Crude oil: a finite mixture, not one compound
| English | 中文 | Pinyin |
|---|---|---|
| crude oil/kruːd ɔɪl/ | 原油 | yuán yóu |
| hydrocarbon/ˈhaɪdrəkɑːbən/ | 烃 | tīng |
What would explain this observation?
- A refinery receives crude oil 原油 containing many compounds. It cannot assign the whole liquid one molecular formula, because a mixture has no single fixed chemical composition.
- 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 a finite resource found in rocks. It formed from ancient biomass, mainly plankton buried in mud, over geological time. Its rate of formation is far too slow to replace present consumption on a human timescale. Crude oil contains a very large number of compounds; most are hydrocarbons 烃. A hydrocarbon molecule contains only hydrogen and carbon atoms. Most hydrocarbons in crude oil belong to the alkane family.
- crude oil: A finite mixture of many compounds, mainly hydrocarbons, formed from ancient biomass; hydrocarbon: A compound containing carbon and hydrogen only.
Which formula represents a hydrocarbon?
A mixture contains different substances together without a fixed bonding ratio between those substances. Each individual compound still has its own definite formula. C₃H₈ is a hydrocarbon; C₂H₅OH contains oxygen and therefore is not a hydrocarbon, even though it contains carbon and hydrogen. Carbon dioxide is not a hydrocarbon either. Finite describes a limited resource, not a prediction that every deposit will disappear on one exact date.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A mixture contains different substances together without a fixed bonding ratio between those substances. Each individual compound still has its own definite formula. C₃H₈ is a hydrocarbon; C₂H₅OH contains oxygen and therefore is not a hydrocarbon, even though it contains carbon and hydrogen. Carbon dioxide is not a hydrocarbon either. Finite describes a limited resource, not a prediction that every deposit will disappear on one exact date.
- Read every element symbol before classifying a formula. Then distinguish statements about an individual molecule from statements about the whole mixture. Use supplied refinery composition data to discuss which components are present and their proportions. A classroom model can use labelled molecular cards; it does not require obtaining or heating crude oil. Keep origin, composition and use as separate parts of an explanation.
Which two habits make the investigation or model in this case more defensible?
Read every element symbol before classifying a formula. Then distinguish statements about an individual molecule from statements about the whole mixture. Use supplied refinery composition data to discuss which components are present and their proportions. A classroom model can use labelled molecular cards; it does not require obtaining or heating crude oil. Keep origin, composition and use as separate parts of an explanation.
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 original sample model contains 20 C₃H₈ molecules, 10 C₂H₆ molecules and 5 oxygen-containing molecules. There are 35 molecules represented, of which 30 are hydrocarbons. Hydrocarbon number percentage = 30/35×100 = 85.7% to one decimal place. This is a count percentage, not a mass percentage or a measured composition of all crude oils.
A model has 24 hydrocarbon molecules among 40 molecules in all. Find the hydrocarbon number percentage. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A model has 24 hydrocarbon molecules among 40 molecules in all. Find the hydrocarbon number percentage.
The result is 60 %. Known: an original sample model contains 20 C₃H₈ molecules, 10 C₂H₆ molecules and 5 oxygen-containing molecules. There are 35 molecules represented, of which 30 are hydrocarbons. Hydrocarbon number percentage = 30/35×100 = 85.7% to one decimal place. This is a count percentage, not a mass percentage or a measured composition of all crude oils.
Check the conclusion and its limits
- Do not call crude oil pure, renewable on a human timescale, or a single alkane. Biomass origin does not make every biomass-derived fuel a fossil fuel. A substance containing carbon is not automatically a hydrocarbon: all of its elements must satisfy the definition. Models and percentages describe only the supplied sample.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Every compound containing carbon is a hydrocarbon. This claim is false: Do not call crude oil pure, renewable on a human timescale, or a single alkane. Biomass origin does not make every biomass-derived fuel a fossil fuel. A substance containing carbon is not automatically a hydrocarbon: all of its elements must satisfy the definition. Models and percentages describe only the supplied sample.
Crude oil: a finite mixture, not one compound: A mixture contains different substances together without a fixed bonding ratio between those substances. Each individual compound still has its own definite formula. C₃H₈ is a hydrocarbon; C₂H₅OH contains oxygen and therefore is not a hydrocarbon, even though it contains carbon and hydrogen. Carbon dioxide is not a hydrocarbon either. Finite describes a limited resource, not a prediction that every deposit will disappear on one exact date.
Every compound containing carbon is a hydrocarbon.
Do not call crude oil pure, renewable on a human timescale, or a single alkane. Biomass origin does not make every biomass-derived fuel a fossil fuel. A substance containing carbon is not automatically a hydrocarbon: all of its elements must satisfy the definition. Models and percentages describe only the supplied sample.
A finite mixture of many compounds, mainly hydrocarbons, formed from ancient biomass: write the technical term.
crude oil means A finite mixture of many compounds, mainly hydrocarbons, formed from ancient biomass.