Data response Example 4

laugh Data Response question on iron pentacarbonyl

 Teacher only box

I have made up this question to help prepare students for the data response questions which appear on Section A of Paper 3 for the examinations on the 2014 programme (i.e. for examinations after May 2016). The information given is new to the students but they should be able to use their knowledge and understanding of the chemistry content of the programme to answer the questions. Because I have tried to make the chemistry interesting it may be a little harder than an actual exam question but exposure to questions like this beforehand should make students able to face the data response question in the final examination with considerable confidence. Since some of the answers require a knowledge and understanding of material from the AHL this particular question is only suitable for Higher Level students.

As well as including model answers I have also explained the chemistry fully and given the 'Complete course for students' links to the pages which cover the theory behind each individual question. If you set it as an assigned task using Student Access, students will not be able to see the model answers until after they have submitted their answers to you. If you simply give students access to the page (rather than assigning it as a task) they will be able to access the model answers themselves for review/revision/self-study etc.

If you do not wish to use student access, links to downloadable versions of the questions and, separately the worked answers, can be found at Printable versions of written tasks.

 

At 25 oC iron pentacarbonyl, Fe(CO)5, is a, straw-coloured liquid with a pungent odour. It can react with chlorine to give Fe(CO)4Cl2.

One of the uses of iron pentacarbonyl is to make nanotubes. When Fe(CO)5 is heated at 1400 K in the presence of carbon monoxide at high pressure it reacts to form nanoparticles of iron.

Fe(CO)5(g) → Fe(s) + 5CO(g)

These iron nanoparticles provide a nucleation surface for the transformation of carbon monoxide into carbon during the growth of the nanotubes (CNT).

xCO(g) → CNT(s) + ½xCO­2(g)

where x is typically 6000 giving a carbon nanotube containing 3000 carbon atoms.

(a) Comment on the fact that iron pentacarbonyl is a liquid under standard conditions (its melting point is - 21 oC and its boiling point is 103 oC). [1]

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(b) Deduce the geometric shape of a molecule of iron pentacarbonyl. [1]

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(c) (i) Draw the Lewis structure of carbon monoxide. [1]

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(ii) Use the concept of formal charge to explain why iron bonds to the carbon atom of the carbon monoxide molecules rather than the oxygen atom. [2]

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(d) (i) Use oxidation states to show whether iron pentacarbonyl is oxidized or reduced when it reacts with chlorine. [1]

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(ii) Deduce all the possible structures for Fe(CO)4Cl2. [2]

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(e) Assuming the carbon dioxide in the above process is lost to the atmosphere and the iron produced is discarded, calculate the atom economy of the reaction assuming it gives 100% yield of carbon nanotubes. [2]

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