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18. Simple distillation can be used to separate mixtures of liquids - OCR Gateway - GCSE Chemistry - Question 18 - 2019 - Paper 3
Question 18
18. Simple distillation can be used to separate mixtures of liquids. A scientist is using simple distillation to separate a mixture of alcohols. Look at the table. I... show full transcript
Worked Solution & Example Answer:18. Simple distillation can be used to separate mixtures of liquids - OCR Gateway - GCSE Chemistry - Question 18 - 2019 - Paper 3
Step 1
Step 2
Describe the change in the arrangement of particles as substances evaporate.
Answer
As ethanol evaporates, the particles gain energy and move apart from each other. Initially, in the liquid state, the particles are closely packed and are held together by intermolecular forces. During evaporation, these forces are overcome as the particles move to a gaseous state, where they are much further apart and move freely.
Step 3
Describe the change in the movement of particles as substances evaporate.
Answer
In the liquid state, the movement of particles is limited; they can slide past one another but are primarily confined to a certain volume. As the particles gain energy upon heating, they begin to move more vigorously. Once they reach the boiling point, they escape into the air as vapor, thereby increasing their movement significantly as they are no longer restricted.
Step 4
Suggest a piece of equipment he could use.
Answer
The scientist could use a fractional distillation column to improve the separation of the mixture of alcohols. This equipment allows for better separation by providing multiple condensation and evaporation cycles, enabling a more efficient separation based on the different boiling points of the alcohols.
Step 5
Explain how this will improve the separation of the mixture of alcohols.
Answer
Using a fractional distillation column increases the surface area for vaporization and condensation processes, allowing for more effective separation of components with close boiling points. Each time a vapor rises and condenses, the composition becomes richer in the component with the lower boiling point, enhancing the purity of the distilled product.
Step 6
Explain why combustion is an exothermic reaction.
Answer
Combustion is an exothermic reaction because it involves the breaking of bonds in the reactants (ethanol and oxygen) and the formation of bonds in the products (carbon dioxide and water). The energy released from forming stronger bonds in the products is greater than the energy required to break the bonds in the reactants, resulting in a net release of energy as heat.
Step 7
Calculate the energy transferred to break all the bonds in the reactants.
Answer
To calculate the energy required to break all the bonds in the reactants, we sum the bond energy of all the bonds in the reactants:
- In CH₃OH, there are 4 C–H bonds and 1 C–O bond.
- The bond energies are:
- C–H = 413 kJ/mol
- C–O = 358 kJ/mol
Thus, the total energy:
ext{Total energy} = 4 imes 413 + 358 = 1652 + 358 = 2010 ext{ kJ/mol}.
So, the energy transferred to break all the bonds in the reactants is 2010 kJ/mol.