Sample Interview Questions

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10-27

2021

My name is Katie, I’m currently studying natural sciences at Murray Edwards college, Cambridge. I’ve just finished my second year of the course and I’ve chosen to specialise in Chemistry. So today I’m going to talk about the interview structure for when I applied 3 years ago for physical natural sciences and then go through an example question so you can see what kind of level they are expecting you to be at and what the best way it is to answer these questions.

So when you apply for natural sciences, you should specify on the SAQ form whether you are applying for physical natural sciences or biological natural sciences. This doesn’t actually limit you once you can get to Cambridge. You could still change your mind later. But it’s more to decide what kind of interview structure they decide to give you.

So I applied for physical natural sciences therefore I had two interviews with my college. This does vary between colleges though. But for mine, I had a physics based interview and a chemistry based interview. My physics based interview was with me and my physics supervisor and a materials sciences supervisor. They mainly went through more mathematical questions. I didn’t have to sit an official maths test but they brought along with them a list of maths questions on a piece of paper which was laid out in a very similar way to a test. I worked through the questions with them and they could basically see how I thought about thought through questions on a maths test. We then discussed a few things on my personal statement and a couple more questions based on more physics based topics. 

So the second interview I had was with a chemistry supervisor and a geology supervisor. This obviously covered mainly chemistry questions, a few geology ones and they also asked a couple of biology related questions which were to do with my personal statement. The chemistry interview didn’t contain nearly as much maths. It was a lot more about how I understood chemistry there were some diagams I had to draw or interpret. There were some graphs, some data. They wanted to see that I could both remember a lot of stuff from A-level chemistry but apply it to different situations and actually understand the reasoning behind it. 

So now to an example question. This was a question I was given in my chemistry interview. I believe it’s actually quite a popular question between different colleges because I’ve heard other people having the similar questions too. It’s actually a reasonably simple question. Explain the trends in bond length and bond dissociation energy for the halogens. Explain why fluorine doesn’t fit the trend. They don’t expect you to remember exactly what the trend is. They gave me a table data which stated the bond energies and the bond lengths for each of the molecules of interests.  

I’ve drawn out this table again for you. It looks like this. You don’t need to look into details into numbers. All they want to see is that you could understand the trend and explain the trend behind this. First thing I did obviously was look at data and visually think about how this look on a graph.

How would you visualise this? So if you think about how it looks on a graph, quite simply the bond length for fluorine is 143 which is quite small and it increases all the way upto iodine at 266. It’s a reasonably linear increase. So the first part of the question is explain the trend in bond length. This is actually very simple. The atoms are bigger so the molecule must be bigger. But the more challenging bit of this question was the second half of the question about the bond dissociation energy. So this isn’t a perfectly linear trend. From iodine to chlorine, there is quite a steady increase as you go down from chlorine down to iodine, the bond dissociation energy decreases. This makes sense when you think about the bond length, the first part of the question.
Often the questions with several parts you can use the earliest of the questions to help later bits of the question. We knew from the first half the question that the bond length were increasing so it makes sense that the bond dissociation enthalpy is decreasing because atoms are further apart.
So it is easier to break the bond. But the pretty hard bit is what happens with fluorine? Because fluorine actually has a lower bond dissociation enthalpy than chlorine, which doesn’t fit the trend. It should be higher.

Let’s comes a bit down to the size of the atoms. Fluorine is a very small atom. So they are put close to together, their interactions between all the electrons around each of them, the atoms, in iodine for example, they are much further apart so any repulsive forces between the electrons is not significant enough to really affect the bond dissociation energy. But for fluorine, the two atoms are very close together. To think about the diagram you often draw at A-Level for halogens, we draw dots and crosses around the edges of each atom. You can see that the electrons on each of the atoms are quite close together and they can repel. And this repulsive force is actually easier to break the bond than you would expect. Therefore, the bond dissociation energy is lower. So when you look at it that way, actually it's quite a simple question. You have to break it down to different parts and think logically and through each of the questions.