Unit 2 – Intermolecular Forces
Unit 2 - Jan 2009
Q1.
The following liquids all have the same number of electrons in each molecule.  Which one is likely to have the lowest boiling point?
   A     CH3CH2CH2CH2OH
   B     CH3CH2CH2CH2CH3
   C     CH3C(CH3)2CH3
   D     CH3CH(CH3)CH2CH3
(Total for question = 1 mark)

Q2.
 This question is about boron and nitrogen compounds.
(a)  Draw and name the shape of a boron trifluoride, BF3, molecule.  Suggest the FBF bond angle.
(3)

Name of shape
 ............................................................................................................................................. 
FBF bond angle
 ............................................................................................................................................. 
(b)  Ammonia has the formula NH3.  Its HNH bond angle is less than the FBF bond angle in boron trifluoride.
(i)   Estimate the HNH bond angle in NH3.
(1)
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(ii)   Explain why the HNH bond angle is less than that for FBF.
(1)
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 (iii)   Name the strongest intermolecular force between BF3 molecules.
(1)
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(iv)   Name the strongest intermolecular force between NH3 molecules.
(1)
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(c)  Ammonia will react with oxygen in the presence of a platinum catalyst at 750°C
       forming water and nitrogen(II) oxide, NO.
(i)   What is the oxidation number of nitrogen in ammonia, NH3?
(1)
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(ii)   The diagram below shows the distribution of molecular energies in the reaction at 750°C.  On the same diagram, draw a curve to show the distribution at 500°C and explain what effect this change in temperature would have on the rate of the reaction.
(3)

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*(d)  Explain how a catalyst speeds up the rate of a reaction.
(3)
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 (Total for question = 14 marks)

Q3.
Which of these is likely to be the best solvent for cyclohexanol?
   A     H2O(l)
   B     CH3COCH3(l)
   C     NaCl(aq)
   D     CH3CH2CH2CH2CH2CH3(l)
(Total for question = 1 mark)

Q4.
 Which intermolecular forces exist between molecules of ethoxyethane?

   A     Instantaneous dipole − induced dipole only
   B     Permanent dipole − permanent dipole only
   C     Instantaneous dipole − induced dipole and hydrogen bonds
   D     Instantaneous dipole − induced dipole and permanent dipole − permanent dipole
(Total for question = 1 mark)

Q5.
 The ability of a liquid to flow is linked to the strength of its intermolecular forces.
 Suggest which of these liquids flows the slowest when poured.
   A     Propane-1,2,3-triol
   B     Propane-1,2-diol
   C     Pentane
   D     Butane
(Total for question = 1 mark)

Unit 2 - Jun 2009
Q6.
 
(a)  Draw a diagram to show the most significant intermolecular force between an ethanol molecule and a water molecule.  Label the bond angle between the molecules and state its value.
(2)

(b)  The student proposed to set up the apparatus as shown below to carry out the distillation to try to separate the ethanol from water.

There are three errors with the set-up.  Draw a circle around each error.
Describe what effect these errors would have if the student attempted to carry out the separation as shown.
[Clamps are not shown in the diagram but you can assume the apparatus is supported adequately.]
(6)

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(c)  If a balance is accurate to two decimal places was used to record the mass of ethanol collected, what would be the percentage error due to the balance readings if the total mass of ethanol collected was 20.10 g?
(1)

(d)  Suggest a suitable drying agent to absorb the water remaining with the ethanol after distillation.  Describe how you would use it to produce a dry sample of ethanol.
(2)
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 (e)  Describe a chemical test you could carry out to confirm the presence of the −OH group in ethanol.  What result would you expect to see?
(2)
Test
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Result
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(f) *(i)  Explain what is meant by a carbon neutral fuel.
(2)
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*(ii)  Suggest TWO reasons why these biofuels may not be carbon neutral and describe TWO effects that large scale production of biofuels may have on society.  Which of the three biofuels do you think is the most sustainable? Justify your choice.
(5)
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(Total for question = 20 marks)

Q7.
 Which of these isomers has the highest boiling temperature?

(Total for question = 1 mark)

Q8.
 The graph below shows the boiling temperatures of the hydrides of Group 7.

(a)  (i)  Identify the type of intermolecular force that gives rise to the unusually high boiling temperature of hydrogen fluoride.
(1)
 ............................................................................................................................................. 
(ii)  State and explain whether the electronegativity of fluorine is greater than, similar to or less than, that of bromine.
Hence explain why hydrogen fluoride can form the type of intermolecular force named in (a)(i) but hydrogen bromide cannot.
(3)
 ............................................................................................................................................. 
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 (iii)  Use the graph to predict what the boiling temperature of hydrogen fluoride
        would be without the presence of the type of intermolecular force named in (a)(i).
(1)
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(b)  Propanone, CH3COCH3, is a useful solvent for cleaning glassware in laboratories.
(i)  Why is propanone able to dissolve a wide range of substances?
(1)
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 (ii)  Propanone can be used to remove both water and octane from glassware.
For each of these substances, identify the strongest intermolecular force formed with propanone and the feature of the propanone molecule involved.
(2)
Water
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 ............................................................................................................................................. 
Octane
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 (Total for question = 8 marks)

Unit 2 - Jan 2010
Q9.
 Which list below shows the compounds in order of increasing boiling temperature?
   A     CH4, HCl, HF
   B     HF, CH4, HCl
   C     HCl, HF, CH4
   D     HF, HCl, CH4
(Total for question = 1 mark)

Q10.
 Which of the following has the highest boiling temperature?
   A     Pentane, CH3CH2CH2CH2CH3
   B     Hexane, CH3CH2CH2CH2CH2CH3
   C     2-methylbutane, CH3CH(CH3)CH2CH3
   D     2-methylpentane, CH3CH(CH3)CH2CH2CH3
(Total for question = 1 mark)

Q11.
 Which of the following has dipole-dipole interactions between its molecules, but no hydrogen bonding?
   A     Methane, CH4
   B     Methanol, CH3OH
   C     Ammonia, NH3
   D     Hydrogen iodide, HI
(Total for question = 1 mark)

Q12.
 Butan-1-ol and three other alcohols, X, Y and Z, are isomers.
(a)  (i)  Give TWO observations you would make when any one of the alcohols reacts with sodium.
(2)
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(ii)  Give the molecular formula of the organic product of the reaction.
(1)
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(b)  Isomer X does not react with a mixture of potassium dichromate(VI) and sulfuric acid.
Draw the displayed formula of X and name it.
(2)

Name
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(c)  When isomer Y is heated under reflux with a mixture of potassium dichromate(VI) and sulfuric acid, it forms 2-methylpropanoic acid.
Deduce the structural formula of the alcohol Y.
(1)

(d)  (i)  Isomer Z reacts with a mixture of potassium dichromate(VI) and sulfuric acid to form a compound Q, which does not react with Fehling's or Benedict's solution.
Deduce the structural formula of the alcohol Z.
(1)

(ii)  What would be the principal difference between the infrared spectrum of Q and the infrared spectrum of 2-methylpropanoic acid?
You are not expected to quote absorption values.
(1)
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 (e)  One of the isomers, X, Y or Z can be converted to 2-chlorobutane.
What reagent would you use to carry out this conversion?
(1)
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(f)  (i)  2-chlorobutane reacts with silver nitrate in a mixture of ethanol and water as a solvent. What would you see when the reaction occurred?
(1)
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*(ii)  Both ethanol and water contain hydrogen bonds. By considering the hydrogen bonding on these two solvents, suggest why 2-chlorobutane is more soluble in ethanol than in water.
(2)
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(Total for question = 12 marks)

Unit 2 - Jun 2010
Q13.
 Consider the following compounds, P, Q, R and S.

The boiling temperatures of compounds P, Q, R and S increase in the order
   A     P Q R S
   B     R S P Q
   C     Q S P R
   D     Q P S R
(Total for question = 1 mark)

Q14.
 This question is about the chemistry of some halogenoalkanes.

Halothane is a colourless and sweet-smelling liquid. It has a boiling temperature of 50°C. Halothane vapour was used as a general anaesthetic in hospitals during the mid to late 20th Century. Patients inhaled the halothane vapour under medical supervision. However, halothane was found to have some adverse side-effects and was therefore replaced by other halogenoalkane anaesthetics.
Halothane has the structure

In an experiment, halothane was heated in a test tube with aqueous silver nitrate and ethanol, using a water bath. Compound X and bromide ions were formed. The structure of compound X is shown below.

(a)  (i)  Give the systematic name of halothane.
(1)
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(ii)  Suggest the types of intermolecular force present between molecules of liquid halothane.
(2)
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 (iii)  In the above experiment, suggest ONE reason why a water bath was used rather than heating the test tube containing the reaction mixture directly over a Bunsen flame.
(1)
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 (iv)  Suggest why ethanol was used in this experiment.
(1)
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 (v)  What would be seen in the test tube as the reaction progressed?
(1)
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 (vi)  Write an ionic equation to show the reaction between aqueous silver ions and aqueous bromide ions. Include state symbols in your equation.
(1)

(b)  Chloroethane, C2H5Cl, can also be used as an anaesthetic. In an experiment, chloroethane was hydrolysed by aqueous sodium hydroxide, NaOH.
(i)  Name, and give the structural formula of, the organic product of the hydrolysis of chloroethane.
(2)
Name
 ............................................................................................................................................. 
Structural formula
 ............................................................................................................................................. 
(ii)  The hydrolysis of chloroethane is an exothermic reaction which takes place in a single step.
On the diagram below, draw the energy profile for the reaction. Label clearly the activation energy for the reaction.
(3)

(c)  In the early 1900s, the CFC with formula CCl2F2, was identified as a refrigerant which was both non-flammable and non-toxic.
(i)  What does the term CFC stand for?
(1)
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(ii)  Suggest ONE use for CFCs other than as a refrigerant.
(1)
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*(iii)  In the stratosphere, CFCs are broken down by absorption of UV radiation to form chlorine free radicals.
The following two reactions occur.

Combine these two equations to give the overall equation for the reaction of ozone in the stratosphere. State the role played by the chlorine free radical in the overall reaction. Hence explain why many scientists consider the effect of CFCs on ozone to be harmful.
(5)

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 (d)  The compound of formula CH2F2 has replaced several CFCs for commercial use. If molecules of CH2F2 reach the stratosphere, they do not break down to produce fluorine free radicals.
(i)  Suggest why C-F bonds are not broken in the stratosphere.
(1)
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*(ii)  The compound CH2F2 acts as a greenhouse gas when it absorbs a particular type of radiation.
Name the type of radiation and explain why a molecule of CH2F2 is able to absorb this radiation.
(2)
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 (Total for question = 22 marks)
Q15.
 Which of the following compounds shows hydrogen bonding in the liquid state?
   A     Hydrogen bromide, HBr
   B     Hydrogen sulfide, H2S
   C     Silane, SiH4
   D     Ammonia, NH3
(Total for question = 1 mark)
Unit 2 - Jan 2011
Q16.
 For parts (a) and (b), use your knowledge of intermolecular forces to predict the compound with the highest boiling temperature.

(Total for question = 2 marks)

Q17.
 This question is about iodine and its compounds.
(a) (i) The element iodine can be obtained from seaweed. One step in the procedure is to extract the iodine from aqueous solution by shaking with a hydrocarbon solvent in a separating funnel.
Draw a diagram of a separating funnel containing the separated layers. Label the hydrocarbon layer, and state its colour. [Density of hydrocarbon layer 0.660 g cm−3]
(3)
Diagram

Colour of hydrocarbon layer
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     (ii) Iodine is also formed when an aqueous solution containing iodide ions reacts with an aqueous solution of iron(III) ions.
 Write the ionic equation for this reaction. State symbols are not required.
(1)

(b) Hydrogen iodide gas is usually prepared by adding phosphoric(V) acid to solid potassium iodide.
(i) Suggest why phosphoric(V) acid is used in this preparation rather than concentrated sulfuric acid.
(1)
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 (ii) Describe what you would see if a test tube of hydrogen iodide gas was inverted in a beaker of water.
(1)
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 (iii) When hydrogen iodide gas reacts with ammonia, dense white fumes form. Write the equation for this reaction, including state symbols.
(2)

(c) 1-iodobutane can be made by reacting butan-1-ol with phosphorus(III) iodide, PI3, formed by reacting moist red phosphorus with iodine.
(i) Complete the following equation for the formation of 1-iodobutane.
(1)
PI3 + .................... C4H9OH →

(ii) Identify the intermolecular forces present between molecules of 1-iodobutane.
(1)
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 (iii) 1-iodobutane reacts with hot aqueous silver nitrate solution. Describe what you would see when this reaction takes place.
(1)
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(iv) Give the structural formula for the organic product of the reaction between 1-iodobutane and ammonia.
(1)

(Total for question = 12 marks)

Q18.
 This question is about methanol, CH3OH, and ethanol, CH3CH2OH.
(a) (i) Draw a dot and cross diagram for methanol, showing outer electrons only.
(1)

     (ii) Give the approximate values for the HCH and COH bond angles in methanol.  Justify your answers.
(4)
HCH angle .........................
Justification
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COH angle .........................
Justification
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     (iii) Using displayed formulae, draw a diagram to show a hydrogen bond between two methanol molecules. On your diagram, show the bond angle around the hydrogen atom of the hydrogen bond and give its value.
(2)

(b) Methanol reacts with sodium.
(i) State what you would observe in this reaction.
(2)
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(ii) Write the equation for this reaction. State symbols are not required.
(1)

(c) Ethanol can be used to make ethanal.
(i) Identify, by name or formula, the two chemicals you would use to make ethanal from ethanol in the laboratory.
(2)
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(ii) Draw a diagram of the apparatus you would use to prepare ethanal from ethanol in the laboratory and collect the product.
(2)

(iii) Both ethanal and propane have a molar mass of 44 g mol−1, but their boiling temperatures are different.
Suggest which substance has the higher boiling temperature. Justify your answer by comparing the intermolecular forces in each compound.
(2)
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 (Total for question = 16 marks)

Unit 2 - Jun 2011
Q19.
 Which of the following molecules does not absorb infrared radiation?
   A    N2
   B    NO2
   C    CO
   D    CO2
(Total for Question = 1 mark)

Q20.
 This question is about ethanethiol, CH3CH2SH. Thiols are like alcohols, but the oxygen atom has been replaced by a sulfur atom. They react in a similar way to alcohols.
(a) (i)   Draw a dot and cross diagram for ethanethiol, showing outer electrons only.
(2)

    (ii)  Give the value for the CSH bond angle in ethanethiol. Justify your answer.
(3)
CSH angle .........................
Justification
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 (b) There are hydrogen bonds between ethanol molecules but not between ethanethiol molecules.
      (i)   Explain why the bond angle around the hydrogen atom involved in a hydrogen bond is 180°.
(2)
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      (ii)  Explain why there are no hydrogen bonds between ethanethiol molecules.
(1)
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(c) (i)   Describe the formation of London forces.
(2)
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      (ii)  Explain why the London forces in ethanethiol are stronger than those in ethanol.
(1)
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 (d) The reaction of sodium with ethanethiol, CH3CH2SH, is similar to its reaction with ethanol.
      (i)    Suggest one observation you would make when sodium is added to ethanethiol.
(1)
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      (ii)   Suggest a balanced equation for this reaction. State symbols are not required.
(1)

(e) Ethanol can be made from bromoethane by reaction with aqueous potassium hydroxide, KOH(aq), under suitable conditions.
      (i)   Write the equation for this reaction. State symbols are not required.
(1)

      (ii)  State the type and mechanism of this reaction.
(2)
Type
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Mechanism
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     (iii)  Suggest the formula of a suitable chemical to make ethanethiol from bromoethane.
(1)
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(f) When ethanethiol undergoes complete combustion in air, a gas is produced which is not formed on the complete combustion of ethanol. Identify the gas and suggest why it is damaging to the environment.
(2)
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(Total for Question = 19 marks)

Unit 2 - Jan 2012
Q21.
 The boiling temperatures of some hydrides are given below.

*(a) Explain, by comparing the forces involved, why HI has a higher boiling temperature than HBr.
(3)
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*(b) Explain, by comparing the types of forces involved, why HF has a higher boiling temperature than HCl.
(3)
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 (c) Suggest why H2O has a higher boiling temperature than HF.
(1)
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 (Total for question = 7 marks)

Q22.
 The difference in boiling temperature between methane (Tb = 109 K) and ethane (Tb = 185 K) is best explained by the different numbers of
   A   protons.
   B   electrons.
   C   covalent bonds.
   D   hydrogen bonds.
(Total for question = 1 mark)

Q23.
 Ethanol is soluble in water. The best explanation for this is
   A   ethanol molecules form hydrogen bonds with water molecules.
   B   ethanol molecules form London (dispersion) forces with water molecules.
   C   ethanol molecules form permanent dipole interactions with water molecules.
   D   ethanol and water are miscible liquids.
(Total for question = 1 mark)

Unit 2 - Jun 2012
Q24.
      Hydrogen iodide has a higher boiling temperature than hydrogen bromide. This is because
   A       the H—I bond is stronger than the H—Br bond.
   B       hydrogen iodide has stronger London forces than hydrogen bromide.
   C       hydrogen iodide has a larger permanent dipole than hydrogen bromide.
   D       hydrogen iodide forms hydrogen bonds but hydrogen bromide does not.
(Total for question = 1 mark)

Q25.
      Butane has a higher boiling temperature than 2–methylpropane. This is because butane has
   A       stronger C—H bonds.
   B       more electrons.
   C       a larger surface area.
   D       hydrogen bonds.
(Total for question = 1 mark)

Q26.
Fuels of the Future
 Concerns about the future availability of fossil fuels, and the fact that their combustion produces greenhouse gases, have led to a search for alternative sources of energy. A great deal of attention has been directed at developing the use of hydrogen as a fuel. Since the only product of its combustion is water, hydrogen is considered to be a clean fuel.
However, the use of hydrogen has major drawbacks. The small size of the hydrogen molecule means that it is difficult to prevent leaks and, to store enough to provide a reasonable amount of fuel for a car, hydrogen must be compressed to around 700 atmospheres. Furthermore, the main source of hydrogen is currently fossil fuels such as methane, which is combined with steam in a series of reactions to form carbon dioxide and hydrogen.
One suggested alternative to hydrogen is ammonia. Ammonia, which is obtained by combining nitrogen and hydrogen at temperatures around 450°C and pressures of about 150 atmospheres, also has serious disadvantages: it is a toxic, corrosive and pungent gas which is difficult to ignite.
However, burning ammonia produces only nitrogen and water and it is relatively easy to liquefy, having a boiling temperature of just −33°C. Furthermore, the technology works: ammonia was used as a fuel for Belgian buses in the Second World War and, in 2007, the 'NH3 Car' project based in Ann Arbor, Michigan, used a mixture of ammonia and petrol to fuel a 2500 mile journey, from Detroit to San Francisco, in a modified pickup truck.
(a)  (i)  Explain the term greenhouse gas.
(2)
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*(ii) State and explain whether or not water (in the gaseous state) is a greenhouse gas.
(2)
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(iii) Write the equation for the formation of hydrogen from methane and steam. State symbols are not required.
(2)

(iv) Suggest why using methane to form hydrogen in this way is preferable to burning methane directly.
(1)
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 (v) Storing hydrogen at a pressure of 700 atmospheres is a disadvantage to its use as a fuel because of the costs involved. Suggest why using such high pressures is so expensive.
(1)
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 (b)  (i)  Draw a dot and cross diagram for ammonia, showing the outer electrons only.
(1)

*(ii) By considering the intermolecular forces involved, explain why methane has a boiling temperature of 109 K while ammonia has a boiling temperature of 240 K, although these two compounds have very similar molar masses.
(4)
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 (c)  (i)  Write the equation for the combustion of ammonia. State symbols are not required.
(2)

(ii) The enthalpy change of combustion of methane is −890.3 kJ mol−1 and that of ammonia is −510.1 kJ mol−1. Suggest two additional items of information, not connected with environmental factors or the fact that methane is non-renewable, which would be useful in comparing methane and ammonia as fuels.
(2)
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(iii) The fact that ammonia has a pungent smell is listed as a disadvantage of its use as a fuel. Suggest why this might also be an advantage.
(1)
 (iv) Suggest why ammonia was mixed with petrol in the 'NH3 Car' project.
(1)
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 (v) State, with a reason, whether hydrogen or ammonia can currently be considered to be long term replacements for fossil fuels.
(1)
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 (Total for question = 20 marks)

Unit 2 - Jun 2013
Q27.
The diagram below is taken from a student's examination paper. It shows the hydrogen bonding between two water molecules.
Identify the error in the diagram.

   A    The H—O—H bond angle within each water molecule should be 90°.
   B    There should only be one lone pair of electrons on each oxygen atom.
   C    The O—H—O bond angle between the water molecules should be 180°.
   D    The hydrogen atoms should be − and the oxygen atoms should be +.
(Total for Question = 1 mark)

Q28.
The boiling temperatures of fluorine and two of its compounds are given below.

(a)  A molecule of F2 has 18 electrons.
Which intermolecular force depends to a large extent on the number of electrons in the molecule?
(1)
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(b)  Calculate the number of electrons in a molecule of CH3F.
(1)

(c)  Explain why the boiling temperature of CH3F is greater than that of F2, referring to the intermolecular forces present.
(1)
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(d)  Explain why the boiling temperature of HF is the highest in the series.
(2)
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(e)  Explain why the values of the boiling temperatures for Cl2, CH3Cl and HCl do not follow the same trend as F2, CH3F and HF.
(1)
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(Total for Question = 6 marks)

Q29.
What are the strongest forces between molecules of hydrogen fluoride, HF?
   A    Dipole-dipole forces.
   B    Hydrogen bonds.
   C    Ionic interactions.
   D    London forces.
(Total for Question = 1 mark)

Q30.
The boiling temperatures from methane to propane increase because
   A    the number of ions increases, so there are stronger electrostatic attractions.
   B    the covalent bonds are getting stronger, so require more energy to break.
   C    there are more covalent bonds, so more energy is needed to break them.
   D    the number of electrons increases, so there are stronger London forces.

(Total for Question = 1 mark)
Q31.
Nanorockets have generated a lot of excitement due to their potential uses in the medicinal field, such as in the delivery of drugs around the body.

Some bacteria have the ability to move at speeds of 100 times their body length per second. Scientists in one study made nanorockets that reached speeds of up to 200 times their length per second. These scientists made their rockets on a nano scale (10−9) from nanotubes with platinum coated on the inside as a catalyst. The fuel used to power these tiny rockets was hydrogen peroxide, H2O2, which forms water and oxygen gas when undergoing decomposition.

Other forms of nanotechnology are already being used. For example, some sun creams use nanoparticles of titanium(IV) oxide which form an invisible protective layer against UV radiation.

(a)  Write an equation for the catalytic decomposition of hydrogen peroxide. State symbols are not required.

(1)

(b)  Draw a dot and cross diagram to show the electronic configuration of the oxygen gas produced in the breakdown of the hydrogen peroxide (only outer electrons should be shown).
(1)

(c)  Suggest a dot and cross diagram for the hydrogen peroxide molecule in which each oxygen atom is covalently bonded to one hydrogen atom (only outer electrons should be shown).
(2)

*(d)  The bond angles in hydrogen peroxide are similar to those in a water molecule. Suggest a bond angle for hydrogen peroxide and reasons for your value.
(3)
Bond Angle
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Reasons
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(e)  In the future, the aim is to develop a nanorocket that can use a fuel such as glucose rather than hydrogen peroxide. Suggest an advantage of using glucose and a disadvantage of using hydrogen peroxide.
(2)
Glucose advantage
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Hydrogen peroxide disadvantage
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(f)  The boiling temperature of hydrogen peroxide is relatively high, about 150°C, for such a small molecule. Explain fully why this is the case.
(2)
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*(g)  It is suggested that hydrogen peroxide is a polar liquid.

Describe how you might carry out an experiment to test whether a liquid is polar.
(3)
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*(h)  The speed of the nanorockets is controlled by the rate of decomposition of hydrogen peroxide. The speed at the body temperature of 37 °C is faster than under normal laboratory conditions. Draw Maxwell-Boltzmann distribution curves on the axes below. Label your diagram and use it to explain why the increase in the speed of the rockets occurred.
(4)

(i)  The scientists used platinum in their nanorockets. Explain the catalytic role of the platinum in the reaction.
(2)
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(j)  Nanotubes can be made from carbon. These carbon nanotubes can be good electrical conductors in a similar way to graphite.
Explain why they are able to conduct electricity.
(2)
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(k)  Some scientists are concerned that the use of nanoparticles in cosmetic products, such as sun cream, could pose a health hazard. Suggest why this might be the case.
(1)
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(Total for Question = 23 marks)

Q32.
Sodium chloride is more soluble in water than in hexane because
   A    the intermolecular forces between water molecules are stronger than those between hexane molecules.
   B    hexane molecules cannot fit between the ions in the sodium chloride lattice.
   C    energy is released when the ions in sodium chloride are hydrated.
   D    sodium ions and chloride ions form hydrogen bonds with water.
(Total for Question = 1 mark)

Unit 2 - Jun 2014
Q33.
 Which of the following molecules has the lowest boiling temperature?

   A    
   B    
   C    
   D    
(Total for question = 1 mark)

Q34.
 Which of the following molecules has the highest melting temperature?

   A    
   B    
   C    
   D    
(Total for question = 1 mark)

Q35.
Which of the following substances does not have intermolecular hydrogen bonds?
   A    Ethanoic acid, CH3COOH
   B    Propanone, CH3COCH3
   C    Methanol, CH3OH
   D    Water, H2O

(Total for question = 1 mark)

Q36.
Insect-borne diseases, such as malaria, affect the lives of millions of people. Chemists are constantly finding new compounds to combat the transmission of these diseases. One such compound is the insect repellent commonly called p-menthane-3,8-diol (this is not its systematic name). It is used to protect both humans and animals.
The structure of p-menthane-3,8-diol is shown below.

p-menthane-3,8-diol is found naturally in the leaves of Eucalyptus citriodora, which is native to Australia and is commonly known as 'Lemon Bush'. It can be extracted from these leaves but is currently commercially prepared by chemical synthetic pathways. However, the commercially-made chemical has been found by some scientists to be less effective than the natural leaf extract.
It is possible that p-menthane-3,8-diol can kill microorganisms and it is this additional potential use and others which are being investigated by the chemical industry.
p-menthane-3,8-diol should not be confused with either methane or methanol.
(a)  p-menthane-3,8-diol has two alcohol functional groups. Classify the type of alcohol group on the far left of the structure drawn above and explain the meaning of the term 'functional group'.
(2)
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(b)  Give the molecular formula of p-menthane-3,8-diol.
(1)
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(c)  p-menthane-3,8-diol is found in the oily extract from the leaves of the 'Lemon Bush'.
One method used to extract the oil is described below.
Initially, the leaves are ground up using a pestle and mortar with some sand and an organic solvent, such as cyclohexane.
(i)  Suggest why sand is used.
(1)
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*(ii)  The solvent cyclohexane forms intermolecular forces with other organic molecules when they dissolve.
Identify these intermolecular forces and explain how they arise.
(3)
Type of intermolecular force
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How they arise
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(iii)  How could the sand and other solid residue be removed from the mixture?
(1)
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(iv)  At this stage, either anhydrous magnesium sulfate or calcium chloride is added. Suggest the reason for this.
(1)
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*(v)  A student suggested using the following apparatus to remove the cyclohexane from the mixture.

Explain, in terms of the processes that occur in the above apparatus, why this method is unsuitable to remove the cyclohexane.
Suggest how this apparatus could be adjusted for a successful separation.
DATA

·	Boiling temperatures: p-menthane-3,8-diol 266 °C; cyclohexane 81 °C(4)
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(d)  Spectroscopic techniques can be used to confirm the presence and identity of organic molecules such as p-menthane-3,8-diol.
(i)  Suggest how infrared spectroscopy could be used to confirm the presence of the functional group in a molecule such as p-menthane-3,8-diol.
(1)
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(ii)  Suggest the identity of two fragment ions, with a m/e value of more than 13 but less than 20, that could be observed in a mass spectrum of p-menthane-3,8-diol.
(2)
First fragment ion
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Second fragment ion
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(e)  One reason why the synthetic p-menthane-3,8-diol may be less effective than the natural extract is because there are many isomers of this molecule.
Complete the structures below to show two structural isomers of p-menthane-3,8-diol which have the same number of alcohol functional groups and the same carbon skeleton.
(2)

*(f)  State two key principles of sustainability, and how the chemical industry might achieve these, when mass-producing a molecule such as p-menthane-3,8-diol.
(4)
Principle 1
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Principle 2
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(Total for question = 22 marks)

Q37.
 Although they have the same relative molecular mass, the boiling temperatures of hexane (69 °C) and 2,2-dimethylbutane (49 °C) are significantly different. The reason for this is that

   A    the intermolecular forces are stronger between hexane molecules because it has more electrons.
   B    there are significantly stronger permanent dipole forces between hexane molecules.
   C    the covalent bonds in hexane are stronger and so it requires more energy to break them.
   D    the molecular shape of hexane molecules allows them to form stronger London forces.
(Total for question = 1 mark)

Q38.
 Spontaneous combustion is often a subject of fantasy in movies, but it does actually happen with some chemical compounds. One such compound is silane, SiH4, which is analogous to methane, CH4. Methane is the main gas that is used in school and college laboratories with Bunsen burners, but it requires a spark or a lighted splint to ignite. Silane does not require any such ignition, and at room temperature is spontaneously flammable. This can make an interesting chemical demonstration.
One method of making silane is by mixing together two solids, silicon dioxide and magnesium, with the magnesium being in excess. The two chemicals are thoroughly mixed together. This mixture is then heated to red-heat and initially produces powdered silicon. The silicon then reacts further with the excess magnesium powder and forms magnesium silicide, Mg2Si. The two reactions which occur are shown in the equations below.
SiO2 + 2Mg → 2MgO + Si
Si + 2Mg → Mg2Si
The magnesium silicide formed is then reacted with hydrochloric acid to form silane, SiH4.

(a)  Complete and balance the equation for this reaction. State symbols are not required.
(2)
Mg2Si + ............HCl → ................................................. + .................................................
(b)  Bubbles of silane rise to the surface in the reaction mixture and spontaneously combust with oxygen in the air.
Suggest the names or formulae of the products of the reaction between silane and oxygen.
(2)
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(c)  Predict the molecular shape of silane, SiH4, and suggest the bond angle.
(2)
Shape
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Bond angle
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(d)  Explain why the Si—H bond is longer than the C—H bond.
(2)
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*(e)  Identify the intermolecular forces present in pure samples of both silane and methane.
Explain why silane has a higher boiling temperature than methane and why both are gases at room temperature.
(4)
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(f)  (i)  Define the term electronegativity.
(2)
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*(ii)  Some Pauling electronegativity values for selected elements are given below.

Using the values in the table above, compare the polarity of the bonds in a molecule of methane with that found in a molecule of silane.
Comment on the significance of any difference.
(3)
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(iii)  Using the table in (f)(ii), choose an element which, when covalently bonded to hydrogen, forms a molecule containing bonds that are more polar than those in silane or methane. Give the formula of the hydride of your chosen element and state the electronegativity difference.
(2)
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(iv)  Explain why it is possible for the bonds within a molecule to be polar, but for the molecule itself to be non-polar. Give an example of such a molecule.
(2)
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(Total for question = 21 marks)