Materials Science C

[Briscon]

It's there now.

There is a mistake on your answer key. For question 10, you are supposed to list materials in order of increasing Young's modulus. However, the answer key has "rubber" twice instead of having "diamond" in its proper spot.
Everything else looks good though! Thanks for the test, it was very well done, not too easy yet not too hard, and just in time too. My state competition is tomorrow.

[andrewwski]

Ah yeah, forgot to correct that. We corrected it on the paper copies we used for grading, but I never fixed the document. I'll put up a corrected version at some point.

As a basis of comparison, the average for the test was right around 50. The high score I believe was 82, and the low 21.

[earthbot25]

Does anyone know who the nats supervisor for this is going to be? I'm just curious.

[earthbot25]

Also, since most states have happened, did anyone have any labs at states? PA had a test based on stress and strain with testing the deformation of fishing line by adding weights to it.

[Briscon]

WA had a lab on contact angles. We got four different surfaces, and had to compare the contact angle between them, draw the drop etc. We also had to model one of the crystal structures (each team got a different one).

[RAntonello]

Could anyone explain how one might determine the packing structure of a particular material (i.e. FCC, BCC)? The question is asked several times in the Clio Invitational test that was posted a while back and there are no explanations given.

[Briscon]

Could anyone explain how one might determine the packing structure of a particular material (i.e. FCC, BCC)? The question is asked several times in the Clio Invitational test that was posted a while back and there are no explanations given.

Unfortunately, that one is something that you sort of have to just know. There isn't really a way to determine it as far as I know from just the name, it is mostly an intuitive sense. You should study crystal structures of common materials as well as the most typical crystal structure for each class of materials in order to have the best idea as to the crystal structure of a given material. In my experience, FCC is the most common structure for a wide range of materials. However, it does vary even for the same material. Iron, for example, can exist as BCC (delta, beta, and alpha iron), FCC (gamma iron), and HCP (Epsilon iron)

To andrewwski:
Can you explain what exactly the prefixes s- and p- on number 15 mean? My partner and I couldn't figure out what exactly you meant by it. Our first guess was sigma and pi bonds, but that would mean the answer would be s-sp3. Our second guess was it had to do with the p orbitals of the CL atoms. Could you clarify what exactly the prefix of the answer means (we understand the sp3 part).

[andrewwski]

Correct, the sp3 hybridized orbitals of Carbon bond with the p orbitals of Chlorine. Carbon is normally 2s2 2p2, it hybridizes to get 4 sp3 orbitals. Chlorine is 3s2 3p5 - it seeks one additional electron in the p-orbital. So each one of the sp3 orbitals of Carbon bonds with a p orbital of Chlorine.

[cjingk96]

WA had a lab on contact angles. We got four different surfaces, and had to compare the contact angle between them, draw the drop etc. We also had to model one of the crystal structures (each team got a different one).

In your lab, did you have to quantitatively measure the contact angles or just compare them? If you did have to get quantitative data, how did you do it? I have no idea what I'd do if I got a lab like that

[Infinity Flat]

WA had a lab on contact angles. We got four different surfaces, and had to compare the contact angle between them, draw the drop etc. We also had to model one of the crystal structures (each team got a different one).

In your lab, did you have to quantitatively measure the contact angles or just compare them? If you did have to get quantitative data, how did you do it? I have no idea what I'd do if I got a lab like that

It was just comparative IIRC.