Fractional distillation is a common topic in C1. When it comes up it is often worth 10/12 marks - 20% of the exam paper. It is important to understand the physical processes that are occurring during fractional distillation.
Describe and Explain the process of Fractional Distillation (6 marks). Not QWC.
The first thing we need to do is look at the command words given to us in the question. Describe and Explain.
Describe: recall facts e.g. what does it look like? what happens? Step-by-step.
Explain: give a clear scientific reason - link it to the question.
Then we need to look at what the question is asking us about. Fractional Distillation.
So we now know that we need to recall facts about fractional distillation and say what happens step by step, then we need to give a scientific reason that this happens.
Description of fractional distillation.
- During fractional distillation a mixture of crude oil is heated to 350 degrees Celsius at the bottom of the fractionating column.
- The column is hotter at the bottom than at the top
- The crude oil starts to vaporise
- These vapors rise up the fractionating column
- The vapors condense at different fractions so they separate
- The condensed fractions are collected.
Explanation of fractional distillation
The different compounds in the mixture have different boiling points so they vaporise at different temperatures, these vapors then rise up the fractionating column. The vapors then condense at different temperatures depending on their boiling point and their size.
Now we have our description and explanation we can put these together and answer the question.
During fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees celsius. Smaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column. The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. The vapors will all condense at different temperatures and they are separated and collected.
In the comments I would like you to mark this answer (4 marks are awarded for describing and two for explaining), I would like you to point out which parts of the above answer are descriptive and which are explanatory and then I would like you to give a six mark answer for this question.
During fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees Celsius. (This is a description of fractional distillation because it is telling us about the stages.)
ReplyDeleteSmaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column. (This is a description as it does not explain why smaller hydrocarbons start to evaporate first.)
The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. (This is an explanation because it is saying why different hydrocarbons rise differently.)
The vapours will all condense at different temperatures and they are separated and collected. (More of description because it is only stating a stage of fractional distillation, but not saying why this happens.)
Overall I will probably give only 4 marks, as the person writing this has not explained in detail why each stage happens. Also they have mixed out on some stages.
My 6 Mark Answer
Fractional distillation is a process used to separate mixtures containing several different substances. It is used to separate crude oil into fractions in a continuous process. Firstly, crude oil placed at the bottom of the column, where it is heated to 350 degrees Celsius. The crude oil begins to vaporise, yet different compounds in the mixture have different boiling points so they vaporise at different temperatures. Smaller chain molecules have a lower melting point, so they vaporise first. These vapours rise up the fractionating column. The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. Then these vapours each condense at different temperatures, due to their boiling points. Finally, they separated and collected.
My 6 Mark Answer.
ReplyDeleteFractional distillation is used to separate mixtures into different substances. It is a tall column with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. It is used to separate crude oil and it is evaporated and its vapours allows it to condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms. Vapour from crude oil rises up the column and smaller chain hydrocarbons will vaporise first as they have lower boiling points. It is then finally cooled down and separated.
My vote goes to Vinusan (my brother) for the better answer as Nafiso fails to mention the fact that crude oil is heated at 350 degrees Celsius, Vinusan also had a structured answer using words such as "firstly" to indicate the steps in the process of fractional distillation.
ReplyDeleteAs a result of this
My six mark answer will be...
Fractional distillation is a process used to separate mixtures containing several different substances. It is used to separate crude oil into fractions in a continuous process. Firstly, crude oil placed at the bottom of the column, where it is heated to 350 degrees Celsius. The crude oil begins to vaporise, yet different compounds in the mixture have different boiling points so they vaporise at different temperatures. Smaller chain molecules have a lower melting point, so they vaporise first. These vapours rise up the fractionating column. The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. Then these vapours each condense at different temperatures, due to their boiling points. Finally, they separated and collected.
- During fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350°C. (This is definitely a description as the sentence is telling you what happens in step one)
ReplyDelete- Smaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column. (This is again a description as it is telling us what will happen but not explaining the reason why)
- The smaller the hydrocarbon the higher it will rise as it has a lower boiling point. (Now this is an explanation as it giving us a reason as to why the smaller molecules rise)
- The vapours will all condense at different temperatures and they are separated and collected. (This is a description again because it is just saying that the vapours will condense, rather than saying that this occurs due to the different boiling points)
- So, I would give this answer 4/6 marks as the description and explanation used is all correct, but needs more explanation to get higher marks.
My answer:
Fractional distillation is a continuous method used to separate the mixture of hydrocarbons in crude oil. Firstly, the crude oil is heated to 350°C at the bottom of the fractionating column, and starts to vaporise. The column is hotter at the bottom and cooler at the top. This is because different compounds in the mixture of hydrocarbons have different boiling points; hence they condense at different temperatures. Small molecules have low boiling points, therefore the vapours start to rise up and condense at different temperatures (Fractions). On the other hand, large molecules have high boiling points, and condense at the bottom. So, the different hydrocarbons are separated and then collected.
I would give it 6 marks, personally. Please don't bother commenting as I haven't got time to reply. 'During fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees Celsius'-description
ReplyDelete'Smaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column'- 2 more description points
'The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. The vapors will all condense at different temperatures and they are separated and collected. ' - Explanation and description in this one
My answer:
ReplyDeleteCrude oil is heated in a fractionating column. The oil rises based on the oiling point. The bottom is the hottest. This causes the substances to separate as each of them have different boiling points so they enter different fractions. They are then collected in each fraction.
Fractional distillation separates mixtures into different parts. These are called fractions. Different condensers come at different heights and the top of the column is cool whereas the bottom of the column is warm. Fractional distillation only works due to the fact that there are different boiling points for the different mixtures.The bottom of the column would be three hundred and fifty degrees Celsius and the top would be around twenty five degrees Celsius. The different boiling points allow the substances in crude oil to be easily separated. The crude oil can be evaporated. Once the crude oil begins to vaporise, the vapors rise up the fractionating column. At the end, the condensed fractions are collected.
ReplyDeleteI've deleted all irrelevant comments. Don't make me spend a Friday night doing this again, guys!
ReplyDeleteDuring fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees celsius. - (This is a description as it is stating the first step for the process of fractional distillation)
ReplyDeleteSmaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column. - ( This is a description as it does not explain the reason why the smaller hydrocarbons begin to evaporate and rise up the column)
The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. - (This is an explanation as it giving the reason why the smaller hydrocarbons rise up the column)
The vapours will all condense at different temperatures and they are separated and collected. - (This is a description as it just describes what happens to the vapours but fails to say the reason why the vapours condense at different temperatures before being separated and collected)
Personally, I would give 4/6, as the description is great but further explanation is needed to ensure the question is answered fully.
My Six Mark Answer:
Fractional distillation is the continuous process used to separate the mixture of hydrocarbons in crude oil. Firstly, the crude oil is heated to 350°C at the bottom of the fractionating column to evaporate it. Vapour from the oil rises up the column. Each fraction condenses at a different temperature, because it has a different range of boiling points. The column is hotter at the bottom and cooler at the top. Small molecules have low boiling points, so the vapours start to rise up and condense at lower temperatures. Whereas, the large molecules would condense at the bottom as they have high boiling points. Finally, the different hydrocarbons are separated and are then collected.
During fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees celsius.
ReplyDeleteSmaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column.
The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. The vapors will all condense at different temperatures and they are separated and collected.
I would give this answer 4 out of 6 because of the points made. the writer has made four points made. The writer need to present more explanation.
My Answer:
Fractional distillation is a process where different types of hydrocarbons are separated from crude oil. The oil enters the fractional distillation column where is is heated at the bottom where temperatures are roughly around 340 to 360 degrees Celsius. This makes the hydrocarbons gain energy and rise. The shorter hydrocarbons rises the highest as it has the lowest boiling point and the longest stays at the bottom as it has the highest boiling point. As the hydrocarbon rises it cools down which means they condense and collected at different levels of the column. This is how fractional distillation works.
I would give 3 marks for description and one mark for explaining so overall i would give four marks to the description.
ReplyDeleteDuring fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees celsius. (Description)
Smaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column. (Description).
The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. (Explanation).
The vapors will all condense at different temperatures and they are separated and collected. (Description)
My 6 mark answer:
ReplyDeleteThe crude oil is heated in a fractionating column at 350 degrees. The vapours start to rise. The bottom is the hottest and so the long chain molecules condense there because they have higher boiling points and the top is the coolest so the small chain molecules condense at the top as they have lower boiling points. The fractions are separated due to the different boiling points of the hydrocarbons and are then collected
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ReplyDeleteCrude oil is heated in a fractionating column. These fractions are different temperatures and is hot at the bottom and is cool at the top. Substances with high boiling points will condense at the bottom and substances with low boiling points with condense at the top. The hydrocarbons at the top have a similar number of carbon atoms and similar properties such substances at the top of the column are small molecules which are flammable, very volatile and have a low boiling point. Whereas substances at the bottom are the exact opposite. The crude oil is heated then the vapours rise up through the column and condense in the fractions and residue is collected at the bottom. After the vapours have fully condensed they can be collected from each fraction.
ReplyDeleteFractional distillation is used to separate crude oil into different substances. It is a column with several different condensers. The various fractions are constantly tapped off at the different levels where they condense. The column is hot at the bottom and cool at the top. Substances with higher boiling points condense at the bottom of the column and substances with lower boiling points condense at the top of the column. It is used to separate crude oil. It is evaporated into vapours which allows it to condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules.The larger hydrocarbon molecules are the first to condense because they have higher boiling points, as the molecules get smaller, they condense higher up the fractionating column. It is then finally cooled down and separated. Fractional distillation is an example of a physical process as there are no chemical reactions.
ReplyDeleteDuring fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees Celsius. - (This is the description of what happens first.)
ReplyDeleteSmaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column. - (Description of what happens to the hydrocarbons as it does not explain why this happens.)
The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. - (Explanation of why the hydrocarbons rise up the fractionating column.)
The vapours will all condense at different temperatures and they are separated and collected. - (Description of what happens to the vapours but does not explain why this happens.)
I would give this answer 4/6 because it gives three points for description and only one for explanation. It needs more details for full marks.
My Six Mark Answer:
Fractional distillation is a continuous process used to separate crude oil into fractions. Firstly, the crude oil is heated at 350 degrees Celsius at the bottom of the fractionating column to evaporate it. The vapours then rise up the column and condense at different temperatures due to the fact they have different boiling points. The fractionating column is cooler at the top and hotter at the bottom. The smaller hydrocarbons have a low boiling point so their vapours rise up and condense towards the top while bigger hydrocarbons have a high boiling point so they condense at the bottom. Finally, the hydrocarbons are separated and collected.
During fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees celsius. (This is a description as its structure seems to be step by step )
ReplyDeleteSmaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column. (Also description)
The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point. (Explanation as it states why the smaller hydrocarbons would rise)
The vapors will all condense at different temperatures and they are separated and collected. (This is a description too)
So, as you can see, this answer would probably gain 4 marks out of 6 ( 3 for description and 1 for explanation)
My Answer:
During fractional distillation, a mixture of crude oil is heated to 350 degrees celsius at the bottom of the fractionating column. The bottom of the column is therefore hot and the top is cooler. As a result, the crude oil would start to vaporise and rise up the column. These vapors would condense at different temperatures/fractions because they have different boiling points. This means that small molecules would rise up and condense at different temperatures as they have low boiling points and large molecules would condense at the bottom of the fractionating column as they have high boiling points. Thus, they would separate and they will be collected at the end of the process.
After reading the answer i have decided to award this answer a maximum of 4 marks as it briefly describes the process however it misses out information that could be crucial to gaining full marks. i would give 3 marks for describing and 1 mark for explaining.
ReplyDeleteMy answer:
A mixture of crude oil is entered at the bottom of the fractioning column and heated to 350 degrees. The bottom of the column is very hot whereas the top is cool at 25 degrees. because of the intense heat the crude oil will start to vaporize and rise up the column and the vapor would condense depending on how long their chins are and how big their molecule are. Because of their different boiling points the small chain molecules would rise to the top and the long chain molecules would condense at the top. eventually, all the vapor will condense and be used for industrial processes once collected.
During fractional distillation a mixture of crude oil is placed into the bottom of a fractionating column where it is heated to 350 degrees celsius.-Describe
ReplyDeleteSmaller hydrocarbons in this mixture start to evaporate and will rise up the fractionating column.-Describe
The smaller the hydrocarbon the higher up it will rise as it has a lower boiling point.-Explain
The vapors will all condense at different temperatures and-Describe
they are separated and collected. – Describe
I would award 5 marks as four description points were made with one explanatory point though it was not in much detail.
My 6 mark answer:
Fractional distillatoiin is where a mixture of crude oil is placed into the bottom of a fractionating colum and heated to 350 degrees Celsius. Smaller hydrocarbons begin first to evaporate and will rise up the column. The smaller the hydrocarbon is, the higher it will rise. Each of the four vapours will condense the further up you go the fractionating column because it is cooler. They are each separated and collected for their various uses.
By Jeetendra Joshi
I will give 3 marks for description to the answer as step 2 and 3 are missing and 1 mark for explanation. Also the answer could have elaborated on "The vapours will all condense at different temperatures" to gain the last mark for explantion.
ReplyDeleteMy answer:
Fractional distillation is used to separate a mixture that contains many different compounds or elements. It is done in a fractionating column which is heated to 350 degrees, where the top is cooler than the bottom. The crude oil, which is at the bottom of the column, starts to vaporise. It has hydrocarbons which have different boiling points. Therefore they will condense at different temperatures. The bigger the hydrocarbons are the higher their boiling point so the lower they will rise. Big hydrocarbons are collected at the bottom while smaller hydrocarbons are collected at the top. They all will condense at different fractions and will be collected.
I would give the answer 5/6 marks because different points have been paraphrased into one sentence and all points have been covered, in my opinion.
ReplyDeleteMy answer:
Crude oil is heated in a fractionating column. The oil evaporates and then rises based on the boiling point. The bottom is the hottest in comparison to the rest of the chamber. The substances then separate and enter different fractions because they have different boiling points. Liquid forms of the substance are then collected.
I would give the answer 5/6 marks because different points have been paraphrased into one sentence and all points have been covered, in my opinion.
ReplyDeleteMy answer:
Crude oil is heated in a fractionating column. The oil evaporates and then rises based on the boiling point. The bottom is the hottest in comparison to the rest of the chamber. The substances then separate and enter different fractions because they have different boiling points. Liquid forms of the substance are then collected.