Organic Families (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Chemistry): Flashcards
Exam code: 0654 & 0973
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- FrontFossil Fuels
Name the three main fossil fuels.
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Cards in this collection (33)
Name the three main fossil fuels.
The three main fossil fuels are coal, natural gas and petroleum (also called crude oil).
Petroleum is separated into useful fractions by ______ ______, which separates the fractions according to their ______ points.
Petroleum is separated into useful fractions by fractional distillation, which separates the fractions according to their boiling points.
True or False?
Fractions collected from the top of a fractionating column have longer carbon chains and higher boiling points than those collected from the bottom.
False.
Fractions collected from the top have shorter carbon chains and lower boiling points. Fractions with longer chains and higher boiling points condense near the bottom of the column.
State the use of each of these petroleum fractions: refinery gas, gasoline and naphtha.
Refinery gas is used for heating and cooking. Gasoline (petrol) is used as fuel for cars. Naphtha is used as a chemical feedstock for making other chemicals.
State the uses of diesel oil and bitumen as petroleum fractions.
Diesel oil (gas oil) is used as fuel for diesel engines. Bitumen is used for surfacing roads.
Why do longer-chain hydrocarbons condense lower in the fractionating column than shorter-chain hydrocarbons?
Longer-chain hydrocarbons have stronger intermolecular forces, so they require more energy to remain as vapour and have higher boiling points. They condense at the hotter, lower section of the column before shorter-chain hydrocarbons do.
The main constituent of natural gas is ______, which has the molecular formula ______.
The main constituent of natural gas is methane, which has the molecular formula CH4.
What is the general formula of the alkanes?
The general formula of the alkanes is CnH2n+2. For example, methane is CH4 (n = 1) and ethane is C2H6 (n = 2).
Alkanes are ______ hydrocarbons because all their carbon-carbon bonds are ______ covalent bonds.
Alkanes are saturated hydrocarbons because all their carbon-carbon bonds are single covalent bonds.
Write the balanced equation for the complete combustion of methane.
Complete combustion of methane produces carbon dioxide and water:
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)
True or False?
Alkanes are generally unreactive compounds, except that they undergo combustion.
True.
Alkanes contain only strong single covalent bonds, making them generally unreactive. Their main chemical reaction is combustion with oxygen to produce carbon dioxide and water.
State the names and molecular formulae of the first four alkanes in order.
Methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10). Each successive member differs by one CH2 unit.
Why are alkanes generally unreactive compared to alkenes?
Alkanes contain only single carbon-carbon covalent bonds, which are strong and do not readily break under normal conditions. Alkenes contain a carbon-carbon double bond, which is more reactive and allows addition reactions to occur.
What is an alkene?
An alkene is an unsaturated hydrocarbon whose molecules contain at least one carbon-carbon double covalent bond (C=C).
When aqueous bromine is added to an alkene and shaken, the orange solution turns ______.
When aqueous bromine is added to an alkene and shaken, the orange solution turns colourless.
Why are alkenes more reactive than alkanes?
Alkenes are more reactive than alkanes because the C=C double bond can open up, allowing new bonds to form more easily than the strong single covalent bonds in alkanes.
True or False?
An alkane will decolourise aqueous bromine in the same way as an alkene.
False. An alkane does not decolourise aqueous bromine, the solution remains orange. Only alkenes, which contain a C=C double bond, react with bromine and decolourise it.
What is cracking?
Cracking is the thermal decomposition of long-chain alkane molecules into shorter-chain alkanes, alkenes and hydrogen.
Cracking requires a high ______ and a ______ such as aluminium oxide.
Cracking requires a high temperature and a catalyst such as aluminium oxide.
Why is cracking economically important?
Cracking is economically important because it converts the excess long-chain hydrocarbons from fractional distillation into more useful shorter-chain fuels (such as petrol) and alkenes needed for polymer production.
What is an addition reaction?
An addition reaction is one in which atoms from a small molecule add across the C=C double bond of an alkene, breaking the double bond and forming only one product.
When ethene reacts with hydrogen gas in the presence of a nickel catalyst, the product formed is ______.
When ethene reacts with hydrogen gas in the presence of a nickel catalyst, the product formed is ethane.
Why is only one product formed in an addition reaction?
Only one product is formed in an addition reaction because both atoms of the added molecule join across the C=C double bond, leaving no atoms unused and producing a single saturated compound.
True or False?
The reaction of ethene with steam to form ethanol requires an acid catalyst.
True.
The hydration of ethene (addition of steam) to form ethanol requires an acid catalyst.
What are the three small molecules that can undergo addition reactions with alkenes?
The three molecules are:
Bromine
Hydrogen (with a nickel catalyst)
Steam (with an acid catalyst).
The addition of ______ to propene in the presence of a nickel catalyst produces propane.
The addition of hydrogen to propene in the presence of a nickel catalyst produces propane.
What type of compound is formed when an alkene undergoes addition of steam?
An alcohol is formed. For example, ethene reacts with steam to produce ethanol.
What functional group do all alcohols contain?
All alcohols contain the hydroxyl (-OH) functional group, which is responsible for their characteristic reactions.
Ethanol burns in excess oxygen to produce ______ and ______.
Ethanol burns in excess oxygen to produce carbon dioxide and water.
True or False?
Ethanol can be used as both a fuel and a solvent.
True.
Ethanol is used as a fuel (for cars) and as a solvent (to dissolve substances that water cannot dissolve).
What are the two main uses of ethanol?
The two main uses of ethanol are as a solvent and as a fuel.
Alcohols belong to a homologous series with the general formula ______.
Alcohols belong to a homologous series with the general formula CnH2n+1OH.
What distinguishes complete combustion of ethanol from incomplete combustion?
Complete combustion of ethanol occurs in excess oxygen, producing only carbon dioxide and water.
Incomplete combustion would occur in limited oxygen and produce carbon monoxide or carbon (soot) as well.
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