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 05-25-2012, 06:16 PM #1 Senior Member   Status: Pre-Dental Join Date: Dec 2011 Posts: 494 Ranking Bases w/ CARDIO mnemonic ? SDN Members don't see this ad. (About Ads) Can someone explain how to rank bases according to Chad's CARDIO mnemonic ...i have the notes for what they stand for but i dont exactly understand.... so C for Charge ...more of a charge is MORE basic or LESS basic? A - atom size - bigger is MORE basic or LESS basic? etc...for the rest? Im getting all of the more complicated problems correct but missing simpler ranking questions like this
 05-25-2012, 06:34 PM #2 Senior Member     Status: Pre-Dental Join Date: Jun 2011 Posts: 467 Charge- more negatively charged species are more basic Atom- Large and/or more electronegative the atom with a negative charge, the more stable it is. More stable would mean a weaker base. Note that size is more important, so first consider the size. If the species are in the same row, then you will have to consider the electronegativity. However, if they are in the same column, then you can just consider the atom size (with the larger anions being more stable, so weaker bases). Resonance- more resonance structure means more stable, so weaker base Dipole induction- EWG near an atom with a negative charge stabilizes the molecule, so weaker base Orbitals: sp3 is more basic than sp2 which is more basic than sp. sp is the most stable, hence the weakest base. Hope this helps!
 05-25-2012, 07:12 PM #3 Senior Member   Status: Pre-Dental Join Date: Dec 2011 Posts: 494 Which of the following is the least acidic 55% A: [Correct] CH4 2% B: PH3 8% C: SH2 23% D: NH3 12% E: [Yours] H2O Explanation To determine the acidity of these structures, we should examine the stability of their conjugate bases. Of the conjugate bases, CH−3 is the least stable; thus, CH4 would be the least acidic. ^^in reference to the above problem....so if we're looking for the least acidic, we're looking for the one that would give the strongest conjugate base and therefore the least stable one? and also, so CH3- is a stronger base/less stable than OH- ?? also do the same rules apply to acids? less stable = stronger acid and more stable = weaker acid? Are these statements true? · Strongest conjugate acid gives weakest conjugate base. Strongest conjugate base gives weakest conjugate acid. Last edited by Member 8586; 05-25-2012 at 07:17 PM.
 05-25-2012, 07:20 PM #4 Member   Join Date: Mar 2012 Posts: 48 Yes. It's the same relationship. Think of the formula HA ---> A- and H+ HA= acid. A-=conjugate base. H+=proton So the more stable A- is, the more WEAK of a base and the STRONGER HA is. If A- is unstable, then it is a STRONG base and HA is a WEAK acid In this problems case, I believe it's just a matter of the atom the charge would be on. If you deprotonated the compounds you could see Carbon is the least electronegative making it unstable because C can't handle (-) as well as O,P,N or S I believe in Chad's lecture, he describes CARDIO as to find the strongest acid. So if you were trying to find the least acidic, you would also be looking for the most basic. So just switch the rules and look for the opposite, if that makes sense. Last edited by Kratoz24x; 05-25-2012 at 07:23 PM. Reason: Clarifying
 05-25-2012, 07:28 PM #5 Senior Member     Status: Pre-Dental Join Date: Jun 2011 Posts: 467 "also do the same rules apply to acids? less stable = stronger acid and more stable = weaker acid? Are these statements true? · Strongest conjugate acid gives weakest conjugate base. Strongest conjugate base gives weakest conjugate acid." Correct.. The person above me described it correctly. C is the least electronegative, so it's the most basic...which means its conjugate acid is the weakest. OH- would be a weaker base because of electronegativity
05-28-2012, 09:35 AM   #6
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Quote:
 Originally Posted by Kratoz24x Yes. It's the same relationship. Think of the formula HA ---> A- and H+ HA= acid. A-=conjugate base. H+=proton So the more stable A- is, the more WEAK of a base and the STRONGER HA is. If A- is unstable, then it is a STRONG base and HA is a WEAK acid In this problems case, I believe it's just a matter of the atom the charge would be on. If you deprotonated the compounds you could see Carbon is the least electronegative making it unstable because C can't handle (-) as well as O,P,N or S I believe in Chad's lecture, he describes CARDIO as to find the strongest acid. So if you were trying to find the least acidic, you would also be looking for the most basic. So just switch the rules and look for the opposite, if that makes sense.
thanks for the explanation!... in reference to the problem though - so CARDIO ...after reading your guys' comments...i justified it as CH4 because C is the smallest atom size? you said charge ...but @diene said atom size takes precedence > electronegativity? can you guys clarify on this please?

Quote:
 Originally Posted by diene "also do the same rules apply to acids? less stable = stronger acid and more stable = weaker acid? Are these statements true? · Strongest conjugate acid gives weakest conjugate base. Strongest conjugate base gives weakest conjugate acid." Correct.. The person above me described it correctly. C is the least electronegative, so it's the most basic...which means its conjugate acid is the weakest. OH- would be a weaker base because of electronegativity
wait isnt my bolded statement actually wrong? isnt it least stable = strongest base/weakest acid & most stable = strongest acid/weakest base?

so this is what ive gathered after fully going through your explanations (bolded constitutes a stronger base)..please correct me if any of it is wrong:

• more negatively charged atom = stronger base/weaker acid
• less stable = stronger base/weaker acid &
more stable = stronger acid/weaker base
• smaller atom = stronger base/weaker acid &
bigger atom = stronger acid/weaker base
• less electronegative negatively charged atom = stronger base/weaker acid &
more electronegative negatively charged atom = weaker base/stronger acid
• less resonance = stronger base/weaker acid &
more resonance = stronger acid/weaker base
• less dipole induction = stronger base/weaker acid &
more dipole induction = stronger acid/weaker base
• sp3>sp2>sp from strongest base/weakest acid --> weakest base/strongest acid

or kinda in chart form:

STRONGEST BASE:
• most negative atom
• least stable
• smallest atom
• smallest EN on (-) atom
• least resonance
• least dipole induction
• sp3

STRONGEST ACID:
• most positive atom
• most stable
• biggest atom
• most EN on (-) atom
• most resonance
• most dipole induction
• sp

Last edited by Member 8586; 05-28-2012 at 09:50 AM.

05-28-2012, 09:47 AM   #7
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Status: Pre-Dental
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Quote:
 Originally Posted by Member 8586 thanks for the explanation!... in reference to the problem though - so CARDIO ...after reading your guys' comments...i justified it as CH4 because C is the smallest atom size? you said charge ...but @diene said atom size takes precedence > electronegativity? can you guys clarify on this please? wait isnt my bolded statement actually wrong? isnt it least stable = strongest base/weakest acid & most stable = strongest acid/weakest base?
Yes, sorry it was wrong...I must not have read properly. Most stable = stronger acid.

Based on what Chad said, atomic size takes preference, but he said that can be used when all the elements you are comparing are in the same column (as you go down the column, size increases and larger anions are more stable). If you are comparing elements in the same row, he said to move on to electronegativity. In this case some are in the same column and some are not, I am guessing it's pretty hard to determine the atomic size, so electronegativity would be a better/easier comparison.

05-28-2012, 09:51 AM   #8
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Status: Pre-Dental
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Quote:
 Originally Posted by diene Yes, sorry it was wrong...I must not have read properly. Most stable = stronger acid. Based on what Chad said, atomic size takes preference, but he said that can be used when all the elements you are comparing are in the same column (as you go down the column, size increases and larger anions are more stable). If you are comparing elements in the same row, he said to move on to electronegativity. In this case some are in the same column and some are not, I am guessing it's pretty hard to determine the atomic size, so electronegativity would be a better/easier comparison.
for the C in Cardio - does charge refer to like an actual (-) on the atom or EN?

05-28-2012, 09:54 AM   #9
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Status: Pre-Dental
Join Date: Jun 2011
Posts: 467

Quote:
 Originally Posted by Member 8586 for the C in Cardio - does charge refer to like an actual (-) on the atom or EN?
An actual (-) charge

 05-28-2012, 09:56 AM #10 Senior Member     Status: Dental Student Join Date: Mar 2012 Location: Gainesville, FL Posts: 179 I always learned that you never compare acids, you only compare conjugate bases to determine acidity. Once you have all of your conjugate bases, you can use CARDIO (wish our professor used that) to determine which of the compounds can BEST stabilize that negative charge. More negative charges are more basic, larger atoms can distribute the negative charge more, more electronegative atoms can better stabilize the charge, more resonance will stabilize the charge, dipole-induction will help stabilize the charge, and more s-character will help stabilize the charge too. The better it can stabilize the negative charge, the more likely the acid of that conjugate base will dissociate, hence a stronger acid. If it isn't stable, then it's a stronger base.
05-28-2012, 09:59 AM   #11
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Status: Pre-Dental
Join Date: Dec 2011
Posts: 494

Quote:
 Originally Posted by diene An actual (-) charge
so then wouldnt H2O's conjugate base be OH-? or they all have a negative charge because we're taking the conjugate base?

also, i dont know if you noticed the little summary i typed in bc i edited the post...can you verify if thats right?

Quote:
 Originally Posted by GatorD I always learned that you never compare acids, you only compare conjugate bases to determine acidity. Once you have all of your conjugate bases, you can use CARDIO (wish our professor used that) to determine which of the compounds can BEST stabilize that negative charge. The better it can stabilize the negative charge, the more likely the acid of that conjugate base will dissociate, hence a stronger acid. If it isn't stable, then it's a stronger base.
so if asked for least acidic or most acidic, always find the conjugate base and then use CARDIO - correct?
and if youre asked for least or most basic straight up - then you can just use CARDIO?

 05-28-2012, 09:50 PM #12 Senior Member     Status: Dental Student Join Date: Mar 2012 Location: Gainesville, FL Posts: 179 No matter what they ask, you always find the conjugate base. The most basic is the least acidic, and the most acidic is the least basic, right? Just take off a proton, even if it looks like a ridiculous unlikely compound. For example, CH4, conjugate base is CH3(-). This thing does not look stable at all, so I think it'll be more basic compared to something like H2C=CH(-), where the double bond can better handle the negative charge. No matter acid or base, don't assume anything. Always get the conjugate base, then arrange them in order of stability using CARDIO. The most stable conjugate base is the most acidic, the least stable conjugate base is the least acidic (and hence most basic).

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