chm Q

[smile101]

Which of the following pH values are possible for an solution described as acidic at room temperature?
I. —1
II. 4
III. 7
IV. 10

At 25 °C, the average osmotic pressure of blood is about 7.7 atm. What concentration of potassium chloride is isotonic with blood? (R = 0.08206 (L•atm)/(mol•K))
A. 0.32M
B. 0.16M
C.6.4M
D. 3.2M
E 1.6M

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[osimsDDS]

haha uhhhh I believe the answer is 4...

 

[baedero1]

pi = MRTi

7.7 = M*0.0821*298*2

M=0.16M

 

[osimsDDS]

Which of the following pH values are possible for an solution described as acidic at room temperature?
I. —1
II. 4
III. 7
IV. 10

At 25 °C, the average osmotic pressure of blood is about 7.7 atm. What concentration of potassium chloride is isotonic with blood? (R = 0.08206 (L•atm)/(mol•K))
A. 0.32M
B. 0.16M
C.6.4M
D. 3.2M
E 1.6M

For the second question, osmotic pressure is a colligative property, meaning you are looking at the particular ions, not at the identity of the molecule.. In this case you are taking potassium chloride (KCl) which will dissociate in solution (plasma in this case) to form 2 ions (K+) and (Cl-)...

Osmotic pressure = MRTi i=the moles of ions in solution

7.7=(M)(.0821)(273+25)(2)
M=.16 molarity

 

[smile101]

haha uhhhh I believe the answer is 4...

Okay..I just wanted to make sure that I wasn't the only one thinking that the answer should be just 4. Kaplan said that the answer should be -1 and 4. If the pH is -1 then the H+ conc should be 0, don't add up...bc its not an acid then.

 

[DentalDeac]

Okay..I just wanted to make sure that I wasn't the only one thinking that the answer should be just 4. Kaplan said that the answer should be -1 and 4. If the pH is -1 then the H+ conc should be 0, don't add up...bc its not an acid then.

pH can be negative
http://www.newton.dep.anl.gov/askasci/chem99/chem99230.htm

 

[Predentknight]

HAha too funny I just took Kaplan practice test 3 yesterday, I had the exact same concern with the negative pH , apparently it is possible for pH to assume a negative value. I thought the chem seection for that test was hard would you agree? and the Bio section was ridiculously easy.

 

[smile101]

HAha too funny I just took Kaplan practice test 3 yesterday, I had the exact same concern with the negative pH , apparently it is possible for pH to assume a negative value. I thought the chem seection for that test was hard would you agree? and the Bio section was ridiculously easy.

I totally agree. I scored like 23 on Bio and 17 on Chm on that one..some of the explanations are just pure lie on that bio section though.

 

[smile101]

pH can be negative
http://www.newton.dep.anl.gov/askasci/chem99/chem99230.htm

good to know!!!
thanks!

 

[doc toothache]

Okay..I just wanted to make sure that I wasn't the only one thinking that the answer should be just 4. Kaplan said that the answer should be -1 and 4. If the pH is -1 then the H+ conc should be 0, don't add up...bc its not an acid then.

[H+]=10, pH = -1

see similar thread
http://forums.studentdoctor.net/showpost.php?p=6792452&postcount=1
http://forums.studentdoctor.net/showpost.php?p=6792903&postcount=4
http://forums.studentdoctor.net/showpost.php?p=6793479&postcount=6