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Oxford Chemistry Interview Questions & Answers

Oxbridge Application Specialists

If you’re interviewing at Oxford to study Chemistry, there are various questions that go beyond the typical syllabus and require lateral thinking available from previous students. Here we’ll take a look at a general approach to answering Science interview questions that is appropriate for Chemistry, and then consider three questions.

Your general approach should be as follows:

First, contextualise the question. What area of your knowledge is the question looking to probe in particular? This may seem more or less obvious depending on how left-field the question itself is. However, there should always be some core A Level knowledge that you can bring to bear.

Next, use that A Level knowledge. Show that you have an ability to recall and deploy core knowledge with ease and apply it to new contexts.

After this, use additional knowledge that you have gained from your general reading. You might bring in books that you’ve read, journal articles, experiments or projects that you’ve carried out, or online articles from reputable sites. You should demonstrate a broad knowledge base and passion.

Finally, use logic to build out your answer using the information that you have to hand, and allow for a back-and-forth discussion with the tutor. Allow them to provide you with new information and try to use that information sensibly, or ask questions that will show an ability to understand where your knowledge is lacking, and what can be done to improve it. Don’t be dogmatic, and show that you can change your point of view as needed.

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Question 1: How many moles of H20 are in a single cup of water?

In this question, you need to first consider the molecular weight of water – this must be 18 (2*1 + 16, for the Hydrogens and Oxygen). That gives a molar weight of 18 (i.e. 18 grams of water contain 6 * 10 to the 23 molecules). Next, you need to consider the density of water – which is 1 gram per cubic centimetre.

You should know that a cup is typically 250ml, or 250cc. Therefore one cup contains approximately 13.89 moles, thus it contains 8.36 *10 to 24 molecules of water. If you were looking to calculate this roughly, in your head, then you would round the values to the nearest 10 or 5, so perhaps use 20 instead of 18, and 15 instead of 13.89.

Question 2: What volume of wine can be drunk to reach the legal concentration of alcohol in the blood for driving?

The blood alcohol reading is the concentration of alcohol in a fixed volume of blood. The legal concentration in the UK is 80mg of alcohol per 100ml of blood. We could therefore attempt to calculate a figure from the total blood volume and this statistic. However, far simpler is to use the common knowledge that 1 pint is the maximum one can drink to drive, and one pint contains 2 units. Given that a bottle of wine commonly contains around 10 units and is 750ml, then a fifth of a bottle of wine is 150ml, or one glass. This question therefore illustrates that something seemingly complex can in fact be solved simply and quickly.

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Question 3: How does a glow stick work?

Assuming you don’t already know the exact way a glow stick works, then your thought process ought to be something along the following lines:

You should be aware that a glow stick generates light when one applies a mechanical force to it and shatters part of it. That means that you can therefore theorise that the glow stick contains one chemical in the ‘stick’ itself and perhaps another in a container within the stick. Therefore you should assume that the inner container breaks when you flex the stick, and that as a result the two chemicals mix. Therefore you should theorise that the two chemicals are highly reactive together. There must be a dye used as well as the stick is typically coloured. You might outline that you are interested in knowing how the reaction releases light rather than heat, and assume it is a result of the energy being released acting on the dye.

In fact, the chemical in the outer tube is typically diphenyl oxalate, (as well as the dye and catalyst) and the chemical in the glass vial is hydrogen peroxide.

The chemical reaction yields two moles of phenol and one mole peroxyacid ester, which decomposes spontaneously to carbon dioxide. This excites the dye, which in turn releases photons. The reaction therefore releases energy as light rather than heat. 

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