modules 4 Flashcards
What is meant by the term structural isomers?
(compounds or molecules having the) same molecular
formula but different structural formulae
A molecule of an alkane has 24 carbon atoms.State the empirical formulae of this alkane.
C12H25
Construct an equation for the complete combustion of octane C8H18.
C8H18 + 12½O2 ⎯→ 8CO 2 + 9H 2O
Alkanes in crude oil can be used to manufacture ethene. Two stages are required.
Name the two stages.
Fractional distillation AND cracking
write an equation for the preparation of ethene from an alkane.
C10H22 ⎯→ C8H18 + C2H4
Give the formula of an acidic toxic gas that could form during combustion of polymer
HCl
State two properties that made CFCs suitable for use as an aerosol.
Low reactivity OR will not burn/non-flammable
Volatile OR low boiling point
non-poisonous OR non-toxic
Explain the following statements, using equations where appropriate.
• Life on Earth benefits from the presence of an ozone layer.
• The concentration of ozone is maintained in the ozone layer.
• Compound G produces radicals which catalyse the breakdown of ozone.
Benefit of ozone layer to life (1 mark) Ozone absorbs UV (radiation) UV at Earth’s surface is reduced Maintenance of O3 concentration (1 mark) O3 O2 + O Production of radicals from G (1 mark) CF2Cl2 ⎯→ C l + CF2Cl Breakdown of O3 (2 marks) Cl + O3 ⎯→ C lO + O2 ClO + O ⎯→ Cl + O2 OR ClO + O3 ⎯→ Cl + 2O2
What happens to molecules when infrared radiation is absorbed?
bond vibrates (more)
OR bond bends (more)
OR bond stretches (more)
What is meant by the term homologous series?
(series of compounds with the) same functional group
OR same/similar chemical properties
OR same/similar chemical reactions
each successive/subsequent member differing by CH2
raw a labelled diagram to show the formation of the π-bond.
First mark
diagram on left with p-orbitals labelled
OR unlabelled diagram AND the statement: (sideways)
overlap of p orbitals
Second mark
(labelled) diagram on right showing π-bond
What does a curly arrow represent in mechanisms?
Movement of an electron pair
What is meant by the term nucleophile?
Electron pair donor
Outline the mechanism for the monochlorination of 1-bromopropane.In your mechanism, you can show the formula of 1-bromopropane as C3H7Br.Include the names of the three stages in this mechanism, state the essential conditions and all termination steps.
(Initiation) Cl2 ⎯→ 2C l AND UV (Propagation) C3H7Br + Cl ⎯→ C 3H6Br + HCl C3H6Br + Cl2 ⎯→ C 3H6BrCl + Cl (Termination) Two from the three termination equations below 2Cl ⎯→ Cl2 C3H6Br + Cl ⎯→ C 3H6BrCl 2C3H6Br ⎯→ C 6H12Br2 names of steps initiation, propagation and termination linked to one correct equation for each step in this mechanism
Radical substitution produces a mixture of organic products.Suggest two reasons why.
further substitution OR produces different termination products OR More than one termination step substitution at different positions along chain
State the general formula for these cycloalkanes.
CnH2n
Explain the increase in boiling points of the cycloalkanes shown in the table.
More carbons (in ring) OR more (surface area of) contact AND more van der Waals forces OR stronger van der Waals forces More energy needed to break the intermolecular forces
The C–C–C bond angles in cyclohexane are 109.5°.
State and explain the shape around each carbon atom in cyclohexane.
tetrahedral
four bonding pairs repel OR four bonds repel
Suggest one advantage of adding cyclohexane to hexane in petrol.
Cyclohexane will burn more efficiently
Explain what is meant by the term stereoisomers.
(Compounds with the) same structural formula but a different arrangement (of atoms) in space
In the presence of ultraviolet radiation, cyclohexane reacts with bromine.
A mixture of cyclic organic compounds is formed, including C6H11Br
Complete the table below to show the mechanism of the reaction between bromine and cyclohexane to form C6H11Br.
Include all possible termination steps in your answer.
Initiation Br2 2Br• Propagation C6H12 + Br• C6H11• + HBr C6H11• + Br2 C6H11Br + Br• Termination C6H11• + Br• C6H11Br C6H11 • + C6H11 • C12H22 Br• + Br• Br2
Explain why the initiation step is an example of homolytic fission
The breaking of a (Br-Br) bond AND forms (two) radicals
OR
the breaking of a (Br-Br) bond AND one electron (from the
bond pair) goes to each atom/bromine
Suggest how the methoxide ion can act as a nucleophile.
It is an electron pair donor OR can donate a lone pair
Explain how sodium hydrogencarbonate removes hydrogen chloride.
Sodium hydrogencarbonate neutralises HCl
The greenhouse effect of carbon dioxide in the atmosphere is dependent on two factors.
What are these two factors?
abundance (in atmosphere) OR amount (in atmosphere)
OR (atmospheric) concentration OR percentage (in air)
OR
ability to absorb infrared/IR (radiation)
OR
residence time
reaction in catalytic converters?
2NO + 2CO 2CO2 + N2
Suggest why 2-methylbut-2-ene is less soluble in water than either of the structural isomers formed.
Does not contain OH group(s)
OR does not contain hydroxyl group(s)
OR is not an alcohol
Does not form hydrogen bonds with water
Describe the oxidation reactions of propan-1-ol when using a suitable oxidising agent.Indicate how the use of different reaction conditions can control which organic product forms.
Include reagents, observations and equations in your answer.
In your equations, use structural formulae and use [O] to represent the oxidising agent.
Reagents: Acid/H+
and (potassium or sodium) dichromate/Cr2O7
2-
seen once
Observations: Orange to Green OR Orange to Blue
Distillation / Distil produces aldehyde/CH3CH2CHO:
CH3CH2CH2OH + [O] CH3CH2CHO + H2O
Reflux (of propan-1-ol) produces carboxylic acid/CH3CH2COOH
CH3CH2CH2OH + 2[O] CH3CH2COOH + H2O
The branched-chain isomer B has a lower boiling point than the straight chain alkane A.
Explain why.
B has less surface (area of) contact OR ORA
AND
B has fewer van der Waals’ forces OR B has weaker
van der Waals’ forces OR ORA
So less energy needed to break the intermolecular forces
in B OR ORA
Why does the petroleum industry process straight-chain alkanes into cyclic hydrocarbons?
Cyclic hydrocarbons promote efficient combustion
The mechanism of the reaction involves three steps, one of which is called termination.Describe the mechanism of the reaction that forms iodomethane and hydrogen bromide.Include in your answer:
• the name of the mechanism
• the names for the othertwo steps of the mechanism
• equations for these two steps of the mechanism
• the type of bond fission• one equation for a termination step.
Your answer should link the named steps to the relevant equations.
(free) radical substitution (Initiation step) IBr Br + I homolytic fission (Propagation steps) Br + CH4 HBr + CH3 CH3 + IBr CH3I + Br (Termination steps) I + CH3 CH3I OR Br + Br Br2 OR I + I I2 OR Br + CH3 CH3Br OR CH3 + CH3 C2H6 OR I + Br IBr QWC propagation linked to correct equations Br + CH4 HBr + CH3 CH3 + IBr CH3I + Br AND initiation linked to correct equation IBr Br + I
Describe and explain, using equations, how the concentration of ozone in the stratosphere is maintained.
O3 O2 + O AND O + O2 O3
rate of ozone decomposition (almost) equals rate of ozone
formation
n the stratosphere,NOcatalyses the breakdown of ozone.
Write two equations to show how NO catalyses this breakdown.
NO + O3 NO2 + O2
NO2 + O NO + O2
Give an everyday use for infrared spectroscopy.
Monitor air pollution OR breathalysers
CFCs were once used as propellants but have now been replaced by biodegradable alternatives.
State one type of a biodegradable alternative.
HCFCs OR hydrocarbons OR HFCs
Explain why this manufacture of poly(propenenitrile) has a 100% atom economy.
All the reactants are made into the desired product
OR
it is an addition reaction
Explain why crude oil can be separated into different fractions.
Because hydrocarbons have different boiling points
Many scientists believe that we should use more fuels such as biodiesel or bio-ethanol rather than petrol and diesel.
Suggest one reason why these scientists take this view.
Bio-fuels produce less carbon dioxide (overall) OR petrol
or diesel produce more carbon dioxide (overall)
Bio-fuels are renewable OR petrol and diesel are nonrenewable
Allows crude oil to be used to make other products OR
petrochemicals (rather than petrol) OR Save crude oil OR
no risk of large scale pollution from exploitation of crude oil
When C12H26 is cracked, a variety of alkanes and alkenes are formed with different chain lengths.Explain why a variety of alkanes and alkenes are formed with different chain lengths.
Idea that carbon–carbon bonds can break anywhere
Draw and explain the shape of an ethene molecule.State the H–C–H bond angle in ethene.
120o
Three areas of electron density repel each other
correct drawn shape
When burnt in excess oxygen, ethene completely combusts.Write the equation for the complete combustion of ethene.
C2H4 + 3O2 2CO2 + 2H2O
Ethane-1,2-diol is much less volatile than ethanol.
Suggest why.
Ethane-1,2-diol has more OH groups (than ethanol)
Stronger hydrogen bonding (between ethane-1,2-diol
molecules)
State two modern analytical techniques that scientists can use to monitor environmental pollution.
IR (spectroscopy) Mass spectrometry UV (spectroscopy) NMR GC
Explain why it is important to establish international cooperation to reduce pollution levels.
Idea that pollution travels (across country) borders
OR idea that all countries contribute towards pollution
OR Cooperation means that scientists can share ideas
OR scientists can warn governments of risk
OR world-wide legislation can be introduced
OR allows monitoring of pollution in different countries
OR richer countries can help poorer countries introduce
pollution controls
OR One country cannot control pollution unless all
countries do
Explain how atmospheric methane molecules can contribute to global warming.
Absorbs IR radiation
Bonds vibrate
Give two reasons why the termination reactions results in many organic products of the reaction between bromine and ethane.
More than one C–H bond can be substituted OR multisubstitution
can occur OR more than one substitution can
happen
Lots of termination steps
termination steps can give products that will also react with
(bromine) radicals
State and explain the difference in the rates of hydrolysis of 1-bromopentane and 1-chloropentane.
1-bromopentane reacts faster OR 1-chloropentane reacts
slower
C–Cl stronger bond (than C–Br bond)
OR C–Cl shorter bond (than C–Br bond)
OR C–Cl bond is harder to break
OR needs more energy to break C–Cl bond
OR bond enthalpy of C–Cl greater (than C–Br bond)
1-Iodobutane also reacts with methoxide ions.Indicate, by placing a tick in one of the boxes, how the use of 1-iodobutane would affect the rate of reaction compared with that of 1-bromobutane. 1-Iodobutane does not change the rate 1-Iodobutane increases the rate 1-Iodobutane decreases the rate Explain your answer.
1-Iodobutane increases the rate AND C—I bonds are weaker (than C—Br) OR C—I bond has a lower bond enthalpy OR C—I bond needs a smaller amount of energy to break OR C—I bond is easier to break
Explain why compound A is both saturated and a hydrocarbon.
(a compound) with no double bond (or triple bond)
containing hydrogen and carbon only
Explain why the petroleum industry processes straight chain alkanes into cyclic hydrocarbons.
Cyclic hydrocarbons have more efficient combustion
What is meant by the term functional group?
Group of atoms (in a molecule or compound) that is
responsible for the reactions
What is meant by the term radical ?
has an unpaired electron
Explain why the overall process to make sulfuric acid has an atom economy of 100%.
Only one (desired) product formed
State the three-dimensional shape of a CF2Cl2 molecule and the F–C–Cl bond angle.
Shape – tetrahedral
Bond angle 109.5o
State one other reason why CF2Cl2 was developed for use as an aerosol.
Volatile OR non-toxic OR non-flammable OR easily
vaporised
Suggest why CF2Cl2 does not hydrolyse in water.
(C–F or C–Cl ) bonds need a large amount of energy to
break
Explain, with the aid of equations, how the presence of CFCs in the upper atmosphere leads to ozone depletion.
CF2Cl2 CF2Cl + Cl AND ANY TWO FROM Cl catalyses the decomposition of ozone Cl + O3 ClO + O2 ClO + O Cl + O2
Why are scientists concerned about ozone depletion?
Because (more) UV will reach the Earth’s surface and risk
of (skin) cancer increased/risk of cataracts/crop mutation
increased
nternational agreements have reduced the use of CFCs. However the concentration of atmospheric CFCs has hardly changed. Suggest two reasons why.
Ideas related to uses
CFCs are still entering the atmosphere (from disused
items) OR CFCs are still used (for some purposes and by
some countries)
Ideas relating to lifetime within the atmosphere
CFCs have a long lifetime in the atmosphere OR it takes a
long time for CFCs to reach upper atmosphere OR CFCs
are inert
what is the general formula of a member of the alcohol homologous series?
CnH2n + 1OH
At room temperature and pressure, the first four members of the alcohol homologous series are liquids whereas the first four members of the alkanes homologous series are gases.
Explain this difference.
Alkanes have van der Waals’ intermolecular forces
Alcohols have hydrogen bonds (and van der Waals’ forces)
Hydrogen bonds are stronger (than van der Waals’ forces)
OR ORA
Methylpropan-1-ol and butan-1-ol are structural isomers. Methylpropan-1-ol has a lower boiling point than butan-1-ol.
Suggest why.
Methylpropan-1-ol has weaker van der Waals’ forces (than
butan-1-ol) OR ORA
Methylpropan-1-ol has less surface contact (than butan-1-ol)
OR ORA
OR
Methylpropan-1-ol has more branching (than butan-1-ol) OR
ORA
Write equations for the complete and incomplete combustion of methanol.
CH3OH + 1½O2 CO2 + 2H2O
CH3OH + O2 CO + 2H2O
Suggest what conditions might lead to incomplete combustion of methanol.
insufficient supply of oxygen
OR limited amount of air
OR poorly ventilated
State another large-scale use of methanol.
Feedstock (in manufacture of organic compounds)
OR manufacture of biodiesel
OR manufacture of esters.
Write an equation for the formation of NO2 from nitrogen monoxide and oxygen.
2NO + O2 2NO2
Describe, with the aid of equations, how nitrogen monoxide catalyses ozone depletion in the stratosphere.
NO is not consumed
OR overall reaction is O3 + O 2O2
NO + O3 NO2 + O2
NO2 + O NO + O2
Outline the use of infrared spectroscopy in identifying air pollutants such as NOx.
To identify the functional groups (in pollutants)
OR to identify the bonds (in pollutants)
Match spectrum to known pollutants
OR each pollutant will have a different spectrum
Idea that you can measure the concentration or abundance of
pollutant
Suggest two reasons why it is a good idea to find uses for the carbon dioxide produced.
Less waste products OR better sustainability OR get 100% atom economy (Stops) greenhouse gas emitted OR (stops) gas that (may) cause global warming
Some scientists believe that it is more important to have a high percentage yield in fermentation but others think that a high atom economy is more important.Is it more important to have high percentage yield or a high atom economy in fermentation?
Explain your answer.
High percentage yield with a simple reason
e.g. because the aim is to manufacture ethanol;
to reduce waste; increases sustainability
BUT
High percentage yield because there is very efficient
conversion from reactant to product
OR to reduce the waste of starting materials
OR
High atom economy with a simple reason
e.g. because it is cheaper or makes less harmful products;
to reduces waste; increases sustainability
BUT
High atom economy to reduce the amount of waste products
OR less by products
OR more desired product
Explain why some molecules show E/Z isomerism.
Non rotating (carbon–carbon) double bond Each carbon atom of the double bond attached to (two) different groups/atoms
Suggest why poly(ethenol) dissolves in water.
Poly(ethenol) has (many) O–H group(s)
Poly(ethenol) forms hydrogen bonds with water
One way of disposing of poly(chloroethene) is incineration. This process can cause environmental damage. Incineration produces a mixture of carbon dioxide, carbon monoxide and hydrogen chloride. Carbon dioxide can cause climate change because it is a greenhouse gas.
• Describe examples of environmental damage that may result from carbon monoxide and hydrogen chloride.
• Outline the methods developed by chemists to reduce environmental damage caused by incineration.
CO is a poisonous gas
HCl is acidic/forms acid rain OR corrosive
OR HCl will react with metalwork
OR HCl will react with marble/limestone buildings
ANY TWO METHODS FROM:
Method 1 Remove HCl by reacting with a base
OR remove HCl by use of a gas scrubber
Method 2 Develop ways of ensuring all CO is oxidised to CO2
OR ensure complete combustion to avoid making CO
Method 3 Remove CO2 by CCS
Method 4 (Use methods to remove the need for incineration
such as) separation AND recycling of the plastics/polymers
Method 5 (Use methods to remove the need for incineration
such as) developing biodegradable/compostable
plastics/polymers
Explain why it is important to establish international cooperation to reduce the pollution levels of waste plastics.
Idea that all countries contribute towards pollution
Idea that atmospheric pollution (from incineration travels)
across borders
OR waste plastics travel across borders
/ waste plastics travel across the sea
Cooperation means that scientists can share ideas
OR scientists can warn governments of risk
OR world-wide legislation can be introduced
OR allows monitoring of pollution in different countries
OR richer countries can help poorer countries introduce
pollution controls
One country cannot control pollution unless all countries do
Fractional distillation is used to separate useful hydrocarbons found in crude oil.Explain, in terms of intermolecular forces, how fractional distillation works.
(The hydrocarbons have) different boiling points
The larger the molecules the stronger the van der Waals’
forces
Deduce the general formula of a cycloalkane.
CnH2n
Explain why cyclohexene is described as unsaturated and as a hydrocarbon.
Unsaturated: Contains (at least one) carbon–carbon
double bond OR C=C OR multiple carbon–carbon bond
hydrocarbon: Contains hydrogen and carbon only
The reaction between chlorine and cyclohexane is an example of radical substitution.
State one problem of using this reaction to prepare a sample of chlorocyclohexane.
More than one hydrogen atom is substituted
OR ‘multisubstitution’ (by chlorine)
OR further substitution occurs
Explain the bonding in a C=C double bond. Use the orbital overlap model.
(Sideways) overlap of p orbitals
Forming a π/pi bond
Suggest why the average bond enthalpy of a C=C bond is not twice the bond enthalpy of a C–C bond.
π bond is weaker (than the σ bond)
OR σ bond is stronger (than the π bond)
Describe and explain the factors that affect the rate of hydrolysis of halogenoalkanes. Include ideas about • the halogen in the halogenoalkanes
• the groups attached to the carbon of the carbon–halogen bond (the type of halogenoalkane)
• the temperature of the hydrolysis.In your answer you should link the evidence with your explanation.
Any correct comparison of rate OR reaction time between at
least TWO of chloroalkane, bromoalkane and iodoalkane
Bond strength OR bond enthalpy/bond energy mentioned
anywhere as a factor (even if reasoning is incorrect)
Any correct comparison of
bond strength
OR bond enthalpy/energy
OR bond length
OR ease of breaking
of at least TWO of C–Cl, C–Br and C–I
Any correct comparison of rate or reaction time between at
least TWO of the bromoalkanes
A sensible comparison of
bond strength
OR bond enthalpy/energy
OR bond length
OR ease of breaking
of the C–Br bond in at least TWO of the bromoalkanes
Effect of temperature (2 marks)
QWC – Use of 50 ºC and 60 ºC using information in the table
to show that rate increases with temperature
At higher temperature, particles have more energy
OR At higher temperature, particles move faster
The combustion of waste polymers can be used for energy production.What problem is caused by disposing of PTFE and PVC in this way?
(PVC) produces hydrogen chloride OR produces acidic gases OR (PVC) produces phosgene OR produces toxic gases OR (PVC) produces dioxins
What evidence is there in the spectrum that the pollutant may be a hydrocarbon rather than an alcohol or a carbonyl compound?
No absorption between 1640 and 1750 cm–1
AND
no (broad) absorption between 3200
and 3550 cm–1
Suggest why biodiesel is not completely carbon-neutral.
(Energy needed) for processing biofuel makes
carbon dioxide
Suggest disadvantages or advantages, other than being carbon-neutral, of using more biofuels.
Fossil fuels are finite resources OR biofuels are renewable Allows fossil fuels to be used as a feedstock for organic compounds Less food crops may be grown OR Land not used to grow food crops (rain) forests have to be cut down to provide land OR deforestation Shortage of fertile soils OR reduces fertility of soils No risk of large scale pollution from exploitation of fossil fuels
Explain why the boiling points increase down the alkane homologous series.
More surface contact OR bigger molecules
More van der Waals’ forces
Both NO and CO are atmospheric pollutants. For each pollutant, describe one environmental problem.
NO for photochemical smog OR low level ozone
CO is toxic
Describe the benefits and disadvantages of changing from diesel to biodiesel.
Save crude oil OR no risk of large scale pollution from
exploitation of crude oil
Biodiesel is renewable OR diesel is non-renewable
Use of biodiesel is (more) carbon-neutral OR plants take up
the carbon dioxide released during combustion
and one disadvantage
Land not used to grow food crops OR (rain)forests have to
be cut down to provide land OR food prices may rise
because less is grown
Outline two ways in which waste polymers can be processed to reduce their environmental impact.
Incineration to produce energy OR combustion to produce
energy
Sorting and recycling OR sorting and remoulding
Cracked (to give monomers) OR as an organic feedstock
