Unit 2 – Bonding & Bond Polarity
Unit 2 - Jan 2009
Q1.
Which of these four molecules, PCl3, CO, CO2 and CCl4, are polar?
   A     All four
   B     PCl3 and CO
   C     CO and CCl4
   D     PCl3 and CO2
(Total for question = 1 mark)
Unit 2 - Jun 2009
Q2.
The bonding in gaseous hydrogen halides is best described as
   A     mainly covalent with an increasing tendency towards ionic as you go down the group.
   B     mainly covalent with an increasing tendency towards ionic as you go up the group.
   C     mainly ionic with an increasing tendency towards covalent as you go down the group.
   D     mainly ionic with an increasing tendency towards covalent as you go up the group.
(Total for question = 1 mark)
Q3.
Which of the following statements is true?
   A     Calcium hydroxide is more soluble in water than magnesium hydroxide.
   B     Chlorine is more electronegative than fluorine.
   C     Iodine is a stronger oxidizing agent than bromine.
   D     The first ionization energy of barium is greater than that of strontium.
(Total for question = 1 mark)
Q4.
An electric field can affect the direction of a stream of some liquids.  Which of these liquids would be affected by an electric field?
   A     1-chloropropane
   B     Pentane
   C     Tetrachloromethane
   D     Cyclopentane
(Total for question = 1 mark)
Unit 2 - Jan 2010
Q5.
 Which of the following molecules contains polar bonds but is not a polar molecule?
   A     Chlorine, Cl2
   B     Hydrogen chloride, HCl
   C     Trichloromethane, CHCl3
   D     Tetrachloromethane, CCl4
(Total for question = 1 mark)
Unit 2 - Jun 2010
Q6.
 The electronegativities of four pairs of elements are given below. Which pair would form the compound with the greatest ionic character?
   A     0.7 and 4.0
   B     0.7 and 3.5
   C     1.0 and 4.0
   D     0.8 and 2.8
(Total for question = 1 mark)
Q7.
Which of the following molecules is polar?
   A     Carbon dioxide, CO2
   B     Beryllium chloride, BeCl2
   C     Ammonia, NH3
   D     Boron trifluoride, BF3
(Total for question = 1 mark)

Unit 2 - Jan 2011
Q8.
Consider the following organic liquids:
A  ethanal
B  ethanol
C  tetrachloromethane
D  trichloromethane

(a) Each liquid is run from a burette. Which liquid would not be deflected significantly by a charged rod?
(1)
   A
   B
   C
   D

(b) Which liquid would react with phosphorus(V) chloride to give a gas which fumes in moist air?
(1)
   A
   B
   C
   D

(c) Which liquid would you expect to have the peak at the greatest mass/charge ratio in its mass spectrum?
(1)
   A
   B
   C
   D

(d) Which liquid has an infrared spectrum with a broad absorption due to hydrogen bonding?
(1)
   A
   B
   C
   D
(Total for question = 4 marks)
Unit 2 - Jun 2011
Q9.
Which of the following molecules is non-polar?
   A    CH3Cl
   B    CH2Cl2
   C    CHCl3
   D    CCl4
(Total for Question = 1 mark)
Unit 2 - Jan 2012
Q10.
Tetrachloromethane, CCl4, is a
   A   polar molecule with polar bonds.
   B   polar molecule with non-polar bonds.
   C   non-polar molecule with polar bonds.
   D   non-polar molecule with non-polar bonds.
(Total for question = 1 mark)
Unit 2 - Jun 2013
Q11.
Which of the following statements about electronegativity is true?
   A    Non-metals have lower electronegativity than metals.
   B    Electronegativity decreases across a period in the Periodic Table.
   C    Electronegativity decreases going down a group in the Periodic Table.
   D    The bonds between atoms with equal electronegativity are always weak.
Total for Question = 1 mark)
Q12.
A charged rod is held beside a stream of liquid coming from a burette. Which of the following liquids would NOT be significantly deflected?
   A    H2O
   B    CCl4
   C    C2H5OH
   D    C2H5Br

Q13.
In which series of compounds does the covalent character increase, going from left to right?
   A    NaCl, MgCl2, AlCl3, SiCl4
   B    SiO2, Al2O3, MgO, Na2O
   C    LiI, NaI, KI, RbI
   D    KI, KBr, KCl, KF
(Total for Question = 1 mark)

Q14.
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)

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(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)

Unit 2 - Jun 2014
Q15.
 Which of the following molecules is polar?
   A    CO2
   B    SO2
   C    SO3
   D    O2
(Total for question = 1 mark)

Q16.
 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)