Exercises and titanium dioxide Case study
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Integrated sun protection in cosmetics is becoming increasingly important. Titanium dioxide nanoparticles are a commonly used as an inorganic UV filter.
Exercises
1. Write the
electronic configuration for the following elements or ions:
(a)
Ti4+
(b)
Fe2+
(c)
Fe3+
(d)
Ru2+
2. What is the
oxidation state of the central metal atom in the following complexes?
(a)
[Fe(C5H5)2]+
(b)
TiCl4
(c)
Ti(C5H5)2Cl2
3. Draw
the energy diagrams displaying the d-orbital splitting for the low and
high-spin complexes of the following examples assuming an octahedral complex.
(a)
Fe3+
(b)
Fe2+
(c)
Ti4+
4. Predict the
geometry of the following complexes:
(a)
Platinum tetrachloride
(b)
Vanadium hexacarbonyl
Case study - titanium dioxide
Integrated sun protection in cosmetics is becoming increasingly
important. Titanium dioxide nanoparticles are a commonly used as an inorganic
UV filter. New formulation techniques allow its integration without the
previously known whitening effect. Sunscreens contain typically between 5% and
20% w/v nanosized titanium dioxide.
There are a variety of different methods to analyse the quantity
of titanium dioxide in cosmetic formulations. One method is based on the
reduction of Ti(+IV) and subsequent re-oxidation with a ferric solution.
Titanium dioxide is typically dissolved in hot sulfuric acid and reduced by
adding metallic aluminium. The resulting Ti(+III) is then titrated against a
standard solution of ammonium iron(III) sulfate in the presence of potassium
thiocyanate as indicator.
(a)
Research the type of titration described.
(b)
Describe the chemical structure and mode of
action of the indicator.
(c)
Formulate all relevant reaction equations.
(d)
The package states that the sunscreen contains
10% w/v titanium dioxide. For the analysis, a volume containing the theoretical
value of 0.5 g of titanium dioxide is dissolved in sulfuric acid and reacted
with metallic aluminium. The resulting solution is titrated against a 0.5 M
solution of ammonium iron(III) sulfate using potassium thiocyanate as
indicator.
For each titration, the following volume of
ammonium iron(III) sulfate has been used:
12.55 ml 12.50 ml 12.60 ml
Calculate the real amount of titanium dioxide present in your
sample. Express your answer in grams and moles.
(e)
How many millilitres of sunscreen have been
used for the analysis?
(f)
Discuss the result in relation to the
typically accepted error values.
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