Chemistry 2006/ 2007 Club*** - page 8

I am starting Chem II this semester. Anyone want to start a club??? :rolleyes:... Read More

  1. by   beepeadoo
    Quote from vitacoconut
    i thought determining whether something is oxidized or reduced had something to do with the charge of the element or compound? when i had someone explain it to me they said that when a solid element turns to a liquid (aqueous) it is oxidized and vice versa, is this correct? thanks!
    It is my understanding, and this is just a newbie at this, oxidation and reduction are associated with gain or loss of electrons and nothing else.

    I can think of examples in which something might lose an electron, thus oxidizing, and not liquify. Case in point, iron oxidizes. Iron oxide is still a solid.

    I remember that REDUCTION is called that because the charge is REDUCED or lessened. I originally thought "Well if you GAIN an electron why do you call it REDUCTION" but it makes sense now. CHARGE is reduced.

    Once I remember that, I remember Oxidation means increase in charge. Increase in charge is only possible through loss of electrons.
  2. by   droopy1592
    Yep.
  3. by   andrea5
    please can anyone help me with the following q's

    Write formulas for conjugate base of HCO3^-

    write formulas for the conjugate acid of PO4^ 3-

    predict whether each of the following pair of susbtance could function as a buffer system in aqueous solution HCN and KCN

    thanks
  4. by   droopy1592
    reactions look like this


    HCl + KOH ---> KCl + H2O

    you can replace them with this terminology or flip it backwards

    acid + base ---> conjugate base + Conjugate acid


    Very simple... the acid, once it loses a Hydrogen (for simplicity, acids always lose an H) becomes a conjugate base. Most equations in Gen chem are substitution reactions, so you are just swapping atoms. The same with the base... the base, once it gains a H (taken from the acid) becomes a conjugated acid (notice H2O has an extra H... it was KOH before and only had one H).

    If your acid is a STRONG acid then your conjugate will be a weak base. If your acid was weak, the conjugate base would be strong, etc. Same with bases, if your base you started with was strong, your conjugate acid would be weak.

    So, in your case, HCO3 and PO4 would be

    HCO3 (HCO3 is tricky because it could be an acid AND or base in some reactions)

    HCO3 conjugate base is CO3
    HCO3 conjugate acid is H2CO3
    PO4 (base) conjugate acid is HPO4

    Remember, in order to obtain a conjugate base, you look at the appropriate conjugate acid and remove one (and only one) H+ ion from it. Be sure to remember that acid-base conjugate pairs differ by a single H+ ion.


    Sometimes they can be tricky, but just remember the rule

    H3O + OH ----> H2O + H2O

    acid + base ----> ca + cb

    or flip the one above

    HCl + KOH ---> KCl + H2O

    flipped

    KCl + H2O ---> HCl + KOH

    base + acid ---> Conjugate acid + Conjugate base

    just remember the rule
    Last edit by droopy1592 on Mar 9, '06
  5. by   droopy1592
    Quote from andrea5

    predict whether each of the following pair of susbtance could function as a buffer system in aqueous solution HCN and KCN

    thanks
    I can help you if you don't post the "following substances"
  6. by   andrea5
    thanks so much for taking the time to explain it to me. Its a lot clearer, thankyou.
    I looked at the "following substances" questions again and there are no other substances listed, so I'm guessing its a error on the question sheet.
    Thanks again :icon_hug:
  7. by   droopy1592
    All a buffer consist of is a weak acid and a weak base. With weak acids and weak bases the Ph stays relatively close to what you design it to be even if you introduce a strong acid or base. A buffer is used to resist change in PH. Since weak acids don't dissociate (lose a hydrogen atom) much at all (usually less than 20%) they only really lose a hydrogen atom if a strong base is introduced into to the buffer in an aqueous solution. So if you have a weak base and a weak acid in a solution they will not interact much with each other. If you put a strong base into the solution with the buffer the acid will react completely with it producing salt and water... The resulting PH will be slightly higher (a little more basic) but not as bad as if the aqueous solution consisted only of a Strong Base or only a strong acid. DO you see the reason for buffers? Your body has plenty of buffers working because you eat a lot of acidic and basic foods (and you have plenty of strong stomach acid) and your body must maintain a certain PH.

    I may have misunderstood that question wrong but (I thought it said an aqueous solution of) but if the aqueous solution contains those items you must find out if HCN and KCN are both weak. A buffer cannot have a strong base/acid at all. That's not the definition of a buffer.
  8. by   FNPhopeful
    Can I just ask (Droopy) and others who get this stuff..........what is your approach to the material?? are you purely memorizing formulas and compounds or is it more about have an understanding of why things are happening?
    I myself am a visual learning so I think thats been my trouble. I just wanna know what you guys do when you study.
    Because I try and do ALL my practice problems but if I get stuck I cant move on and I dont know WHY things are happening?

    And also how much time do you spend every day on chemsitry?

    -FNPHopeful
  9. by   droopy1592
    Let me be honest with you... I'm am one of those guys that can memorize anything easily and do math problems in my head without every writing anything down....






    But chemistry is different. Chemistry is the first and only subject (including other chemistry classes) that YOU MUST understand why things do the things they do. My first and second semester of Gen chem I spent more time studying for chemistry than all other subjects combined.

    I could study for a political science or history test the night before for 2 hours (not really paying attention in those classes or taking notes at all). I'd study for statistics test the night before for 30 minutes. I'd study for A and P for two hours before the test.

    The weeks of the third and fourth test in second semester I spent 16 hours each week studying, doing every pratice test question three or four times, not just memorizing the answer but working it out. Most other tests in chemistry I spent at least 6-8 hours of vigorous studying in addition to working the problems out over and over again. I also did all of this because chemistry is the first subject I fell in love with as it's the first to challenge me.

    Out of my class of 46 (20 dropped out), only 2 As were given (I was one) but it's not an easy subject because there's not as much memorization as there is understanding. My professor also just came out with a 98% effective treatment for breast cancer, so he is a pretty smart guy.

    Sometimes you need to google concepts so you understand them better.

    Maybe I should over a service where people can download some of my chem notes or Power point files taken from my professors.
  10. by   FNPhopeful
    Thanks Droopy I appreciate your reply. I guess I have a terrible instructor and Im not putting my lack of effort onto him by any means but he tests us on things we never even talked about in class so Im struggling, where like you said I can easily pull out an A in Micro and Anatomy. So I know Im not dumb........

    anyway Im only in Intro Chem, and we are in the chemical reactions/oxidations/ balancing equations areas. We were given the models for what combination, single-replacement, double-replacement reactions might look like but not told anything about them specifically, like what the trends are when you combine metals + H2O or metals+ O2

    So I guess I will continue to study study study. It gets confusing because there are so many different classifications of reactions and each one has its own set of possible combinations metal+nonmetal = or metal+H2O= or nonmetal+nonmetal=

    How do you keep it staight in your head!


    We are allowed a note card w/ notes for our exams, so I definitely fill that up
  11. by   droopy1592
    HA! Just hope you never have to take organic. There's no more math (other than bond angles) but you have to remember TONS of reactions and exactly how they work, step by step! IN 3D!

    Chemistry is something you have to commit to, as it's not memorization. YOu just have to suck it up this semester and knock it out. The latter part of Gen Chem 2 is very hard so don't let up.
  12. by   FNPhopeful
    I can memorize stuff thats just pure memorization, thats why I think I'll do good in organic. Its the taking the time to actually understand whats happening in a reaction that holds me up.......... I need something visual. Know of any animations of reactions?
  13. by   droopy1592
    U just have to google it. I don't have anything as far as animation.

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