Nbde Q

[SuperC]

---

Members do not see this ad.

Which of the following represents the pH of a solution that has a 10-3 M concentration of OH- ion?
1. 5
2. 7
*3. 9
4. Determinable only if the pka is known.
5. Determinable only if the base composition is known.


I don't get this....
Kw = [H+][OH-] where
pH = -log[H+]
pOH = -log[OH-]
14 = pH + pOH

I get pH = 11...

Am I ******ed?

and I am having trouble with this one too

For a reaction catalyzed by an enzyme with a Km = 1 mM, which of the following represents the effect on the velocity if is changed from 10 mM to 20 mM? (Assume that the enzyme obeys Michaelis-Menten kinetics.)
1. Small decrease
*2. Small increase
3. Twofold decrease
4. Twofold increase
5. Twentyfold increase

I am not sure how to set this up, lacking Vmax... If I assume that Vmax remains constant I can get ratios but I am not sure how to interpret them

 

[Bugab00]

you're right. pH is 11

 

[armorshell]

Remember that Km is the concentration of substrate at which the enzyme is 50% saturated. Increasing the concentration from 10x Km to 20x Km isn't going to increase the velocity to a great degree, because at 10x Km the enzyme is probably already saturated.

 

[endless summer]

Which of the following represents the pH of a solution that has a 10-3 M concentration of OH- ion?
1. 5
2. 7
*3. 9
4. Determinable only if the pka is known.
5. Determinable only if the base composition is known.


I don't get this....
Kw = [H+][OH-] where
pH = -log[H+]
pOH = -log[OH-]
14 = pH + pOH

I get pH = 11...

Am I ******ed?

++++
Given the two questions you posted, it looks like you're looking at the same practice exam I am (Dec 1996). This is question #153 and it asks what the pH of a solution that has a concentration of 10-5 OH- ion.

That would make answer choice C. correct.