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(Chem Unit 1) 6/13,1/13,6/12,1/12,6/11,1/11,6/10,1/10 > Alkanes > Flashcards

Alkanes Flashcards

1
Q

State the meaning of the term structural isomers.

A

(Compounds with the) same molecular formulaBut different structural formula

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2
Q

But-1-ene (C4H8) burns in a limited supply of air to produce a solid and water only. Write an equation for this reaction.

A

C4H8 + 2O2 ->4C + 4H2O

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3
Q

State 2 hazards associated with the solid product produced above

A

*Exacerbates asthma / breathing problems / damages lungs *smog / smoke global dimming

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4
Q

In cars fitted with catalytic converters, unburned octane reacts with nitrogen monoxide to form carbon dioxide, water and nitrogen only.Write an equation for this reaction

A

C8H18+25NO-> 8CO2 +12.5N2 +9H2O

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5
Q

Identify a catalyst used in a catalytic converter.

A

Ir / iridiumORPt / platinumORPd / palladiumORRh / rhodium

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6
Q

State a process used to separate an alkane from a mixture of alkanes.

A

Fractional distillation GLC gas liquid chromatography

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7
Q

The following table shows the boiling points of some straight-chain alkanes. Boiling point / oCCH4 –162C2H6 –88C3H8 -42C4H10 -1C5H12 36Both C3H8 and C4H10 can be liquefied and used as fuels for camping stoves. Suggest, with a reason, which of these two fuels is liquefied more easily.

A

C4H10Because it has a higher bp / has stronger IMF / larger molecule / longer chain / larger surface (area)

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8
Q

Write an equation for the complete combustion of C4H10

A

C4H10 + 6 1⁄2 O2 →4CO2 +5H2O

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9
Q

Explain why the complete combustion of C4H10 may contribute to environmental problems.

A

CO2 or H2O evolved is a greenhouse gas / CO2 or H2O evolved contribute to global warming / the products are greenhouse gases

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10
Q

Balance the following equation that shows how butane is used to make the compound called maleic anhydride………..CH3CH2CH2CH3 + ………. O2 → ……….C2H2(CO)2O + ………. H2O

A

CH3CH2CH2CH3 + 3.5O2 → C2H2(CO)2O + 4H2O

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11
Q

Ethanethiol (C2H5SH), a compound with an unpleasant smell, is added to gas to enable leaks from gas pipes to be more easily detected.Write an equation for the combustion of ethanethiol to form carbon dioxide, water and sulfur dioxide

A

C2H5SH + 4.5O2 → 2CO2 + 3H2O + SO2

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12
Q

Identify a compound that is used to react with the sulfur dioxide in the products of combustion before they enter the atmosphere.Give one reason why this compound reacts with sulfur dioxide.

A

Calcium oxide / calcium carbonateNeutralises the SO2 / acid base reaction / it is a base

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13
Q

Ethanethiol and ethanol molecules have similar shapes. Explain why ethanol has the higher boiling point.

A

)Ethanol contains Hydrogen bondingWhich is stronger than IMF (VDW / dipole-dipole forces) in ethanethiol/ (H bonding) is the strongest IMF

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14
Q

State the type of cracking that produces a high proportion of ethene and propene. Give the two conditions for this cracking process.

A

Thermal (cracking)High pressure AND high temperatureORPressure of ≥ 10 atm, ≥ 1 MPa ≥ 1000 kPa ANDtemp of 4000C≤T≤10000C or650K≤T≤ 1300K

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15
Q

Hexane (C6H14) is a member of the homologous series of alkanes.Name the raw material from which hexane is obtained.

A

Crude oil

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16
Q

Name the process used to obtain hexane from this raw material.

A

Fractional distillation

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17
Q

State the type of cracking that produces a high percentage of alkenes. State the conditions needed for this type of cracking.

A

Thermal cracking High temperature(400°C ≤ T ≤ 900°C) or (650 K ≤ T ≤ 1200 K) andHigh pressure (≥ 10 atm, ≥ 1 MPa, ≥1000 kPa)

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18
Q

Explain the main economic reason why alkanes are cracked.

A

To produce substances which are (more) in demand / produce products with a high value / products worth more

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19
Q

Hexane can react with chlorine under certain conditions as shown in the following equation.C6H14 + Cl2 → C6H13Cl + HClBoth the products are hazardous. The organic product would be labelled ‘flammable’.Suggest the most suitable hazard warning for the other product.

A

Corrosive

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20
Q

C6H14 + Cl2 → C6H13Cl + HClCalculate the percentage atom economy for the formation of C6H13Cl (Mr = 120.5) inthis reaction.

A

( 120.5 / (86 +71) × 100 ) =76.75(%) or 76.8(%)

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21
Q

Alkanes are used as fuels. A student burned some octane (C8H18) in air and found that the combustion was incomplete.Write an equation for the incomplete combustion of octane to produce carbon monoxide as the only carbon-containing product.Suggest one reason why the combustion was incomplete.

A

C8H18 + 81/2 O 2 → 8 CO + 9H2ONot enough oxygen or air (available for complete combustion) /lack of oxygen or air

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22
Q

Catalytic converters are used to remove the toxic gases NO and CO that are produced when alkane fuels are burned in petrol engines.Write an equation for a reaction between these two toxic gases that occurs in a catalytic converter when these gases are removed.

A

2CO+2NO→2CO2 +N2

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23
Q

Identify a metal used as a catalyst in a catalytic converter.Suggest one reason, other than cost, why the catalyst is coated on a ceramic honeycomb.

A

Pt / Pd / Rh / Ir or namesBig(ger) surface area / increased reaction rate / removes more of the gases / ensures complete reaction

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24
Q

If a sample of fuel for a power station is contaminated with an organic sulfur compound, a toxic gas is formed by complete combustion of this sulfur compound.State one environmental problem that can be caused by the release of this gas.

A

Acid rain

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25
Identify one substance that could be used to remove this gas. Suggest one reason, other than cost, why this substance is used.
CaO/ lime / CaCO3 /limestoneNeutralises the gas or words to that effect/it is basic/ SO2 is acidic
26
There is a risk of gas explosions in coal mines. This risk is mainly due to the presence of methane. If the percentage of coal-mine methane (CMM) in the air in the mine is greater than 15%, the explosion risk is much lower. CMM slowly escapes from the mine into the atmosphere.Write an equation to show the complete combustion of methane.Suggest one reason why there is a much lower risk of an explosion if the percentage of CMM is greater than 15%.State why it is beneficial to the environment to collect the CMM rather than allowing it to escape into the atmosphere.
CH4+2O2---->CO2 +2H2O Not enough oxygen / airCMM / methane is a greenhouse gas / contributes to global warming
27
Methane can be obtained from crude oil. Some of this crude oil contains an impurity called methanethiol (CH3SH). This impurity causes environmental problems when burned.Write an equation to show the complete combustion of methanethiol.State why calcium oxide can be used to remove the sulfur-containing product of this combustion reaction.State one pollution problem that is caused by the release of this sulfur-containing product into the atmosphere.
CH3SH + 3O2 --->CO2 +2H2O+SO2Calcium oxide is basic (and SO2 is acidic) / CaO neutralises SO2 /CaO reacts with SO2 to form gypsum / salt / solid / CaSO4 / CaSO3Allow CaO + SO2 --> CaSO3 Acid rain
28
Pentane is a member of the alkane homologous series.Give the general formula for the homologous series of alkanes
Cn H2n + 2
29
State why high temperatures are necessary for cracking reactions to occur. Give one reason why thermal cracking reactions are carried out in industry.
To break the (C-C and/or C-H) bondsTo make products which are in greater demand / higher value / make alkenes
30
Write an equation for the incomplete combustion of pentane to form a solid pollutant. Suggest why this solid pollutant is an environmental problem.
C5H12 +3O2---->5C+6H2OCauses global dimming exacerbates asthma/causes breathing probsmakes visibility poor / smog
31
Pentane can react with chlorine as shown in the following equation. C5H12 + Cl2 ------>C5H11Cl + HClCalculate the percentage atom economy for the formation of C5H11Cl Deduce how many straight-chain isomers of C5H11Cl could be formed.
106.5 / 143 (x 100 ) 74.48% 3
32
Cetane (C16H34) is a major component of diesel fuel.Write an equation to show the complete combustion of cetane.
C16H34 + 24.5O2 --->16CO2 + 17H2O
33
Cetane has a melting point of 18 oC and a boiling point of 287 oC.In polar regions vehicles that use diesel fuel may have ignition problems. Suggest one possible cause of this problem with the diesel fuel.
Solidifies/freezes/goes viscous/waxing occurs
34
The pollutant gases NO and NO2 are sometimes present in the exhaust gases of vehicles that use petrol fuel.Write an equation to show how NO is formed and give a condition needed for its formation.
N2 + O2 >2NOSpark/ (very) high temp/ 2500 o C – 4000 o C
35
Write an equation to show how NO is removed from the exhaust gases in a catalytic converter. Identify a catalyst used in the converter.
2CO + 2NO----->2CO2 + N2
36
Cetane (C16H34) can be cracked to produce hexane, butene and ethene. State one condition that is used in this cracking reaction.
High temp/anywhere in range 400 o C – 900 o C/anywhere in range 670-1200K / high pressure/ anywhere in range 5000 kPa up to 8000 kPa/NOTcatalystheat
37
Write an equation to show how one molecule of cetane can be cracked to form hexane, butene and ethene.
C16H34 ---> C6H14 + 2C4H8 + C2H4
38
State one type of useful solid material that could be formed from alkenes.
Polymers or plastics
39
Octane is the eighth member of the alkane homologous series.State two characteristics of a homologous series.
*(Same) General formula /allow a named homologous series with its general formula*Chemically similar/same (chemical) reactions *Same functional group*Trend in physical properties/ eg inc bp as Mr increases*(Molecules) increase by CH2/Mr = 14
40
Name a process used to separate octane from a mixture containing several different alkanes.
Fractional distillation
41
The alkane butane is used as a fuel.Write an equation for the complete combustion of butane.
C4H10 + 6 12 O2----->4CO2 + 5H2O
42
State a condition which may cause carbon to be formed as a product in the combustion of butane.
insufficient oxygenNOTincomplete combustion
43
Butane obtained from crude oil may contain trace amounts of an impurity.When this impurity burns it produces a toxic gas that can be removed by reacting it with calcium oxide coated on a mesh.Suggest the identity of the toxic gas.
Sulfur dioxide / SO2
44
Suggest why the calcium oxide is coated on a mesh.
bigger surface area to react
45
Suggest why calcium oxide reacts with the toxic gas.
It is basic / the gas (SO2) is acidic
46
State the meaning of the term saturated and of the term hydrocarbon as applied to alkanes.
single (C-C) bonds only/ no double (C=C) bondsC and H (atoms) only/purely/solely/entirely
47
Give the general formula for the alkanes.
CnH2n+2
48
Pentane burns completely in oxygen. Write an equation for this reaction.
C5H12 + 8O2 → 5CO2 + 6H2O
49
State how the products of this reaction may affect the environment.
gases produced are greenhouse gases/contribute to Global 1 warming/effect of global warming/climate change
50
Give the name of a solid pollutant which may form when pentane burns incompletely in air.
C
51
One molecule of C9H20 can be cracked to form one molecule of pentane and one other product.Write an equation for this cracking reaction.
C9H20 C5H12 + C4H8
52
Suggest a type of compound that can be manufactured from the other product of this cracking reaction.
Plastics, polymers
53
why is a high temperature is needed for cracking reactions to occur.
so the bonds break OR because the bonds are strong
54
Thermal cracking of large hydrocarbon molecules is used to produce alkenes. State the type of mechanism involved in this process. Write an equation for the thermal cracking of C21H44 in which ethene and propene are produced in a 3:2 molar ratio together with one other product
Homolytic bond fission, is the breaking of a bond that results in one electron going to each atom in the bond. Homo, meaning same, simply refers to the bond breaking evenly and one electron going to each atom.Homolytic cleavage is the source behind free radicals.C21H44 ----> 3C2H4 + 2C3H6 + ?The thermal cracking of an alkane produce another shorter alkane and one alkene ( which is here propene)we started with 21 atoms of carbon C21H44Ethene ( first product) contains 2 atoms of carbon.Propene (Second product) contains 3 atoms of carbon.Ethene and propene are produced in a 3:2 molar ratio; therefore we have 2 moles of C2H4 and 3 moles of C3H6The unknown third product must be an alkane of ( 21-6-6=9 atoms of Carbon) The general formula of alkane is C9H20C21H44 ----> 3C2H4 + 2C3H6 + C9H20
55
Write equations, where appropriate, to illustrate your answers to the questions belowi- Explain why it is desirable that none of the sulfur-cointaining impurities naturally found in crude oil are present in petroleum fractions.ii- The pollutant gas NO is found in the exhaust gases from petrol engines. Explain why NO is formed in petrol engines but is not readily formed when petrol burns in the open air.
The internal combustion engine produces most of the pollutants listed above, though sulfur is now removed from petrol so that sulfur dioxide has become less of a problem. The sulfur impurities when burned form SO2The sulfur dioxide is a contributor to acid rain. It is produced from sulfur-containing impurities present in crude oil. This Oxide combines with water vapour and oxygen in the air to form sulfuric acid.S + O2 ----> SO2SO2 + H2O -----> H2SO3 + ½ O2---->H2SO4b-iiNitrogen oxides, NO,NO2 and N2O4 often abbreviated to NOx, produced when there is enough energy for N2 and O2 in the air to combine for example:N2 + O2 ---> 2NOThis happens in a petrol engine, at the high temperatures present when the sparks ignite the fuel.These oxides may react with water vapour and oxygen in the air to form nitric acid. They are therefore contributors to acid rain and photochemical smog. Therefore NO is formed in petrol engines and not readily formed when petrol burns in the air because it needs the high combustion temperature or spark in engine to provide sufficient heat energy to break
56
The pollution gas CO is also found in the exhaust gases from petrol engines. Explain how CO and NO are removed from the exhaust gases and why the removal of each of them is desirable
As explained in part b-ii, NO need to be removed because it contributes to the formation of acid rain.CO needs as well to be removed because it is a poisonous gas.All new cars with petrol engines are now equipped with catalytic converters in their exhaust systems. These reduce the output of carbon monoxide, nitrogen oxides and unburnt hydrocarbons in the exhaust gas mixture.The catalytic converter is a honeycomb made of a ceramic material coated with platinum and rhodium metals. These are the catalysts. The honeycomb shape provides an enormous surface area, so a little of these expensive metals goes a long way.As the polluting gases pass over the catalyst, they react with each other to form less-harmful products by the following reactions:1.2CO + 2NO ----> N2 + 2CO2carbon monoxide + nitrogen oxide ----> nitrogen + carbon dioxide 2.hydrocarbons + nitrogen oxide---> nitrogen +carbon dioxide +waterFor example,C8H18 + 25NO ----> 25/2 N2 + 9H2O +8CO2The reactions take place on the surface of the catalyst, on the layer of platinum and rhodium metals
57
Crude oil is separated into fractions by fractional distillation. Outline how different fractions are obtained by this process
To convert crude oil into useful products we have to separate the mixture. Its done by heating it and collecting the fractions that boil over different ranges of temperatures. Each fraction is a mixture of hydrocarbons of similar chain length and therefore similar products. The process is called fractional distillation and it is done in a fractionating tower.The crude oil is first heated in a furnaceA mixture of liquid and vapour passes into a tower that is cooler at the top than at the bottom.
58
why catalytic cracking of crude oil fractions is commercially important
The catalytic cracking is used mainly to produce: 1: motor fuels2: aromatic compounds
59
Name a catalyst used in catalytic cracking. State the type of mechanism involved and outline the industrial conditions used in the process.
The catalyst is Zeolite, consisting of silicon dioxide and aluminium oxide.The zeolite catalyst has sites which can remove a hydrogen from an alkane together with the two electrons which bound it to the carbon. That leaves the carbon atom with a positive charge. Ions like this are called carbonium ions (or carbocations). Theses are the intermediates formed during catalytic cracking.Catalytic Cracking takes place at a lower temperature ( approximately 720K) and lower pressure ( but more than atmospheric)
60
Crude oil is composed mainly of alkanes, which are saturated hydrocarbons.i-State what is meant by the term hydrocarbonii- state what is meant by the term saturated, as applied to a hydrocarbon
hydrocarbon is a substance that contain hydrogen and carbon elements onlySaturated hydrocarbons , contain only single bonds
61
i- Give the molecular formula of an alkane with ten carbon atoms.ii- Write an equation to illustrate the thermal cracking of one molecule of tetradecane,C14H30 in which the products are ethene and propene, in the ratio of 2:1 and one other product.iii- Name the mechanism involved in the thermal cracking
iThe general formula of alkane is CnH2n+2n = 10 carbon atomsC10H22iiC14H30 ----> 2 C2H4 + C3H6 + ?The ration of ethene to propene is 2 to 1, that means we have two molecules of C2H4 and one molecule of C3H6 as products.We started with 14 carbon atoms as reactant C14H30. .The first product C2H4 contain 2 carbon atoms but since we have 2 molecules, therefore we have 4 carbon atoms..The second product C3H6 contain 3 carbon atoms..The third product will be an alkane since it is a thermal cracking will contain ( 14 - 3 - 4 = 7 atoms of Carbon).The general formula of alkane is CnH2n+2n = 7 carbon atomsC7H16C14H30 ----> 2 C2H4 + C3H6 + C7H16iiiHomolytic bond fission, is the breaking of a bond that results in one electron going to each atom in the bond. Homo, meaning same, simply refers to the bond breaking evenly and one electron going to each atom.Homolytic cleavage is the source behind free radicals.
62
Butane,C4H10 is a hydrocarbon which is used as a fuel.i- Explain what is meant by the term hydrocarbon.ii- Explain what is meant by the term fuel.iii- Write an equation for the complete combustion of butane.iv- Write an equation for the incomplete combustion of butane to produce carbon monoxide and waterv- Under what conditions would you expect incomplete combustion to occur?
a-ihydrocarbon is a substance that contain hydrogen and carbon elements only.a-iiSubstance that release heat energy when burned.a-iiiC4H10 + 13/2 O2 ----> 4CO2 + 5H2Oa-ivC4H10 + 9/2 O2 ----> 4CO + 5H2Oa-vIncomplete combustion happens in a limited supply of oxygen
63
Explain what is meant by the term by the term fraction as applied to fractional distillation
To convert crude oil into useful products, we separate the mixture, by heating it and collecting the fractions that boil over different ranges of temperatures. Each fraction is a mixture of hydrocarbons of similar chain length and therefore similar properties.Hence in each fraction we find compounds/alkanes with similar boiling points.
64
State a property of the molecules in petroleum which allows the mixture to be separated into fractions
The molecules are separated in different fractions, by different boiling points or different chain lengths.
65
Describe the temperature gradient in the column
The crude oil is first heated in a furnace. The mixture of liquid and vapour passes into a tower that is cooler at then top than at the bottom.
66
The fractions from petroleum contain alkane hydrocarbonsWrite an equation for the incomplete combustion of the alkane C8H18 to produce carbon monoxide and water only
C8H18 + 17/2 O2 ----> 8CO + 9H2O
67
State one economic reason for the cracking of petroleum fractions
Cracking of petroleum fractions produces shorter chain products alkenes and motor fuels,which are economically more valuable than the longer chain. To meet the demand for the shorter chain hydrocarbons, many of the longer chain fractions are broken into shorter lengths (cracked)
68
Give the type of reactive intermediate formed during catalytic cracking
The zeolite catalyst has sites which can remove a hydrogen from an alkane together with the two electrons which bound it to the carbon. That leaves the carbon atom with a positive charge. Ions like this are called carbonium ions (or carbocations). Theses are the intermediates formed during catalytic cracking
69
Identify a catalyst used in catalytic cracking
The catalyst is a Zeolite consisting of silicon dioxide and aluminium oxide. Zeolites have a honeycomb structure with an enormous surface area
70
Give the type of reactive intermediate formed during thermal cracking.State how this reactive intermediate is formed
The thermal cracking involves heating alkanes at a high temperature, 700-1200K, under high pressure, up to 7000kPa. Carbon-carbon bonds break in such a way that one electron from the pair in the covalent bond goes to each carbon atom. So, initially two shorter chains are produced each ending in a carbon atom with an unpaired electron. These intermediates are called free radicals.
71
Identify the different type of hydrocarbon produced in a high percentage by the thermal cracking of alkanes.
Thermal cracking tends to produce a high proportion of alkenes
72
The burning of fossil fuels can produce atmospheric pollutants.The combustion of petrol in an internal combustion engine can lead to the formation of carbon monoxide, CO, and nitrogen monoxide, NO.Write an equation for the incomplete combustion of octane, C8H18 to produce CO and water
C8H18 + 17/2 O2 ----> 8CO + 9H2O
73
State one essential condition for the formation of NO in an engine. Write an equation for the reaction in which NO is formed
The one essential condition for the formation of NO in a petrol engine is the high temperature ( in a range of 2500-4000C) when the sparks ignite the fuel.N2+O2 ---> 2NO
74
All new petrol-engined cars must be fitted with a catalytic converter.Name one of the metals used as a catalyst in a catalytic converter.
The catalytic converter is a honeycomb made of a ceramic material coated with platinum andrhodium metals. These are the catalysts.
75
Write an equation to show how CO and NO react with each other in a catalytic converter.
2CO + 2NO ----> N2 + 2CO2
76
State why sulfur dioxide gas is sometimes found in the exhaust gases of petrol-engined cars. Give one adverse effect of sulfur dioxide on the environment.
Sulfur dioxide gas is sometimes found in the exhaust gases of petrol-engined cars due to the sulfur-containing impurities present in crude oil which burn to give SO2This oxide (SO2)combines with water vapour and oxygen in the air to form sulfuric acid. Therefore SO2 is another contributor to acid rain. One of the specific effect is killing the trees since the soil gets too acid.

(Chem Unit 1) 6/13,1/13,6/12,1/12,6/11,1/11,6/10,1/10 (15 decks)

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