyde. Conditions. Gentle Heating, Acidified Potassium. This is the oxidising agent, Acts as a source of oxygen. Immediate distilling. If we want to obtain this aldehyde we need to immediately distil the mixture. This prevents any further reaction. Observation. Colour change from orange to green. Forming a Carboxylic Acid. If we do not immediately distil the reaction mixture, further reactions will occur. The aldehyde can be further oxidised. Conditions. Heating Under Reflux. This is a process of constant boiling and condensing, This process ensures that the reaction goes to completion and minimises loss of reactants and products as vapour. Excess acidified potassium dichromate. Observation. Colour change from orange to green.
Oxidation: Secondary Alcohols
Conditions. Heat Under Reflux, Acidified Potassium Dichromate. Process. Secondary alcohols will oxidise to form ketones. No further reactions occur. Observation. Colour change from orange to green.
Oxidation: Tertiary Alcohols
Tertiary alcohols are not easily oxidised.
Summary
Alcohols form a homologous series
a. CnH2n+1OH
They can be Primary, Secondary or Tertiary
Boiling point increases as chain length increases
a. Higher than similar alkanes, due to presence of hydrogen bonding
Less volatile than similar alkanes
Alcohols are soluble in water
a. They are polar, as water molecules are
Primary and Secondary alcohols can be oxidised
a. Tertiary alcohols cannot easily be oxidised
Primary alcohols are oxidised to aldehydes then carboxylic acids
a. To fully oxidise a primary alcohol, the reaction must be carried out under reflux
b. To obtain aldehydes, they must be distilled off right away
c. Acidified potassium dichromate is used as an oxidising agent
Secondary alcohols are oxidised to form ketones
a. Acidified potassium dichromate is also used
The oxidation of primary and secondary alcohols involves a colour change from orange to green
5 سال پیش
در تاریخ 1398/06/04 منتشر شده
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