1. The SDN iPhone App is back and free through November! Get it today and please post a review on the App Store!
    Dismiss Notice
  2. Dismiss Notice
  3. 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
  4. Dismiss Notice
Dismiss Notice

Interview Feedback: Visit Interview Feedback to view and submit interview information.

Interviewing Masterclass: Free masterclass on interviewing from SDN and Medical College of Georgia

Gchem: Acid and Bases

Discussion in 'DAT Discussions' started by Envision, Aug 8, 2006.

  1. Envision

    Envision Envisioning...
    7+ Year Member

    Joined:
    Jun 14, 2005
    Messages:
    1,000
    Likes Received:
    1
    Status:
    Dentist
    Hi guys, ok so im having some trouble understanding titration problems. here are 2 examples.

    1) What volume of HCl was added if 20 ml of 1M NaOH is titrated with 1 M HCl to produce a pH=2?

    a 10.2 ml
    b 20.2 ml
    c 30.4 ml
    d 35.5 ml
    e none
    answer: E
    i noticed that the molarity of both are equal, so they should probably neutralize each other if given the same volume. however, im not sure where to go from there.

    2) A 10 ml sample of HCl solution has a pH of 2. what volume of water must be added in order to change pH=4?

    Answer: 990ml H2O

    thanx in advance.
     
  2. Note: SDN Members do not see this ad.

  3. dat_student

    dat_student Junior Member
    5+ Year Member

    Joined:
    Apr 4, 2005
    Messages:
    2,068
    Likes Received:
    0
    Do a search on #1. I've probably solved it 10 times already

    #2)
    10^-2 * 10
    ______________ = 10^-4 (pH = 4 so [H+] = 10^-4)
    10 + V

    10^-1
    _______ = 10 + V
    10^-4

    1000 = 10 + V

    V = 990 ml


    If you want to be more accurate you should consider that water itself has some H+. Since that amnt is small you can ignore it.
     
  4. DonExodus

    DonExodus Dentist in Virgin Islands
    10+ Year Member

    Joined:
    Jul 6, 2006
    Messages:
    121
    Likes Received:
    1
    Status:
    Dentist
    I had always set it up like (.01)(.01)=(.0001)(V2) and solved from there, getting 100.

    Ive seen you answer several questions in this format, but Im unclear how to follow it. I was just doing CV=CV, and I think this is a similar set up, but Im still lost.
    Could you show me how you set those up please?
    Thanks,
    Don
     
  5. dat_student

    dat_student Junior Member
    5+ Year Member

    Joined:
    Apr 4, 2005
    Messages:
    2,068
    Likes Received:
    0
    # of moles of H+
    ______________ = molarity
    total volume


    # of moles of H+
    _____________________________ = [H+] (i.e. concentration of H+)
    volume of HCl + volume of water
     
  6. Envision

    Envision Envisioning...
    7+ Year Member

    Joined:
    Jun 14, 2005
    Messages:
    1,000
    Likes Received:
    1
    Status:
    Dentist
     
  7. joonkimdds

    joonkimdds Senior Member
    7+ Year Member

    Joined:
    Jun 30, 2005
    Messages:
    2,780
    Likes Received:
    2
    Status:
    Pre-Dental
    let me solve it with my own way, i hope this makes it easier

    pH = concentration of H
    pH=2 = 10^(-2) = 0.1 = very very acidic
    pH=4 = 10^(-4) = 0.001 = less acidic which means u added water here.

    M1V1=M2V2
    (0.1)(10mL) = (0.001)(10ml+x)
    how?
    becuz. 0.1 = molarity of H before u add water and so it's the 10ml HCL with pH=2.
    and then it becomes pH=4 = 0.001 when u add water, x amount to 10mL.

    and X is how much u added water and if u solve for it, u get 0.99mL and
    that's 990L.
     
  8. gogiantsss

    2+ Year Member

    Joined:
    Feb 4, 2007
    Messages:
    142
    Likes Received:
    1
    Status:
    Pre-Dental
    Remember that in the lab, never add water to acid!
     
  9. joonkimdds

    joonkimdds Senior Member
    7+ Year Member

    Joined:
    Jun 30, 2005
    Messages:
    2,780
    Likes Received:
    2
    Status:
    Pre-Dental
    why not?:confused:
     
  10. Chga

    Chga Member
    7+ Year Member

    Joined:
    Jan 11, 2006
    Messages:
    346
    Likes Received:
    86
    Status:
    Pre-Health (Field Undecided)
    b/c its always acid to water:)
     
  11. Lonely Sol

    Lonely Sol cowgoesmoo fan!
    10+ Year Member

    Joined:
    Dec 13, 2005
    Messages:
    684
    Likes Received:
    1
    Status:
    Pre-Dental
    A large amount of heat is released when strong acids are mixed with water. Adding more acid releases more heat. If you add water to acid, you form an extremely concentrated solution of acid initially. So much heat is released that the solution may boil very violently, splashing concentrated acid out of the container! If you add acid to water, the solution that forms is very dilute and the small amount of heat released is not enough to vaporize and spatter it.

    So Always Add Acid to water, and never the reverse, unless you want to get ur instructors attention!
     
  12. joonkimdds

    joonkimdds Senior Member
    7+ Year Member

    Joined:
    Jun 30, 2005
    Messages:
    2,780
    Likes Received:
    2
    Status:
    Pre-Dental
    :scared:
    I am so glad I made my table members do everything for me :D
     

Share This Page