module 4 apology

As someone has just pointed out, the links I put into a recent post for module 4 resources for the mark schemes for two papers actually took you to the paper itself, not the answers.

Never mind.

As some of you will have already worked out, if you follow the link further down the post to older module 4 papers you can find all the papers and mark schemes your heart desires, including the ones with the erroneous links.

I've put the link here again if you need it.

old module 4 papers and mark schemes

CHEM4 resources

With CHEM4 just around the corner in January, you may need to download these mark schemes for the past papers you have been given in class in case you have missed any of the feedback. Remember to ignore any reference to Kp calculations (and partial pressures) in equilibria questions as they are no longer on your syllabus. Likewise, if you try any of the older papers you may see some titration curves involving two seperate equivalence points (for either sodium carbonate or ethanedioic acid). Again, ignore them, they are no longer on your syllabus.

Jan 08 mark scheme

Jan 09 mark scheme

If you still feel the need for a bit more practise from the older papers, you can find any other examples you may need on the AQA website.

other old module 4 papers

You should also have received a specimen paper for the new CHEM4 exam, the mark scheme is below.

CHEM4 specimen mark scheme

Finally, these have been posted elsewhere on this blog and some of you may have had them from me directly, but the following are essential resources for revision of organic reactions and mechanisms.

organic mechanisms

organic reaction scheme

august kekulé

Friedrich August Kekule von Stradonitz (also August Kekulé) (1829 – 1896) was a German organic chemist. One of the most prominent chemists in Europe from the 1850s until his death, especially in the theoretical realm, he was the principal founder of the theory of chemical structure.

The theory of chemical structure (1857-1858) was a descripton of the ability of carbon atoms to link to each other tetravalently. The idea of the self-linking of carbon atoms provided the first formulae where lines symbolise bonds connecting the atoms. For organic chemists the use of structural formulae to explain the formation of molecules provided dramatic new clarity of understanding, and as a consequence the field of organic chemistry developed explosively from this point.

However, Kekulé's most famous work was based on the structure of benzene. Early suggestions at the time had been based on a linear chain of 6 carbon atom with 4 double bonds. The empirical formula for benzene had been long known, but its highly unsaturated structure was challenging to determine. The study of aromatic compounds was in its earliest years, and too little evidence was then available to help chemists decide on any particular structure. In 1865 Kekulé published a paper in French suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German (his native language) on the same subject.

When Kekulé spoke of the creation of the theory, he said that he had discovered the ring shape of the benzene molecule after having a day-dream of a snake (dirty boy! Freud would have a field day) seizing its own tail. This vision, he said, came to him after years of studying the nature of carbon-carbon bonds.

Although it was an exciting and well thought out idea at the time, further evidence soon came to light that demonstrated that Kekulé was perhaps mistaken in his proposed structure of benzene. You will need to be able to describe and explain this evidence for your module 4 exam.

The evidence includes:

a) problem with bond lengths
b) lack of reaction with bromine (benzene will not undergo electophilic addition)
c) problem with enthalpy of hydrogenation data

Check your notes to make sure you can explain each piece of evidence.

module 4 kinetics

Some of you have had problems drawing gradients on curves in order to deduce the rate of reaction on concentration/time graphs. The powerpoint below will allow you to check this skill and compare it to the graphs that you produced on your recent homework.

gradients from graphs

This next download is a set of interactive kinetics questions of a similar type to the ones you will find on your module 4 exam. Answers are provided.

kinetics exam questions

organic mechanisms

All the organic mechanisms you need for CHM3 (now CHEM2) and CHM4 (CHEM4). The link below will take you to a file sharing site where you can either view or download the presentation.

organic mechanisms