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

Kaplan blue page 671, #49 Gen CHEM

Discussion in 'DAT Discussions' started by joonkimdds, Jul 27, 2006.

  1. joonkimdds

    joonkimdds Senior Member
    7+ Year Member

    Joined:
    Jun 30, 2005
    Messages:
    2,780
    Likes Received:
    2
    Status:
    Pre-Dental
    what is the percentage of oxygen by mass in a 200gram sample of CuSo4 * 5H2O?

    I just added all the masses, got the mass of oxygens.

    mass of oxygen / total mass * 100 % = percentage of oxygen in CuSo4 * 5H2O.

    What I don't understand is why does it say 200 gram sample?

    mass of oxygen = 144
    total mass = 250

    is it because no matter what the total mass is, the percentage of oxygen doesn't change becuz the mass of oxygen will also inc or dec at the same rate as the total mass?
     
  2. Note: SDN Members do not see this ad.

  3. dental#1

    dental#1 Fla DDS
    2+ Year Member

    Joined:
    Jul 22, 2006
    Messages:
    62
    Likes Received:
    0
    Status:
    Pre-Dental
    I think your thinking is on the right path. But what was your answer?72% or 57.6%. I am thinking.... maybe you should do this( I am not sure i am looking it up!)

    ([given]gof compound)(mole/gcompound)= moles of compound

    (molcomp)(moleO/molcomp)(gO/1mol)=gO

    massO/Total*100%=?

    g/250g*100= % or g/200g*100%= %. Let me know. this is either really easy or tricky
    Kaplan doesn't explain this well :mad: I originally would think to do it just massofO2/total mass but the 200g is throwing me.
     
  4. issa

    issa Senior Member
    5+ Year Member

    Joined:
    Aug 24, 2005
    Messages:
    561
    Likes Received:
    0

    200g sample * 1mole sample/total sample weight * 9 mole O/ 1 mole sample * 1 mole O/ 16g O = g oxygen/total sample weight * 100 = % O

    it says 200g sample because it is using specific amount of sample. think about what if you use 200g water instead of 2000g water what will happen? in the 2000g water the oxygen % will will a lot higher than the Oxygen level in the 200g sample.
     
  5. dental#1

    dental#1 Fla DDS
    2+ Year Member

    Joined:
    Jul 22, 2006
    Messages:
    62
    Likes Received:
    0
    Status:
    Pre-Dental
    Good I am glad to know I was on the right track!!!!!!!!!!!!!!!!
     
  6. joonkimdds

    joonkimdds Senior Member
    7+ Year Member

    Joined:
    Jun 30, 2005
    Messages:
    2,780
    Likes Received:
    2
    Status:
    Pre-Dental
    Isn't the oxygen % of oxygen same in both 200g and 2000g of water because H2O always have H:O = 2:1 ratio?
     
  7. issa

    issa Senior Member
    5+ Year Member

    Joined:
    Aug 24, 2005
    Messages:
    561
    Likes Received:
    0
    yes,
    i just looked in the kaplan blue book and it says that we don't have to worry about the 200g or any sample size, so the size of the sample doesn't affect the oxygen compoistion percentage.
     

Share This Page