Form 6 / AL Chemistry / Reading Assignment 3 / 1
Heep Woh College
F.6 Reading Assignment 3
Group Name: ______Class: 6 S
Group Member:1. ______( )2. ______( )
3. ______( )
2002 A-Level Chemistry Sample Question [12 marks]
Read the passage below and answer the questions that follow:
Chain carbon molecules such as HC5N are found in space. To find out if these molecules might be formed in the extreme conditions existing in the atmospheres of stars, scientists of Britain and the United States laser-vaporized graphite at 1200oC in a helium atmosphere. To their surprise, the mass spectrum of the product showed that a stable molecular species C60 was formed. C60 was found to be stable and has a closed cage-like structure(Figure 1). This type of molecule, with many carbon atoms in a cage-like structure is called a fullerene. C60 looks like a football, and is the most stable of all fullerences. When C60 molecules are fired at steel surfaces at velocities similar to that of the space shuttle (27000 km h-1), the molecules simply bounce back unharmed. Other examples of fullerenes are C32, C44, C50, C58 and C70. The smallest, stable fullerene has 28 carbon atoms, with the formula C28H4.
As a result of many theoretical and experimental studies of fullerenes, the following conclusions have been made:
(i)The smaller fullerenes are nearly spherical, whereas the larger ones have more complex shapes.
(ii)All fullerenes contain some five-membered carbon rings in addition to the six-membered carbon rings.
(iii)In most fullerenes, three of the outer electrons of carbon occupy the sp2 hybrid orbitals, and the fourth electron is delocalized. Some fullerenes (such as C28H4, Figure 2) also contain a small number of sp3 hybridized carbon atoms and hydrogen is needed for the bond of the fourth valence electron.
In 1991, scientists in Japan made a further breakthrough when they prepared elongated carbon cage-like structures in the form of tubes, called carbon nanotubes. These materials are flexible, light, stronger than steel, and can conduct electricity.
Questions
(a)Draw a linear structure for the molecule HC5N.[1]
(b)State how the conditions in the experiment resemble those found in the atmospheres of stars. [2]
(c)Suggest how scientists could show, from the mass spectrum, that C60 had been formed. [1]
(d)From the examples of fullerences given, what do you notice about the number of carbon atoms in fullerene molecules? [1]
(e)In the C28H4 molecule, the four H atoms are bonded to C atoms where three five-membered rings meet.
(i)In Figure 2, circle a C atom to which a H atom is attached.
(ii)Explain why H atoms can only be bonded to this type of C atoms.[3]
(f)From a structural point of view, suggest why fullerenes contain five-membered rings, as well as six-membered rings? [1]
(g)Suggest why Si does not form cage-like structures as C does. [1]
(h)Suggest why carbon nanotubes are able to conduct electricity.[1]
(i)Suggest one possible use of carbon nanotubes. Justify your answer[1]
The End
S.Mo & C.K.Lau