[intrepid]

Hey Guys, I am a college grad but taking a standardized exam, hence I do not have professors to go to for help. Could some one please help me with few questions?

Question 1. Which of the following is closest to the pH of a solution that contains 5 millimolar per liter of H+ ions.

A. 1.2
B. 2.3
C. 3.7
D. 6.5
E. 7.5

The answer is B, but I don't know how to calculate.

Question 2. The ionic strength of MgCl2 is

A. 0.25
B. 0.5
C. 1.0
D. 1.5
E. 5.0

The answer is D, I don't know how to do it though.

Question 3. What is the pKa of trimethylammonium in water if the base ionization constant Kb for trimethylamine is 7.4 * 19^-5? (log 7.4 * 10^-5 = -4.13)

A. -4.13
B. 2.87
C. 4.13
D. 9.87
E. 11.13

The answer is D. I don't know how to get the answer though.

Question 4. In an intact cell, the free energy change associated with an enzyme catalyzed reaction is frequently different from the standard free energy change of the same reaction because in the intact cell the

A. activation energy is different
B. reaction is always near equilibrium
C. enzyme may be regulated allosterically
D. Reactants are not at 1 M concentrations
E. Reaction may be catalyzed by more than one enzyme.

The answer is D, but can some one explain a little more?

Question 5. The pH of a 10^-4 molar HCl solution prepared with pure water at pH 7.0 is closest to.

A. 6.0
B. 6.9
C. 7.1
D. 7.9
E. 8.0

The answer is B.

The nucleoside adenosine exists in a pronated form with a pKa of 3.8. The percentage of pronated form at pH 4.8 is closest to

A. 1
B. 9
C. 50
D. 91
E. 99

The answer is B.

[csrscience.com]

It wouldn't hurt us to show how you've tried to work through this, so we can help you build the foundations you are missing. Plus.. it will save us time since we wouldn't have to explain everything!

writing out a box of what you know and don't know about the situation is always helpful.

[nj_bartel]

Hey Guys, I am a college grad but taking a standardized exam, hence I do not have professors to go to for help. Could some one please help me with few questions?

Question 1. Which of the following is closest to the pH of a solution that contains 5 millimolar per liter of H+ ions.

A. 1.2
B. 2.3
C. 3.7
D. 6.5
E. 7.5

The answer is B, but I don't know how to calculate.  -log[H+]

Question 2. The ionic strength of MgCl2 is

A. 0.25
B. 0.5
C. 1.0
D. 1.5
E. 5.0

The answer is D, I don't know how to do it though.  What does magnesium chloride dissociate into upon addition to water?

Question 3. What is the pKa of trimethylammonium in water if the base ionization constant Kb for trimethylamine is 7.4 * 19^-5? (log 7.4 * 10^-5 = -4.13)

A. -4.13
B. 2.87
C. 4.13
D. 9.87
E. 11.13

The answer is D. I don't know how to get the answer though. pKa + pKb = 14

Question 4. In an intact cell, the free energy change associated with an enzyme catalyzed reaction is frequently different from the standard free energy change of the same reaction because in the intact cell the

A. activation energy is different
B. reaction is always near equilibrium
C. enzyme may be regulated allosterically
D. Reactants are not at 1 M concentrations
E. Reaction may be catalyzed by more than one enzyme.

The answer is D, but can some one explain a little more? Define the conditions associated with standard free energy change

Question 5. The pH of a 10^-4 molar HCl solution prepared with pure water at pH 7.0 is closest to.

A. 6.0
B. 6.9
C. 7.1
D. 7.9
E. 8.0

The answer is B. HCl is a strong acid and dissociates 100% in solution

The nucleoside adenosine exists in a pronated form with a pKa of 3.8. The percentage of pronated form at pH 4.8 is closest to

A. 1
B. 9
C. 50
D. 91
E. 99

The answer is B. Henderson Hasselbalch equation

[Borek]

Question 5. The pH of a 10^-4 molar HCl solution prepared with pure water at pH 7.0 is closest to.

A. 6.0
B. 6.9
C. 7.1
D. 7.9
E. 8.0

The answer is B.

Question doesn't make sense to me. Aren't volumes given?

[intrepid]

I found the answers guys. THanks.

[blightcutter]

Question 5. The pH of a 10^-4 molar HCl solution prepared with pure water at pH 7.0 is closest to.

A. 6.0
B. 6.9
C. 7.1
D. 7.9
E. 8.0

The answer is B.

Question doesn't make sense to me. Aren't volumes given?

The folks who design the standardized tests try to design the questions so that they don't confuse the people taking them. There are probably a few assumptions involved in there.

[Borek]

No matter what assumptions you make, this doesn't make sense. pH of 10^-4 solution is 4.

It occured to me - could be there is a typo in the question, and it should read

pH of a 10^-7 molar HCl solution

[intrepid]

Sorry guys, yes, there was a typo in the question. If I remember correctly, I think it was 10^-8