Hard exam questions

Question 1

Describe ways that research chemists are trying to minimise climate change resulting from global warming caused by the release of greenhouse gases.

Answer 1

Provide evidence to governments OR international conferences (e.g. Kyoto) OR reports to United Nations etc  Educating society OR writing in journals OR producing documentaries OR writing books OR making posters  Monitoring atmospheric changes  Develop alternative energy sources  One example of an alternative energy source e.g. develop fuel cells OR developing solar power OR fuels that do not produce CO 2  (Develop) more efficient engines for transport OR lean burn engines OR hybrid engines OR electric cars  Find uses for carbon dioxide OR named use: e.g. dry cleaning OR making decaffeinated coffee OR blowing agent OR fizzy drinks, etc 

Question 2

What is the equation for working out change in combustion of bond enthalpies?

Answer 2

(Sum of bond enthalpies of bonds broken) - (Sum of bond enthalpies of bonds made)

Question 3

What is the equation for enthalpy changes of formation?

Answer 3

Change in H = (Sum of enthalpy of formation of products) - ( Sum of the enthalpy of formation of reactants)

Question 4

What is the equation for calculating enthalpy change of combustion?

Answer 4

Change in H = (Enthalpy of combustion of reactants) - (Enthalpy of combustion of products)

Question 5

In a reaction, what makes it exothermic?

Answer 5

In an exothermic reaction, the bonds that are formed are stronger than the bonds that are broken.

Question 6

In a reaction what determines wether it is exothermic?

Answer 6

In an endothermic reacttion, the bonds that are formed are weaker than the bonds that are brocken.

Question 7

Suggest ways in which the use of catalysts helps chemical companies to make processes more stable.

Answer 7

• Catalyst not used up in reaction
• Reactions take place at low temperatures with lower activation energy so less CO2 emitted into atmoshpere/ fossil fuels last longer.
• Less waste/less hazadrous chemicals.

Question 8

Identify the two main methods of producing ethanol.

Answer 8

Method 1 - Fermentation of sugars or carbohydrates.

• C₆H₁₂O₆ —> 2C₂H₅OH + 2CO₂

Method 2 - Hydration of ethene

• C₂H₄ + H₂O —> C₂H₅OH

Question 9

What is the functional group of the product made from reacting an alcohol with a carboxylic acid?

Answer 9

ester

Question 10

CFC’s were banned a long time ago, suggest why there is still concern about ozone depletion.

Answer 10

• CFC’s take a long time to reach the ozone layer/ long residence time.
• CFC’s are still being used.
• There are other ozone depleting substances.

Question 11

Outline ways that waste polymers are processed usefully, rather than just dumped into landfill sites.

Answer 11

• Sort plastics, melt and remould.
• Combustion for energy generation.
• Used for cracking/feedstock for plastics or chemicals.

Question 12

Outline the stages that take place in a catalystic converter to allow CO to react with NO.

Answer 12

1) CO and NO are adsorbed(onto surface)
2) There is a weakening of the bonds/lowering of activation energy.
3) CO₂ and N₂ desorbed (from surface).

Question 13

Outline methods that could be developed to achieve carbon capture and storage.

Answer 13

• Stored deep in the oceans.
• Storage in geological locations or under sea-bed.
• By reaction ( with metal oxides) to form carbonates.
• Piped into disused oil wells.

Question 14

Write out the standard enthalpy of formation of hexane ( include state symbols ).

Answer 14

6C(s) + 7H₂(g) —–> C₆H₁₄(l)

Question 15

Why is it very difficult to determine the standard enthalpy change of formation of hexane directly?

Answer 15

• Many diffirent hydrocarbons would form.
• Activation energy to high.
• Reaction to slow.

Question 16

What are two benefits of using enzymes to catalyse reactions apart from cost?

Answer 16

• Lower temperature can be used.
• Reduces CO₂ emissions (from burning fuels).

Question 17

Give some uses of methanol.

Answer 17

Methanol is used as a petrol additive and as a solvent, feedstock ( in the manufacture of organic compounds), manufacture of biodiesel, manufacture of esters.

Question 18

Infrared spectroscopy is used in identifying air pollutants such as NO_x in identifyinh what?

Answer 18

• Functional groups
• Match spectrum to known pollutants.
• Concentration/ Abundance of pollutant.

Question 19

A fermentation process has an atom economy of 51.1% and a percentage yield of 88.6%
.

1) Give two reasons why it is a good idea to find uses for the carbon dioxide produced.
2) Is it important to have a high percentage yield or a high atom economy in fermentation?

Answer 19

1) - Less waste products/better sustainability/100% atom economy.
- Stops green house gases being emitted.
2) One of two arguments:

Percentage yield: - Increase sustainability.

• To reduce waste from starting materials.

Atom economy:

• Cheaper/makes less harmful products/increases sutainability.
• Less by products/ more desired products.

Question 20

Poly(ethene) is found as a waste plastic in the pacific ocean but poly(ethenol) is not because it slowly dissolves in water.

Why does poly(ethenol) dissolve in water?

Answer 20

• has O-H groups
• poly(ethenol) forms hydrogen bonds with water.

Question 21

Describe examples of environmental damage that may result from carbon monoxide and hyrogen chloride.

Answer 21

1) CO is a poisonous gas.
2) HCl forms acid rain/ is corrosive.

Question 22

Outline the methods developed by chemists to reduce environmental damage caused by incineration.

Answer 22

1) Remove HCl by reacting with a base.
2) Ensure complete combustion to avoid making CO.
3) Remove CO₂ by CCS.

Question 23

Explain why it is important to establish international coorperation to reduce pollution levels of waste plastics.

Answer 23

• Idea that atmospheric pollution travels across borders.
• Idea that all countries contribute towards pollution.
• Coorperation means scientists share ideas.
• Richer countries can help poorer countries introduce pollution controls.
• One country cant control pollution unless all countries do.

Question 24

Ozone in the stratosphere is broken down to make O₂ and O.

Describe and explain how the concentration of ozone in the stratosphere is maintained.

Answer 24

O + O₂ —–> O₃

• Reaction is reversible
• Rate of formation of ozone is the same as the rate of depletion of the ozone.

Question 25

In the past, hydrogen peroxide was manufactured by reacting barium with ice-cold dilute sulfuric acid.

BaO₂ (s) + H₂SO₄(aq) —-> BaSO₄(s) + H₂O₂(aq)

This method required the disposal of poisonous barium compounds and has low atom economy.

Nowadays, it manufactured like so:

H₂ + anthraquinone —-> anthraquinol

O₂ + anthraquinol —-> H₂O₂ + anthraquinone

Explain the advantages of the manufacture of H₂O₂ frp, hydrogen and oxygen.

Answer 25

1) Oxygen comes from air.
2) No poisonous materials formed, no poisonous materials involved.
3) No waste products/atom economy is 100%
4) Anthraquinone is regenerated/recycled/used again/acts as catalyst.

Question 26

Some reactions of H₂O₂ are exothermic.

Use ideas about the enthalpy changes that tke place during bond breaking and bond making to explain why some reactions are exothermic.

Answer 26

Bond breaking absorbs energy and bond making releases energy.

More energy released than absorbed.

Question 27

When looking at infrared spectrometry for determining an uknown compound, what should you always say?

Answer 27

• Peaks that suggest bonds in the structure.
• Peaks not present which suggest the bonds not in a structure.

Question 28

Research scientists working the Antartic have measured the concentration of carbon dioxide in the ice. This study has allowed the scientists to estimate the atmosperic concentration of carbon dioxide over many thousands of years.

Do the graphs provide reliable evidence that an increase in atmospheric carbon dioxide concentration will result in global warming?

Answer 28

1) There are times when CO₂ has a high concetration and the temperature is also high.
2) It is impossible to measure with certainty the average temperature years ago.
3) There are other factors that may cause the green house effect.
4) There are very few anomalous results.

Question 29

Fractional distillation is used to seperate useful hydrocarbons found in crude oil.

Explain in terms of intermolecular forces, how fractional distillation.

Answer 29

• The hydrocarbons have different boiling points.
• The larger the molecules the stronger the van der Waals’ forces.

Question 30

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.

Answer 30

More than one hydrogen atom is substituted OR further substitution occurs.

Question 31

Explain why many industrial manufacturing processes use catalysts.

Include in your answer ideas about sustainability, economics and pollution control.

Answer 31

• Enable reactions to occur with less waste/ enable reactions with higher atom economy.
• Enable reactions to happen with less toxic solvents/reactants.
• Reactions can occur at lower temperatures and pressures, which saves energy costs.
• reduce carbon dioxide emissions.
• Enable reactions to occur with more specificity.

Question 32

A space probe has detected the presence of the element iron on the surface of the planet of Mars.

Outline how a mass spectrum would show the presence of iron.

Answer 32

• Would give m/z peaks around 56

-

Question 33

The space probe also detected different isotopes of sulfur on Mars.

• Outline how the mass spectrum would show how many different isotopes of sulfur were present on Mars.

Answer 33

The number of m/z values(around 32).

Question 34

The relative atomic mass of the sulfur found by the space probe was different from the relative atomic mass of sulfur on Earth.

Suggest why.

Answer 34

Different isotopic abundance/Different percentage of each isotope.

Question 35

Biofuels such as bioethanol and biodiesel are increasingly being used as an alternative to fossil fuels to provide energy.

Describe, with the aid of an equation , how bioethanol is manufactured by fermentation.

Answer 35

C₆H₁₂O₆ —-> 2C₂H₅OH + 2CO₂

• Uses ofyeast/zymase at 25-37*C.
• Anaerobic/ lack of oxygen.
• Seperate bioethanol by fractional distillation.

Question 36

What is the general formula for an alkyne?

Answer 36

C_nH_2n-2

Question 37

Many lorries and some cars use diesel powered engines.

Biodiesel is being developed as a substitute for diesel from crude oil.

Biodiesel is a methyl ester of a long chain carboxylic acid. The flow chart shows how it is produced:

plants —> plant oil —> long chain carboxylic acids —> biodiesel

Describe the benefits and disadvantages of changing from diesel to biodiesel.

Answer 37

• Save crude oil/no risk of large scale polluton from exploitation of crude oil.
• Biodiesel is renewable.
• Use of biodiesel is(more) carbon neutral/plants take up the carbon dioxide released during combustion.
• Land not used to grow food crops/ rainforests have to be cut down to provide land/ food prices may rise because less is grown.

Question 38

A student decides to prepare butan-1-ol by the alkaline hydrolysis of 1-chlorobutane.

Suggest,with reasons, any change in the conditions from those used in the alkaline hydrolysis of 1-iodobutane.

Answer 38

• Use of reflux/heat for more than 20 minutes.
• C-Cl stronger bond than C-I bond.
• heat for longer.

Question 39

What colour does acidified dichromate solution becomes when it oxidises a primary/secondary alcohol?

Answer 39

Orange to green.

Acidified dichromate is reduced.

Question 40

H₂(g) + Cl₂(g) —–> 2HCl(g) ΠH= -184 KJ mol^-1

Calculate the bond enthalpy for the H-Cl bond using the information.

Bond: H-H = +436 KJ mol^-1

Bond: Cl-Cl = +243 KJ mol^-1

Answer 40

431.5

Question 41

When asked for the formula of a molecular ion, what do you always have to add?

Answer 41

The “+” sign because its a positive ion.

Question 42

Suggest why CF₂Cl₂ does not hydrolyse in water.

Answer 42

(C–F or C–C l ) bonds need a large amount of energy to break 

ALLOW ( the C–F or C–C l ) bonds are strong / bonds have a large bond enthalpy ALLOW the molecule is not polar enough / non-polar molecule is not sufficient ALLOW the activation energy is too high DO NOT ALLOW dissolves IGNORE references to hydrogen bonding

Question 43

Two reasons that CF₂Cl₂ was used as an aerosol propellant are that it has low reactivity and will not hydrolyse in water.

State one other reason why CF₂Cl₂ was developed for use as an aerosol propellant.

Answer 43

volatile OR non-toxic OR non-flammable OR easily vaporised 

Question 44

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.

Answer 44

Any one from: 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 non- renewable  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

Question 45

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.

Answer 45

Idea that carbon–carbon bonds can break anywhere 

Question 46

A chemical factory uses 200 tonnes of methane a day. The factory produces 68.4 tonnes of hydrogen per day by reacting methane with steam.

CH₄(g) + H₂O(g) ⇔ CO(g) + 3H₂(g)

Calculate the percentage yield of hydrogen.

Answer 46

91.2%

Question 47

Describe how hydrogen can be used in the manufacture of margarine.

Answer 47

Unsaturated (vegetable) oils OR oils containing C=C bonds  (reacted with hydrogen) in the presence of a nickel catalyst

Question 48

Scientists monitor pollutant gases in the atmosphere.

State two modern analytical techniques that scientists can use to monitor environmental pollution.

Answer 48

IR (spectroscopy)  Mass spectrometry  UV (spectroscopy) 

Question 49

Explain why it is important to establish international cooperation to reduce pollution levels.

Answer 49

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 

Question 50

Give two reasons why there are many organic products of the reaction between bromine and ethane.

Answer 50

Any two from: More than one C–H bond can be substituted OR multi- substitution can occur OR more than one substitution can happen  Lots of termination steps 