AP Chemistry challenge

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Discus: SAT/ACT Tests and Test Preparation: July 2004 Archive: AP Chemistry challenge
By Etsrep78328 (Etsrep78328) on Monday, July 26, 2004 - 10:26 am: Edit

Answer the following questions:
1. Nitric acid is produced commercially by the Ostwald process, represented by the following equations:
4NH3(g) + 5O2(g) ---> 4NO(g) + 6H2O(g)
2NO(g) + O2(g) ---> 2NO2(g)
3NO2(g) + H2O(l) ---> 2HNO3(aq) + NO(g)

What mass of NH3 must be used to produce 1.0 x 10^6 kg HNO3 by the Ostwald process? Assume 100% yield in each reaction and assume that the NO produced in the third step is not recycled.

2. When M2S3(s) is heated in air, it is converted to MO2(s). A 4.000-g sample of M2S3(s) shows a decrease in mass of 0.277 g when it is heated in air. What is the average atomic mass of M?

3. A sample of a mixture containing only sodium chloride and potassium chloride has a mass of 4.000 g. When this sample is dissolved in water and excess silver nitrate is added, a white solid (silver chloride) forms. After filtration and drying, the solid silver chloride has the mass 8.5904 g. Calculate the mass percent of each mixture component.

By Massdad (Massdad) on Monday, July 26, 2004 - 11:58 am: Edit

You are kidding, right?

Maybe you shouldn't take AP chem until you've finished algebra? (just kidding)

Where are you stuck on these problems? The key to the last two is just setting up the algebraic equation.

I'll give you a big hint for number 1: 3 moles of NH3 produce 2 moles of HNO3. Can you figure it from there?

By Etsrep78328 (Etsrep78328) on Monday, July 26, 2004 - 01:57 pm: Edit

These are not questions that I am stuck up on. I am curious whether or not people can answer this question (these questions are similar to what is on an AP chemistry exam).

By Massdad (Massdad) on Monday, July 26, 2004 - 02:10 pm: Edit

Oh. I sure hope someone taking AP Chem can answer them. They're pretty basic college chem 101 type questions.

Wanna get tougher? Throw in a buffer question or two! I always had to think about them for a moment.

By Etsrep78328 (Etsrep78328) on Monday, July 26, 2004 - 02:12 pm: Edit

Here is a question that most chemists cannot answer: How is it that water, a liquid that can put out fires, is composed of two flammable/explosive gases?

By Daria1000 (Daria1000) on Monday, July 26, 2004 - 02:33 pm: Edit

man I hated buffers like none other!! argh!!!! Supposedly the first question on free response is an acid base question involving buffers, but it wasn't this year. So I got away with never understanding buffers ===> 5 on exam, I win!!

By Miamidude (Miamidude) on Monday, July 26, 2004 - 03:53 pm: Edit

err, the answer is infinity

By Piman3141 (Piman3141) on Monday, July 26, 2004 - 04:17 pm: Edit

hydrogen bonding is so strong that H20 cant split into its component elements, and thus, its not flammable?

2H20+O2>2H202, formation of hydrogen peroxide in the presence of oxygen, and no combustion.

I have no idea. good question. yeah, I didnt like buffers either, though if you work with them long enough, you get an intuitive sense of where the answer lies.

By Feuler (Feuler) on Monday, July 26, 2004 - 04:45 pm: Edit

Water is the PRODUCT of the combustion of Hyrdrogen with oxygen, so obviously it itself cannot be flammable, because it is the lower energy state. Substances are flammable only if there is another arrangement of the same atoms that has less potential energy. It's like asking why a cannonball on the ground doesn't smash the thing under it like a cannonball 100 feet in the air does. It's the same cannonball and the same ground, but in different energy states with relation to each other.

By Miamidude (Miamidude) on Monday, July 26, 2004 - 07:16 pm: Edit

im still going with infinity

its funny how no one is answering the original questions....

By Massdad (Massdad) on Monday, July 26, 2004 - 08:45 pm: Edit

Feuler is right. Put another way, water is NOT " composed of two flammable/explosive gases?" It is made FROM them.

So, it is not that a chemist cannot answer such a question. A good chemist just won't waste time answering a flawed question.

By Etsrep78328 (Etsrep78328) on Monday, July 26, 2004 - 08:46 pm: Edit

Please answer the following question that troubles chemists: How can a LIQUID, water, be formed from the combustion of two GASES (hydrogen and oxygen)?

By Kewlkiwi102 (Kewlkiwi102) on Monday, July 26, 2004 - 09:38 pm: Edit

in a chemical reaction the states of the products are independent of the state of the reactants.
a product need not retain the same chemical or physical properties of the reactants.
which actually answers both your questions.

in response to your first 3 posted questions: yes, AP chem students can do those easily.
but no, i do not feel in particular like doing the math out right now.

By Feuler (Feuler) on Monday, July 26, 2004 - 09:50 pm: Edit

Etsrep, please tell me you're joking. Any chemist "troubled" by something that's not even true in most combustion reactions (water VAPOR is formed) would light their lab apron on fire on the first day and burn to death. And mind you, it takes some hardcore dumbassitude to light a fire-resistant apron on fire.

By Kewlkiwi102 (Kewlkiwi102) on Monday, July 26, 2004 - 09:54 pm: Edit

LMAO feuler.
funny and a genius...marry me?

By Tongos (Tongos) on Monday, July 26, 2004 - 10:10 pm: Edit

your really intelligent feuler, both in math and chemistry. I saw your cauchy proof and the sequence thread, and i've got to say that your very bright.

By Eastsoldier (Eastsoldier) on Tuesday, July 27, 2004 - 11:06 am: Edit

1. 9.3e7g
2. 126g
3. 57.5% 42.5%

Etsrep, you don't see many chemical equations, do you?
There's more than one way to get H2O(liquid or gas)
Don't think every chemical is made out of elements

BTW Feuler is... famous? (I wouldn't want to be famous, then)

By Adidasty (Adidasty) on Tuesday, July 27, 2004 - 01:58 pm: Edit

Where the hell did biology go man? Math, physics, chemistry, where's the bio-love around here? Man CC is becoming bio-deficient.

By Miamidude (Miamidude) on Tuesday, July 27, 2004 - 02:44 pm: Edit

east soldier ur wrong, the answer is infinity for all of em

By Eastsoldier (Eastsoldier) on Tuesday, July 27, 2004 - 05:22 pm: Edit

If you bring a element with inifite mass, I'll say I was wrong
If you prove there's an infinite percentage, I'll say I was wrong
But for #1, I agree with you

By Miamidude (Miamidude) on Tuesday, July 27, 2004 - 07:07 pm: Edit

eastsoldier- it was a joke dude....

o and havent taken chemistry, can someone show the steps to the problems????? i got close answers to east but i think i did it a really retarded way

By Etsrep78328 (Etsrep78328) on Tuesday, July 27, 2004 - 10:27 pm: Edit

A compound contains only C, H, and N. Combustion of 35.0 mg of the compound produces 33.5 mg carbon dioxide and 41.1 mg water. What is the empirical formula of the compound?

By Etsrep78328 (Etsrep78328) on Tuesday, July 27, 2004 - 10:48 pm: Edit

Here is another challenging problem like the previous one: A compound contains only C, H, and O. Combustion of 10.68 mg of the compound yields 16.01 mg carbon dioxide and 4.37 mg water. The molar mass of the compound is 176.1 g/mol. What are the empirical and molecular formulas of the compound?

By Eastsoldier (Eastsoldier) on Wednesday, July 28, 2004 - 10:19 am: Edit

4. CH6N2
5. C3H4O3, C6H8O6

Miamidude - Comes with a joke, goes with a joke (I was kidding, too) I think I did it the way you did it, too. So.. Don't worry?

Etsrep - Those questions were good enough to refresh my memory. And I have no need to solve any more problems.
Well, I can't say those problems are AP chem challenge. I'd say it's Chem1H with a lot of Algebra. (Especially 2 & 3)

Chem AP tests the concepts and ways not the math.
Sorry - I get pissed after doing problems

By Etsrep78328 (Etsrep78328) on Wednesday, July 28, 2004 - 12:54 pm: Edit

The oxyanion of nitrogen in which it has the highest oxidation state is the nitrate ion (NO3 with a -1 charge). The corresponding oxyanion of phosphorous is PO4 (with a -3 charge). The NO4 (-3 charge) ion is known but not very stable. The PO3 (-1 charge) ion is not known. Account for these differences in terms of the bonding in the four anions.

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