## Materials Science C

raxu
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### Re: Materials Science C

In the sonic powerpoint there are a few formulas for weight distribution I don't quite understand...

Number Average $\overline{M_n}=\frac{\sum N_iM_i}{\sum N_i}$ ,
Weighted average = $\overline{M_w}=\frac{\sum N_iM_i^2}{\sum N_iM_i}$ ,
Molecular weight average $\overline{M_z}=\frac{\sum N_iM_i^\alpha}{\sum N_iM_i^{\alpha-1}}$ .

Can someone explain what they are for?
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sonred
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### Re: Materials Science C

raxu wrote:In the sonic powerpoint there are a few formulas for weight distribution I don't quite understand...

Number Average $\overline{M_n}=\frac{\sum N_iM_i}{\sum N_i}$ ,
Weighted average = $\overline{M_w}=\frac{\sum N_iM_i^2}{\sum N_iM_i}$ ,
Molecular weight average $\overline{M_z}=\frac{\sum N_iM_i^\alpha}{\sum N_iM_i^{\alpha-1}}$ .

Can someone explain what they are for?

number average is doesn't take into account that heavier molecules contribute more to the molecular weight than lighter molecules where as weighted average does.

sonred
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### Re: Materials Science C

raxu wrote:In the sonic powerpoint there are a few formulas for weight distribution I don't quite understand...

Number Average $\overline{M_n}=\frac{\sum N_iM_i}{\sum N_i}$ ,
Weighted average = $\overline{M_w}=\frac{\sum N_iM_i^2}{\sum N_iM_i}$ ,
Molecular weight average $\overline{M_z}=\frac{\sum N_iM_i^\alpha}{\sum N_iM_i^{\alpha-1}}$ .

Can someone explain what they are for?

number average is doesn't take into account that heavier molecules contribute more to the molecular weight than lighter molecules where as weighted average does.

greekyogurt
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### Re: Materials Science C

Hello! I just started a team this year, and was wondering what would be an example of a cheap+fairly easy practice lab for materials science? Additionally, is roughly 40 questions an unreasonable amount for the given time? (we looked at the practice tests on the wikia, but were hoping for something more recent)
thanks!

Unome
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### Re: Materials Science C

greekyogurt wrote:Hello! I just started a team this year, and was wondering what would be an example of a cheap+fairly easy practice lab for materials science? Additionally, is roughly 40 questions an unreasonable amount for the given time? (we looked at the practice tests on the wikia, but were hoping for something more recent)
thanks!

It sounds like you're trying to write a test?
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Concord
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### Re: Materials Science C

greekyogurt wrote:Hello! I just started a team this year, and was wondering what would be an example of a cheap+fairly easy practice lab for materials science? Additionally, is roughly 40 questions an unreasonable amount for the given time? (we looked at the practice tests on the wikia, but were hoping for something more recent)
thanks!

40 questions definitely isn't an unreasonable amount of questions on a test, but it may depend on the formatting of the questions. I.e. 40 essay/short answer questions may be too much, but something like 30 M/C, 5 Matching, and then 5 SAR would be a perfectly fine formatting. Additionally, the difficulty of the questions may factor in as well. If you want me to take a look at a potential test, just PM me and I would definitely be willing to give you feedback on it! Additionally, I can send you one or two previous invite tests for matsci, which should be more recent than the ones on the test exchange if you are willing!

Additionally, there are many good examples of easier practice labs. For example, using polymer specimens (i.e. ones used in forensics), you can determine which polymers (PVC,PET,LDPE,etc) are which based on sink/float testing in liquids of varying densities. Additionally, various Young's modulus labs involving rubber bands or trash bags may work as well.
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jaah5211
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### Re: Materials Science C

I had a question for the material science organic nomenclature naming. Would they ask the IUPAC (Systematic) naming or the common naming for the test?
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Concord
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### Re: Materials Science C

jaah5211 wrote:I had a question for the material science organic nomenclature naming. Would they ask the IUPAC (Systematic) naming or the common naming for the test?

I've seen tests with both questions about IUPAC naming as well as common naming, and there are also some tests that offer bonus points on nomenclature sections if you can provide both, i.e. UT Invitational 2017.
William P. Clements '20

Skink
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### Re: Materials Science C

Re: length, 40 MC is super short unless it's a small Regional. It's a fifty minute event, and MC (unless very well-written, which they usually aren't) don't take that long. A rule of thumb is that you want twice the number of questions as teams in attendance at minimum, but I'd have more questions, yet, if they're MC.

Re: nomenclature, know the IUPAC rules in and out, but know commonplace common names. I've found even higher-end teams using systematic names that no chemist would seriously use when given the freedom to choose any acceptable name.

Raleway
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### Re: Materials Science C

Adding on to Skink, most tests are designed to either have teams just barely finish or not finish to separate top end teams. Some tests can range from 60 MC, Lab, 30 nomenclature, and 10 SAQ to some that are just 5 really long open-ended with a lab. It is in your best interest especially for your own team to make a test that they cannot finish as it forces them to really assess how long they spend on each question.

Regarding IUPAC vs Industry, just know both. No self-respecting scientist says ethanoic acid as a common way to refer to acetic acid. A very common mistake many make is to use the common name "isopropyl." Many times, using "isopropyl" will change the main chain number of alcohols and thus completely screw up IUPAC naming. No one will say IUPAC is wrong; some may say industry names are wrong. When in doubt (or not specifically stated), use IUPAC.
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### Re: Materials Science C

https://abmpk.files.wordpress.com/2014/ ... lister.pdf

Can anybody tell me what chapters of this book are most relevant to materials science this year?

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### Re: Materials Science C

I just got put into this event for a competition on Saturday...

What are some of the more common things seen on tests, and are there any good overviews of what we need to know?
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Tesel
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### Re: Materials Science C

Know the basics of organic nomenclature, at least how to identify each group and name simple molecules.

Understand tensile tests and stress strain curves, if nothing else.

Understand what thermoset and thermoplastic polymers are, with at least limited detail.

Have some info about recycling codes and those 6 groups of polymers.

Hopefully, have working definitions and equations for other topics.
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### Re: Materials Science C

Tesel wrote:Know the basics of organic nomenclature, at least how to identify each group and name simple molecules.

Understand tensile tests and stress strain curves, if nothing else.

Understand what thermoset and thermoplastic polymers are, with at least limited detail.

Have some info about recycling codes and those 6 groups of polymers.

Hopefully, have working definitions and equations for other topics.

Thank you for the tips!
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luanne
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### Re: Materials Science C

Hi guys,
So my school's scioly program is relatively less funded and we basically self study for all our events.
Can someone give me an overview of the math needed and topics that I should try to learn?
Thanks