40 terms

iGCSE Chemistry: Alkanes & Crude Oil - core

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What do each of the following state symbols represent: (s), (l), (g), (aq)
(s) - solid. (l) - liquid. (g) - gas. (aq) - aqueous (in solution)
Explain why carbon dioxide gas, CO₂, is a gas at room temperature
Carbon dioxide has a simple molecular structure with weak intermolecular forces that require little energy to overcome
Explain why methane gas, CH₄, is a gas at room temperature
Methane has a simple molecular structure with weak intermolecular forces that require little energy to overcome
If a substance has a simple molecular structure, what physical state might it be at room temperature?
Gas or liquid (low melting point)
Why is the boiling point of a larger molecule higher than that of a smaller molecule?
Larger molecules have more attractions between them which must be overcome when a substance boils
Explain the term hydrocarbon
A hydrocarbon is a molecule containing only hydrogen and carbon
Show the empirical formulae, molecular formulae, general formulae, structural formulae and displayed formulae of ethane
What is a general formula?
The simplest algebraic formula of a member of a homologous series. Eg CnH2n+2 for alkanes
Explain the term homologous series
A homologous series is a family of compounds with 1) the same general formula 2) similar chemical properties 3) trends in their physical properties
Explain the term isomerism
Molecules with the same molecular formula but with a different structure
Draw the displayed formula for 2,3-dimethyl hexane
Write all the possible different structural and displayed formulae of C₄H₁₀
What is crude oil?
A mixture of hydrocarbons
Explain how crude oil is separated into fractions
Crude oil is separated by fractional distillation. Crude oil is heated and the oil evaporates. It then goes into the tower. As the vapours rise up the tower the temperature falls. Different sized fractions condense at different heights because they have different boiling points. Smaller molecules condense high up the tower. Larger molecules condense low down in the tower. Then the fractions are collected.
What is the name of the process in which crude oil is separated into its various components?
Fractional distillation
Recall a use of bitumen
Surfacing roads
Recall a use of diesel
Fuel for lorries
Recall a use of fuel oil
Fuel for ships
Recall a use of gasoline
Fuel for cars
Recall a use of kerosene
Fuel for aeroplanes
Recall a use of refinery gases
Cooking
Recall the names of the main fractions obtained from crude oil, in order of lowest boiling point first
Refinery gases, gasoline, kerosene, diesel, fuel oil and bitumen
Describe the trend in boiling points of the main fractions in crude oil
Boiling point increases as the number of carbon atoms (chain length) increase
In the fractional distillation of crude oil, how does boiling point change as the chains get longer?
Increases
What is meant by the term viscosity?
The viscosity of a fluid describes how easily it flows. Water has a low viscosity, it flows very easily. Crude oil has a higher viscosity than water, it does not flow very easily.
What is a fuel?
A fuel is a substance that, when burned, releases heat energy
Recall the products of the complete combustion of alkanes
Carbon dioxide and water
Recall the products of the incomplete combustion of alkanes
Carbon, carbon monoxide, carbon dioxide and water
What is produced when alkanes burn with insufficient oxygen?
Carbon monoxide and water (and possibly also carbon and carbon dioxide)
Write a chemical equation for the complete combustion of propane
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Explain why carbon monoxide is dangerous to humans
It is poisonous because it reduces the capacity of the blood to carry oxygen
Why does incomplete combustion occur?
When there is an insufficient supply of oxygen for complete combustion
State the general formula of alkanes
CnH2n+2
State the names and molecular formulae of the first 5 alkanes
methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), pentane (C₅H₁₂)
Explain the term saturated
A molecule containing only single bonds
Draw the displayed formulae for ethane
Draw the displayed formulae for pentane
Draw the displayed formulae for propane
What is the molecular formula for butane?
C₄H₁₀
What is the molecular formula for methane?
CH₄
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