1. Dismiss Notice
  2. Guest, be sure to check out How To Get Into Dental School, our free downloadable PDF with step-by-step details for dental school applicants!
    Dismiss Notice
  3. Dismiss Notice
  4. Download free Tapatalk for iPhone or Tapatalk for Android for your phone and follow the SDN forums with push notifications.
    Dismiss Notice

Acid/ pH

Discussion in 'DAT Discussions' started by Dencology, May 27, 2008.

  1. Dencology

    2+ Year Member

    Joined:
    Mar 7, 2008
    Messages:
    396
    Likes Received:
    0
    Status:
    Pre-Dental
    [​IMG][​IMG][​IMG]100g of a compound of unknown identity is dissolved in 10L of water to produce a solution with a pH of 2. which of the following statements with regard to the compound is most likely true?

    a. the compound is a strong acid with a formula weight less than 100g/mol
    b. the compound is a weak base with a formula weight greater than 100g/mol
    c. " "" is a strong base with fromula weight less than 50g/mol
    d. " " is a strong acid with a formula weight of greater than 100g/mol
    e. the compound is a weak acid with a formula weight of less than 100g/mol

    the answer is a but why guys?
     
  2. Note: SDN Members do not see this ad.

  3. Zerconia2921

    Zerconia2921 Bring your A-game!
    2+ Year Member

    Joined:
    Mar 24, 2008
    Messages:
    207
    Likes Received:
    0
    Status:
    Pre-Pharmacy
    Common logic tells us the a pH of 2 is very acidic from that we can eliminate e, and c. Also a strong acid will dissociate and among the strong acids formula weight dosent exceed 100g/mol (from what I can think of) so this eliminaes answer b, and d. thats how i would reason this problem.
     
  4. doc3232

    7+ Year Member

    Joined:
    Feb 15, 2008
    Messages:
    3,809
    Likes Received:
    9
    Status:
    Dental Student
    It is definitely a strong acid because weak acids could never get to a pH of 2.
    So the question is: Is it less than or more than 100 g/mol?
    Try each one. If it is 100 grams/mol then it is will have a pH of 1 and if it is something like 20 grams/mol, then we get pH of 1.7. If you went the other way, saying it is greater than 100 grams/mol, then you would get a pH of less than 1. I don't know if this is the right way or if I am right but it sort of works.
     
  5. Zerconia2921

    Zerconia2921 Bring your A-game!
    2+ Year Member

    Joined:
    Mar 24, 2008
    Messages:
    207
    Likes Received:
    0
    Status:
    Pre-Pharmacy
    doc3232
    i was thinking of all of the strong acids like HCl for example its mw is 36g/mol right and whats another strong acid HI 56g/mol, HNO3 63g/mol are all below 100g/mol thats what i was thinking about from my post is this corret?
     
  6. Hugh Mannity

    2+ Year Member

    Joined:
    May 15, 2008
    Messages:
    228
    Likes Received:
    0
    Status:
    Pre-Dental
    Well I may be doing something wrong since my answer is D but here is how I tried to solve for the MW. pH=2 means [H+]=0.01. Now I set up a stoichiometry type thing like this: (100g)(1/(x g/mol))(1/(1 L)) = mol of acid. Since we treat it as a strong acid then [HA]i = [H+]eq. so 100/(10x) = 0.01. x=1000g/mol. But then why answer A? All common strong acids are under 100g/mol but according to wikipedia there are extremely strong acids that are above 100g/mol. If anyone can tell me why my reasoning is wrong it would be greatly appreciated because if the answer is A then it is obviously wrong.
     
  7. doc3232

    7+ Year Member

    Joined:
    Feb 15, 2008
    Messages:
    3,809
    Likes Received:
    9
    Status:
    Dental Student
    I agree with you but if you do the math, none of those numbers will give a pH of 2.
     
  8. Dencology

    2+ Year Member

    Joined:
    Mar 7, 2008
    Messages:
    396
    Likes Received:
    0
    Status:
    Pre-Dental
    I like your approach.
     
  9. TempleDMDKrazd

    7+ Year Member

    Joined:
    Mar 10, 2008
    Messages:
    232
    Likes Received:
    0
    Status:
    Dental Student
    a stronger acid then all those are HClO4.....= molecular weight of 100g/mole
     

Share This Page