Fractional distillation: separate by evaporation and condensation
| English | Français |
|---|---|
| fraction/ˈfrækʃn/ | fraction |
| feedstock | feedstock |
What would explain this observation?
- A distillation column can collect a fuel fraction 馏分 containing many compounds. Separating a useful boiling range does not make every molecule in that collected liquid identical.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Crude oil is heated so many components evaporate. Vapour enters a fractionating column that is hotter at the bottom and cooler at the top. Components condense in regions cool enough for them to become liquid. Higher-boiling hydrocarbons condense lower down; lower-boiling ones travel farther up before condensing. Each collected fraction contains molecules with similar carbon numbers and a range of boiling points, rather than one pure substance.
- fraction: A separated mixture of hydrocarbons with similar carbon numbers and boiling ranges; feedstock 化工原料: A starting material used to manufacture other chemicals or materials.
Why does a higher-boiling component generally condense lower in the column?
Evaporation and condensation are physical changes: molecules are separated without breaking their carbon chains. A sufficiently volatile fraction can remain gaseous at the top; heavy material can remain near the base. Fuels include petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases. Fractions also provide feedstock for the petrochemical industry, producing materials such as solvents, lubricants, polymers and detergents. Carbon atoms can bond to each other in families of related structures; this helps explain the wide variety of natural and synthetic carbon compounds.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Evaporation and condensation are physical changes: molecules are separated without breaking their carbon chains. A sufficiently volatile fraction can remain gaseous at the top; heavy material can remain near the base. Fuels include petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases. Fractions also provide feedstock for the petrochemical industry, producing materials such as solvents, lubricants, polymers and detergents. Carbon atoms can bond to each other in families of related structures; this helps explain the wide variety of natural and synthetic carbon compounds.
- Trace a labelled vapour through the temperature-gradient diagram and explain where it condenses using its supplied boiling range. Compare a fraction’s intended fuel use with a feedstock use. Do not replace an explanation with a memorised order of names alone; names of other specific fractions are not required. School demonstrations must use an approved substitute apparatus and risk assessment, not a sealed heated crude-oil container.
Which two habits make the investigation or model in this case more defensible?
Trace a labelled vapour through the temperature-gradient diagram and explain where it condenses using its supplied boiling range. Compare a fraction’s intended fuel use with a feedstock use. Do not replace an explanation with a memorised order of names alone; names of other specific fractions are not required. School demonstrations must use an approved substitute apparatus and risk assessment, not a sealed heated crude-oil container.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: an illustrative column region is at 180 °C. A component with a supplied boiling point of 250 °C can condense as vapour cools into this region; one with a boiling point of 100 °C can remain gaseous and rise farther. The difference between those supplied boiling points is ΔT=250−100=150 °C. These fictional values demonstrate the separation principle, not official fraction boundaries.
Two supplied component boiling points are 220 °C and 80 °C. Find their difference. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Two supplied component boiling points are 220 °C and 80 °C. Find their difference.
The result is 140 °C. Known: an illustrative column region is at 180 °C. A component with a supplied boiling point of 250 °C can condense as vapour cools into this region; one with a boiling point of 100 °C can remain gaseous and rise farther. The difference between those supplied boiling points is ΔT=250−100=150 °C. These fictional values demonstrate the separation principle, not official fraction boundaries.
Check the conclusion and its limits
- Do not say large molecules rise farther because they are heavier or that the column creates new alkanes. Position depends on boiling behaviour within a temperature gradient. A collected fraction is not necessarily pure, and industrial temperatures vary. Cracking is a later chemical process, not another name for fractional distillation.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Fractional distillation breaks carbon–carbon bonds to make smaller molecules. This claim is false: Do not say large molecules rise farther because they are heavier or that the column creates new alkanes. Position depends on boiling behaviour within a temperature gradient. A collected fraction is not necessarily pure, and industrial temperatures vary. Cracking is a later chemical process, not another name for fractional distillation.
Fractional distillation: separate by evaporation and condensation: Evaporation and condensation are physical changes: molecules are separated without breaking their carbon chains. A sufficiently volatile fraction can remain gaseous at the top; heavy material can remain near the base. Fuels include petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases. Fractions also provide feedstock for the petrochemical industry, producing materials such as solvents, lubricants, polymers and detergents. Carbon atoms can bond to each other in families of related structures; this helps explain the wide variety of natural and synthetic carbon compounds.
Fractional distillation breaks carbon–carbon bonds to make smaller molecules.
Do not say large molecules rise farther because they are heavier or that the column creates new alkanes. Position depends on boiling behaviour within a temperature gradient. A collected fraction is not necessarily pure, and industrial temperatures vary. Cracking is a later chemical process, not another name for fractional distillation.
A separated mixture of hydrocarbons with similar carbon numbers and boiling ranges: write the technical term.
fraction means A separated mixture of hydrocarbons with similar carbon numbers and boiling ranges.