Organic Chemistry Starting Check · G2 Science Chemistry

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A power company is choosing between piped natural gas and bioethanol made from sugarcane. Which statement about the two fuels is correct?

Natural gas, which is mainly methane, is a non-renewable energy source, and so is crude oil. Sugarcane bioethanol is renewable because the crop is regrown, and the carbon dioxide released when it burns is offset by the carbon dioxide the sugarcane took in as it grew — although the emissions from growing, processing and transporting it still count against that offset.
Natural gas is mainly carbon dioxide and, like sugarcane bioethanol, is renewable, because fresh natural gas forms underground every year at the rate it is used.
Natural gas, which is mainly methane, and crude oil are non-renewable, and sugarcane bioethanol is renewable because the crop is regrown; burning bioethanol releases no carbon dioxide at all, so nothing else about its production matters.
Natural gas, which is mainly methane, and crude oil are non-renewable, and sugarcane bioethanol is renewable because the crop is regrown; the carbon dioxide taken in as the sugarcane grows is irrelevant, and bioethanol counts as the more sustainable fuel only because it burns at a lower temperature.

A refinery runs crude oil through a fractionating column. Which statement describes crude oil and this separation correctly?

Crude oil is a mixture of hydrocarbons, so it can be separated without any chemical change; fractional distillation collects fractions that boil over different temperature ranges, and the same fractions are wanted both as fuels and as a source of chemicals.
Crude oil is a single compound, so fractional distillation is a chemical reaction that converts it into new substances, and every fraction it makes is wanted only as a fuel.
Crude oil is a mixture of hydrocarbons, but the column separates it by density, spinning the denser fractions to the bottom, and each fraction has only one possible use.
Crude oil is a mixture of hydrocarbons separated by fractional distillation into fractions with different boiling ranges, but those fractions are valuable only as a source of chemicals and are never used as fuels.

Which row describes the alkanes and their first three unbranched members correctly?

General formula CₙH₂ₙ₊₂; every carbon-to-carbon bond is a single bond, so the molecules are saturated; methane is CH₄, ethane is CH₃CH₃ and propane is CH₃CH₂CH₃; the members react in the same ways, while their melting points, boiling points and viscosity change gradually as the molecules get larger.
General formula CₙH₂ₙ₊₁; every carbon-to-carbon bond is a single bond; methane is CH₄, ethane is CH₃CH₃ and propane is CH₃CH₂CH₃; the members react in the same ways and their physical properties change gradually.
General formula CₙH₂ₙ₊₂; every carbon-to-carbon bond is a single bond; methane is CH₃CH₃, ethane is CH₄ and propane is CH₃CH₂CH₂CH₃; the members react in the same ways and their physical properties change gradually.
General formula CₙH₂ₙ₊₂; every carbon-to-carbon bond is a single bond; methane is CH₄, ethane is CH₃CH₃ and propane is CH₃CH₂CH₃; but because they belong to one series they all melt and boil at the same temperature, and each member reacts differently from the others.

Alkanes, such as methane, are described as generally unreactive. Which statement correctly describes the reactions they do undergo?

They burn in air, and in ultraviolet light they react with chlorine, a chlorine atom taking the place of a hydrogen atom in the molecule; apart from these they take part in very few reactions.
They are unreactive in every circumstance, including in a flame, which is why they can be piped safely and used as fuels.
They react readily with almost every reagent they meet, and their reaction with chlorine runs fastest when the mixture is kept in the dark.
They burn in air, and in ultraviolet light chlorine joins on to the molecule without anything leaving it, so the molecule keeps all its hydrogen atoms.

A refinery has more long-chain hydrocarbon molecules than it can sell and too few short-chain ones, and a nearby plant treats waste plastic the same way. Which statement about cracking is correct?

Cracking breaks large hydrocarbon molecules into smaller ones, producing alkenes and hydrogen alongside the shorter chains; the refinery cracks because the demand is for the smaller molecules it is short of, and cracking waste plastic turns its long molecules into short ones that can be used as fuel.
Cracking joins small hydrocarbon molecules into larger ones, which is how the refinery makes more of the short-chain molecules it is short of, and it lengthens the molecules in waste plastic so that they burn as fuel.
Cracking breaks large hydrocarbon molecules into smaller ones but produces only shorter alkanes, never alkenes or hydrogen; the refinery cracks simply to dispose of fractions nobody wants, and plastic cannot be cracked at all.
Cracking strips all the hydrogen out of large hydrocarbon molecules and leaves solid carbon, which the refinery sells in place of the short-chain fraction; waste plastic is cracked to the same solid carbon.

Ethene and propene are the C2 and C3 unbranched alkenes, and ethene is the monomer of poly(ethene). Which statement gives both structures and describes the polymer correctly?

Ethene is CH₂=CH₂ and propene is CH₂=CHCH₃. A polymer is one large molecule built from many small monomer units joined together, and different monomers give different repeat units. When ethene polymerises, the double bond in each molecule opens so the units join end to end and every atom of the monomer is kept, giving the repeat unit –CH₂–CH₂–; restoring that double bond gives CH₂=CH₂ back as the monomer.
Ethene is CH₂=CHCH₃ and propene is CH₂=CH₂. A polymer is one large molecule built from many small monomer units joined together, and different monomers give different repeat units. When ethene polymerises, the double bond opens so the units join end to end and every atom is kept, giving the repeat unit –CH₂–CH₂–; restoring the double bond gives the monomer back.
Ethene is CH₂=CH₂ and propene is CH₂=CHCH₃. A polymer is a single small molecule, and when ethene polymerises the double bonds are kept and a molecule of water is released at every join, giving the repeat unit –CH=CH–.
Ethene is CH₂=CH₂ and propene is CH₂=CHCH₃. A polymer is one large molecule built from many monomer units, but the repeat unit of poly(ethene) is –CH₂–CH₂–CH₂– because three monomer molecules join at a time, and no monomer can be worked back out from a repeat unit.

Two colourless hydrocarbon gases, P and Q, are each shaken with aqueous bromine. P turns the orange solution colourless at once; Q leaves it orange. Which statement is correct?

P is unsaturated and Q is not. The alkenes are the homologous series of unsaturated hydrocarbons with the general formula CₙH₂ₙ, so P could be an alkene such as ethene. Aqueous bromine tells the two apart because bromine adds to an unsaturated molecule, and alkenes also burn in air.
Q is unsaturated and P is not, because an unsaturated molecule already holds as much as it can and so leaves the bromine colour unchanged. The alkenes have the general formula CₙHₙ.
P is unsaturated and Q is not, and the alkenes are the unsaturated hydrocarbons with the general formula CₙH₂ₙ; but the colour goes because the bromine replaces a hydrogen atom in P, and alkenes do not burn.
P is unsaturated and Q is not, and bromine adds to P; but the alkene general formula is CₙH₂ₙ₋₂, and aqueous bromine cannot really tell saturated from unsaturated hydrocarbons because Q would decolourise it too if it were shaken long enough.

Poly(ethene) is a cheap, flexible, waterproof plastic that softens when it is heated. Which pair of everyday products is made from it?

Plastic carrier bags and clingfilm.
Saucepan handles and electrical plug casings.
Car engine blocks and bicycle frames.
Window glass and drinking glasses.

A town is deciding whether to collect its waste poly(ethene) for physical recycling instead of sending it to landfill. Which statement is correct?

Plastic that is non-biodegradable is not broken down by decay organisms, so discarded plastic stays in the ground and in waterways for a very long time and builds up. Physical recycling sorts, cleans, melts and reshapes the waste into pellets of the same plastic. A fair decision has to weigh the cost of collecting and sorting, the jobs and facilities involved, the energy used, and the emissions and raw materials the recycling avoids.
Non-biodegradable plastic rots away in landfill within a few months, so the only reason to recycle it is to create jobs in the sorting plant.
Non-biodegradable plastic builds up because decay organisms do not break it down, and physical recycling burns the waste so that its energy is recovered; the decision is purely an economic one.
Non-biodegradable plastic builds up because decay organisms do not break it down, and physical recycling melts and reshapes it into pellets of the same plastic; but since recycling is better for the environment, the cost of collecting and sorting the waste and the energy the plant uses need not be considered.

A food manufacturer passes hydrogen through a polyunsaturated vegetable oil over a catalyst to make margarine. Which statement is correct?

Polyunsaturated means that each of the oil's molecules contains more than one carbon-to-carbon double bond. Hydrogen adds across some of those double bonds, so the molecules become more saturated and the product is more solid than the oil it was made from.
Polyunsaturated means that the oil is a mixture of many different fats. Hydrogen is removed from the molecules, and that is what makes the product more solid.
Polyunsaturated means that each of the oil's molecules contains more than one carbon-to-carbon double bond, and hydrogen adds across some of them, but this leaves the molecules less saturated and makes the product runnier than the oil.
Polyunsaturated means that each of the oil's molecules contains exactly one carbon-to-carbon double bond; hydrogen adds across it, so the molecules become more saturated and the product is more solid.

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Which statement correctly describes polymers and a prescribed use of poly(ethene)?

Polymers are large molecules built from many monomer units; different monomers give different repeating units, and poly(ethene) is used for items such as plastic bags and clingfilm.
Polymers are single unjoined monomers, and poly(ethene) is used only as a gas.
Every polymer has the same repeating unit, regardless of its monomer, and poly(ethene) is a metal coating.
A polymer must contain only one molecule of monomer, and bags cannot be made from poly(ethene).

Which row pairs each unbranched alkane with the correct structure?

methane CH₄; ethane CH₃CH₃; propane CH₃CH₂CH₃
methane CH₃CH₃; ethane CH₄; propane CH₃CH₂CH₃
methane CH₄; ethane CH₃CH₂CH₃; propane CH₃CH₂CH₂CH₃
methane CH₄; ethane CH₃CH₃; propane CH₃CH₂CH₂CH₃

Which row pairs each unbranched alkene with the correct structure?

ethene CH₂=CH₂; propene CH₂=CHCH₃
ethene CH₂=CHCH₃; propene CH₂=CH₂
ethene CH₂=CH₂; propene CH₂=CHCH₂CH₃
ethene CH₃CH=CH₂; propene CH₂=CHCH₂CH₃

Waste plastic can be recycled chemically by cracking it. What does the cracking step do to the plastic?

It breaks the long molecules of the plastic into shorter molecules that can be used as fuel.
It joins the long molecules of the plastic into even longer ones, which are then sold as fuel.
It strips all the hydrogen out of the long molecules and leaves solid carbon behind as the fuel.
It rearranges the atoms inside each long molecule without breaking it, so every molecule keeps its original length.

A monomer with the structure CH₂=CHCH₃ is used to make an addition polymer. Which repeat unit does it give?

[–CH₂–CH(CH₃)–]ₙ
[–CH₂–CH₂–]ₙ
[–CH₂=CHCH₃–]ₙ
[–CH₂–CH(CH₃)–O–]ₙ

What happens in mechanical recycling of a thermoplastic?

It is sorted, cleaned and remelted without deliberately breaking every polymer chain
It is completely hydrolysed back to its monomers
It is burned to carbon dioxide and called the same polymer
Every covalent bond is deliberately broken to recover isolated atoms

Which statement about bioethanol is appropriately cautious?

It is non-renewable because every fuel must come from crude oil
It is renewable, but farming, processing and transport can add life-cycle emissions
It is automatically carbon neutral under all production methods
It cannot release carbon dioxide when burned

Which molecular formula belongs to an open-chain three-carbon alkene with one C=C bond?

C₃H₄Cl₂
C₃H₇OH
C₃H₆
C₃H₈

What happens when propene is shaken with bromine water?

A squeaky pop is produced
The bromine water stays orange because propene is saturated
A white precipitate forms because propene contains chloride ions
The orange bromine water is decolourised

Why can crude oil be separated by fractional distillation?

Its hydrocarbons have different boiling ranges
Each fraction has a different proton number for carbon
Crude oil is one compound that decomposes into elements
Its hydrocarbons all boil at exactly the same temperature

Which is a balanced reason to recycle plastics?

It can conserve raw materials and reduce waste, but collection, sorting, energy and product quality still matter
It guarantees unlimited material with no economic or environmental cost
It is always worse than disposal under every local condition
It is worthwhile only if the recycled plastic can be sold, regardless of effects on people or the environment

Why are long-chain fractions often cracked?

To make their molecules larger and less volatile
To make smaller, more useful hydrocarbons including alkenes
To turn every carbon atom into crude oil
To separate immiscible water from oil

Why can disposal of non-biodegradable plastic cause persistent pollution?

It always evaporates immediately into harmless oxygen
Its carbon atoms cease to exist after disposal
It is rapidly digested by every microorganism
It can accumulate because microorganisms do not readily break it down

Which feature identifies an addition polymer?

A small molecule is eliminated every time two alkene monomers join
Its carbon backbone can arise by opening alkene C=C bonds without a small-molecule product
Every repeat unit contains an ester linkage and releases water
Its monomer must contain both –NH₂ and –COOH groups

Why do boiling points generally rise from ethane to propane to butane within the alkane homologous series?

Larger molecules have stronger intermolecular attractions, so more energy is needed to separate them.
Covalent bonds inside each molecule become ionic as the chain length grows.
Smaller molecules have the strongest intermolecular forces because they move faster.
Boiling breaks every carbon-carbon bond, so longer chains need fewer bonds broken.

What does polyunsaturated mean when describing a food oil molecule?

It contains more than one carbon-carbon double bond in its hydrocarbon chains.
It contains many separate water molecules.
Every carbon-carbon bond is single but the oil contains many molecules.
It contains one double bond in the entire food sample.

What does saturated mean for an alkane?

It has no carbon-carbon double or triple bonds and has the maximum hydrogen count for its acyclic carbon skeleton.
It contains as much liquid hydrocarbon as a container can hold.
It contains at least one carbon-carbon double bond.
It cannot contain any hydrogen atoms.

Why is a newly discovered crude-oil reserve still classified as non-renewable?

Its geological formation takes far longer than the rate at which people extract and use it.
It cannot release energy when burned.
Every non-renewable resource must already have been completely exhausted.
It contains no carbon and therefore cannot enter any carbon cycle.

What chemical change helps convert liquid unsaturated vegetable oil into more solid margarine?

Hydrogen adds across some C=C bonds, decreasing unsaturation and increasing the melting range.
Oxygen removes every carbon atom from the oil.
Water hydrolyses all molecules into methane gas.
Hydrogen creates extra C=C bonds and increases unsaturation.

Methane and chlorine are exposed to ultraviolet light at room temperature. What is the first substitution product pair?

chloromethane and hydrogen chloride
methanol and chloric acid
ethene and hydrogen
carbon dioxide and water

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Which statement correctly identifies the two prescribed non-renewable energy sources?

Natural gas, which is mainly methane, and crude oil are non-renewable energy sources.
Natural gas, which is mainly oxygen, and sugarcane are both non-renewable.
Crude oil and bioethanol are both renewable because each can be burned.
Methane is a renewable crude-oil fraction whenever it is supplied through a pipe.

Which row correctly describes the unbranched C1–C3 alkane homologous series?

Saturated, CₙH₂ₙ₊₂; methane CH₄, ethane CH₃CH₃, propane CH₃CH₂CH₃; similar chemistry with gradual physical-property changes as molecular size rises.
Unsaturated, CₙH₂ₙ; methane CH₂, ethane CH₂=CH₂, propane CH₂=CHCH₃; identical physical properties.
Saturated, CₙH₂ₙ₋₂; methane CH₄, ethane C₂H₄, propane C₃H₆; unrelated chemical properties.
No general formula; methane CH₃CH₃, ethane CH₄, propane CH₃OH; boiling point must be identical.

Which statement correctly connects the named C2–C3 alkenes with food-product unsaturation?

Ethene is CH₂=CH₂ and propene is CH₂=CHCH₃. Polyunsaturated food molecules contain more than one C=C bond, and adding hydrogen across some C=C bonds makes vegetable oil more saturated and solid for margarine.
Ethene is CH₃CH₃ and propene is CH₃CH₂CH₃; polyunsaturated means no C=C bonds, and hydrogenation removes hydrogen.
Ethene is CH₄ and propene is C₂H₆; polyunsaturated means many –OH groups, and margarine forms by adding oxygen.
Ethene and propene have only C–C single bonds; hydrogenation creates extra C=C bonds and keeps the oil equally unsaturated.

A learner calls piped natural gas renewable and says it is mainly hydrogen. Which correction is accurate?

Natural gas is mainly methane and, like crude oil, is a non-renewable energy source.
Natural gas is mainly hydrogen but becomes non-renewable only after combustion.
Natural gas is renewable because methane contains hydrogen atoms.
Crude oil is renewable, but natural gas is not, because only crude oil can be distilled.

What is crude oil?

A compound with one fixed boiling point
A mixture of hydrocarbons
A single long-chain alkane
An aqueous solution of carbon

Which statement about bioethanol is appropriately cautious?

It is non-renewable because every fuel must come from crude oil
It is renewable, but farming, processing and transport can add life-cycle emissions
It is automatically carbon neutral under all production methods
It cannot release carbon dioxide when burned

A learner writes propane as CH₂=CHCH₃ and calls alkanes CₙH₂ₙ. Which replacement is fully correct?

Alkanes are saturated CₙH₂ₙ₊₂ homologues; methane is CH₄, ethane is CH₃CH₃ and propane is CH₃CH₂CH₃, with similar chemistry and gradual physical-property changes.
Alkanes are unsaturated CₙH₂ₙ homologues; propane is CH₂=CHCH₃ and every member has the same boiling point.
Alkanes are saturated but have no general formula; methane, ethane and propane all have formula CH₄.
Propane is CH₃OH, while methane and ethane are unrelated compounds with different chemical properties.

Why is ultraviolet light used when methane reacts with chlorine?

It acts as a reagent that becomes part of chloromethane
It provides the carbon atoms needed to make chloromethane
It supplies energy to start the substitution reaction
It makes methane undergo addition at a C=C bond

Which molecular formula belongs to an open-chain three-carbon alkene with one C=C bond?

C₃H₄Cl₂
C₃H₇OH
C₃H₆
C₃H₈

Which correction accurately links propene, polyunsaturated oil and margarine manufacture?

Propene is CH₂=CHCH₃. Polyunsaturated oil molecules contain more than one C=C bond; adding hydrogen across C=C bonds increases saturation and can turn the oil into a more solid margarine product.
Propene is CH₃CH₂CH₃. Polyunsaturated means no double bonds, and margarine forms by removing hydrogen.
Propene is CH₂=CH₂. Polyunsaturated means many polymers, and hydrogenation adds bromine to the oil.
Propene contains no double bond, and hydrogenation makes the vegetable oil more unsaturated and more liquid.

Which change is cracking?

An alcohol reacts with oxygen to form an acid
Several alkene molecules join to make one long-chain molecule
A long-chain alkane forms a shorter alkane and an alkene
An alkene adds hydrogen to form one alkane

What happens when propene is shaken with bromine water?

A squeaky pop is produced
The bromine water stays orange because propene is saturated
A white precipitate forms because propene contains chloride ions
The orange bromine water is decolourised

Which correction fixes the claim that a polymer is one small molecule and that poly(ethene) has no everyday use?

A polymer is a large molecule built from many monomer units; different monomers can make different polymers, and poly(ethene) is used in products such as plastic bags and clingfilm.
A polymer is a single monomer that has been melted, and poly(ethene) is used only as fuel.
All polymers contain the same unit and must have the same uses, including metal extraction.
Poly(ethene) contains no repeating units, so bags and clingfilm must be made from crude oil itself.

Which repeat unit represents poly(propene)?

[–CH=CH–]ₙ
[–CH₂–CH₂–]ₙ
[–CH(CH₃)–CH(CH₃)–]ₙ
[–CH₂–CH(CH₃)–]ₙ

Which statement is a balanced evaluation of plastic incineration?

It can recover energy but may emit carbon dioxide and requires pollution controls
It removes all environmental impacts and emits only oxygen
It always recycles polymer chains unchanged
It recovers no energy and can have no emissions under any conditions

What is the prescribed physical-recycling example for waste poly(ethene)?

Leave it in the environment to biodegrade rapidly
Oxidise it completely to carbon dioxide and water
Melt cleaned small pieces and form pellets
Crack it into shorter fuel molecules

Which process turns waste long-chain hydrocarbons into shorter chemical feedstocks?

Simple washing with cold water
Fractional filtration through paper
Addition polymerisation
Cracking

Which summary correctly connects the G2 fuel-source and sustainability ideas?

Natural gas, mainly methane, and crude oil are non-renewable energy sources. Crude oil is a hydrocarbon mixture separated into fractions by boiling range. Sugarcane bioethanol is renewable, and carbon dioxide taken in during growth can partly offset that released in burning, although its full life cycle still matters.
Natural gas is mainly carbon dioxide and is renewable; crude oil is one pure compound; burning bioethanol releases no carbon dioxide.
Crude oil is renewable because fractions can be distilled repeatedly, while bioethanol is non-renewable because plants absorb carbon dioxide.
Fractional distillation chemically converts natural gas into crude-oil fractions, and plant growth has no relevance to a biofuel carbon comparison.

Which statement correctly describes the G2 alkane homologous series?

Its saturated members follow CₙH₂ₙ₊₂, have similar chemical properties and show gradual physical-property changes as molecular size rises. The unbranched C1–C3 members are methane CH₄, ethane CH₃CH₃ and propane CH₃CH₂CH₃; alkanes undergo combustion and chlorine substitution under ultraviolet light.
Its unsaturated members follow CₙH₂ₙ, all have identical boiling points, and methane rapidly decolourises bromine water in the dark.
Methane is CH₃CH₃, ethane is CH₄ and propane is CH₂=CHCH₃; chlorine substitution requires no initiating condition.
A homologous series has unrelated formulae and chemical properties, and alkane viscosity must fall as molecules become larger.

Which summary correctly links alkene structures, reactions and unsaturation in food molecules?

The unbranched alkenes here have one C=C bond and follow CₙH₂ₙ; ethene is CH₂=CH₂ and propene is CH₂=CHCH₃. Cracking larger hydrocarbons can make smaller molecules including alkenes and hydrogen. Alkenes undergo combustion; their C=C bonds undergo bromine addition and hydrogenation. Polyunsaturated food molecules contain more than one C=C bond, and hydrogenation makes vegetable oils more saturated and solid for margarine.
Alkenes are saturated CₙH₂ₙ₊₂ hydrocarbons; ethene is CH₃CH₃. Cracking only makes larger molecules, and hydrogenation creates extra C=C bonds.
Propene is CH₃CH₂CH₃, bromine water stays orange with every alkene, and polyunsaturated means that a food contains several separate polymer chains.
Hydrogenation removes hydrogen from a saturated oil to make a liquid, while bromine reacts by removing carbon atoms from an alkene.

Ethene has the formula CH₂=CH₂. Which statement correctly describes polymers, the repeat unit formed from this monomer, and uses of poly(ethene)?

Polymers are large molecules built from repeating monomer units, and different monomers give different repeat units. Ethene forms poly(ethene) when its C=C bond opens to give [–CH₂–CH₂–]ₙ; reversing that change recovers CH₂=CH₂ as the monomer. Poly(ethene) is used for products such as plastic bags and clingfilm.
Every polymer is a small molecule made from one atom, and poly(ethene) forms by retaining C=C bonds and releasing water.
The repeat unit [–CH₂–CH₂–]ₙ comes from methane CH₄, and different polymers must all contain the same repeating unit.
Poly(ethene) is used only as a gaseous fuel, and its monomer is found by adding an –OH group to the repeat unit.

Which evaluation correctly distinguishes the G2 plastic-waste and recycling ideas?

Non-biodegradable plastics can persist and accumulate. Physical recycling can sort, clean, melt and pellet poly(ethene), while chemical recycling can crack plastic waste into shorter fuel or feedstock molecules. A balanced decision also considers collection and sorting, jobs and access, costs and product value, energy use, emissions and avoided raw materials.
Non-biodegradable plastics disappear rapidly in soil; remelting always breaks every polymer into monomers; cracking changes only the shape of the plastic.
Physical and chemical recycling are identical, and a recycling decision needs only the selling price of the final pellet.
Burning mixed plastic without controls preserves its polymer chains and has no environmental cost if it produces useful heat.

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Organic Chemistry Starting Check · G2 Science Chemistry

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