Help me with by basic chem homework thx

Discussion in 'General Off-Topic Chat' started by Dwight, Oct 17, 2008.

Oct 17, 2008
  1. Dwight
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    Member Dwight Gawb. Gawb Bluth.

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    Ok, so I was absent a few days ago when we learned about mass, moles, molecules, and atoms, and I have no clue how the fuck to convert them to eachother, aside from atoms=mcls*2 which is pretty fucking basic. I also know that to get from moles to mcls you have to do something with 6.02*10^24 or something.
    And we have a quiz tomorrow. And I had a tennis match during after school help.

    So, if you could do a few problems for me, and explain how to do it step by step, I would be really happy.

    1: Give 14.6 g of KMnO4, find:
    a)moles
    b)molecules
    c)atoms

    2: Given 0.00302 moles of fluorine, how many grams, molecules, and atoms are present.

    THANKS GBATEMP
     
  2. sfunk

    Member sfunk GBAtemp Regular

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    My teacher taught me something called the mol hill for conversions in Chem 11. Makes it real easy.

    [​IMG]

    ...................mol
    ....................^
    ........A.M.U / \Avogadro's number
    .............../ \
    .........grams molecules

    When going up the hill divide by the value on the side of the hill (AMU or Avogadro's number). When going down the hill multiply. Because going up a hill is harder work, when going up the mol hill you do the harder operation. Stupid logic? Yes, but it still helps when remembering.

    As for your examples:

    1. A.M.U. of KMnO4
    K - 39.10
    Mn - 54.94
    O - 16 * 4
    Total = 158.04g/mol (Just add. Multiply O by 4 because there's 4 of them)

    a)14.6g/158.04g/mol (divide because you're going up the hill, from grams -> mol) = 0.0923816755mol

    b)0.0923816755mol * 6.0221415E23(mol^-1) (multiply because you're going down, from mol -> molecules, 1/mol units on Avogadro's number because the outcome (number of molecules) is unitless) = 5.56335522E22molecules

    c) Number of atoms in each molecule of KMnO4 = 1 K, 1 Mn, 4 O = 5 atoms per molecule
    5atoms/molecule * 5.56335522E22molecules = 2.78167761E23atoms

    2. Repeat this on your own. It's pretty much the same as the first question. I think fluorine is only found as F2 naturally.

    Edit: Mole hill fucked up. Trying to fix.

    Edit2: Shitty paint image added. ASCII art failure left intact. Man I hate chemistry. Organic chemistry will be the death of me.

    Edit3: Edited for clarity.

    Edit4: This link does the same job I just did but with different numbers: http://dbhs.wvusd.k12.ca.us/webdocs/Mole/Grams-to-Moles.html Also, in my mol hill, the bottom right is supposed to read "molecules" not just mole. I reuploaded the image but maybe your cache caught the old image.
     
  3. Dwight
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    Member Dwight Gawb. Gawb Bluth.

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    Ah... Thanks so much
    That's just what I needed.
     
  4. OrcMonkey©

    Banned OrcMonkey© Banned

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    wOW I dont even get a thing your saying?!?!?!?!?
     
  5. Dwight
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    Member Dwight Gawb. Gawb Bluth.

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    Have a good time in Chemistry haha
     
  6. tinymonkeyt

    Member tinymonkeyt GBAtemp brat

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    yeah basically what sfunk said
    you might wanna take off some digits though
    mind the sig figs yeah?

    if you need any clarification:
    (putting what sfunk said in simpler terms and how to do it)
    a. since you have 14.6 g of KMnO4
    you multiply by the molar mass of KMnO4 (add every element of KMnO4 together. 1 of K and Mn, and 4 of oxygen. you get the numbers from the periodic table). it would be like a fraction, with 1 mol of KMnO4 on top, and the molar mass on the bottom in grams.
    b. once you found how many moles it has, just multiply by avagadros number: 6.022 x 10^23
    once again, you can set it up in fraction form, with 1 mole of KMnO4 on the bottom, and 6.022x10^23 molecules of KMnO4 on the top (so the bottom units will cancel out and you end up w/ molecules)
    c. well for atoms, i thought it was the same thing as molecules (just change the units) but i could be wrong. im taking AP chem though.

    2. yeah. this time, multiply it by the molar mass, except with the 1 mol of F on the bottom and grams on top. the rest should be the same as ^
     
  7. Link5084

    Member Link5084 Sword & Shield at your service

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    I'm in Chem right now and we havent learned this stuff. Are you a high school junior?
     
  8. sfunk

    Member sfunk GBAtemp Regular

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    I'm crazy for my decimal places. I keep everything until asked for a final answer only after which point do I round. Calculators have store functions for a reason [​IMG].

    Edit: I just realized that I made a mistake. Avogadro's number has units of 1/mol. The outcome is unitless as it is just a counting number.
     
  9. Dwight
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    Member Dwight Gawb. Gawb Bluth.

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    ugh my teacher is such an ass about those.

    So I tried a problem myself, tell me how I did:
    3.28 moles
    Fine grams, molecules, and atoms.
    3.28 mol * 6.02*10^23= 1.97*10^24 molecules
    1.97*10^24 molecules * 2 atoms/molecule = 3.95*10^24 atoms
    3.28 mole/107.87 atomic mass= 0.0304 grams

    I think I messed up on finding the grams...
     
  10. sfunk

    Member sfunk GBAtemp Regular

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    Maybe I missed something but what compound are we dealing with...?
     
  11. Dwight
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    Member Dwight Gawb. Gawb Bluth.

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    Oops, it's Ag.
    My bad.
     
  12. tinymonkeyt

    Member tinymonkeyt GBAtemp brat

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    for grams
    multiply by 107.87, instead of dividing
    because since youre starting with moles
    youre going to be multiplying by g/mol, to get rid of the mol unit
    a good indication if you done it right or wrong
    is to check if the mole value is more than the grams (it will always be)

    and why are there 2 atoms per molecule?
    not that its wrong
    i just dont see why
     
  13. sfunk

    Member sfunk GBAtemp Regular

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    Well Ag2 isn't a compound to my knowledge, silver is only found as Ag. So number of molecules = number of atoms, unless of course you've got something else written on your sheet. Other than that the math looks right to me, I'm not calculating it out but it looks good so far as I can see. Moles to grams looks right. As does everything else (minus the molecules to atoms).

    Edit:Whoops, not thinking today. tinymonkeyt is right, multiply don't divide.
     
  14. Dwight
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    Member Dwight Gawb. Gawb Bluth.

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    Ok, I get it now.
    Thanks for the help guys.
     
  15. jabjab

    Member jabjab GBAtemp Fan

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    1c) 6 atoms/molecule

    Give your answer in max of 3 sig figs as thats whats used for all data supplied - make sure to carry through all intermediates unrounded though or you will introduce rounding errors.
     

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