Four Destroyer GC Questions

[Incis0r]

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Good Evening!

I just finished the first 60 GC questions in DAT Destroyer 2015, and I have selected four questions that I would appreciate your input on!

I didn't include question text in order to avoid violating copyright law, so I apologize in advance if this seems very confusing.

#3- So I understand why Delta H and Delta S are negative for the condensation of NH3. My issue is with the rationale for Delta G being negative. I had originally thought that Delta G would be negative since vaporization is spontaneous above the boiling point, and condensation is spontaneous below the boiling point? Is this line of reasoning accurate? The answer key states that there is a low enough temperature for Delta G to be negative; is this solely because the T is below the BP? Is there a mathematical way I could confirm this? I tried rearranging the Delta G = Delta H - T Delta S equation, but I'm not sure on exactly how to apply this here.

#27- The pH I initially calculated was 12, but the answer key states 7 due to the negligible concentrations of H+ ions. Is the following statement true then? Any acidic solution with an [H+] concentration below 1E-7, or any basic solution with an [OH-] concentration below 1E-7, has a pH of 7 since water is more acidic/basic?

#36- I approached this problem with the viewpoint that most metals (excluding Group 1 and Group 2) are Lewis Acids, and that acids are most soluble in bases. So, I reasoned that Ag+ would be the most soluble in the provided substance. Is this line of reasoning appropriate?

#58- This problem was solved with the concept of "valences"- I am a bit unclear on this, however. I understand that Mg can only be +2, and that Argon is non-reactive. I do not understand how to rule out C and Hg, however. Do you take advantage of the groups the elements are in to determine this?

Thank you in advance for all of your help!

 

[DAT Destroyer]

#36
No.....you missed the main concept !!!! Ag can react with NH3 to form a Complex ion.......which has a HUGE formation constant, Kf. Transition metals such as Ag, Cu, Zn, Cd react with Ammonia to produce these complex ions. The values of these constants range from 1x10 exp 7 to well beyond 1x10exp15 !!!!!!!! Hope this helps.

 

[DAT Destroyer]

Good Evening!

I just finished the first 60 GC questions in DAT Destroyer 2015, and I have selected four questions that I would appreciate your input on!

I didn't include question text in order to avoid violating copyright law, so I apologize in advance if this seems very confusing.

#3- So I understand why Delta H and Delta S are negative for the condensation of NH3. My issue is with the rationale for Delta G being negative. I had originally thought that Delta G would be negative since vaporization is spontaneous above the boiling point, and condensation is spontaneous below the boiling point? Is this line of reasoning accurate? The answer key states that there is a low enough temperature for Delta G to be negative; is this solely because the T is below the BP? Is there a mathematical way I could confirm this? I tried rearranging the Delta G = Delta H - T Delta S equation, but I'm not sure on exactly how to apply this here.

#27- The pH I initially calculated was 12, but the answer key states 7 due to the negligible concentrations of H+ ions. Is the following statement true then? Any acidic solution with an [H+] concentration below 1E-7, or any basic solution with an [OH-] concentration below 1E-7, has a pH of 7 since water is more acidic/basic?

#36- I approached this problem with the viewpoint that most metals (excluding Group 1 and Group 2) are Lewis Acids, and that acids are most soluble in bases. So, I reasoned that Ag+ would be the most soluble in the provided substance. Is this line of reasoning appropriate?

#58- This problem was solved with the concept of "valences"- I am a bit unclear on this, however. I understand that Mg can only be +2, and that Argon is non-reactive. I do not understand how to rule out C and Hg, however. Do you take advantage of the groups the elements are in to determine this?

Thank you in advance for all of your help!

#3

This is a bit tricky. Since this is condensation..... a gas goes to a liquid,,,,,thus BOTH delta H and delta S are negative. Now,,,,,,IF and only IF we are at a low temperature.....does it become spontaneous...NEGATIVE delta G. What is this temperature ? It is the EQUILIBRIUM POINT....namely the boiling point. We are most DEFINITELY below the -33 degrees...we are at -43, hence spontaneous indeed. This is a VERY important DAT question.

Hope this helps

 

[OSUkid]

Good Evening!

I just finished the first 60 GC questions in DAT Destroyer 2015, and I have selected four questions that I would appreciate your input on!

I didn't include question text in order to avoid violating copyright law, so I apologize in advance if this seems very confusing.

#3- So I understand why Delta H and Delta S are negative for the condensation of NH3. My issue is with the rationale for Delta G being negative. I had originally thought that Delta G would be negative since vaporization is spontaneous above the boiling point, and condensation is spontaneous below the boiling point? Is this line of reasoning accurate? The answer key states that there is a low enough temperature for Delta G to be negative; is this solely because the T is below the BP? Is there a mathematical way I could confirm this? I tried rearranging the Delta G = Delta H - T Delta S equation, but I'm not sure on exactly how to apply this here.

#27- The pH I initially calculated was 12, but the answer key states 7 due to the negligible concentrations of H+ ions. Is the following statement true then? Any acidic solution with an [H+] concentration below 1E-7, or any basic solution with an [OH-] concentration below 1E-7, has a pH of 7 since water is more acidic/basic?

#36- I approached this problem with the viewpoint that most metals (excluding Group 1 and Group 2) are Lewis Acids, and that acids are most soluble in bases. So, I reasoned that Ag+ would be the most soluble in the provided substance. Is this line of reasoning appropriate?

#58- This problem was solved with the concept of "valences"- I am a bit unclear on this, however. I understand that Mg can only be +2, and that Argon is non-reactive. I do not understand how to rule out C and Hg, however. Do you take advantage of the groups the elements are in to determine this?

Thank you in advance for all of your help!

Aw man I cant wait to study for the DAT -_-

 

[Incis0r]

#36
No.....you missed the main concept !!!! Ag can react with NH3 to form a Complex ion.......which has a HUGE formation constant, Kf. Transition metals such as Ag, Cu, Zn, Cd react with Ammonia to produce these complex ions. The values of these constants range from 1x10 exp 7 to well beyond 1x10exp15 !!!!!!!! Hope this helps.

This helps a lot, thank you!

#3

This is a bit tricky. Since this is condensation..... a gas goes to a liquid,,,,,thus BOTH delta H and delta S are negative. Now,,,,,,IF and only IF we are at a low temperature.....does it become spontaneous...NEGATIVE delta G. What is this temperature ? It is the EQUILIBRIUM POINT....namely the boiling point. We are most DEFINITELY below the -33 degrees...we are at -43, hence spontaneous indeed. This is a VERY important DAT question.

Hope this helps

Thank you so much for clarifying these two questions, Dr. Romano! I appreciate it, especially when you're so busy!!

Aw man I cant wait to study for the DAT -_-

When are you taking the DAT?

 

[DAT Destroyer]

Good Evening!

I just finished the first 60 GC questions in DAT Destroyer 2015, and I have selected four questions that I would appreciate your input on!

I didn't include question text in order to avoid violating copyright law, so I apologize in advance if this seems very confusing.

#3- So I understand why Delta H and Delta S are negative for the condensation of NH3. My issue is with the rationale for Delta G being negative. I had originally thought that Delta G would be negative since vaporization is spontaneous above the boiling point, and condensation is spontaneous below the boiling point? Is this line of reasoning accurate? The answer key states that there is a low enough temperature for Delta G to be negative; is this solely because the T is below the BP? Is there a mathematical way I could confirm this? I tried rearranging the Delta G = Delta H - T Delta S equation, but I'm not sure on exactly how to apply this here.

#27- The pH I initially calculated was 12, but the answer key states 7 due to the negligible concentrations of H+ ions. Is the following statement true then? Any acidic solution with an [H+] concentration below 1E-7, or any basic solution with an [OH-] concentration below 1E-7, has a pH of 7 since water is more acidic/basic?

#36- I approached this problem with the viewpoint that most metals (excluding Group 1 and Group 2) are Lewis Acids, and that acids are most soluble in bases. So, I reasoned that Ag+ would be the most soluble in the provided substance. Is this line of reasoning appropriate?

#58- This problem was solved with the concept of "valences"- I am a bit unclear on this, however. I understand that Mg can only be +2, and that Argon is non-reactive. I do not understand how to rule out C and Hg, however. Do you take advantage of the groups the elements are in to determine this?

Thank you in advance for all of your help!

I would rather you understand the concept than memorize a silly rule, but yes....you have the right idea. If you have an acid concentration of 1 "x 10 exp -12 for HCl for example.....the amount ionized is so very small.....we say it is aproximately 7. This is because the contribution from water is 1x10 exp -7.

The best way to tell this is a trick problem is to first calculate the pH as you said....then stop and think.....Can an HCl solution have a pH of 12 ? No ! Thus the answer will be 7. You may someday see this problem.....

Know it !!!

Hope this helps.

 

[OSUkid]

When are you taking the DAT?[/QUOTE]
spring 16'

 

[DAT Destroyer]

Good Evening!

I just finished the first 60 GC questions in DAT Destroyer 2015, and I have selected four questions that I would appreciate your input on!

I didn't include question text in order to avoid violating copyright law, so I apologize in advance if this seems very confusing.

#3- So I understand why Delta H and Delta S are negative for the condensation of NH3. My issue is with the rationale for Delta G being negative. I had originally thought that Delta G would be negative since vaporization is spontaneous above the boiling point, and condensation is spontaneous below the boiling point? Is this line of reasoning accurate? The answer key states that there is a low enough temperature for Delta G to be negative; is this solely because the T is below the BP? Is there a mathematical way I could confirm this? I tried rearranging the Delta G = Delta H - T Delta S equation, but I'm not sure on exactly how to apply this here.

#27- The pH I initially calculated was 12, but the answer key states 7 due to the negligible concentrations of H+ ions. Is the following statement true then? Any acidic solution with an [H+] concentration below 1E-7, or any basic solution with an [OH-] concentration below 1E-7, has a pH of 7 since water is more acidic/basic?

#36- I approached this problem with the viewpoint that most metals (excluding Group 1 and Group 2) are Lewis Acids, and that acids are most soluble in bases. So, I reasoned that Ag+ would be the most soluble in the provided substance. Is this line of reasoning appropriate?

#58- This problem was solved with the concept of "valences"- I am a bit unclear on this, however. I understand that Mg can only be +2, and that Argon is non-reactive. I do not understand how to rule out C and Hg, however. Do you take advantage of the groups the elements are in to determine this?

Thank you in advance for all of your help!

Incis0r

#58- This problem was solved with the concept of "valences"- I am a bit unclear on this, however. I understand that Mg can only be +2, and that Argon is non-reactive. I do not understand how to rule out C and Hg, however. Do you take advantage of the groups the elements are in to determine this?


Carbon can easily be ruled out,,,,,think about it.....CF3 is not stable,,,,carbon needs 4 bonds. Mercury forms ions of + 2 charge...Forget about it !!!!! Why Arsenic ? As I told my class in DAT DESTROYER BOOTCAMP today,,,,,NEVER trust a metalloid. Metalloids such as As, Sb, etc can form positive or negative ions..... Arsenic can form ions of +3, -3, or +5.......Since Y has a +3 charge,,,,,Arsenic, As,,,,,is your choice !

Hope this helps.

Dr. Jim Romano

 

[Incis0r]

Incis0r

#58- This problem was solved with the concept of "valences"- I am a bit unclear on this, however. I understand that Mg can only be +2, and that Argon is non-reactive. I do not understand how to rule out C and Hg, however. Do you take advantage of the groups the elements are in to determine this?


Carbon can easily be ruled out,,,,,think about it.....CF3 is not stable,,,,carbon needs 4 bonds. Mercury forms ions of + 2 charge...Forget about it !!!!! Why Arsenic ? As I told my class in DAT DESTROYER BOOTCAMP today,,,,,NEVER trust a metalloid. Metalloids such as As, Sb, etc can form positive or negative ions..... Arsenic can form ions of +3, -3, or +5.......Since Y has a +3 charge,,,,,Arsenic, As,,,,,is your choice !

Hope this helps.

Dr. Jim Romano

Thank you so much for all of your help, Dr. Romano!!! This helps a lot! I understand these questions now 🙂

I really appreciate you taking the time to go over each one.