METALS: TITANIUM
Titanium, the seventh most abundant metal in the Earth's crust (0.6%),
is usually found as an oxide (e.g., in the ores rutile and ilmenite).
This transition element, which has a high melting point (1660C) but
only a moderately-high density (4.51 g cm-), shows variable oxidation
states [e.g., (coloured) Ti(III) and (colourless) Ti(IV)].
[.. K > Ca > Na > Mg > Al > Ti > Zn > Fe > Pb > (H) > Cu > Hg > Ag ..]
1. The extraction of titanium from its principal ores is complex, but the final process involves chemical reduction of titanium(IV) chloride with magnesium at 1050C in an atmosphere of argon.
(a) Titanium metal is expensive, because its extraction involves high
costs in terms of energy, raw materials, and ensuring safety. From a
consideration of the above equation, suggest and explain one possible
way of reducing energy costs. _________________________________________
_______________________________________________________________________
_______________________________________________________________________
                                                                    [2]
Suggest one reason why it is necessary to carry out this reduction in
an atmosphere of argon. _______________________________________________
_______________________________________________________________________
                                                                    [1]
(b) The covalent compound titanium(IV) chloride, a liquid at room 
temperature, rapidly hydrolyzes to give an acidic solution and a white 
solid (Mr = 80). Construct the symbol equation for this hydrolysis. ___
_______________________________________________________________________
                                                                    [2]
2.  Titanium, despite its high position in the reactivity series, does 
not react with water, steam, or cold dilute acids; this observed lack 
of reaction is due to the presence of a protective oxide layer. Explain 
why this oxide layer reduces titanium's rate of reaction with several
reactants to effectively zero. ________________________________________
_______________________________________________________________________
                                                                    [2]
3.  There is a demand for alloys which incorporate both titanium and 
aluminium. Suggest two properties of such alloys. _____________________
_______________________________________________________________________
                                                                    [2]
4.  During the past few decades, manufacturers have used alternatives 
to lead compounds as pigments in paint; in particular, there is now 
extensive use of titanium(IV) oxide - which is very stable, non-toxic,
and brilliant white. Perhaps surprisingly, this titanium pigment is not 
usually obtained from purified rutile (TiO2), but from ilmenite.
(a) Analysis showed that a 5.00 g sample of pure ilmenite had this 
composition by mass: iron, 1.86 g; titanium, 1.56 g; and oxygen as the
only other element present.
 
    Fe    
    Ti   
    O    
 Mass combining (m) / g 
 
 
 
 Molar mass (M) / g mol- 
 
 
 
 Number of moles combining (m  M) 
 
 
 
 
 Simplest ratio of number of moles 
 
 
 
Complete the above Table, so as to determine the empirical formula of 
ilmenite. _____________________________________________________________
                                                                    [5]
(b) Suggest one reason why there has been a decrease in the use of lead
compounds in the manufacture of paints (and petrol). __________________
_______________________________________________________________________
                                                                    [1]

5.  A characteristic reaction of alkenes is addition polymerization.
One of the many versatile reaction schemes used to synthesize addition
polymers is summarized below:
The general formula given above for an addition polymer is, however,
a shade misleading because analyses have shown that most addition
polymers can be obtained in at least three different forms: i.e.,
(a) What name is given to compounds which have the same molecular 
formula but different structural formulae? ____________________________
                                                                    [1]
(b) Suggest two physical methods which could be used to distinguish 
between the different forms of an addition polymer (containing the same 
functional group R). __________________________________________________
                                                                    [2]
(c) Several transition metal compounds are known to act as catalysts
for the polymerization of alkenes; their use usually results in higher
yields of the isotactic and syndiotactic forms of addition polymers.
Titanium(IV) chloride is often stated to be a polymerization catalyst:
however, experiments have shown that the true catalyst is titanium(III)
chloride [which is formed by adding triethylaluminium, (C2H5)3Al, to a
reaction mixture of titanium(IV) chloride and alkene]. State the two
measurements that are required to determine whether a substance is
acting as a catalyst (apart from a comparison of reaction rates with
and without the substance). ___________________________________________
_______________________________________________________________________
                                                                    [2]
6.  Naturally occurring titanium contains five isotopes; the three most
abundant are Ti-46 (8.0%), Ti-47 (7.3%), and Ti-48 (73.8%). The most 
stable radioactive isotope, titanium-44, has a half-life of 47 years.
Calculate the exact relative atomic mass of a sample of titanium which 
contains only the three most abundant isotopes. _______________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
                                                                    [3]
Dr. R. Peters Next Contents' List