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# struggling with basic chem

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Hey guys! Im in need of some chem help!

1) When 0.72g of a liquid is vaporized at 110 degrees C and 0.967atm, the gas occupies a volume of 0.559L. The empirical formula of the gas is CH2. What is the molecular formula of the gas? Answer: C3H6

2) The diffusion rate of N2 gas is 1.73 times as great as a noble gas (both gases are at the same temperature). What is hte noble gas? Answer: Kr

3) An oxybromate compound, KBrO(x) (x is a subscript), where x is a whole number, is analyzed and found to contain 47.84% Br by mass. What is x? Answer: 3

4) 5.00 moles of a monatomic ideal gas goes from P1= 3.00 atm, V1 = 15.0L to P2= 3.00 atm, V2= 55.0L. Calculate delta H for this process.

If I don't do well on this midterm I am probably going to end up giving up on school all together. Thanks for your time though!

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lol you're going to give up on school just because you did bad on one midterm? Probably should've just saved your money and did something else in the first place if you're approaching it with that kind of attitude.

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Hey guys! Im in need of some chem help!

1) When 0.72g of a liquid is vaporized at 110 degrees C and 0.967atm, the gas occupies a volume of 0.559L. The empirical formula of the gas is CH2. What is the molecular formula of the gas? Answer: C3H6

2) The diffusion rate of N2 gas is 1.73 times as great as a noble gas (both gases are at the same temperature). What is hte noble gas? Answer: Kr

3) An oxybromate compound, KBrO(x) (x is a subscript), where x is a whole number, is analyzed and found to contain 47.84% Br by mass. What is x? Answer: 3

4) 5.00 moles of a monatomic ideal gas goes from P1= 3.00 atm, V1 = 15.0L to P2= 3.00 atm, V2= 55.0L. Calculate delta H for this process.

If I don't do well on this midterm I am probably going to end up giving up on school all together. Thanks for your time though!

1) Use PV=nRT, where n=(Mass of the compound)/(Formula Weight of the compound)

2) Use Graham's Law, where

Effusion Rate of N2/Effusion Rate of noble gas

= Square root(Formula Weight of noble gas/Formula Weight of N2)

3) Let the compound be 100 grams, then there are 47.84g of Br. Divide by the formula weight of Br to get the mole of Br. Then you know the mole of K. Convert the mole of K to gram, and add gram K and gram Br together. The rest is O.

4) Use PV=nRT, and calculate delta T from the first and second condition, then use q=mc(delta T) to calculate heat change

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These are VERY basic questions. As the poster above me indicated, these are very formulaic and you can easily do them based on an example. Why do you think you are unable to answer them? Is it because you have fallen behind in school and the material is therefore unfamiliar (i.e. no background knowledge from high school)? Or are you just ridiculously bad at chem?

Either way, I STRONGLY suggest you go see a chem tutor at your school and request some one-on-one sessions. Basic chem CAN be learned, but if you do not know the basics, you need someone to sit down with you and go over it. (P.S. you will NOT be able to survive through the school year without this knowledge. It doesn't mean quit, but it does mean that you need to re-evaluate a plan of action.)

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Is it bad I dont' remember how to do any of those questions?

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Quick question, do you learn how to do these in university? I can't answer a single one with my grade 12U chemistry knowledge... (I haven' taken chemistry yet...)

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Quick question, do you learn how to do these in university? I can't answer a single one with my grade 12U chemistry knowledge... (I haven' taken chemistry yet...)

I took AP so I can't speak for everyone, but I'm fairly certain you should have at least been introduced to these concepts in high school. It sucks that there is such a disparity in high school education that some kids come to university completely unprepared. I found that at least in my first year chem class, the profs were teaching in a style that really expected students to have been familiar with the material.

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Just finishing first year, I can say that these concepts were all familiar with the exception of the Graham's Law for the noble gas question.

I suppose there will always be slight variations in the content across universities.

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Quick question, do you learn how to do these in university? I can't answer a single one with my grade 12U chemistry knowledge... (I haven' taken chemistry yet...)

Not at all by my experience. None of these concepts (gas law, thermodynamics,etc.) was taught in the BC Chemistry 12 curriculum. You do have to know the basic stoichiometry, or it will haunt forever...

I find the introduction to chemistry (year 1 chem) to be a combination of grade 11 and 12 chemistry, only much advanced.

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i knew most of the stuff on the exam but ran out of time! missed a BUNCH of questions on a 50 minute midterm!

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i knew most of the stuff on the exam but ran out of time! missed a BUNCH of questions on a 50 minute midterm!

1 midterm means nothing. Dont give up so easily!

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Just finishing first year, I can say that these concepts were all familiar with the exception of the Graham's Law for the noble gas question.

I suppose there will always be slight variations in the content across universities.

+1. I learned all those concepts in high school chemistry, except Graham's Law (that was taught in 1st year chem).

Not at all by my experience. None of these concepts (gas law, thermodynamics,etc.) was taught in the BC Chemistry 12 curriculum. You do have to know the basic stoichiometry, or it will haunt forever...

Really? That's surprising...

OP, don't give up! you can still come through! Good luck

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i knew most of the stuff on the exam but ran out of time! missed a BUNCH of questions on a 50 minute midterm!

maybe it's time to try a new testing strategy? you'll find that sometimes the people who do best on tests are not the ones who know the material best, but those that have the best test taking strategies. this is something you can talk to your school's center for student development about.

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you may want to see a chemistry tutor, because numbers 1,3 are covered nowadays by the grade 11 curriculum(I'm from ontario, but IB)

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You could always pick up a copy of chemistry for dummies.....I never took 12U chem and went ahead and took a general chem class, the book honestly saved my life. In hindsight taking a course without the suggested prereqs (ie: highschool level classes) is not the greatest idea, but it can be done and you can probably have alot of success in your course if you are willing to put in the extra effort and time in order to succeed. I used to have to spend 10 times more time studying and attempting to grasp concepts that my counterparts who had 12U chem easily grasped. But yeah chem for dummies is a good idea if you want to get familiar with chemistry and some basic concepts, it was a lifesaver for me!

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Yeah, chemistry for dummies is actually really good. I used it to study for the MCAT since I hadn't taken chemistry in about 9 years and I ended up with a 13 in PS!

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