A student was carrying out an investigation into alcohols, aldehydes and ketones - Scottish Highers Chemistry - Question 6 - 2017
Question 6
A student was carrying out an investigation into alcohols, aldehydes and ketones.
(a) The student was given three alcohols labelled as A, B and C. These alcohols we... show full transcript
Worked Solution & Example Answer:A student was carrying out an investigation into alcohols, aldehydes and ketones - Scottish Highers Chemistry - Question 6 - 2017
Step 1
Draw a structural formula for the secondary alcohol with the formula C4H10OH.
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Answer
The structural formula for the secondary alcohol, with the molecular formula C4H10OH, can be depicted as follows:
H H H
| | |
H--C--C--OH
| |
H C--H
|
H
This shows that the hydroxyl (–OH) group is attached to a carbon that is also bonded to two other carbon atoms, characteristic of secondary alcohols.
Step 2
Suggest why a water bath is an appropriate method of heating the reaction mixture.
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Answer
A water bath is an appropriate method of heating the reaction mixture because it provides a uniform temperature distribution and reduces the risk of overheating or igniting volatile substances. This controlled heating method ensures that the reaction proceeds safely and maintains the integrity of the reactants.
Step 3
Describe the colour change that would have been observed with alcohols A and C.
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With alcohols A and C, a colour change from orange to green would be observed. This change indicates the reduction of the dichromate ions as they are reduced in the presence of alcohols that can be oxidised.
Step 4
State the type of alcohol that cannot be oxidised by acidified dichromate solution.
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The type of alcohol that cannot be oxidised by acidified dichromate solution is a tertiary alcohol. Tertiary alcohols lack hydrogen atoms attached to the carbon bearing the hydroxyl group, which prevents them from undergoing oxidation.
Step 5
When alcohol A (C4H10OH) is oxidised the product turns the pH paper red.
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Answer
The product formed when alcohol A is oxidised would typically be an acid, producing hydrogen ions that lead to a decrease in pH, subsequently turning the pH paper red.
Step 6
Complete the ion-electron equation for the oxidation reaction.
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Answer
The balanced ion-electron equation for the oxidation of alcohol A can be expressed as:
ightarrow C_4H_8O_2 + 4H^+ + 4e^-$$
This indicates the loss of hydrogen ions along with electrons during the oxidation process.
Step 7
Name the aldehyde that has a boiling point of 119°C.
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The aldehyde that has a boiling point of 119°C is 2-methylpentanal.
Step 8
Predict the boiling point, in °C, of the following molecule.
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Answer
The boiling point of the molecule with the formula C5H10O is predicted to be approximately 166°C to 181°C, based on its molecular size and structure.
Step 9
Describe one way in which differences in structure affect the boiling point of isomeric aldehydes.
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One way in which differences in structure affect the boiling point of isomeric aldehydes is through branching. More branching in the carbon chain generally lowers the boiling point due to decreased surface area, leading to weaker van der Waals forces among the molecules.
Step 10
State what would be observed when an aldehyde is gently heated with Tollens’ reagent.
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Answer
When an aldehyde is gently heated with Tollens’ reagent, a silver mirror is produced on the inside of the test tube. This is due to the reduction of silver ions to metallic silver.
Step 11
Name the type of intermolecular interaction between ketone molecules.
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The type of intermolecular interaction between ketone molecules is predominantly London dispersion forces and permanent dipole attractions due to the carbonyl group present in ketones.
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